Convert Peavey Deuce to all tube

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Convert Peavey Deuce to all tube

Postby Newbietube » Wed Jan 14, 2009 2:46 pm

Hi all I've just aquired a working but rather old peavey deuce amp chassis as the basis of a bass amp project. My plan is to completely gut the entire amp and start over. This will mean removing the pre amp pcb which is all transistor and probably replacing the power tube sockets and psu also. I've found a pre amp circuit I want to copy but the main issue is the driver circuit which is transistorised. I need a circuit which will work with the existing power amp as i do not wish to change that too radically as I'm not sure if the O/P transformer will handle other circuits too well. I have a schematic of the original peavey circuit and it appears to be similar to a fender bassman but uses no screen resistors and has diodes going to ground from the O/P tranformer primarys.
Any idea on this will be gratefull recieved.
Cheers Just
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Postby cartoonweirdo » Wed Jan 14, 2009 8:09 pm

Can you post a link to the schematic?
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Postby Newbietube » Thu Jan 15, 2009 5:20 pm

Hi I'm having difficulty in accessing the peavey site. It appears the manual archive is rather prone to jamming up and only downloading half the manual. I did manage to down load it the other day so I could email it to you. I'll send you a pm. If you go to the peavey site click on support, then manuals, then look in the archive for deuce or deuce VT series. I'm pretty sure the power amp cicuit is the same.
Cheers Just
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Postby Gingertube » Thu Jan 22, 2009 6:49 pm

The schematic (probably) - anyway the power amp section is likely to be the same.
http://www.schematicheaven.com/newamps/ ... euce-b.pdf

I had to repair one of these - horrible distortion, low power, it was one those 25uF electrolytics on the transistror phase splitter inputs gone leaky pulling it way off balance. New 25uF caps this time 63V rated instead of the old 25V rated and it sounded great.

Note 24.4 Volts across the 10K tail resistor means 2.4mA or 1.2mA each side of the diffamp. It would be simple to substitute a 12AX7 or 12AT7 for the 64278 transistors.

Keeping the Peavey flavour, perhaps copy the EVH5150 phase splitter / driver from here.
http://www.schematicheaven.com/newamps/ ... vh5150.pdf

Having said that you could simply keep the transistor phase splitter / driver. It does work very well and does not influence the sound much - BUT do change those 25uF/25V electrolytic coupling caps to new 25uF/63V types.

Changing the preamp to tube will influence the sound a lot more.

Hope this is of help to you.
Cheers,
Ian
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Re: Convert Peavey Deuce to all tube

Postby jukingeo » Wed Feb 25, 2009 10:12 am

Newbietube wrote:Hi all I've just aquired a working but rather old peavey deuce amp chassis as the basis of a bass amp project. My plan is to completely gut the entire amp and start over. This will mean removing the pre amp pcb which is all transistor and probably replacing the power tube sockets and psu also. I've found a pre amp circuit I want to copy but the main issue is the driver circuit which is transistorised. I need a circuit which will work with the existing power amp as i do not wish to change that too radically as I'm not sure if the O/P transformer will handle other circuits too well. I have a schematic of the original peavey circuit and it appears to be similar to a fender bassman but uses no screen resistors and has diodes going to ground from the O/P tranformer primarys.
Any idea on this will be gratefull recieved.
Cheers Just


This amp really isn't anything to write home about. I service Peavey amps in my shop and I got one of these things in right now. I would say that your idea of a complete gutting, outside of the output stage is a wise choice.

Most of the expense and work is already done for you in lieu of the power and output transformers and the physical connection of the output tubes. So that is the most expensive part done right off the bat.

What I will say is to look over this site:
www.ax84.com

Click on the "building blocks" tab and from there you can go to various pre-amp and power amp designs.

They do have a 50 watt EL34 amp listed there I believe. You could also copy the output driver/splitter section for a Fender Twin. These amps used 6L6 output tubes.

One thing you will have to add is a filament transformer for the pre-amp tubes. Reason being is that if you are going to add 4 or 5 preamp tubes, the currents do add up and it can tax the existing power transformer. So you can get an extra 2-3 amp 6.3 volt transformer and bolt it to the chassis. Given that the average 12AX7 draws 8ma, you might be ok. But with 4 tubes that would be 32ma extra on the B+ supply. The existing transformer MAY handle that. If in doubt or you want to have a 5 or 6 pre-amp tube design then you are going to have to with a second full transformer that will supply both the filament AND the B+ to the output drive. This is realistically better because you can totally isolate the pre-amp supply from the power section.

What you also might want to do is put a bias selector in, in case you want to try out EL34 tubes in the amp. The EL34 has a similar loading to the 6L6, but you have to bias it differently. This will expand more options in terms of the types of output tubes. You probably can use KT-66 and KT-77 tubes too.

You will also need to get a nice Greenlee punch to punch out perfect holes in the chassis so this way the job looks 'pro'.

I believe the end result will be vastly superior to the amp's original design. But if you follow the AX84 site, you can taylor the pre-amp stage to your musical tastes/playing preference. Combine that with any special mods you made to your guitar and you can created your own nice signature sound.

Hope that helps.

Geo
Exit Light, Enter Night, Take My Hand...We're off to Never Never Land.
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