How to repair noise Fender Dual Showman 100 watt 6L6 tube guitar amp
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- Опубліковано 19 сер 2016
- This amp came to D-lab in desperate need of repair. One tube socket was burnt, Bad reverb transformer. Many bad connections. 6L6 tubes were shot. Many hours went into troubleshooting & repairing. However, now it plays well. Great to restore life to the vintage amps. I hope the info presented is of value to you. TD
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Dear Terry @ D-lab, I am sorry for addressing you as Uncle Doug. I follow you faithfully and I appreciate you abilities. Thank you for your productions.
Wow, that poor old Showman needed some TLC. Very nice resurrection Terry.
The best troubleshooting video I have seen so far. Everything was wrong with the old showman. Great Sherlocking!!!!! cracked internal connection in a resistor?? open transformers??, bad pot noisy tubes, burnt resistor, unsoldered components, dry solder connections, corrosion, noise wrong value resistors, sheesh. I learned a bunch. I would have never caught that intermittent resistor.
Something I've learned from watching amp repairs here and elsewhere is that it seems to be a pretty common thing to find a random unsoldered connection or two even after being built and used for decades lol
Wow, it's been a few years since I worked on a Fender Dual Showman. The last one I repaired was a 1969 vintage. Dual Showman is basically a Fender Twin Reverb in a separate cabinet. I took notice to the RCA 6L6GC's you had there. One thing I can vividly remember was, once 1971 rolled around, RCA started to make lousy tubes. Mainly the tubes which had the RCA printing in Block letters. I had so many new defective tubes back then it wasn't funny. I used to make trips back to my old parts distributor almost daily! I used to go through a whole sleeve of 5 tubes to find a quiet 12AX7/AT7. i switched to GE and Sylvania tubes. No problems with them. Good video as always! :)
This is the 1st Showman to come into my shop. I would have replaced the eyelet board, but my investment is quickly equaling the amps value. Yes, it was loaded with bad connections. A new eyelet board would do this thing wonders.
A few months ago, I was working on a customer's '66 BF Bassman that had just as many different noisy sources from broken bias supply cap leads, to drifted resistors all throughout the preamp, to finally a partially shorted output transformer (yes, partially--that was replaced in the 70's probably). After weeks of chasing noise sources, that amp turned out better than any other 50w Bassman in the area.
I couldn't believe the amount of internal damage--a little bit of TV tech hacking from 40 years ago, but it seemed to have been thrown over a cliff or something. This vid reminded me so much of that repair. Gotta be thorough.
Thanks Terry!
I had one of these silver face duel showmans about 20 yers ago. Bought it for $175, in mint condition. It made an amazing bass amp. I used it with a 6 x10 cabinet and a 2x15 cabinet. Forget ratteling the walls, i could crumble them. As a guitar amp, they are very under rated. No idea why they don't have more collector appeal. Great info, and a great reminder of my youth. Good job Terry, seems like this one was kinda a tedious repair.
Thank you for a good video. It is good to see someone who really showing the basics, like tapping on the board and the components until the right component is found, as it could be very hard to spot a crack. I have the same amp and mine has a problem on the vibrato channel. When the amp starts getting warm it will distort and at the same time the volume increases a bit. I will check all the solders and resistors as I think there might be something wrong there. I have already changed out all the caps and the tubes as I had some new laying around (and the power tubes was really shot). IMO these amps are gold with a sound to adore and I really need to get mine up running again.
I remember those old Fender Showmans from the 60s. Great amps. The one that came into
your shop has obviously seen better days , but still deserved to be resurrected into working
condition. Lots of work on it.l.especially replacing that burnt out tube socket. and
transformer.
Some of them developed overheating due to corroded socket terminals or tube shorts.
These 100 watt amps were great. Good repair video.
Always learning from your videos,thanks Terry
Yes, D-Lab, I did enjoy that production. Thank you.
Another great video with wonderful troubleshooting tips. Great stuff as always :-)
Great show man by a great showman repairing a great showman!
I had a 67 dual showman that bought new and never had a problem with it. I used it for auditorium gigs. It would make your ears bleed. Great videos.
You did it again! Another fantastic Video! Other's might have given up or just called it completed leaving a few bugs. You restored it to like new. Great job!
It is amazing how well made these Fender amp are, to take all that hard abuse and still work glad you can bring back to life.. good job
Bob Barcus not this one. It was poorly built at the factory as you just saw.
Great job! I like how thorough you are. I repaired commercial aopliances back in the 80's. Sometimes it was a very long drive to the job site. You had to be thorough like that too, if you didn't want to make a long return ride for free! Nice work!☺
Great video. Your Chicago accent always cracks me up too. Thanks.
You do good work Sir. Always learning something new.
Enjoyed the when the tube socket was tossed in the trash can...very satisfying! 😀
I recently got a vintage Showman amp head (non-reverb) 1967-69 era with a production number 4. I don't know if it is the 4th in production of this blackface or what, but thanks to your insightful vids she is well taken care of.
Although I would like to become a ham operator, I really, really enjoy and learn from these jewels of videos on guitar amp repair and mods. Keep um' comin Terry! Thank you for sharing your vast knowledge. The first thing I learned about electronics is you have to have the courage to open the cabinet and troubleshoot the problems. You have to have confidence! You most surely have It! Thankz
Yes it is a beautiful painting of wires and resistors
Nicely done and very interesting.. your sound check sounded like an episode of Lost & Space or Star Trek!!!
Excelent video I appreciate you take the time to share your experience and knowledge. Greetings
Very informative, Well done Uncle Doug !
Terry is not Uncle Doug.
That was one I'll Showman! Great video!
enjoy and aprieciate your vids Terry! Cheers!
another great video....good stuff Maynard!!! :)
Nice job Terry
Very nice Young Terry!! Wine looks great! (amps are a bit of a distraction though?!) ha ha!
DAyum, that was a lot of work. The owner most really like it.
Thank you my teacher
Great job!
Great skill . My Dual Showman needs also to be repaired/ Tubes??. Wished you lived in The Netherlands.Thanks.
By the time you are doing the standard electrolytic cap/470 ohm screen replace on a 40+ year old Fender amp you are hereby commanded to replace all the 100K ohm preamp plate resistors, the ones arranged in the "V" shape. next time you do an old Fender, replace the e-caps and fire her up. Now go replace the 100K plate resistors with 2 watt metal film resistors. The amount of hiss and static that will take out of the amp will knock your socks off. For 30 cents each, you just gotta trust me.
Another brilliant repair..
Nice work - on some of those sf's the cathode resistor an the verb tube is too low -- underbiased -- try 2k2
I keep getting drawn back to this one. I remember paralleling the 6L6s in a 50 watt Bandmaster head. Quite a challenge cutting out the holes for the extra 6L6 tube sockets
to try and get more power out of it. 4 x 6L6Gc. It worked but I was always worried about
the O/P transformer primary winding and it's current capabilty. Also saturatiion of the core,
but regular guitar frequencies are not as consistent as sine waves from a audio generator,
so it may not been an issue.
Hello, I'd say the OT primary was mis-matched after adding the two extra 6L6's. However if it didn't melt down and sounded OK, mission accomplished. Theres nothing wrong with experimenting + enjoying the hobby. Of course, these days collector value would make this mod a second thought. Do you still have the amp?
No, it was sold or traded in on a guitar back in '67. As they say, I was young and stupid, oblivious to the fact that 50 years afterwards these
would be highly sought after as collectors amps.
Had I managed to hang on to it all these years, I would have done a more scientific measurement re-mod, doing a plate current/primary winding impedance match and set the bias accordingly. Replacing the o/p transformer with beefier version from Hammond or other manufacturer.
Same with some Kalamazoo made Epiphones that I traded for something else that I would have held onto today...who knew back then.
As it turned out, the o/p tubes and transformer held up remarkably well
to normal guitar volumes, a testament to how good these 60s Fender amps were put together, but I never did an audio generator frequency
sweep on it with a proper 50watt load resistor to find out what kind of
power I actually gained by doing this seat of the pants mod.
Suggestion? Please do a review of the Tremlord 30 by Orange Amps? It would be good to see even an online review of your thoughts.
I have one just like it, is there any possibility to covert it to twin reverb?
Very informative video. One question though, when you were checking the neg DC bias voltage to balance the output tubes, shouldn’t you have checked one of the inside tubes and one of the outside tubes rather than just the two inside ones? I thought the pairs were the two outside and the two inside. The way you did it seems like you just balanced one side. Am I missing something here?
Another nice trouble shooting/repair video Terry...... those chopsticks really do come in handy! Being that the amplifier was so original, do you think all the poor soldering connections (which seemed to cause most of the issue's) were from poor quality control at Fender? Just a thought Terry, I understand the necessity of the signal generator for diagnosing and repairing, but for the audio testing it always reminds me of a 50's sci-fi movie... maybe you could get Tony to make a guitar recording just playing a 12 bar blue's riff, or even just a couple chord strums, and play that through for the audio test... Thanks for sharing your knowledge.....Take care, Tom
The signal generator is used to produce a nice clean sine wave at a constant frequency. A guitar chord progression would hard to use to diagnose.
What is the difference between this amp chassis and my Twin Reverb (also -w- a master volume) chassis ???
I have got the same amp. Sometimes I hear a soft low deep sound like an explosion. And the sound(power) volume gets lower.
I’m working on two Silverface Fenders, a Deluxe Reverb and A Bassman 100.
Both have some “ac scratchiness” on the chassis near the input sections,
I’ve swapped out every component, changed all pots and tube sockets, and even looked at the bottom of the tag board and eliminated all extra solder blobs.
Any ideas as to why I’m getting low-level sputtering and “ac scratchiness” when I drag pliers across the chassis near the preamp circuit?
Occur to you to clean the board up?
Because of the warping to the board, would you not have considered changing out the eyelet board completely? I know several companies provide replacement boards, in both eyelet and turret versions.
Its a lot of work for sure but is it a case of keep it original for history sake or is it better to have a working, great sounding amp? I personally dont hold much in the 'carbon resistors are better' school, my view is that most of the sound comes from the better iron in the older transformers. Some say i'm a heathen for putting in metal film resistors if the originals are suspect but in blind tests, most people cannot hear a difference. Your views?
Anyway, keep the videos coming, its great to see someone else having the same two hobbies as myself, guitar amps and ham radio!
George G0JKZ
Learned a great deal from this video as I usually do from your theater productions, Thank you! My question, after testing the RCA'S and finding them faulty in circuit, what's the take away? I might have looked elsewhere after just checking the tubes.
The suspect tube was microphonic. Then of course there wer other sources of noise. I just take it one step at a time.
+D-lab Electronics Thanks.
He taught me how Link Tube le 84 easily available
I enjoyed that.... as a matter of fact, I enjoy them all... Just wondering why you don't, especially this amp, blow the bottom out with compressed air and get out all that Mummy Dust out of there....?
Hi, mine is a '69 (no master volume). Great amp but tremolo is weak in my opinion, it becomes just perceptible at about 4 on the intensity: do you think it's not working as it should? What about yours?
That Bias issue is why people usually "blackface" the silver face amps.
The End was awesome. 😂
When it comes to replacing noisy ceramic disc caps, are silver mica an appropriate replacement or am I better off getting the sprauge/vishay polypropylene orange drops? Thanks
Orange drops are the widely used choice of today for most amp shops. Ceramic disc caps are very robust though and rarely go bad.
At 12:06 you missed a blasted Resistor?
cool vid. love your troubleshooting technique. one quirk these later silverface fenders had was they coated the eyelet board with wax and it trapped moisture and would become conductive between components to a measurable degree. Are you familiar with the blackface mod. It is probably the most popular silverface fender mod and it involves changing back to a variable bias circuit. the consensus is that it is a large improvement.
curious, what does a repair like this cost? I have a 68' Twin Reverb i'd like to have gone through and tuned up back to factory specs.
Hello, it is a moving target. Cost is hard to specify until I see the patient.
3:30 I spot leaky old filter caps... 4:00 Yup, I was right.
Where do you find the schematics for the 73' Dual Showman and what numbers are used to Identify them? I've looked all over.
I believe I found the schematic on Wattstubeaudio.com
I've found a few schematics but I guess my real question is which one is the right one for my particular Dual Showman. Some of the options were the AA270 schematic another was the AA769. I've heard one way to tell is to look at the tube layout diagram inside; however, my diagram must be missing the part with the schematic number on it. Is there any other way of telling which schematic to go by?
Also, at cursory glance the circuit layouts look the same so any variations would be minor. Are there any particular nuances I could look for in the amp that might indicate which Dual Showman schematic to go by?
For that same amp as a twin it is circuit sf100. Mine is a 73 twin
Hi Terry, what's your go/no-go emission cutoff for a tube? 80%?
Yes, in that ball park, unless they are still matched, not noisy and the customer is good with the sound/performance
really really good work there.. i'm very curios how much cost a work like this one.. i live in italy and i love to have d-lab here near me for fix my fender deluxe 85 little noise ( hmmm) hehe
on trasformer and i ear it on speaker too.. same volume noise with o without guitar in.! some idea? tranformer?
tks lot if u answer me ..!ciao...
! big ciao from italy
Often, noise is from a tube that's old and worn out. The tube farthest from the big power tubes is usually the culprit. But not always, because the outputs from that tube go through more stages of gain than the rest of the tubes, and any noise there gets the most gain. You can try putting in different tubes, and see if that works. Use a 7025 for that first tube, it's a military-spec 12AX7 that's been selected for low noise output.
If you try new tubes and still have noise, here's an inexpensive thing to do: If the noise is a fairly steady hiss, the chances are that it's caused by certain old resistors in the preamp. Those are almost always 100kOhm resistors in Fender amps, on the tube plates and grids. Replace every 100kOhm resistor in the preamp section, and see if the hiss goes away.
If the noise is a steady hum, it's probably the large capacitors in the power supply, the ones under the pan. Follow our Uncle Doug's safety precautions and discharge those caps using a resistor. Use an insulated alligator clip to hold the resistor to the leads of each cap, with the other end of the resistor connected to ground, and give each cap several seconds to discharge, The longer, the better. Even then, caps have a "memory", and won't be totally discharged, so be extremely careful. Do not touch the leads while you replace those caps.
While you're in there, look over everything carefully, and check for any loose solder connections, damaged wires, burnt areas, etc.. Always leave the standby switch in the "off" position when you turn on your amp, and try to leave it for at least 5-10 minutes before turning the standby "on". Stripping is for dancers, not cathodes.
If you aren't sure what you're doing, take the amp to a qualified repair person. Just my two cents' worth, hope it helps.
Hi im so tks for this help... and im very sorry.. becouse i didnt tell u that my amp is solid state amp type... is it the same ? What i can check before go tu the assistance?
GK asked a similar question: Any concern about the warped turret board components shorting against the chassis? Thanks
Is the tube with the top hat from a "Ham" radio? LOL
Hello, no worries on the board shorting. If the owner requested it replaced, I'd hop to it. I agree, the board is in sad shape. TD
My AB763 board had an internal short (many old fenders do) and made noise. So I sandwiched a piece of plastic between the 2 layers of board. I cut the plastic from a Large Folgers coffee can.
they are good valve socket it's all i use
What were they called?
molex sockets
www.fishpond.co.nz/9319236845264
www.karltone.co.uk/valve-tube-sockets-79-c.asp
www.aliexpress.com/item/9pin-Belton-Style-Tube-Socket-Bottom-Mount-12AX7-EL84/2031085874.html?spm=2114.40010708.4.19.3WsoCw
Looks like dude kept it in a wet basement or something... that Eyelet board got moist for sure.
I agree, not a barn, but maybe a humid Michigan basement
I know what's that like... Being from the Cleveland area... lake humidity.
650 Volts + Wine.. ...well, what could be wrong? ;)
holy crap!!! lmao!!
That is not how to bias that amplifier. That not even how u balance the tubes. Please do not follow those instructions. U still need to see what the current draw is on the tubes and make sure its idling at a safe plate dissipation.
Lol Funny comments “BarkCity” hahahahaha