Peavey Deuce VT 212 Tubes overheating/redplating

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Peavey Deuce VT 212 Tubes overheating/redplating

Postby Fireproof13 on Sat Feb 13, 2016 1:26 am

I'm relatively new to diy amp work, but I'm fairly knowledgeable with electronics. This amp started doing this a couple of years ago and I just left it alone for awhile, I've decided to get it working again. With all 4 tubes, the 3 and 4 tubes redplate after about 20-30 seconds. I tried just 2 tubes, and if there was a tube in 3 or 4 it would redplate. With tubes in just 1 and 2 it would go for about 2 minutes before the tubes start getting way too hot, not redplating, but you can feel the heat coming off of them about 2 feet away. I tried deoxit on all the pins and sockets and it didn't help. Just wondering if someone has any experience with these amps or any ideas of where to start.

I'm numbering the tubes from right to left if you're looking at the back of the amp, not sure if it's right but that's how i'm explaining it.
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Re: Peavey Deuce VT 212 Tubes overheating/redplating

Postby stratele52 on Sun Feb 14, 2016 3:19 pm

Tubes are short or bias is tooooo hot.

Check bias and adjust. If tubes are short , replace them , check bias
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Re: Peavey Deuce VT 212 Tubes overheating/redplating

Postby Fireproof13 on Mon Feb 15, 2016 2:51 pm

It must be a bias issue, I've tried 8 different tubes, 2 of which were brand new Ruby's. And all of the tubes work in another of my amps. Does anyone know any specifics to biasing these amps, or is it pretty much standard.
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Re: Peavey Deuce VT 212 Tubes overheating/redplating

Postby stratele52 on Mon Feb 15, 2016 3:34 pm

Fireproof13 wrote:It must be a bias issue, I've tried 8 different tubes, 2 of which were brand new Ruby's. And all of the tubes work in another of my amps. Does anyone know any specifics to biasing these amps, or is it pretty much standard.


Bias is always "standard" for AB class amp or A class amp. Bias is for tubes not for amps.
If you ask, you may not have skill to work in amp , be careful , lethal voltage can kill you.

Bias issue ; wrong bias ( toooo hot ) or bias circuit not working / bad contact.
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Re: Peavey Deuce VT 212 Tubes overheating/redplating

Postby Unit_1 on Mon Feb 15, 2016 8:00 pm

Hey Fireproof13,

Let me start with, the voltage in your amp can run anywhere from 300v to as high as 800v (and I've seen higher), but most often between 350v and 500v. If one of your hands is grounded, and the other hand touches this power, the current will flow directly across your heart and you may wake up dead. :Zap:

Therefore it is IMPERATIVE that you always keep one hand behind your back, preferable tucked into your belt so you don't unconsciously touch a grounded object with it.

And now for the rest of the lesson in bias :mrgreen:

Bias is often misunderstood, in it's most simple form it means "setting the proper voltage for the tube"

The voltage you are setting to adjust bias is negative polarity. The higher the negative voltage, the cooler the tube runs, the lower the negative voltage, the hotter the tube runs.

The HIGH DC voltage that your amp uses as a power source is positive, the negative voltage that you use to set the bias therefore 'cools' off the tube the higher it is set. There's an equation that you need to determine the proper negative voltage and it's based on the tube used, how hot you want to run the tube, and how high the B+ (which is what we call the positive high voltage power supply to save words :mrgreen: )

It's best left to someone that does this on a regular basis, but if you want to learn how to do it yourself you can look starting at page 27 of this document.

http://www.metroamp.com/downloads/50_WA ... CTIONS.pdf

Velvet George, one of our members is the owner of Metroamp and makes the Metropolis plexi's, so here's a big *Thank You* to George for making such a valuable document available to the public. :not_worthy:

I used this as a reference when I made my JTM50 and it was invaluable for helping me through those 'WTF?' moments, lol....

Also you can go to Ted Weber's site and put in the B+ and the tube you're using and it does the math for you. That website address is:
http://www.tedweber.com/bias-calc

And of course many thanks to the late Ted Weber for his many contributions :not_worthy:
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Re: Peavey Deuce VT 212 Tubes overheating/redplating

Postby EHansen on Tue Feb 16, 2016 10:47 pm

I've just finished work on a Deuce VT212, break on the pcb for the heater circuit, and another pcb break from preamp
to power tubes.(ohh those nasty old pcb's...). bias circuit was ok , on this amp, but always measure the bias to be correct or high - dc volt, before putting in the power tubes, or else redplating , fuse popping will occur.

Remember safety first !!



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Re: Peavey Deuce VT 212 Tubes overheating/redplating

Postby Dean Jr. on Sat Mar 05, 2016 4:02 pm

Tubes 3 and 4 function on one side or the OT's primary. If all tubes redplate on that side, then the current draw on that side of the OT primary...those two tubes...is too high. There could be more than one reason for this. When you had tubes only in 1 and 2, you were running only one side of the OT primary...that is not advisable in a push/pull circuit. Things need to be balanced.
+1 on the safety concerns. +1 on reading and studying audio amplification. Jack Darr's book might be useful to you, Fireproof. With an electronics background, you should quickly get a grasp on things, and he covers not just tubes but also solid state.
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