Good stuff Uncle Doug 👍 I had a 1965-66 GA 45 Saturn that I could play directly through the Reverb with the volume off, lol. Two 10 inch CTS ceramic speakers, bright sounding and lots of Orange drops.
Thanks, JGK. It's a 1981 Vantage Performer Model VS-695 that I picked up, in lousy shape, from a pawn shop several years ago.....for about $200 (with a nice case). After a whole bunch of work, it turned out to be a very playable, good-sounding guitar. The key to these old Matsumoku guitars is the MMK-45 humbucker pickups.....extremely hot and responsive. Before I got hooked on amps, I was a dedicated guitar restorer.
I have one Vantage with matsumoku pick ups just like yours Uncle Doug, Ive owned it for many years and its been thru a lot, including the body completely broke in like three pieces fortunately the neck didnt break so I put it all together and is working better then before! :) I just love it!
Nice videos, I like what you've done here. I had one of these for a few years in college and found that the cabinet can be much improved for bass response as it is quite small and lacking in diamention front to back. First I removed the baffle and installed foam weatherstrip all around it. Then I installed 2 or 3 layers of weatherstrip between the chassis and the top of the baffle for a more complete baffle. This yellded tighter bass and more or some push. Big improvements.....
Back in 1974-75 The other guitar player in the band I was in had one of these gems. I used it for about 6 months for gigs and band practice. This amp was as good or better than anything fender had in this wattage range. The reverb was to die for (and I'm a big fan of fender reverbs). Dale Moore did most of the country lead playing and I did most of the Rock leads. Other than a crybaby pedal (and not often) I just turned the amp up and the tone took care of itself with the right amount of gain. I was using a black 1970 Rickenbacker 330....My Mom loved me :-)
Amen, CD. Trying to repair transformers, coils, reverb transducers, etc. can be a daunting task. I got one of those visor magnifiers, like jewelers wear, so I can at least see......or sort of see......the microscopic wires. It's usually a crap shoot and you can't always succeed, but when you do (as you did) it's a very rewarding experience.
You're welcome, Joey, and thanks for the tip on the liquid tape. Re the Crate amp, I have no experience with them at all, but it sounds like you are making some good changes. One thing that really affects head room and gain is to get the output tubes properly biased. Too low and you lose headroom, too high and you gain headroom but burn up tubes.....it's a balancing act, but definitely worth the trouble once you get it set properly.
You made the amp sound and look allot better than it was, but still not my cup of tea at all. One is for sale locally, and before I contacted the seller I thought I would come here. Glad I did, saved me allot of time and trouble. My 1974 Vibrolux eats that amps lunch.
Michael McGlynn Thanks so much, Mike. Actually, it's more of a hobby for me. Hearing positive comments from viewers (like you) is the only "payment" I seek :)
These have an optical tremolo that is very prone to failure. There is a little light bulb that flashes onto a photo resistor, and the light bulb burns out. I believe it's a 28 volt bulb and hard to find. It's in my video. Humming (that does not obey the volume control) could be due to leaky filter capacitors, which may need to be replaced, unless it's very slight, and then it's probably OK. Many amps hum a little louder when the reverb is turned up, so that's not a problem. I hope this helped.
I gleaned some valuable info on one of these that I'm working on. Will do the sound improvement mod. The reverb transformer had both lugs missing, so I found a replacement from mercury magnetics.I'm having a tougher time finding replacement knobs. The amp was a barn find so I was prepared for the worst, but I put tubes in it and It works. So it needs caps but the tremolo works and the pots are quiet. I will also put in a second rca jack chassis mount for the reverb so the lugs / wires won't get pulled out again. Thanks for helping me get through the Gibson wIlderness.
+kevin healy You're welcome, Kevin. These amps are generally inexpensive and readily repairable to acceptable tone standards, but the reverb transformer is an accident waiting to happen.....as you discovered. Best of luck with your restoration.
I have no experience with the GA-77 RET amp, but a chart I have says that it should use a Gibbs Model C Reverb Tank which is the same as an Accutronics 4FB2A1C Tank. I hope this helps.
....further in the circuit. They are intentional gain suckers meant to keep the amp from overdriving. Jumper these out, and really enjoy what these amps can do!! Much more gain!!
Hey Uncle Doug, If the bed springs are sqeakin', don't bother peekin'. Just kiddin'. I hope your all well. Best tube amp channel bar none. Take care, C.
just realizing now, most of the videos I enjoy most in this category -are rescues of some of the worst-cared -for devices of their species. It's a thrill to watch them claw their majestic ways back to life to scream again.
Doug, Love your videos, very informative. I am glad I watched this one, because it convinced me to stay away from a GA35 I was considering. I hate working with linguini ;^) Thanks
Thanks so much, WC. I have to admit that it was indeed a healthy serving of linguini, but now that I reflect on the experience.....it wasn't all that bad :)
Bought a Lancer several years ago, needed some work. All it did was hum, loud enough to probably blow the speakers. After checking everything , I found a bad connection associated with the RCA plugs on the reverb tank. Played great after cleaning those plugs. I bought another with a fried power transformer. Replaced it with a slightly smaller Hammond unit, new, in the parts stash, worked great, seems none of the tubes were affected by the "fire". I always wake tube equipment up s l o w l y on my variable transformer, when it's been inactive a while.
+sierraromeo The Variac is always a nice, gently way to bring dormant electrical equipment back into use, SR. Thanks for sharing your experiences with Lancer amps :)
Nice amp and sounds good now. Seems to sound like it should. I had one with nothing wrong with it but the cap. The volume was not great but were not real beefy. Good luck!
Thanks, Dennis. These 60's Gibson's are generally a bargain to buy, due to their tone deficiencies, but they can be turned into decent amps with a little work......
These amps have a unique reverb circuit (if it is like my ga-15RVT which uses el84's...and is currently blown up...ouch). If you use the footswitch to turn the reverb off, you can turn up the reverb level and get a small amount of added gain. They have a gain circuit in them that stays on and inline I believe.
There are two different types. One is a washable waterproof type and the other is not meant to be washed and is water soluble, it can be watered down to whatever consistency you like.
Another great video from Uncle Doug! Love this amp. When you were demoing the Tremolo, I was sure you were gonna break into some Turtles or Beau Brummels. Very much their sound. Just a couple of questions: Does the "35" in this amp's name denote the wattage of the amp and was that a 10" speaker or a 12? Ok, going to watch your tone improvement video on this amp now, as I agree, it is a little "tinny" overall. Thanks for creating this channel. Very entertaining and some really great info here. -b
You're welcome, Dean. Yes, it is rated at about 35W. I believe the speaker was 12". I did find a way to improve the tone quite a bit, but never could get it to sound quite the way I hoped. Perhaps it was just this amp; however, I have since had the opportunity to try out an identical one.....and it sounded just the same, with all sorts of reverb and tremolo problems. It appears that this was not a terribly reliable circuit, at least for the two I tested. Hopefully, others have had better luck with it.
All information is helpful. Thanks alot. the humming is very slight. and its always there, i can live with it. One more question; is the 6FQ7/6CG7 driving the reverb? does it do anything else? I will be taking this guy into a tech, it needs a checkup. thanks for taking the time to answer me.
Not sure if you take "requests", :-) but I would love to see you make a video that's all about your Hickok 600A tube tester. It's use and operation and how to test multiple tubes. I've thought about getting one but am worried it would be overwhelming. But with your knowledge and ability to convey said knowledge, I think it would be thoroughly fascinating! Just a thought.
Kirk Jones Greetings, Kirk, and thanks for the suggestion. To be honest, using a tube tester is rather simple. The 600A has a scroll chart showing the settings for each tube. You simply plug the tube into the correct socket, set all the knobs to the prescribed values, and then push a button to test for emission (output strength) and internal shorts. It is so basic that a video showing the testing of more than one tube would be a little tedious. Don't be intimidated by tube testers.....get one and, through usage and experience, it will become one of your favorite and most useful tools.
Uncle Doug...love your vids as always.... Got this amp and replaced all tubes...did your mods and it sounds great! Thanks! Can't get trem to work - rebuilt my roach (seems I may be getting a steady 4.5v across the opto lamp but not lighting up) (6.5v with OA2 tube removed).. checked the footswitch and even bypassed it manually to test. Cant see to get the trem to work . What to check next? Note: I rewired the 6EU7's to 12AX7's. Also noticed I need to engage reverb footswitch to get any sound at all on reverb channel - engaging reverb footswitch seems to act like a relay of sorts to get any sound coming through reverb channel. Replaced opto lamp with recommended replacement but no luck.. OA2 is a new NOS also and lighting up.....
Thanks, T. Congratulations on your successful modifications. Photo-resistor tremolos can be a real challenge in many amps. As I recall, the voltage to my neon bulb was much higher than yours.....around 150VDC. What is the plate voltage on V5b ? The OA2 is a voltage regulator and should be maintaining about 150VDC in the neon bulb loop.
Thanks, I have 2 gibsons the Lancer 35 only had chassis its in a custom cabinet but it has the Ice Pick Tone. I have 1 35 Watt Gibson DuoMedalist 12 inch speaker like new with the orginal Gibson Cover its very brilliant. I put an older anico speaker which gave it some better tonal response. Only needed a White Block Resistor change.
My son is going to the tone stack mod. And new power cord grounding and check the death cap. Ee really appreciate it. This amp can really crank out some powerful sound and with some incredible tone.
Sissy, IMHO these 60's Gibson amps are tough to work on. I can try to answer some specific questions, but I simply can't provide any in-depth long-distance diagnosis and repair work. Tell me the issues and perhaps I can give you some help you with some of them, but any heavy repairs will have to be done by an amp tech.
A shrill treble is actually a good thing, set the Bass at about 4, and the treble at 5, and then strum the Guitar In D with the tone knob on the Guitar at max high. Keep turning the amp treble up till it's a little too shrill (maybe even a notch up from that) . Then turn the tone knob on the Guitar down to choke the treble to where you like it. That's how Albert Collins does it. Always worked for me.
Thanks for posting this. I have an Epiphone EA 26 RVT Electra and the Reverb control has no effect. Reverb sounds like it is at max output all the time. I shorted the center wiper of the reverb pot to ground. No change. I removed the wire from the center wiper to the tube. No change. Any thoughts?
Sadly, the only schematic I can find for the amp in question is unreadable. If you can provide a link to a clear, legible schematic, I may be able to help.
Hey thanks for posting this. It is next to impossible to get any info on these old gibson amps. I'm new to amp repair so forgive my ignorance. I recently found an old GA95 RVT "Apollo" amp in my storage room. I got all new tubes (2x6EU7, 2x12AU7, 1x12AX7, 4x6L6, 1x0A2), cleaned the sockets, checked main the fuse, the power cable seems to be intact, and yet when I turn it on I get nothing. My question is do I need a fuse in the housing for the aux power plug in the back as well? That housing is missing it's cap and has no fuse in it. These also seems to be a tube socket that is not on the schematic that I have and I have no idea what it's for and as with your amp from this video the chassis is not marked as to what belongs there. Currently it has these in it 2x6EU7, 2x12AU7, 1x12AX7, 4x6L6, 1x0A2. Thanks. as ever, Skimbo
Greetings, Skimbo. There are many reasons why an amp can be stone dead. You seem to have all 10 tubes. If there is an empty socket, it should be a small one for the footswitch, and the amp can run without it. You don't need a fuse in the aux. outlet to make the amp run. Be sure the amp fuse is good (test it, don't go by appearance). Do any of the tubes light up or get warm when the amp is in Standby or either of the On positions? If not, it could be the cord, the plug, the switch, the power transformer, etc. etc. You need to start at the wall outlet and check (with a VOM) to see if the proper voltage is getting to each of the amp components, in order. Good luck.
Uncle Doug Correct I see in the schematic that that small socket is in fact for the foot switch. Still learning how to read this stuff. Negative, nothing lights up/gets warm. Cord is the original two prong and is likely to be at fault. My VOM is coming in the mail that's how new I am to this. Thank you for your patience with this electronics 101 student. as ever, Skimbo
Good luck, Skimbo. Be VERY careful when working on an amp that is electrically "live". As you probably know, there are potentially lethal voltages within the circuit.
I have a 1965-1966 Epiphone Futura EA12RVT, it matches the schematic for a Gibson GA45RVT. I'm having a few issues with the amp. I was wondering if you'd be willing to help me out? There is a lack of good info about these amps online and most techs don't have any experience with them.
Do you have a manual for this amp? I too am restoring one and don't know the difference between "On" #1 and "On" #2. I replaced the electrolytics and also rewired V1 to take a 12AX7 rather than a 6EU7. Still having trouble with reverb, I am wondering if the little transformer tips are in a similar shape to what you fixed. Finally, well done on your restoration.
Greetings, Roger. No, I have no technical info on this amp other than the schematic, downloaded from the Internet. Also, please see a follow-up video in which I significantly improve the tone of this amp. I believe the two "On's" allow you pick the one with least hum, like the old hum switch on Fender amps, which selects which AC lead the "death capacitor" is connected to. The Reverb (and Tremolo) in these amps are a common problem. Be sure your 12AU7 is strong (mine was shorted) and that your cables and tank transducers are in good shape (Impedance: 1475 Ohms in and 2250 Ohms out for Gibbs Model C #6619). If the tank has been replaced (the correct replacement is an Accutronics 4FB2A1C) be sure it's the right tank. I encountered another GA-35 recently that had a weak reverb due to an incorrect replacement tank. The little transformer is generally an all-or-nothing situation: if the connection is broken the reverb is dead. Good luck !!!!
Hello. Working with a early-mid sixties Vanguard GA77 RET? Think it had the tel ray oil can reverb removed. It has three RCA style jacks on the chassis, can I run a spring reverb tank? which one? Also curious as to the ohms output of the amp. Sorry for the questions but any help or guidance is appreciated.
Sissy, the reverb tank is actually "driven" by a transformer, just like a speaker is driven by its output transformer. The tube that drives the transformer is a 12AU7 and the tube that receives and processes the reverb signal is a 6EU7......at least in a Gibson GA45 and GA35. Hopefully, a competent amp tech can fix it up for you. Good luck.
Thanks for the reply, tremolo is not working, fairly sure it is the footswitch which is identical to the one in your video(reverb comes on with the switch, but nothing happens engaging tremolo)I do have a slight 60hz hum that gets louder with reverb ON/Vol. close to 10. I wouldn't attempt heavy repairs, mostly looking for possible explanations. tubes are 0A2,2x6L6s,6FQ7,4x6EU7,1x12AU7 but has a 12AX7 in its place. Could improper biasing cause hum? it sounds great otherwise. THANKS!
Hi uncle Doug enjoyed the video, I just got one of these amps, it's sounds ok, but don't have much output, any ideas , caps have been changed, new phase inverter trans former and reverb transformer. But everything else looks stock
I have pretty well given up on mid-60's Gibson amps, TM. I posted a video showing how I coaxed some tolerable tone out of one.....but it's quite a chore.
@@UncleDoug I got a Gibson falcon 63, it's my best amp, well I'm going to try acouple things, I noticed on the amp. Afew changes in the circuit, I'm not worried about original, some animal already was inside of it. Thanks though
@@UncleDoug half the signal on V1 goes to ground, it goes through a .0047 cap then through a 470k resistor then to the to ground before it goes to grid pin on both channels. Then it has 250k volume pots which cuts gain, it's so confusing, I work on fenders and Marshall amps, so I'm going to fenderize it abit. The transformer for phase inverter seems like more work.
***** Greetings, Felix. Many years ago, I restored antique jukeboxes for a living (as well as several other "careers"), but have long since retired. Guitars and amps are now simply a hobby for me; however, I still do some work for musicians and collectors. Good luck with the GA-35. The circuit is overly complex, somewhat self-defeating, and a little challenging to work on, but they are potentially very good amps.
i have a question i am a bit rusty with the ohms law i need to know how to work out the bias resistor for a 6v6 i am using cathode bias resistor. or just work out cathode bias resistors in general. i have a plate EHT is 290 thanks ian
ian forster Ian, bias resistor values are generally adjusted on a trial-and-error, common sense basis. After you calculate the plate dissipation (see my videos on SE and DE amp biasing), if it's too high, you increase the bias resistance and if it's too low, you reduce it......and then re-measure and re-calculate the PD. Repeat until the PD is acceptable.
I'm not sure where the 19 or the .074A (PC of this magnitude is in Amps not mA) came from, Ian. But if PV = 285V and a single bias resistor of 256 ohms was used to bias two 6V6's to produce a PC of 37mA in each tube, the PD for each 6V6 would be 10.5W, which is an acceptable value.
grid number 1 voltage -19 volts. zero signal plate current .070 ma. zero signal screen currant .4 ma @ 285 volts i got theses number from my RCA data book i send you photos of the amps i built = 256 ohm
You are reading from the Class AB column (Two tubes in Push Pull), so this data (i.e. 70mA PC) is referring to two tubes, not one. What formula are you using to calculate the bias resistance ?
nice work on getting the twang lost... one player of a band i repaired for played his base guitar as hawaiian steel and so i used a relay and added a switch to defeat your modification, so he could use the twang.....ka1bbg
brian foley Thanks, Brian. Your switchable modification sounds interesting. I guess the twangy-ness might work for a steel guitar.....it sure doesn't with a regular guitar :)
yea at 250 watts you could pierce ear lobes.. when you only have 3 mebers on a band, they played 50-80 rock, started out 5 years singing country and western....i used a delay with a tremelo very slowly and feed to the audio back into the stage amp.... made it sound like 2 lead guitars.....innovative using a base guitar as steel guitar.... they played and sang almost every request..... including dean hoe in hawiian bar...brian
I got a very clean example at G. Center years ago, I fought with it to the point of madness .... And then got out my side cutters , put a garbage can by my side, and completely gutted and threw away everything in it . Made a Princeton rev. Eyelet board , got a schematic , and made me a Damn good amp. Beware of this line of Gibson's!
Hi Uncle Doug. Got my hands on one of these and working through it. I found there are 2 schematics for this. Mine is here. www.infernalracketstudios.com/Gibson%20GA-35RVT%20Schematic%2012-65.pdf My current problem: B+ is very low 240v and my filaments at 2.8v. Would an open rectifier diode cause this? Bad power xformer? other ideas? Also, signal gets through even with volume pots zeroed and it's loud. Thanks for your wisdom. (I love linguini btw)
+Corey Collins Since the filament supply isn't rectified, a bad diode couldn't cause the low voltage. Assuming that the voltage measurements are correct, are you sure it isn't a 220VAC power transformer....being operated at 110VAC ? I'm surprised that the signal has any volume at the voltage levels you reported, let alone a high volume. Perhaps the volume pot(s) have lost their continuity and/or connection to ground. Good luck.
Maybe. I'll check the pots again next ensure that he correct windings are used. Can't find a schematic for this Gibson transformer (is there a 220v winding?)- the part # is correct so I'll have to check the leads...
I wish I were lucky enough to find the cool vintage amps that you find. Best one I landed was a GA-5T (63' brown Skylark)..... Needed caps and the cord... It's alive, but Holy treble! What I found, that MAYBE Gibson was aiming for... I take my Gibson guitar, with the tone knob in the MIDDLE position, and it sounds great... not shrill. The GA-5T has NO tone control, so I Guess they expected you to use the tone control on your guitar. Gibson amps do sound WEIRD with non-humbucking guitars plugged into them though.
I think you're right, DK. The built-in shrillness of many Gibson amps may well be to compensate for "muddy" humbucker pickups. God help you if you plug in a Telecaster set to full treble, however. It can melt the fillings in your teeth :)
Uncle Doug Well, as you know, Once upon a time, Guitars and amps were sold as "sets"... so it would make sense that Gibson amps were optimized for Gibson guitars. My associate plugged a strat into the GA-5T, and freaked out... but his SG sounded right. I'm really thinking that Gibson amps high treble output WAS to brighten the HB pickups.... The Gibson amp sounds great (stock tone) with HB pickups of various makes... The guitar's tone knob is actually pretty handy for these. Many current guitar amps are too dark.... Dare I say it, I want both extremes so I can have a happy medium. My own kit built amp "Mr. Big" is such an example. It's like lots of the Fender amps that had a bright switch... that'll make it sound just like one of these Gibson amps... Unless you play with fingertips, I just think the bright switch is too much.
Good stuff Uncle Doug 👍
I had a 1965-66 GA 45 Saturn that I could play directly through the Reverb with the volume off, lol.
Two 10 inch CTS ceramic speakers, bright sounding and lots of Orange drops.
I believe the "bright sounding" part, for sure ;)
Used to have a GA5T Skylark from this era, when you started playing that tremolo it brought that old feeling back. Love these little Gibson amps!
It's good to hear from someone who appreciates 60's Gibson amps, RC.
Thanks, JGK. It's a 1981 Vantage Performer Model VS-695 that I picked up, in lousy shape, from a pawn shop several years ago.....for about $200 (with a nice case). After a whole bunch of work, it turned out to be a very playable, good-sounding guitar. The key to these old Matsumoku guitars is the MMK-45 humbucker pickups.....extremely hot and responsive. Before I got hooked on amps, I was a dedicated guitar restorer.
I have one Vantage with matsumoku pick ups just like yours Uncle Doug, Ive owned it for many years and its been thru a lot, including the body completely broke in like three pieces fortunately the neck didnt break so I put it all together and is working better then before! :) I just love it!
Nice videos, I like what you've done here. I had one of these for a few years in college and found that the cabinet can be much improved for bass response as it is quite small and lacking in diamention front to back. First I removed the baffle and installed foam weatherstrip all around it. Then I installed 2 or 3 layers of weatherstrip between the chassis and the top of the baffle for a more complete baffle. This yellded tighter bass and more or some push. Big improvements.....
Thanks for your nice comments, and for sharing your modifications, AO :)
Back in 1974-75 The other guitar player in the band I was in had one of these gems. I used it for about 6 months for gigs and band practice. This amp was as good or better than anything fender had in this wattage range. The reverb was to die for (and I'm a big fan of fender reverbs). Dale Moore did most of the country lead playing and I did most of the Rock leads. Other than a crybaby pedal (and not often) I just turned the amp up and the tone took care of itself with the right amount of gain. I was using a black 1970 Rickenbacker 330....My Mom loved me :-)
+dalekenjarvis It's nice to hear something good about Gibson Lancer amps, Dale. Thanks for your input :)
Amen, CD. Trying to repair transformers, coils, reverb transducers, etc. can be a daunting task. I got one of those visor magnifiers, like jewelers wear, so I can at least see......or sort of see......the microscopic wires. It's usually a crap shoot and you can't always succeed, but when you do (as you did) it's a very rewarding experience.
You're welcome, Joey, and thanks for the tip on the liquid tape. Re the Crate amp, I have no experience with them at all, but it sounds like you are making some good changes. One thing that really affects head room and gain is to get the output tubes properly biased. Too low and you lose headroom, too high and you gain headroom but burn up tubes.....it's a balancing act, but definitely worth the trouble once you get it set properly.
You made the amp sound and look allot better than it was, but still not my cup of tea at all. One is for sale locally, and before I contacted the seller I thought I would come here. Glad I did, saved me allot of time and trouble. My 1974 Vibrolux eats that amps lunch.
Thanks, P. To be honest, your Vibrolux would eat the lunch of most amps :)
Doug, I hope you get paid a lot of money for this stuff, you are a true expert.
Michael McGlynn Thanks so much, Mike. Actually, it's more of a hobby for me. Hearing positive comments from viewers (like you) is the only "payment" I seek :)
Thanks, Edwin. Please stay tuned for more vintage amp videos...........
These have an optical tremolo that is very prone to failure. There is a little light bulb that flashes onto a photo resistor, and the light bulb burns out. I believe it's a 28 volt bulb and hard to find. It's in my video. Humming (that does not obey the volume control) could be due to leaky filter capacitors, which may need to be replaced, unless it's very slight, and then it's probably OK. Many amps hum a little louder when the reverb is turned up, so that's not a problem. I hope this helped.
I gleaned some valuable info on one of these that I'm working on. Will do the sound improvement mod. The reverb transformer had both lugs missing, so I found a replacement from mercury magnetics.I'm having a tougher time finding replacement knobs. The amp was a barn find so I was prepared for the worst, but I put tubes in it and It works. So it needs caps but the tremolo works and the pots are quiet. I will also put in a second rca jack chassis mount for the reverb so the lugs / wires won't get pulled out again. Thanks for helping me get through the Gibson wIlderness.
+kevin healy You're welcome, Kevin. These amps are generally inexpensive and readily repairable to acceptable tone standards, but the reverb transformer is an accident waiting to happen.....as you discovered. Best of luck with your restoration.
Great videos as always Doug. Thanks for posting these.
+Michael Streets You're welcome, Michael. Thanks for watching :)
I have no experience with the GA-77 RET amp, but a chart I have says that it should use a Gibbs Model C Reverb Tank which is the same as an Accutronics 4FB2A1C Tank. I hope this helps.
....further in the circuit. They are intentional gain suckers meant to keep the amp from overdriving. Jumper these out, and really enjoy what these amps can do!! Much more gain!!
Great video Doug, many thanks!
You're welcome, SS
Hey Uncle Doug, If the bed springs are sqeakin', don't bother peekin'. Just kiddin'. I hope your all well. Best tube amp channel bar none. Take care, C.
Thanks, Cass. All is very well indeed. If your shorts are a squirmin'..... it's time for a de-wormin' :)
just realizing now, most of the videos I enjoy most in this category -are rescues of some of the worst-cared -for devices of their species. It's a thrill to watch them claw their majestic ways back to life to scream again.
An interesting observation, Malcolm. I agree.....the ones brought back from the dead are generally the most impressive :)
Doug,
Love your videos, very informative. I am glad I watched this one, because it convinced me to stay away from a GA35 I was considering. I hate working with linguini ;^)
Thanks
Thanks so much, WC. I have to admit that it was indeed a healthy serving of linguini, but now that I reflect on the experience.....it wasn't all that bad :)
Bought a Lancer several years ago, needed some work. All it did was hum,
loud enough to probably blow the speakers. After checking everything , I found
a bad connection associated with the RCA plugs on the reverb tank. Played great
after cleaning those plugs. I bought another with a fried power transformer. Replaced it with a slightly smaller Hammond unit, new, in the parts stash, worked great, seems
none of the tubes were affected by the "fire". I always wake tube equipment up
s l o w l y on my variable transformer, when it's been inactive a while.
+sierraromeo The Variac is always a nice, gently way to bring dormant electrical equipment back into use, SR. Thanks for sharing your experiences with Lancer amps :)
Nice amp and sounds good now. Seems to sound like it should. I had one with nothing wrong with it but the cap. The volume was not great but were not real beefy. Good luck!
Thanks, Dennis. These 60's Gibson's are generally a bargain to buy, due to their tone deficiencies, but they can be turned into decent amps with a little work......
These amps have a unique reverb circuit (if it is like my ga-15RVT which uses el84's...and is currently blown up...ouch). If you use the footswitch to turn the reverb off, you can turn up the reverb level and get a small amount of added gain. They have a gain circuit in them that stays on and inline I believe.
TheDogpa An interesting observation, TD. Thanks for your input and good luck with your GA-15 repair project :)
I use fabric glue for speaker repairs. It works great and stays flexible. For large rips a little piece of cigarette paper and fabric glue woks well.
Mike Powers I never thought of using fabric glue, but it sounds like a very appropriate choice. Thanks for your input, Mike.
There are two different types. One is a washable waterproof type and the other is not meant to be washed and is water soluble, it can be watered down to whatever consistency you like.
Good info. Thanks again, Mike.
Another great video from Uncle Doug! Love this amp. When you were demoing the Tremolo, I was sure you were gonna break into some Turtles or Beau Brummels. Very much their sound. Just a couple of questions: Does the "35" in this amp's name denote the wattage of the amp and was that a 10" speaker or a 12? Ok, going to watch your tone improvement video on this amp now, as I agree, it is a little "tinny" overall. Thanks for creating this channel. Very entertaining and some really great info here. -b
You're welcome, Dean. Yes, it is rated at about 35W. I believe the speaker was 12". I did find a way to improve the tone quite a bit, but never could get it to sound quite the way I hoped. Perhaps it was just this amp; however, I have since had the opportunity to try out an identical one.....and it sounded just the same, with all sorts of reverb and tremolo problems. It appears that this was not a terribly reliable circuit, at least for the two I tested. Hopefully, others have had better luck with it.
All information is helpful. Thanks alot. the humming is very slight. and its always there, i can live with it. One more question; is the 6FQ7/6CG7 driving the reverb? does it do anything else? I will be taking this guy into a tech, it needs a checkup. thanks for taking the time to answer me.
Not sure if you take "requests", :-) but I would love to see you make a video that's all about your Hickok 600A tube tester. It's use and operation and how to test multiple tubes. I've thought about getting one but am worried it would be overwhelming. But with your knowledge and ability to convey said knowledge, I think it would be thoroughly fascinating! Just a thought.
Kirk Jones Greetings, Kirk, and thanks for the suggestion. To be honest, using a tube tester is rather simple. The 600A has a scroll chart showing the settings for each tube. You simply plug the tube into the correct socket, set all the knobs to the prescribed values, and then push a button to test for emission (output strength) and internal shorts. It is so basic that a video showing the testing of more than one tube would be a little tedious. Don't be intimidated by tube testers.....get one and, through usage and experience, it will become one of your favorite and most useful tools.
Uncle Doug...love your vids as always.... Got this amp and replaced all tubes...did your mods and it sounds great! Thanks! Can't get trem to work - rebuilt my roach (seems I may be getting a steady 4.5v across the opto lamp but not lighting up) (6.5v with OA2 tube removed).. checked the footswitch and even bypassed it manually to test. Cant see to get the trem to work . What to check next? Note: I rewired the 6EU7's to 12AX7's. Also noticed I need to engage reverb footswitch to get any sound at all on reverb channel - engaging reverb footswitch seems to act like a relay of sorts to get any sound coming through reverb channel. Replaced opto lamp with recommended replacement but no luck.. OA2 is a new NOS also and lighting up.....
Thanks, T. Congratulations on your successful modifications. Photo-resistor tremolos can be a real challenge in many amps. As I recall, the voltage to my neon bulb was much higher than yours.....around 150VDC. What is the plate voltage on V5b ? The OA2 is a voltage regulator and should be maintaining about 150VDC in the neon bulb loop.
Thanks, I have 2 gibsons the Lancer 35 only had chassis its in a custom cabinet but it has the Ice Pick Tone. I have 1 35 Watt Gibson DuoMedalist 12 inch speaker like new with the orginal Gibson Cover its very brilliant. I put an older anico speaker which gave it some better tonal response. Only needed a White Block Resistor change.
+James McCutcheon I like that term "Ice Pick" tone. It describes it quite well.....almost like fingernails on a blackboard :(
My son is going to the tone stack mod. And new power cord grounding and check the death cap. Ee really appreciate it. This amp can really crank out some powerful sound and with some incredible tone.
Good luck, James.
Sissy, IMHO these 60's Gibson amps are tough to work on. I can try to answer some specific questions, but I simply can't provide any in-depth long-distance diagnosis and repair work. Tell me the issues and perhaps I can give you some help you with some of them, but any heavy repairs will have to be done by an amp tech.
A shrill treble is actually a good thing, set the Bass at about 4, and the treble at 5, and then strum the Guitar In D with the tone knob on the Guitar at max high. Keep turning the amp treble up till it's a little too shrill (maybe even a notch up from that) . Then turn the tone knob on the Guitar down to choke the treble to where you like it. That's how Albert Collins does it. Always worked for me.
Autojones Very interesting, AJ. I'll give it a try :)
Nice demo. What kind of guitar were you playing?
Thanks for posting this. I have an Epiphone EA 26 RVT Electra and the Reverb control has no effect. Reverb sounds like it is at max output all the time. I shorted the center wiper of the reverb pot to ground. No change. I removed the wire from the center wiper to the tube. No change. Any thoughts?
Sadly, the only schematic I can find for the amp in question is unreadable. If you can provide a link to a clear, legible schematic, I may be able to help.
Hey thanks for posting this. It is next to impossible to get any info on these old gibson amps. I'm new to amp repair so forgive my ignorance. I recently found an old GA95 RVT "Apollo" amp in my storage room. I got all new tubes (2x6EU7, 2x12AU7, 1x12AX7, 4x6L6, 1x0A2), cleaned the sockets, checked main the fuse, the power cable seems to be intact, and yet when I turn it on I get nothing. My question is do I need a fuse in the housing for the aux power plug in the back as well? That housing is missing it's cap and has no fuse in it. These also seems to be a tube socket that is not on the schematic that I have and I have no idea what it's for and as with your amp from this video the chassis is not marked as to what belongs there. Currently it has these in it 2x6EU7, 2x12AU7, 1x12AX7, 4x6L6, 1x0A2. Thanks.
as ever,
Skimbo
Greetings, Skimbo. There are many reasons why an amp can be stone dead. You seem to have all 10 tubes. If there is an empty socket, it should be a small one for the footswitch, and the amp can run without it.
You don't need a fuse in the aux. outlet to make the amp run. Be sure the amp fuse is good (test it, don't go by appearance). Do any of the tubes light up or get warm when the amp is in Standby or either of the On positions? If not, it could be the cord, the plug, the switch, the power transformer, etc. etc.
You need to start at the wall outlet and check (with a VOM) to see if the proper voltage is getting to each of the amp components, in order. Good luck.
Uncle Doug
Correct I see in the schematic that that small socket is in fact for the foot switch. Still learning how to read this stuff. Negative, nothing lights up/gets warm. Cord is the original two prong and is likely to be at fault. My VOM is coming in the mail that's how new I am to this. Thank you for your patience with this electronics 101 student.
as ever,
Skimbo
Good luck, Skimbo. Be VERY careful when working on an amp that is electrically "live". As you probably know, there are potentially lethal voltages within the circuit.
Uncle Doug
Yes I am aware that this giant hunk of metal filled with wires can kill me. Thank you.
I have a 1965-1966 Epiphone Futura EA12RVT, it matches the schematic for a Gibson GA45RVT. I'm having a few issues with the amp. I was wondering if you'd be willing to help me out? There is a lack of good info about these amps online and most techs don't have any experience with them.
Nice!
Do you have a manual for this amp? I too am restoring one and don't know the difference between "On" #1 and "On" #2. I replaced the electrolytics and also rewired V1 to take a 12AX7 rather than a 6EU7. Still having trouble with reverb, I am wondering if the little transformer tips are in a similar shape to what you fixed. Finally, well done on your restoration.
Greetings, Roger. No, I have no technical info on this amp other than the schematic, downloaded from the Internet. Also, please see a follow-up video in which I significantly improve the tone of this amp.
I believe the two "On's" allow you pick the one with least hum, like the old hum switch on Fender amps, which selects which AC lead the "death capacitor" is connected to.
The Reverb (and Tremolo) in these amps are a common problem. Be sure your 12AU7 is strong (mine was shorted) and that your cables and tank transducers are in good shape (Impedance: 1475 Ohms in and 2250 Ohms out for Gibbs Model C #6619). If the tank has been replaced (the correct replacement is an Accutronics 4FB2A1C) be sure it's the right tank. I encountered another GA-35 recently that had a weak reverb due to an incorrect replacement tank. The little transformer is generally an all-or-nothing situation: if the connection is broken the reverb is dead.
Good luck !!!!
Hello. Working with a early-mid sixties Vanguard GA77 RET? Think it had the tel ray oil can reverb removed. It has three RCA style jacks on the chassis, can I run a spring reverb tank? which one? Also curious as to the ohms output of the amp. Sorry for the questions but any help or guidance is appreciated.
Sissy, the reverb tank is actually "driven" by a transformer, just like a speaker is driven by its output transformer. The tube that drives the transformer is a 12AU7 and the tube that receives and processes the reverb signal is a 6EU7......at least in a Gibson GA45 and GA35. Hopefully, a competent amp tech can fix it up for you. Good luck.
Thanks for the reply, tremolo is not working, fairly sure it is the footswitch which is identical to the one in your video(reverb comes on with the switch, but nothing happens engaging tremolo)I do have a slight 60hz hum that gets louder with reverb ON/Vol. close to 10. I wouldn't attempt heavy repairs, mostly looking for possible explanations. tubes are 0A2,2x6L6s,6FQ7,4x6EU7,1x12AU7 but has a 12AX7 in its place. Could improper biasing cause hum? it sounds great otherwise. THANKS!
Hi uncle Doug enjoyed the video, I just got one of these amps, it's sounds ok, but don't have much output, any ideas , caps have been changed, new phase inverter trans former and reverb transformer. But everything else looks stock
I have pretty well given up on mid-60's Gibson amps, TM. I posted a video showing how I coaxed some tolerable tone out of one.....but it's quite a chore.
@@UncleDoug I got a Gibson falcon 63, it's my best amp, well I'm going to try acouple things, I noticed on the amp. Afew changes in the circuit, I'm not worried about original, some animal already was inside of it. Thanks though
@@wesleymorris1 Good luck with it, TM. They can be saved......but it's a struggle.
@@UncleDoug half the signal on V1 goes to ground, it goes through a .0047 cap then through a 470k resistor then to the to ground before it goes to grid pin on both channels. Then it has 250k volume pots which cuts gain, it's so confusing, I work on fenders and Marshall amps, so I'm going to fenderize it abit. The transformer for phase inverter seems like more work.
@@wesleymorris1 You know that the input circuit is not optimum, TM. Changing it to a Fender style would definitely be a step in the right direction.
I have a '66 Minuteman, and the trick with these amps is to bypass the useless resistor networks in the input, and also, furt
Very nice.
Uncle Doug: Do you do this for a living or as a side job? I might be getting a ga35 project.
***** Greetings, Felix. Many years ago, I restored antique jukeboxes for a living (as well as several other "careers"), but have long since retired. Guitars and amps are now simply a hobby for me; however, I still do some work for musicians and collectors. Good luck with the GA-35. The circuit is overly complex, somewhat self-defeating, and a little challenging to work on, but they are potentially very good amps.
Thank you!
You're welcome :)
i have a question i am a bit rusty with the ohms law i need to know how to work out the bias resistor for a 6v6 i am using cathode bias resistor. or just work out cathode bias resistors in general. i have a plate EHT is 290 thanks ian
ian forster Ian, bias resistor values are generally adjusted on a trial-and-error, common sense basis. After you calculate the plate dissipation (see my videos on SE and DE amp biasing), if it's too high, you increase the bias resistance and if it's too low, you reduce it......and then re-measure and re-calculate the PD. Repeat until the PD is acceptable.
yar i worked out the basic with my valve book at 285 volts 256 ohm or bit higher 19 divided into .074 MA =256 ohms
I'm not sure where the 19 or the .074A (PC of this magnitude is in Amps not mA) came from, Ian. But if PV = 285V and a single bias resistor of 256 ohms was used to bias two 6V6's to produce a PC of 37mA in each tube, the PD for each 6V6 would be 10.5W, which is an acceptable value.
grid number 1 voltage -19 volts. zero signal plate current .070 ma. zero signal screen currant .4 ma @ 285 volts i got theses number from my RCA data book i send you photos of the amps i built = 256 ohm
You are reading from the Class AB column (Two tubes in Push Pull), so this data (i.e. 70mA PC) is referring to two tubes, not one. What formula are you using to calculate the bias resistance ?
nice work on getting the twang lost... one player of a band i repaired for
played his base guitar as hawaiian steel and so i used a relay and added a switch
to defeat your modification, so he could use the twang.....ka1bbg
brian foley Thanks, Brian. Your switchable modification sounds interesting. I guess the twangy-ness might work for a steel guitar.....it sure doesn't with a regular guitar :)
yea at 250 watts you could pierce ear lobes..
when you only have 3 mebers on a band, they played 50-80 rock, started out 5 years singing country and western....i used a delay with a tremelo very slowly and feed to the audio back into the stage amp.... made it sound like 2 lead guitars.....innovative using a base guitar as steel guitar.... they played and sang almost every request..... including dean hoe in hawiian bar...brian
I think that degree of shrillness at 250 watts would probably be in violation of the Geneva Convention.....definitely "cruel and unusual punishment".
thanks.
I got a very clean example at G. Center years ago, I fought with it to the point of madness .... And then got out my side cutters , put a garbage can by my side, and completely gutted and threw away everything in it . Made a Princeton rev. Eyelet board , got a schematic , and made me a Damn good amp. Beware of this line of Gibson's!
I agree completely, Gary. They are solid, good looking amps that sound like fingernails on a blackboard......and a nightmare to work on.
Vast reverb!!!
Glad you liked it, CP.
MWA in the us supplies speaker parts Doug
ian forster Thanks, Ian.
Hi Uncle Doug. Got my hands on one of these and working through it. I found there are 2 schematics for this. Mine is here. www.infernalracketstudios.com/Gibson%20GA-35RVT%20Schematic%2012-65.pdf My current problem: B+ is very low 240v and my filaments at 2.8v. Would an open rectifier diode cause this? Bad power xformer? other ideas? Also, signal gets through even with volume pots zeroed and it's loud. Thanks for your wisdom. (I love linguini btw)
+Corey Collins Since the filament supply isn't rectified, a bad diode couldn't cause the low voltage. Assuming that the voltage measurements are correct, are you sure it isn't a 220VAC power transformer....being operated at 110VAC ? I'm surprised that the signal has any volume at the voltage levels you reported, let alone a high volume. Perhaps the volume pot(s) have lost their continuity and/or connection to ground. Good luck.
Maybe. I'll check the pots again next ensure that he correct windings are used. Can't find a schematic for this Gibson transformer (is there a 220v winding?)- the part # is correct so I'll have to check the leads...
I wish I were lucky enough to find the cool vintage amps that you find. Best one I landed was a GA-5T (63' brown Skylark)..... Needed caps and the cord... It's alive, but Holy treble!
What I found, that MAYBE Gibson was aiming for... I take my Gibson guitar, with the tone knob in the MIDDLE position, and it sounds great... not shrill. The GA-5T has NO tone control, so I Guess they expected you to use the tone control on your guitar.
Gibson amps do sound WEIRD with non-humbucking guitars plugged into them though.
I think you're right, DK. The built-in shrillness of many Gibson amps may well be to compensate for "muddy" humbucker pickups. God help you if you plug in a Telecaster set to full treble, however. It can melt the fillings in your teeth :)
Uncle Doug
Well, as you know, Once upon a time, Guitars and amps were sold as "sets"... so it would make sense that Gibson amps were optimized for Gibson guitars. My associate plugged a strat into the GA-5T, and freaked out... but his SG sounded right. I'm really thinking that Gibson amps high treble output WAS to brighten the HB pickups.... The Gibson amp sounds great (stock tone) with HB pickups of various makes... The guitar's tone knob is actually pretty handy for these. Many current guitar amps are too dark.... Dare I say it, I want both extremes so I can have a happy medium. My own kit built amp "Mr. Big" is such an example.
It's like lots of the Fender amps that had a bright switch... that'll make it sound just like one of these Gibson amps... Unless you play with fingertips, I just think the bright switch is too much.
I agree with your analysis, DK. Thanks for your input.
What a mess better had an original one. Then you could restaurate the right way.
Try it and see, WW. The original versions sound awful.
@@UncleDoug I bet it does😂