My 1972 came with the JBL's, but the cab was falling apart. The former owner had extra screws and even nails holding it loosely together, so disassembled it. I actually prefer the Jensen C12N's for an original warm round tone or the WeberVST equivalent. I didn't know Eric Johnson had signature speakers by Eminence. I'll have to investigate!
I am humbled that Lyle forgets stuff too. I bought a cheap whatever the midline squeeze action cabinet 24 inch clamp is at Harbor Fright and turned the toe piece around so the clamp is now a spreader. A couple of light squeezes after the clamp is tight enough to hold itself in place and those chassis will slide out much easier. If there are screws to loosen up, LOOSEN them up FIRST! Always a pleasure to watch such a high level of truly professional pride in workmanship from the impeccable Mr. Lyle. When I was 12 years old I blew a part of my finger off fixing Mom's Supro amp. That was 45 years ago. I have had ONE worse shock working as an industrial electrician on 4160 volts so guitar amp hazards are no joke.
One one occasion when I was working on a Marshall 50 watt plexi I forgot to discharge the mains filter caps. DOH! I had both arms on the chassis and I touched something which I should not have done. About 450 volts went in one arm, across my chest and out the other arm. It blew me backwards off of my feet and hurt like hell. I am amazed it did not stop my heart
Nice to hear about the new style cable glands. I recently had to replace one in a Vibrolux Reverb I had just bought, and the one I ordered from AES was too small for the massive 3-prong cable that was in the amp. (I did measure the cable with my "Executive Pocket Chum" caliper, and thought I ordered the correct gland). I ended up using a power drill to make the hole in the cable gland slightly larger and managed to finally get it installed. Hopefully it will never have to be removed. I think most of us interested in amp servicing will sit through a long video, even if it contains the same info as a previous video. Sometimes repetition is good for learning. Have a banana!
I still use foam to hold down the caps in the doghouse. I use the current shunt method to bias as well, and you’re right. It’s dangerous ass heck if you don’t have a secure connection. Very easy to short out 400vdc + to the chassis/tubes, or worse, YOU. Great restoration on this fantastic amp! Those WGS G12A’s are amazing speakers. They just cost as much as a ratty mid 70’s Twin for a pair.
I was measuring plate voltage on a Super Reverb power tube and my multimeter probe slipped so it contacted both B+ and a tube socket tab connected to ground. Half of the tab on the tube socket disappeared in a flash. Talk about a brown pants moment …
I use the output transformer resistance method to measure bias. I use the clip on style meter probes, and do the connections to the tube sockets before powering up the amp. Having 2 meters helps.
I recommend buying a bias probe for biasing, its the safest way, u just plug into the power tube sockets and plug the tubes into it, it reads in ma. And it reads both tubes to make sure your within spec.
Definitely love seeing all the work done, and sometimes the shorter videos are great too. I know the setup and editing has got to be a chore, but it's appreciated!
Ive never seen those "newer style" strain reliefs before but i think love them already lol. Im also not a fan of the older ones for a few reasons. With my own amp builds i just install an IEC socket. But for vintage radios and other older equipment that needs a new mains cable id really love to try out the newer ones. I cant say one hundred percent that ill like it better without trying it but by the looks of it and your description it seems far superior. And its perfect you get them from mouser cause thats where I try to get all my components cause i live close enough to their Mansfield warehouse to use their will call and avoid shipping costs. Thanks for mentioning it!
Love the long videos cause they deep dive into an amp, especially if you can include trouble shooting. Maybe you could do the shorter ones here and there and then pick one amp to do a few long in depth videos on the whole amp so we can follow along. Some fenders, maybe next time a Marshall, Traynor etc. Love the channel!
I noticed that all the WGS Speakers I installed / used (and that's quite a few, including Green Berrets, Reapers (55/75Hz, HPs), ET65, G12C, Black Hawks ) required a quite long time to break in, usually +20h. Same for Jupiter Speakers which are also manufactured by WGS. This drew me off on the first pair but being to lazy to deinstall I noticed how they develop over time....
Lyle always good learning in any of your video's long or short. Im like a baby mesmerized by a ball when im watching your skills. I look forward to hearing the new speakers to compare with these "plain jane" Fenders.
Thank you for showing that power cable clamp. I hate the old style… mostly because I do not have the special tool. That hayco(?) clamp looks like a better mousetrap.
I'm guessing you do the actual bias calculations based on the output transformer resistance and voltage drop. I'm so happy to hear that if that's true. I love you presentation style and you're calm demeanor. Thanks again for all your videos
Great video, thanks Lyle. I have a ‘68 JBL twin just like this, and it has a hum I just can’t get rid of. I haven’t tried the additional cap on the bias, and I wonder if that’s what’s happening on my ‘68 Bassman as well. I leave the JBLs in my amp for originality, but I honestly prefer ceramic speakers in a twin.
As caps fail (which gets more likely as they run near or at their rated max voltage) they generate heat themselves, which speeds up the failure process, which makes them run hotter… It’s a separate issue than ambient temperature, and that is fine inside the doghouse.
Hey Lyle - do you mind to share the model number of the Heyco cable glands you use? Those original snap-ins are a pain and I’d love to try the ones you like to use. Thanks for all you do!
Longer format all day! I have an almost identical 1968 Twin Reverb circuit (AC568) I've converted like this, although the original dropping resistors in the doghouse are 2.2k and 10k. Should these be changed to the AB763 values? The power transformer is a 022798 (350-0-350-140ma).
Lyle, first, thanks again for the great detail in the video. Because I own this same twin, I'm checking all the fine points. I've recapped mine and will look at your service carefully here. I'm sure it's down to owner preference, but why would one not want to add a variable bias pot to the bias balance? I was thinking about doing so on mine but haven't gone that direction yet. I'm curious if you have preference or opinion on this. Thanks for sharing so much invaluable amp service information. Your viewers, myself included, are quite fortunate.
I don’t understand how AC grounds (which are super important) get stuck to the chasis with just a giant solder blob, and no mechanical joins. In all other cases the advice is to avoid tag soldering and always have mechanical support. What’s the difference? I would guess you’d have to drill a small hole in the chasis to secure the ground a bit more.
I'm an electrician and use those cord grips and would be made fun of all day for putting one of those on backwards, but it honestly looks less cheesy this way.
did anyone catch what size Heyco gland he was using- i never liked the old style either and am looking to upgrade-- typically use 16 awg wire -i mean he was right about to say it ...?
Anyone have a part # for the Heyco strain relief that fits Fender amp chassis please? There are lots of sizes on Mouser. The number of options is bananas!
My hole size is approx .5 x .625”, and cable diameter is .34”. I’ve looked at quite a few of the data sheets and have been struggling to find a proper match for both, which is why I came here to ask for help. You mention the SJT cable size in the video, but I see no reference to that on the data sheets. Additional guidance would be appreciated. I’m a busy guy, and sifting thru multiple data sheets is time consuming.
Trying to figure out how to add gain to one. I hardwired a 2008 reissue during the pandemic because I was bored and it was staring to have problems. I pulled all the pc boards. Are their any ‘gain stage’ modifications?
My 1972 came with the JBL's, but the cab was falling apart. The former owner had extra screws and even nails holding it loosely together, so disassembled it.
I actually prefer the Jensen C12N's for an original warm round tone or the WeberVST equivalent.
I didn't know Eric Johnson had signature speakers by Eminence.
I'll have to investigate!
Masterpiece of an amplifier. Twins sound so good and "big" even at low volumes.
Alternating between long and short form videos is an excellent idea. Thank you!
Yes this!!
I am humbled that Lyle forgets stuff too. I bought a cheap whatever the midline squeeze action cabinet 24 inch clamp is at Harbor Fright and turned the toe piece around so the clamp is now a spreader. A couple of light squeezes after the clamp is tight enough to hold itself in place and those chassis will slide out much easier. If there are screws to loosen up, LOOSEN them up FIRST! Always a pleasure to watch such a high level of truly professional pride in workmanship from the impeccable Mr. Lyle. When I was 12 years old I blew a part of my finger off fixing Mom's Supro amp. That was 45 years ago. I have had ONE worse shock working as an industrial electrician on 4160 volts so guitar amp hazards are no joke.
One one occasion when I was working on a Marshall 50 watt plexi I forgot to discharge the mains filter caps. DOH! I had both arms on the chassis and I touched something which I should not have done. About 450 volts went in one arm, across my chest and out the other arm. It blew me backwards off of my feet and hurt like hell. I am amazed it did not stop my heart
Nice to hear about the new style cable glands. I recently had to replace one in a Vibrolux Reverb I had just bought, and the one I ordered from AES was too small for the massive 3-prong cable that was in the amp. (I did measure the cable with my "Executive Pocket Chum" caliper, and thought I ordered the correct gland). I ended up using a power drill to make the hole in the cable gland slightly larger and managed to finally get it installed. Hopefully it will never have to be removed.
I think most of us interested in amp servicing will sit through a long video, even if it contains the same info as a previous video. Sometimes repetition is good for learning. Have a banana!
This amp will live well beyond most of us. Your work is impeccable Sir.
Jeez so much good info in this video, thank you Lyle!
Hello Lyle, good cup of coffee and good content. Have a great weekend.
Just finished that long format video. Watched another before that. I like to binge watch. So no, not bored.
I still use foam to hold down the caps in the doghouse. I use the current shunt method to bias as well, and you’re right. It’s dangerous ass heck if you don’t have a secure connection. Very easy to short out 400vdc + to the chassis/tubes, or worse, YOU.
Great restoration on this fantastic amp!
Those WGS G12A’s are amazing speakers. They just cost as much as a ratty mid 70’s Twin for a pair.
I was measuring plate voltage on a Super Reverb power tube and my multimeter probe slipped so it contacted both B+ and a tube socket tab connected to ground. Half of the tab on the tube socket disappeared in a flash. Talk about a brown pants moment …
I use the output transformer resistance method to measure bias. I use the clip on style meter probes, and do the connections to the tube sockets before powering up the amp. Having 2 meters helps.
I recommend buying a bias probe for biasing, its the safest way, u just plug into the power tube sockets and plug the tubes into it, it reads in ma. And it reads both tubes to make sure your within spec.
Voltage drop/OT resistance method is slightly more accurate, and safe enough with the right probes.
Definitely love seeing all the work done, and sometimes the shorter videos are great too. I know the setup and editing has got to be a chore, but it's appreciated!
Thanks again for sharing your Expertise!!!
Thank you for the post. I enjoyed the longer video. It is an opportunity for me to learn.
Ive never seen those "newer style" strain reliefs before but i think love them already lol. Im also not a fan of the older ones for a few reasons. With my own amp builds i just install an IEC socket. But for vintage radios and other older equipment that needs a new mains cable id really love to try out the newer ones. I cant say one hundred percent that ill like it better without trying it but by the looks of it and your description it seems far superior. And its perfect you get them from mouser cause thats where I try to get all my components cause i live close enough to their Mansfield warehouse to use their will call and avoid shipping costs. Thanks for mentioning it!
I love the detailed long format stuff!
Love the long videos cause they deep dive into an amp, especially if you can include trouble shooting. Maybe you could do the shorter ones here and there and then pick one amp to do a few long in depth videos on the whole amp so we can follow along. Some fenders, maybe next time a Marshall, Traynor etc. Love the channel!
Nice looking work as always! Thank you for the info on those power cable strain reliefs, much better version!
I noticed that all the WGS Speakers I installed / used (and that's quite a few, including Green Berrets, Reapers (55/75Hz, HPs), ET65, G12C, Black Hawks ) required a quite long time to break in, usually +20h. Same for Jupiter Speakers which are also manufactured by WGS. This drew me off on the first pair but being to lazy to deinstall I noticed how they develop over time....
Lyle always good learning in any of your video's long or short. Im like a baby mesmerized by a ball when im watching your skills. I look forward to hearing the new speakers to compare with these "plain jane" Fenders.
Great video, thanks for sharing your knowledge! I enjoy watching and learning!
Thank you for showing that power cable clamp. I hate the old style… mostly because I do not have the special tool. That hayco(?) clamp looks like a better mousetrap.
I'm guessing you do the actual bias calculations based on the output transformer resistance and voltage drop. I'm so happy to hear that if that's true. I love you presentation style and you're calm demeanor. Thanks again for all your videos
love a good cliffhanger, thanks!
Great video, thanks Lyle. I have a ‘68 JBL twin just like this, and it has a hum I just can’t get rid of. I haven’t tried the additional cap on the bias, and I wonder if that’s what’s happening on my ‘68 Bassman as well.
I leave the JBLs in my amp for originality, but I honestly prefer ceramic speakers in a twin.
If "heat is a thing in capacitors" why would they be underneath the doghouse? Just curious, Lyle. Love your stuff, long or short form.
As caps fail (which gets more likely as they run near or at their rated max voltage) they generate heat themselves, which speeds up the failure process, which makes them run hotter…
It’s a separate issue than ambient temperature, and that is fine inside the doghouse.
Hey Lyle - do you mind to share the model number of the Heyco cable glands you use? Those original snap-ins are a pain and I’d love to try the ones you like to use. Thanks for all you do!
That is the end of the interwebs/google machine I can die a happy man.
Longer format all day! I have an almost identical 1968 Twin Reverb circuit (AC568) I've converted like this, although the original dropping resistors in the doghouse are 2.2k and 10k. Should these be changed to the AB763 values? The power transformer is a 022798 (350-0-350-140ma).
Was part 5 for the ‘68 twin reverb posted? Can’t find it 🤷🏾♂️
Lyle, first, thanks again for the great detail in the video. Because I own this same twin, I'm checking all the fine points. I've recapped mine and will look at your service carefully here.
I'm sure it's down to owner preference, but why would one not want to add a variable bias pot to the bias balance? I was thinking about doing so on mine but haven't gone that direction yet. I'm curious if you have preference or opinion on this. Thanks for sharing so much invaluable amp service information. Your viewers, myself included, are quite fortunate.
Thanks! See the various ‘70s Fender videos. In those I usually add bias level while retaining bias balance.
I don’t understand how AC grounds (which are super important) get stuck to the chasis with just a giant solder blob, and no mechanical joins. In all other cases the advice is to avoid tag soldering and always have mechanical support. What’s the difference?
I would guess you’d have to drill a small hole in the chasis to secure the ground a bit more.
I wouldn’t build a new amp this way, but this is how Leo built these.
What kind of silicone do you use for keeping the caps in place.
Is there a part number for the new style cable clamp? I missed it in the video if you mentioned it.
Awesome!
How often do you find yourself moving power transformers to fit the cable glands?
I'm an electrician and use those cord grips and would be made fun of all day for putting one of those on backwards, but it honestly looks less cheesy this way.
I like it.
Xlnt info. Long format please!
did anyone catch what size Heyco gland he was using- i never liked the old style either and am looking to upgrade-- typically use 16 awg wire -i mean he was right about to say it ...?
I tend to like 5881's ... I presume the plate voltage is too high to run those in this amp ...
Anyone have a part # for the Heyco strain relief that fits Fender amp chassis please? There are lots of sizes on Mouser. The number of options is bananas!
Datasheets. Datasheets, yo.
My hole size is approx .5 x .625”, and cable diameter is .34”. I’ve looked at quite a few of the data sheets and have been struggling to find a proper match for both, which is why I came here to ask for help. You mention the SJT cable size in the video, but I see no reference to that on the data sheets. Additional guidance would be appreciated. I’m a busy guy, and sifting thru multiple data sheets is time consuming.
Trying to figure out how to add gain to one. I hardwired a 2008 reissue during the pandemic because I was bored and it was staring to have problems. I pulled all the pc boards. Are their any ‘gain stage’ modifications?
Do what you do and we will watch. Trying to predict what people want is a downward trajectory.
Oooo. Silver MOD caps into the doghouse….
Aren’t svt and sjt two different types of wire? Wouldn’t the amperage be based upon gauge of wire?
Two different types of cable. The wire diameters are different, so the current ratings are. As are the resulting cable diameters.
Svt and sjt wire diameters are different? Aren’t they referenced by wire gauge?
Lyle how are spelling power cord clamp companies name Hakko?
Heyco
Zinc powder finger
Did you get the bananas you were looking for?
Oh no need to be sorry baby. Just traffic. But I appreciate that
Mahalo Lyle! Have a banana.
Heat shrink will never not be satisfying