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zenith PP 6bq5 console amp

I still wonder why its there. Some kind of a mod? It is not on the schematic. I would be tempted to remove it all together and wire like the schematic. Maybe increase the 70&80uf to 100uf.
 
coman61 said:
I still wonder why its there. Some kind of a mod? It is not on the schematic. I would be tempted to remove it all together and wire like the schematic. Maybe increase the 70&80uf to 100uf.
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He says it's connected between the pots and ground. The schematic has 125 ohm, 2W resistors from the hum pots to ground. Maybe recheck the markings? I could see a 100uF 25V cap for a bias supply filter though but nothing like that on the schematic. It would be good to have that part of the cct drawn out so we could see exactly where that item is in the circuit. You may be right about being mods in this amp.

Yes, I'd be tempted to replace that 70/80uF with a 100/100uF 500V JJ can and add a 40uF underneath.
 
Maybe ltr317 who posted earlier will chime in at some time; it seemed he had one of these and maybe he could check vs. how his is wired.
 
Lets hope so. At this point I think JGlenn can proceed on recapping to the power supply and we can fry the other fish later. I don't see where that cap can do any harm at this point.
 
All the wiring to the cap can looked original. That 100uf cap im not so sure. I just got done putting some caps underneath to replace the cap can. Im still getting some 60cyc hum on my bench though. That 100uf two section wasnt holding any voltage when I checked for power before working on the amp. It doesnt look like any other wiring was changed to add that cap there
 
coman61 said:
Lets hope so. At this point I think JGlenn can proceed on recapping to the power supply and we can fry the other fish later. I don't see where that cap can do any harm at this point.
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Sounds like a plan
 
That 100uf 2 section cap probably wouldnt cause a hum would it ? The 125 ogm resistors are still in place so I was thinking about trying to remove that cap and see if it affected anything for better or worse. I also decided to order that JJ 100uf 2 section can like you guys said and putting that in place of the 70 and 80 uf caps I got.
 
Damm Tinkerbelle you sure know how to throw a wrench in things. That amp in the schematic is a single ended EL84 which strangely enough has the 100uF cap in the bias circuit. So we can say that, that should not cause any problems. I would still replace them with new ones but I'm not so sure it will cure his 60Hz hum but you never know. At this point I would lean more towards a power wire being to close to something in the audio path. I will check my work computer tommorrow for the schematic I was hopeing to find.
 
Hmmm so that two section cap should be there after all ? My input wires are a little close to the power tx that could be whats doing it.
 
I'm not sure that cap is stock. I would think it is put there as a filter as Tinkerbelle said earlier. Its always good to keep the wires in the audio path as far as possible from the power supply.
 
JGlenn said:
That 100uf 2 section cap probably wouldnt cause a hum would it ? The 125 ogm resistors are still in place so I was thinking about trying to remove that cap and see if it affected anything for better or worse. I also decided to order that JJ 100uf 2 section can like you guys said and putting that in place of the 70 and 80 uf caps I got.
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I would finish recapping first. If you already have the 70uF & 80 uF caps, then I would use them; no sense spending more money. I only mentioned the 100/100uF as an option as I wasn't aware at the time that you already had the other caps.

Good to know the 125 ohm resistors are still there as they are needed along with the pot to bias the cathode positive. According to the schematic, the grid is 0V and the cathode 10V.
 
coman61 said:
Damm Tinkerbelle you sure know how to throw a wrench in things. That amp in the schematic is a single ended EL84 which strangely enough has the 100uF cap in the bias circuit. So we can say that, that should not cause any problems. I would still replace them with new ones but I'm not so sure it will cure his 60Hz hum but you never know. At this point I would lean more towards a power wire being to close to something in the audio path. I will check my work computer tommorrow for the schematic I was hopeing to find.
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Just so we don't get confused here, that link in post 7 of this thread has the schematic for this PP Zenith in post 2 from Tom Bavis. The one that I posted there at post 5 in that other thread is a different SE Zenith, which as you picked up does show a 100uF cap in the bias.

Sorry if it confused.

Yes, the hum could be a number of things, shielding, bad ground, ground loop, etc.
 
Yeah, my mind is turnning to mush, better call it a night. I hope to wake up in the morning and read that you two have it all fixed.:thmbsp::yes::banana:
 
I can't stay up late tonight either, I have an early start in the morning. It seems like we're almost there anyway.
 
Tinkerbelle said:
Maybe ltr317 who posted earlier will chime in at some time; it seemed he had one of these and maybe he could check vs. how his is wired.
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I was busy with the Gotham audio flea market the last couple of days. I just saw all the recent postings. I don't have that black cap on my 7B31, nor is it on my schematic. Looking at your 7D31 schematic I don't see a cap there either. My feeling is someone wanted more capacitance and added it there. It's gotta be at least 450v if it's wired to the can cap. I would just leave it there and recap the other values on the can cap. Make sure to change the 0.1 caps too.
 
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