Deluxe Reverb problem

[Leo_Gnardo]

Also, the B+ was 433, screens 429, PI 365, preamp 304. Preamp plates still running pretty high but maybe they'll drop when the bias is set right.

Yay, those voltages are much more in line with what we expect, even the preamp node. Last we saw, bias current was 17 mA which is just a pinch low but still good. OTOH bias voltage at -23V, if that is what you're measuring at pin 5 of your 6V6's, that is unusually low. Makes me think the 6V6's are way off in a far corner of the usual emissivity we expect. Either they're very "hard" tubes, or they've been baked to death by having been way overheated. I'd expect a bias voltage between -30 and -40V, current say 18 to 25 mA per 6V6. FWIW I find JJ's been making the toughest 6V6 for some years now. They seem to put up with use & abuse that wreck EH/TungSol or any China made ones.

[g1]

Are you sure about your 17mA idle current measurement?
You said this was with -23V bias. Fender schem. shows -35V bias and with lower plate voltage. To me, that seems it would give much colder bias than what you have.
Regardless, with 17mA and 430V plate, you are idling around 60% of the 12W rating for 6V6. How hot do you want to go?

[tyler8611]

Yay, those voltages are much more in line with what we expect, even the preamp node. Last we saw, bias current was 17 mA which is just a pinch low but still good. OTOH bias voltage at -23V, that is unusually low. Makes me think the 6V6's are way off in a far corner of the usual emissivity we expect. Either they're very "hard" tubes, or they've been baked to death by having been way overheated. I'd expect a bias voltage between -30 and -40V, current say 18 to 25 mA per 6V6. FWIW I find JJ's been making the toughest 6V6 for some years now. They seem to put up with use & abuse that wreck EH/TungSol or any China made ones.

They're JJs rated 26. As I understand that's kinda lower than average. JJs are the only 6v6s I've ever gotten along with, besides the RCA blackplates in my tweed deluxe.

Do you think moving the range resistor value up is a good first move to try to get the bias current and negative voltage closer to normal?

[tyler8611]

Are you sure about your 17mA idle current measurement?
You said this was with -23V bias. Fender schem. shows -35V bias and with lower plate voltage. To me, that seems it would give much colder bias than what you have.
Regardless, with 17mA and 430V plate, you are idling around 60% of the 12W rating for 6V6. How hot do you want to go?

Yep the hottest I could get was 17ma and the neg voltage was -23. 60-65% is probably the range I want to go. No more than 70 obviously. I will try to hit a sweet spot. I think the JJs are rated 14W but I'm not positive on that.

[tyler8611]

I was kinda concerned because I noticed earlier that my vib channel volume was for some reason up around 2-3, so I did this again just to be sure.

No phase splitter:

B+ 435
Screens 432
PI 368
Preamp 312

Neg voltage -23

Max bias: 13.8 and 14.2

[tyler8611]

Also concerning is the fact that B+ is going over 500v on standby- more than what the caps are rated for.

[tyler8611]

Are you sure about your 17mA idle current measurement?
You said this was with -23V bias. Fender schem. shows -35V bias and with lower plate voltage. To me, that seems it would give much colder bias than what you have.
Regardless, with 17mA and 430V plate, you are idling around 60% of the 12W rating for 6V6. How hot do you want to go?

Using the weber bias calculator I get 43% dissipation, assuming the JJs are 14w.

[Leo_Gnardo]

They're JJs rated 26. As I understand that's kinda lower than average. JJs are the only 6v6s I've ever gotten along with, besides the RCA blackplates in my tweed deluxe.

Do you think moving the range resistor value up is a good first move to try to get the bias current and negative voltage closer to normal?

I'd rather see another pair of 6V6's. For the time being you could drop the bias voltage a bit by paralleling say a 47K resistor across the 10K to ground, but we're in scary low territory here. Be prepared to remove that parallel resistor for a different set of output tubes.

Agree with the 6V6 brand choices. Old Sylvanias can be pretty good too.

Rated "26" on somebody's test rig. Of course tube vendors don't much talk about what voltages they apply to tubes under test, that's par for the course. If 26 is well lower than average, find out what's average and get a pair of those. It's not right to panel-beat output tubes into yielding good current figures by running the bias so low. Doing so has other effects, including severely limiting your clean headroom.

When you get around to measuring output power, I've seen healthy Deluxes range between 13 and 22 watts at clip. Don't be disappointed if it's near the low end. If the amp sounds robust when played that's close enough for rock 'n roll.

Hi voltage over 500 on standby, hmmm, how much over. 5 or 10 V, no problem. Just don't leave it on standby for extended periods. There's a 5AR4/GZ34 rectifier, right? That's a slow warmup type - it's actually safe to skip the so called warmup on initial switch on. Hi voltage won't be up to full for 15-20 seconds anyway. The overvoltage problem will be in evidence when you switch to standby with the amp warmed up. Also, it might be half an idea to use a 5Y3 instead, a "real" one, not the Russian made ones that deliver too much high voltage. 5Y3 aren't as efficient as GZ34, they'll leave you with a lower B+, a more relaxed sound, less to worry about. A bit less power but no biggie unless you're determined to get every last watt you can.

[tyler8611]

I'd rather see another pair of 6V6's. For the time being you could drop the bias voltage a bit by paralleling say a 47K resistor across the 10K to ground, but we're in scary low territory here. Be prepared to remove that parallel resistor for a different set of output tubes.

Agree with the 6V6 brand choices. Old Sylvanias can be pretty good too.

Rated "26" on somebody's test rig. Of course tube vendors don't much talk about what voltages they apply to tubes under test, that's par for the course. If 26 is well lower than average, find out what's average and get a pair of those. It's not right to panel-beat output tubes into yielding good current figures by running the bias so low. Doing so has other effects, including severely limiting your clean headroom.

When you get around to measuring output power, I've seen healthy Deluxes range between 13 and 22 watts at clip. Don't be disappointed if it's near the low end. If the amp sounds robust when played that's close enough for rock 'n roll.

Ok I have another healthy pair of JJs (labeled 23) that I can try. If that doesn't succeed, raising the tail resistor value would be the way to go? Parallel a 47k with the 10k?

[tyler8611]

I'd rather see another pair of 6V6's. For the time being you could drop the bias voltage a bit by paralleling say a 47K resistor across the 10K to ground, but we're in scary low territory here. Be prepared to remove that parallel resistor for a different set of output tubes.

Agree with the 6V6 brand choices. Old Sylvanias can be pretty good too.

Rated "26" on somebody's test rig. Of course tube vendors don't much talk about what voltages they apply to tubes under test, that's par for the course. If 26 is well lower than average, find out what's average and get a pair of those. It's not right to panel-beat output tubes into yielding good current figures by running the bias so low. Doing so has other effects, including severely limiting your clean headroom.

When you get around to measuring output power, I've seen healthy Deluxes range between 13 and 22 watts at clip. Don't be disappointed if it's near the low end. If the amp sounds robust when played that's close enough for rock 'n roll.

Hi voltage over 500 on standby, hmmm, how much over. 5 or 10 V, no problem. Just don't leave it on standby for extended periods. There's a 5AR4/GZ34 rectifier, right? That's a slow warmup type - it's actually safe to skip the so called warmup on initial switch on. Hi voltage won't be up to full for 15-20 seconds anyway. The overvoltage problem will be in evidence when you switch to standby with the amp warmed up. Also, it might be half an idea to use a 5Y3 instead, a "real" one, not the Russian made ones that deliver too much high voltage. 5Y3 aren't as efficient as GZ34, they'll leave you with a lower B+, a more relaxed sound, less to worry about. A bit less power but no biggie unless you're determined to get every last watt you can.

It got up to 503v. I do have a NOS 5Y3 as well as a NOS 5U4GB, which the PT can handle.

[tyler8611]

I'd rather see another pair of 6V6's. For the time being you could drop the bias voltage a bit by paralleling say a 47K resistor across the 10K to ground, but we're in scary low territory here. Be prepared to remove that parallel resistor for a different set of output tubes.

Agree with the 6V6 brand choices. Old Sylvanias can be pretty good too.

Rated "26" on somebody's test rig. Of course tube vendors don't much talk about what voltages they apply to tubes under test, that's par for the course. If 26 is well lower than average, find out what's average and get a pair of those. It's not right to panel-beat output tubes into yielding good current figures by running the bias so low. Doing so has other effects, including severely limiting your clean headroom.

When you get around to measuring output power, I've seen healthy Deluxes range between 13 and 22 watts at clip. Don't be disappointed if it's near the low end. If the amp sounds robust when played that's close enough for rock 'n roll.

Hi voltage over 500 on standby, hmmm, how much over. 5 or 10 V, no problem. Just don't leave it on standby for extended periods. There's a 5AR4/GZ34 rectifier, right? That's a slow warmup type - it's actually safe to skip the so called warmup on initial switch on. Hi voltage won't be up to full for 15-20 seconds anyway. The overvoltage problem will be in evidence when you switch to standby with the amp warmed up. Also, it might be half an idea to use a 5Y3 instead, a "real" one, not the Russian made ones that deliver too much high voltage. 5Y3 aren't as efficient as GZ34, they'll leave you with a lower B+, a more relaxed sound, less to worry about. A bit less power but no biggie unless you're determined to get every last watt you can.

Oh forgot to answer- yes it's a JJ GZ34. A rare new production rectifier that actually works well.

[tyler8611]

I'd rather see another pair of 6V6's. For the time being you could drop the bias voltage a bit by paralleling say a 47K resistor across the 10K to ground, but we're in scary low territory here. Be prepared to remove that parallel resistor for a different set of output tubes.

Agree with the 6V6 brand choices. Old Sylvanias can be pretty good too.

Rated "26" on somebody's test rig. Of course tube vendors don't much talk about what voltages they apply to tubes under test, that's par for the course. If 26 is well lower than average, find out what's average and get a pair of those. It's not right to panel-beat output tubes into yielding good current figures by running the bias so low. Doing so has other effects, including severely limiting your clean headroom.

When you get around to measuring output power, I've seen healthy Deluxes range between 13 and 22 watts at clip. Don't be disappointed if it's near the low end. If the amp sounds robust when played that's close enough for rock 'n roll.

Hi voltage over 500 on standby, hmmm, how much over. 5 or 10 V, no problem. Just don't leave it on standby for extended periods. There's a 5AR4/GZ34 rectifier, right? That's a slow warmup type - it's actually safe to skip the so called warmup on initial switch on. Hi voltage won't be up to full for 15-20 seconds anyway. The overvoltage problem will be in evidence when you switch to standby with the amp warmed up. Also, it might be half an idea to use a 5Y3 instead, a "real" one, not the Russian made ones that deliver too much high voltage. 5Y3 aren't as efficient as GZ34, they'll leave you with a lower B+, a more relaxed sound, less to worry about. A bit less power but no biggie unless you're determined to get every last watt you can.

I also have an RCA 5V4GA. Not sure about the max input capacitance on that one though.

A bit less power is ok. As long as I get the tubes biased where they're supposed to be and the negative voltage closer to schematic.

Also hope the motorboating doesn't return. I guess that might indicate a bad coupling cap somewhere.

[tyler8611]

I'd rather see another pair of 6V6's. For the time being you could drop the bias voltage a bit by paralleling say a 47K resistor across the 10K to ground, but we're in scary low territory here. Be prepared to remove that parallel resistor for a different set of output tubes.

Agree with the 6V6 brand choices. Old Sylvanias can be pretty good too.

Rated "26" on somebody's test rig. Of course tube vendors don't much talk about what voltages they apply to tubes under test, that's par for the course. If 26 is well lower than average, find out what's average and get a pair of those. It's not right to panel-beat output tubes into yielding good current figures by running the bias so low. Doing so has other effects, including severely limiting your clean headroom.

When you get around to measuring output power, I've seen healthy Deluxes range between 13 and 22 watts at clip. Don't be disappointed if it's near the low end. If the amp sounds robust when played that's close enough for rock 'n roll.

Hi voltage over 500 on standby, hmmm, how much over. 5 or 10 V, no problem. Just don't leave it on standby for extended periods. There's a 5AR4/GZ34 rectifier, right? That's a slow warmup type - it's actually safe to skip the so called warmup on initial switch on. Hi voltage won't be up to full for 15-20 seconds anyway. The overvoltage problem will be in evidence when you switch to standby with the amp warmed up. Also, it might be half an idea to use a 5Y3 instead, a "real" one, not the Russian made ones that deliver too much high voltage. 5Y3 aren't as efficient as GZ34, they'll leave you with a lower B+, a more relaxed sound, less to worry about. A bit less power but no biggie unless you're determined to get every last watt you can.

I paralleled the 47k with the 10k and bias current 14.3 max. Looks like the resistance has to even lower on the pot.

[pdf64]

I wonder if something is wacky; with respect to circuit common 0V, what are the actual measured Vdc at the power tubes' terminals 3, 4, 5 and 8 at idle, without a tube in V6 socket.

[Tom Phillips]

I sense a basic misunderstanding.

...As long as I get the tubes biased where they're supposed to be and the negative voltage closer to schematic...
.

You are saying that you want to bias your 6V6s hotter. I.e. more bias current. At the same time you say you are trying to make the bias voltage more negative. Those are incompatible goals. The -35V shown on the schematic is just a guideline reference value. Furthermore, it was based on the original tube brands used 50 years ago with the amp operating at the line voltages of the day. You need to set the bias voltage "less negative" to achieve hotter bias or use different power tubes.

As stated above I agree that 17ma at your plate voltage may be fine. How does the amp sound at that setting? Listen with your ears not your DVM.