Lesle tube amp giving me fits.. Amp guys can you help?

[Leo_Gnardo]

The only other winding is the green wire for the filaments and bias supply. You should get about 12vac to ground on that lead.

Yikes, 460uF of capacitance on the doubler/215 volt supply! That's something you don't see very often.

Now that we have some photos - that sure isn't the standard 122 or 147 Leslie amp. It's a "quadraphonic" model, 4 separate amps each with a pair of EL84. Don't know the model number, but I did disassemble one for parts many years ago.

For high value hi-voltage electrolytics you may want to check out the DigiKey catalog for Panasonic caps. (No multisections, sorry). These are commonly used for rejuvenating good old McIntosh and Harmon-Kardon tube amps with voltage-doubler power supplies.

[Enzo]

Leo, he posted the schematic link in post #1, top of the thread. Says Leslie 610.

The original used can caps, but there is no compelling reason to do so now. He could just as well use discrete caps.


Or in the space of those two cans, one could even create a cap board with eyelets or turrets similar to the one Fender put in so many "dog houses" over the years.

[Rich Rice]

A big thank you to all. I found a couple of bad diodes in there, and started replacing them. I ended up replacing D 3,4,5,6,7,8- and it appears to be holding. I haven't tried any music through the amps yet, but this is a huge step in the right direction. I touched the input pins and heard a familiar sound through the various speakers, so the amps are at least functioning, the fuse is holding. What a relief. I will still need to deal with the filter caps, but the big hurdle has been cleared.

Again, thank you all for the help!

[Rich Rice]

Well, I figured I would let the amp idle for a while, in an attempt to reform the caps.. It held for 2 - 3 hours, gave a bit of a hissing, static noise, and blew the fuse. I was in the next room when I heard it, but couldn't cut the power before the fuse blew. No smoke, no bad smells- just a bit of noise and then it croaked. I felt the tubes, transformers, and cap cans- all were hot, but didn't seem excessively so. I guess I'll have to pull the amp out and have another look.. Darn. It was great while it lasted...

[Leo_Gnardo]

tubes, transformers, and cap cans- all were hot, but didn't seem excessively so.

Failing caps will heat themselves up, but it's hard to tell in an amp that's been on for hours and heating everything in the amp. Good hunting on the rectifier diodes. They rarely fail but if yours did - now the fuse is poppin' again so re check them too.

Since there are eight output tubes also under suspicion, you could run the amp at first with just a pair, and if they run for hours without distress, add a second pair, etc. until the bad one reveals itself.

It's always a good idea to be in the same room as the amp you're testing. Not only can you switch it off faster, but you can see what's going on to some extent - output tubes glowing orange or shooting sparks.

[Rich Rice]

Failing caps will heat themselves up, but it's hard to tell in an amp that's been on for hours and heating everything in the amp. Good hunting on the rectifier diodes. They rarely fail but if yours did - now the fuse is poppin' again so re check them too.

Since there are eight output tubes also under suspicion, you could run the amp at first with just a pair, and if they run for hours without distress, add a second pair, etc. until the bad one reveals itself.

It's always a good idea to be in the same room as the amp you're testing. Not only can you switch it off faster, but you can see what's going on to some extent - output tubes glowing orange or shooting sparks.

I just realized that the Mercotac connector to the lower rotary speaker appears to be a dead short.. The speaker responds directly to a battery, but not through the Mercotac. I pulled the Mercotac off the spindle and ran continuity check on it. The thing reads as if it was one solid piece of metal. Damn.



I wonder if that could have caused the problem, and if it did any damage to that channel as well.

I just opened up the newly installed diodes (lifted one leg of each) and they test out fine..

The cap cans were the coolest part on the amp. Even the chassis next to the tubes was considerably warmer. Caps are *probably* ok, but untested...

[Gtr_tech]

If the caps are getting even slightly warm (provided they are not in close prox to any output/recto tubes) replace them *now*. When they get old, they become electrically leaky and draw current which makes them heat up and eventually spew their guts all over the place. This condition can and will kill recto diodes. Replace every lytic cap in there.

[soundguruman]

A big thank you to all. I found a couple of bad diodes in there, and started replacing them. I ended up replacing D 3,4,5,6,7,8- and it appears to be holding. I haven't tried any music through the amps yet, but this is a huge step in the right direction. I touched the input pins and heard a familiar sound through the various speakers, so the amps are at least functioning, the fuse is holding. What a relief. I will still need to deal with the filter caps, but the big hurdle has been cleared.

Again, thank you all for the help!

Both the Hammond site and antique electronics (above) has can caps that will work in this amp.

The newer can caps don't have the high temperature rating of the original, unfortunately....but that's what you can get. They still work acceptably.

JJ and F&T are probably the best sounding ones, if you can adapt. The CED can caps I suspect are made in Mexico, even though they say "made in USA..."
But I have used them, and they still work OK. Have not had any failures on those.

I also like "Holy Grail" caps, the temp rating is 105C. The availability seems to be few and far between.

[Rich Rice]

Both the Hammond site and antique electronics (above) has can caps that will work in this amp.

The newer can caps don't have the high temperature rating of the original, unfortunately....but that's what you can get. They still work acceptably.

JJ and F&T are probably the best sounding ones, if you can adapt. The CED can caps I suspect are made in Mexico, even though they say "made in USA..."
But I have used them, and they still work OK. Have not had any failures on those.

I also like "Holy Grail" caps, the temp rating is 105C. The availability seems to be few and far between.

Thank you for taking the time to reply. I have been on those sites repeatedly, no luck on the values I need.. 80, 20, 170 doesn't seem to exist. They carry the common ones, but I haven't seen anything even close to these values. My first place to look is at CE Dist., as I am a dealer.. :-(

[Leo_Gnardo]

I just realized that the Mercotac connector to the lower rotary speaker appears to be a dead short.. The speaker responds directly to a battery, but not through the Mercotac. I pulled the Mercotac off the spindle and ran continuity check on it. The thing reads as if it was one solid piece of metal. Damn.

I wonder if that could have caused the problem, and if it did any damage to that channel as well.

Doubtful there's any damage from your latest test with no signal. Wire up a "home run" to that driver & have a listen. Who knows if there was a short before and someone was trying to drive speaker signal past it, could weaken the output tubes (just the pair running that speaker) and possibly that OT too.

[Rich Rice]

I measured the caps, too. A little higher than nominal, I couldn't get an accurate reading on the 170uf legs.. My meter maxes out at 200uf. It crept right up to 200, barely getting there, then registered OL.. I guess if it went that high quickly I would be more worried..

Don't get me wrong- I want to replace them ASAP- but getting the right ones is a PITA. Don't seem to exist..

[soundguruman]

Thank you for taking the time to reply. I have been on those sites repeatedly, no luck on the values I need.. 80, 20, 170 doesn't seem to exist. They carry the common ones, but I haven't seen anything even close to these values. My first place to look is at CE Dist., as I am a dealer.. :-(

You can use 100/100 parallel can for the 170.
100+100 in parallel is 200. That' a good substitute for 170.
That's how most would do it probably.
Capacitor - Electrolytic, 100/100 µF @ 500 VDC, JJ Electronic | Antique Electronic Supply

Cap voltage: use a cap with equal or greater voltage rating. It's OK to use 500 or 525 volt, in place of 450 volt....etc.....

You don't need to worry about the exact replacement value. You are over-thinking it.
Approximate or a little larger or a little smaller will usually work just fine.

Put caps in parallel or series. Use multi-section cans to combine for the value you need.

In many amps you can use a larger value and the amp likes it.
Less noise or sound better than original anyhow.

Use this for the 80 and the 20:
Can Capacitor, Multi-section, 40/40/20/20uF 525VDC, CE Manufacturing | Antique Electronic Supply
2X 40 in parallel = 80...and one of the 20s
Or I would put 2X 20 in parallel and use that instead of 1X 20.

You need to get more creative...and less worrisome.

In amps that have soldered to chassis can capacitors, you can use a mounting clamp instead.
http://www.tubesandmore.com/products/S-H122
And add your ground wire to the chassis, instead of soldering the whole can to the chassis.

This is pretty much how old amps are being restored.
It will work just as good as original.

[Rich Rice]

You can use 100/100 parallel can for the 170.
100+100 in parallel is 200. That' a good substitute for 170.
That's how most would do it probably.
Capacitor - Electrolytic, 100/100 µF @ 500 VDC, JJ Electronic | Antique Electronic Supply

Cap voltage: use a cap with equal or greater voltage rating. It's OK to use 500 or 525 volt, in place of 450 volt....etc.....

You don't need to worry about the exact replacement value. You are over-thinking it.
Approximate or a little larger or a little smaller will usually work just fine.

Put caps in parallel or series. Use multi-section cans to combine for the value you need.

In many amps you can use a larger value and the amp likes it.
Less noise or sound better than original anyhow.

Use this for the 80 and the 20:
Can Capacitor, Multi-section, 40/40/20/20uF 525VDC, CE Manufacturing | Antique Electronic Supply
2X 40 in parallel = 80...and one of the 20s
Or I would put 2X 20 in parallel and use that instead of 1X 20.

You need to get more creative...and less worrisome.

In amps that have soldered to chassis can capacitors, you can use a mounting clamp instead.
Clamp for capacitor, 1-3/8" diameter | Antique Electronic Supply
And add your ground wire to the chassis, instead of soldering the whole can to the chassis.

This is pretty much how old amps are being restored.
It will work just as good as original.

Thank you for taking the time to spell it out for me. Please bear in mind I'm more musician than technician.. lol

I follow your line of thinking, and it makes good sense. I think I will have a friend do this, as I have a checkered past when it comes to improvising inside amps.. I'll be right there with him, but I'm not confident enough in my own abilities to start rewiring to this extent. Luckily, Leslie installed the cap can sockets- but when I start trying to figure this out I don't have the depth of knowledge nor experience to make sure all is kosher.
I've ruined amps years ago trying to do this type of thing, and lived long enough to regret it..

It looks like I fixed the Mercotac, which is great- but there is a short running through the whole amp now. That's what I heard this morning right before it quit. I think it's time to have somebody competent finish this part before I destroy it or hurt myself.

[52 Bill]

I follow your line of thinking, and it makes good sense. I think I will have a friend do this, as I have a checkered past when it comes to improvising inside amps.. I'll be right there with him, but I'm not confident enough in my own abilities to start rewiring to this extent. Luckily, Leslie installed the cap can sockets- but when I start trying to figure this out I don't have the depth of knowledge nor experience to make sure all is kosher.
I've ruined amps years ago trying to do this type of thing, and lived long enough to regret it..

It's a good thing to know one's own limitations.

Both of the can caps are wired as basically two capacitors. One is an 80uF/350v and the other is a 460uF/350v. If you and your tech want, you could leave the cans disconnected in place for looks and wire two new caps into the circuit.

[Leo_Gnardo]

no luck on the values I need.. 80, 20, 170 doesn't seem to exist. They carry the common ones,

Those filter cap uF values aren't terribly critical (but the voltage values are) so pick the nearest you can to what was there. Instead of 170, use 200 or 220 uF for instance. 460 uF? Two 220 uF in parallel gives you 440, close enough for jazz...