Deville 410 Redplating Power Tubes

[Perkinsman]

Hi all,

The Deville had been running fine until this morning when I put in 2 new power tubes (NOS Russian 6L6's from the 50's). After a minute the amp starting loosing power so I immediately looked at the new power tubes and they were orangey....I shut down and pulled the tubes, and noticed that they were both loose in their own bases. I didn't notice whether they were loose when I put them in but I suspect they were. I put the old tubes back in and they now redplated as well. Any thoughts or suggestions to cure this problem. Thanks.

[Enzo]

There is a test point on the corner of the socket board, factory setting is 60mv. What does yours read? And did you adjust it with each set of tubes?

[Justin Thomas]

If these are NOS Russian "6L6"s from the 50s, any possibility that they are not 6L6GC spec and are closer to vintage 6L6G or real 5881 spec instead? Or that they are not an actual 6L6 at all, but rather sonething that would "compare" & "work like" a 6L6? If these things are from the 50s they're Soviet-era, not direct-fits like today.

Just a theory...

Justin

[Perkinsman]

Yes, I adjusted that voltage to 60mv for both pairs as the schematic required but the NOS pair still redplated. I just pulled both tubes and measured approx 490v at pins 3 & 4, the plate & screen respectively. The other 6 pins read 0v. Is that expected?

[Perkinsman]

If these are NOS Russian "6L6"s from the 50s, any possibility that they are not 6L6GC spec and are closer to vintage 6L6G or real 5881 spec instead? Or that they are not an actual 6L6 at all, but rather sonething that would "compare" & "work like" a 6L6? If these things are from the 50s they're Soviet-era, not direct-fits like today.

Just a theory...

Justin

I suppose there is a chance these aren't the "correct" 6L6 specs BUT I got them from my tube supplier who is very tube savvy. It's not the issue since as I previously stated, the old tube pair redplated when I put them back in. Something else is obviously responsible, just trying to figure out what that is.

[Enzo]

Pin 5 of the power tube sockets MUST have bias voltage roughly -50v.

[Perkinsman]

Pin 5 of the power tube sockets MUST have bias voltage roughly -50v.

My mistake, I had the standby on. Once turned on, 5 read -55 and was adjustable from -49 to -57 so I set it at -50 with no power tubes. When I put the tubes in, TP bias point read 110 (not sure how it got that high!) I tried to lower it to 60 but the bias pot only let me go to 64mv. Still, that allowed me to put the old tubes back in with no redplating...but that still doesn't explain what happened. I don't understand%*!#

[Randall]

Can we work from the same schematic? I don't even see a bias adjust on the one I'm looking at? If you have - 50v+ on your pin 5, then it should be easy to figure out what's up.

[Enzo]

I almost said something on that earlier. Is this a Hot Rod DeVille or a Blues DeVille? The original Blues DeVille had no adjust, but the re-issue Blues DeVille does, as do the Hot Rods.

Perk, please resolder all the pins on the two power tube sockets. I would wager you could see little cracks if you looked, but even if not visible, solder them all anyway.

[Chuck H]

...measured approx 490v at pins 3 & 4, the plate & screen respectively. The other 6 pins read 0v. Is that expected?

My mistake, I had the standby on. Once turned on, 5 read -55

Nope. Doesn't work like that. If the amp were in standby you would have read bias voltage and nothing else. The standby removes the plate and screen voltage and the bias supply is not dependent on the standby switch. So there must be an error in the reporting. I'm not being snarky, this is an important detail. It seems possible you DID have plate and screen volts with no bias voltage at some point. Which would have to mean the amp was NOT in standby when you measured for bias voltage and found none.

Here is the schematic:

https://schematicheaven.net/fenderam...od_deville.pdf

[nevetslab]

Yes, I adjusted that voltage to 60mv for both pairs as the schematic required but the NOS pair still redplated. I just pulled both tubes and measured approx 490v at pins 3 & 4, the plate & screen respectively. The other 6 pins read 0v. Is that expected?

Earlier in your post # 6, you were seeing the negative bias voltage on pin 5, yet here, it being the 'other 6 pins" with respect to pins 3 & 4, if you're now seeing 0V on pin 5, you WILL see your power tubes redplating, as they're turned on like gangbusters. Voltage at bias TP must be really high.

[The Dude]

Nope. Doesn't work like that. If the amp were in standby you would have read bias voltage and nothing else. The standby removes the plate and screen voltage and the bias supply is not dependent on the standby switch. So there must be an error in the reporting. I'm not being snarky, this is an important detail. It seems possible you DID have plate and screen volts with no bias voltage at some point. Which would have to mean the amp was NOT in standby when you measured for bias voltage and found none.

Here is the schematic:

https://schematicheaven.net/fenderam...od_deville.pdf

^^^^^^ That! Standby would remove B+, not bias V. I suspect you might have an intermittent connection in your bias supply circuit- maybe even the pot itself. I would leave the tubes out and monitor bias voltage at the tubes while chopsticking around the unit. Make sure bias V stays stable before reinstalling tubes.

[Perkinsman]

I almost said something on that earlier. Is this a Hot Rod DeVille or a Blues DeVille? The original Blues DeVille had no adjust, but the re-issue Blues DeVille does, as do the Hot Rods.

Perk, please resolder all the pins on the two power tube sockets. I would wager you could see little cracks if you looked, but even if not visible, solder them all anyway.

It's the HR Deville, I should have stated that...after resoldering all the power tube pins, it resolved the bias issue. I. Set at 60mv & calling it good. Thanks again guys!

[The Dude]

FWIW: As a matter of course, when I pop the hood on a Hot Rod Deville, Deluxe, etc., I automatically resolder the output tube pins. It's a common enough problem to just take care of it- even if simply preventative maintenance.

[Chuck H]

FWIW: As a matter of course, when I pop the hood on a Hot Rod Deville, Deluxe, etc., I automatically resolder the output tube pins. It's a common enough problem to just take care of it- even if simply preventative maintenance.

And... Since this was an issue with the bias supply, which is really important, you might just go ahead and do a nice clean flow on any solder joints related to bias supply circuit AND clean the tube sockets.