Phil_S wrote:Yes, good news and good call, Hans-Jorg!
Perhaps you didn't realize I was joking about "semi-short." I knew what you meant. No body language in the conversation here sometimes makes it hard.
I am wondering if isolating the trem circuit also addresses the high mA draw at the OT. If so that's a big two-fer. Also, how is it sounding with the tremolo totally out of circuit? If tone cleans up, it's a 3-fer.
I must not have communicated this clearly earlier in the thread. I disconnected the tremolo over a week ago. At the moment the current and tone issues are seemingly unrelated to that part of the circuit unless, of course, there is a bad cap in there somewhere.
Earlier on I tried disconnecting the trem from the rest of the circuit by disconnecting that section's plate resistor. This seemed to blow my first EZ80, so, Phil, at your suggestion I disconnected the trem by disconnecting the Depth wiper and grounding the two 220k resistors. I also removed the footswitch completely as that didn't seem to be functioning well either.
That EZ80 was a good match for those little 6AQ5s that were in the original amp. But you have upgraded to bigger (more power/current) EL84s and the EZ80 is now too lightweight. Replace the EZ80 (90mA) with an EZ81 (150mA) and see if that makes a difference. Same pinout so it's plug 'n play.
@Phil,
I understood it very well and liked your "almost, or little pregnant", or so.
@BungleSlim:
I remember your tries to disconnect trem.
First you disconnected the anode R without to ground the 2 Bias R.
That blew your fuse. Than you discon. the whiper, but now you have still a part in the circuit, because you have the anode R again in.
Cut it complete down - you are now safe because of grounding the two 220k (I think it was 220k), which is necessary for the power stage.
As long you grounded them you can hang the whole circuit out without a danger.
Than you can say you have no influence.
hans-jörg wrote:I remember your tries to disconnect trem.
First you disconnected the anode R without to ground the 2 Bias R.
That blew your fuse. Than you discon. the whiper, but now you have still a part in the circuit, because you have the anode R again in.
Cut it complete down - you are now safe because of grounding the two 220k (I think it was 220k), which is necessary for the power stage.
As long you grounded them you can hang the whole circuit out without a danger.
Than you can say you have no influence.
I thought you done this.
Hans-Jörg
OK, I'll give this a shot and see if anything changes.
hans-jörg wrote:I remember your tries to disconnect trem.
First you disconnected the anode R without to ground the 2 Bias R.
That blew your fuse. Than you discon. the whiper, but now you have still a part in the circuit, because you have the anode R again in.
Cut it complete down - you are now safe because of grounding the two 220k (I think it was 220k), which is necessary for the power stage.
As long you grounded them you can hang the whole circuit out without a danger.
Than you can say you have no influence.
I thought you done this.
Hans-Jörg
OK, I'll give this a shot and see if anything changes.
Sorry for the long delay. I had other customer repairs and some mishaps with parts getting ordered. I am referring to the attached schematic's reference designators.
I rebuilt the power supply with the following values:
V5 = EZ81
C20 = 47uF
C21 = 40uF
C22 = 20uF
C23 = 20uF
R22 = 2k
R23 = 10k
R24 = 4.7k
B+0 = 338V
B+1 = 316V
B+2 = 287V
B+3 = 276V
There was still about 25V of sag when I turned the amp up and played hard. I started to look at the other components on the board. I bent down to pick up something from the floor and I saw something funny on C15. I lifted it up and there was a hole blown out of it but it was facing down on the PCB so I never saw it when looking from above. Replaced that cap and the amp sounds awesome now, as simple as that.
I've still got a dozen or so things to do to this amp to make it gig-worthy, but I just wanted to thank everyone for their help, especially Phil_S and hans-jörg!
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Hey, that's great news! Did you get the tremolo working?
I'm thinking that B+ for the EL84's is a bit higher than it should be. If you have JJ's in there, or Sovtek EL84M (7189 wannabe), it is probably OK. Otherwise, I might think about dropping screen voltage by increasing from 2K to maybe 5K. If I'm right, that should put screens under 300 and will drop preamps also, which might be beneficial, too.
Phil_S wrote:Hey, that's great news! Did you get the tremolo working?
I'm thinking that B+ for the EL84's is a bit higher than it should be. If you have JJ's in there, or Sovtek EL84M (7189 wannabe), it is probably OK. Otherwise, I might think about dropping screen voltage by increasing from 2K to maybe 5K. If I'm right, that should put screens under 300 and will drop preamps also, which might be beneficial, too.
Adding the tremolo back in is the next step. The shop was closing right when I found the bad cap, so I packed it in for the night. I'm sure I'll be back as soon as that gets hooked up.
Good point about the B+1 voltage. JJ's are in there now but I know the owner wants to put some NOS tubes in there, so I should most certainly drop that voltage. Thanks for the tip.
