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 Post subject: schematics - non-bias - Classic 212 VT
PostPosted: Tue Jul 31, 2012 10:13 am 
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Hi all,

I have a Peavey Classic 212 VT series. This is the amp with the Phaser FX, the Automixer, solid state preamp and a 2x 6L6 Tube power amp section. There are lots of OP amps at the preamp pcb and there is no bias pot.

I'm desperately searching for the schematics of that amp. Can anybody help me with this?

2nd question: I want to change the tubes .How can I set up the bias or is it not necessary with this amp (because there is no bias pot). Does it some sort of self bias?

I'm planning also to change the power supply caps (4x 100uF 350V).

Currently the amp sound a bit glazed I've already changed the speakers (to a Jensen Jet Series Tornado)

Any other hints? I can provide serial number and photos if necessary

thanks in advance,
Cheers, Karsten


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 Post subject: Re: schematics - non-bias - Classic 212 VT
PostPosted: Tue Jul 31, 2012 1:27 pm 
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Joined: Thu Feb 09, 2012 6:16 pm
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Location: frederick md
Hello, I have the same amp and there is no bias adjustment on that model. Most of the Peavey amps from the late seventys and up were all plug and play with a fixed, non adjustable bias. No need to worry about setting the bias when installing the power tubes. I did perform a mod to my amp where I replaced the bias feed resistor with a 50ohm pot and resistor in series to allow me to adjust it. To be honest, I really couldn't hear much of a difference when running the tubes at 70% dissipation, so I now keep it right at 50% so my tubes will last a bit longer. The best thing I did for the amp when I bought it was to have the filter caps replaced. It really tightened up the amp and took away alot of the hum I was getting from it. Also installed some Celestion seventy/80's on the advice of a fellow forum member and I really like the sound of them for playing classic/southern rock. You can do a search on the forum and find some of the threads about different mods for the Classic VT 212.


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 Post subject: Re: schematics - non-bias - Classic 212 VT
PostPosted: Tue Jul 31, 2012 7:49 pm 
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Location: Lansing, Michigan
As always, you can get any Peavey product schematics by contacting customer service at Peavey.

Other than that, what Danman said.


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 Post subject: Re: schematics - non-bias - Classic 212 VT
PostPosted: Wed Aug 01, 2012 3:24 am 
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Hi all,

thanks Enzo - I just ordered the schematics from customer care
and to danman: Thanks. What Do you meant with filter caps. Do you meant all caps in the tone stack? The bias resistor. Is it a 50Ohm pot in series with a 50 Ohm fixed resistor?

May be I should wait for the schematics ;-)

anyway thanks a lot :-)

Cheers, Karsten


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 Post subject: Re: schematics - non-bias - Classic 212 VT
PostPosted: Wed Aug 01, 2012 9:06 pm 
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Joined: Thu Feb 09, 2012 6:16 pm
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Location: frederick md
I was referring to the four electrolytic capacitors in the power supply that you mentioned in your original post. When I bought the amp it was a little noisy even after replacing the power tubes with a new set. After having the caps replaced, the amp was perfectly quiet and felt punchy and tight again. Those electrolytic caps have a normal service life of ten to fifteen years so its a good idea to change them in amps that have some age on them. They are often referred to as filter caps because they help to smooth the ripple in ac current and effectively "filter" it before it reaches the preamp. When the caps get old and dry out you may start to hear ghost notes and excessive hum from the amp and your lower notes may start to sound loose and flubby.


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 Post subject: Re: schematics - non-bias - Classic 212 VT
PostPosted: Wed Aug 01, 2012 9:40 pm 
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Location: frederick md
I forgot to mention the bias. You will see on the schematic that IR9 is a 68k resistor in the bias supply. All I did was remove that resistor and replace it with a 50k bias pot and a 18k resistor in series to give me a bit of adjustment. I think I actually used a 15k resistor because I couldnt find an 18k (close enough). As I mentioned earlier, the factory bias resistor is set in a pretty safe range and allows you to swap power tubes without the need to rebias. Even after taking a plate voltage reading and doing the math to set the dissipation at 70%, I didnt really notice any difference, so i keep it set a little lower where it was before the mod. Be warned, there are very high voltages inside the amp even if it is unplugged! Be sure to drain the filter caps first and check everything with a voltmeter before starting
any work!

I wanted to mention that fellow forum member "Skynyrd" had given me the details for this mod several months back. He seemed very happy with his results and has several threads here of other mods he made to the same amp. You should be able to locate them using the search feature here in the forum.


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 Post subject: Re: schematics - non-bias - Classic 212 VT
PostPosted: Thu Aug 02, 2012 3:06 pm 
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Hi
I too have a classic vt series, bought it new back in 1982.
Sometimes when i turn it off I get this loud pop from the speakers (volume pots set at 0), could that be a sign that new filter caps are needed ?
I just recently changed the 6L6 tubes otherwise it's untouched inside.
Or maybe the pop at power off is just normal ?

Thanks.


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 Post subject: Re: schematics - non-bias - Classic 212 VT
PostPosted: Thu Aug 02, 2012 6:06 pm 
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Joined: Fri Sep 12, 2008 10:24 pm
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Location: Lansing, Michigan
Many many MANY many amps pop when you flip the power switch. If it does it only sometimes, it is probably the amap reacting to a spark inside the switch. That only occurs sometimes due to the nature of AC current. FUnny filter caps would usually make it do whatever it is going to do all the time.


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