Peavey CS 800 Power Amplifier

Willarado

Willarado

Active Member
I was recently given some PA equipment including a 1980's Peavey CS 800 power amplifier. This thing looks like it partied on tour with Keith Richards. The case is scratched to hell and both level pots were broken off. I was planning on giving it away but curiosity got the better of me. I opened it up and the inside looks pretty good, nothing is visibly fried or tampered with except one of the pots. The fuses were good.

After giving it a cleaning I plugged it into the dim bulb. The bulb lit up and then dimmed about 70% but stayed on. Would this be normal for an amp like this? I was using a 150-watt bulb. Should I be using a different wattage bulb?

Can anyone recommend replacement pots for the level controls?

I'll check the DC offset next. Thanks for any input.

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I've worked on a few peaveys for local clubs. All are beat to h*ll and stinky.

I'd probably use any pot with the same resistance and taper. They were sh*tty when new.

Good luck getting DC offset down. Clubs don't really care. Also no one will want to buy it once you fix it.

Still kind of fun.

Swing by and I have a working Peavey in the band 'pile'. I'll give it to you.
 
I was curious so I dug in the pile. I found my Peavey head. Musician 400. Missing a couple knobs but no broken pots.

Yours looks newer than mine.

My guess the 150w bulb is fine. You might need to replace the diff pairs to lower DC offset. I don't recall any adjustment. Anything lower than 100mV is fine.
 
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rickl said:
I've worked on a few peaveys for local clubs. All are beat to h*ll and stinky.

I'd probably use any pot with the same resistance and taper. They were sh*tty when new.

Good luck getting DC offset down. Clubs don't really care. Also no one will want to buy it once you fix it.

Still kind of fun.

Swing by and I have a working Peavey in the band 'pile'. I'll give it to you.
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Thanks for the info, I will test the pots. I don't see a way to adjust DC offset so I guess I'll just check it to make sure it's not off the charts.

I will probably switch out the pots, install a new power cord, and call it good. It might make a good amp for a stereo guitar rig... :idea: The Universal Audio amp pedals are insanely good and I've been wanting to try them out in stereo.

Yeah, what is it with Peavey gear? People seem to abuse the heck out of it. At least this one doesn't stink!
 
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Willarado said:
Yeah, what is it with Peavey gear? People seem to abuse the heck out of it. At least this one doesn't stink!
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I think they are cheap and somewhat reliable. Most are kind of heavy for gigging. But good for sound board or sound reinforcement/PA.
 
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The CS800 is one of the best sounding amps that ever powered my infinity speakers. Not just a "pretty good" amp. It's a tank that sounds really good. The only downside is the fan noise in a home environment. I suggest you to fix it and listen and judge by yourself.
 
fan would be easy enough to fix. If its not a 12v unit, swap it for one of the same dimensions and add a thermal fan controller to the mix. Attach the sensor to the heat sink and let it vary fan speed based on heat sink temp.

if I ever decide to put my Phase Linear into regular service, that mod is on the list. Currently its running the two 120v fans in series so they don't sound like a hair dryer.
 
elnaldo said:
The CS800 is one of the best sounding amps that ever powered my infinity speakers. Not just a "pretty good" amp. It's a tank that sounds really good. The only downside is the fan noise in a home environment. I suggest you to fix it and listen and judge by yourself.
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Good to know, thanks. If I get it running well it would be interesting to try on my power-hungry AR-3a speakers.
 
gadget73 said:
fan would be easy enough to fix. If its not a 12v unit, swap it for one of the same dimensions and add a thermal fan controller to the mix. Attach the sensor to the heat sink and let it vary fan speed based on heat sink temp.

if I ever decide to put my Phase Linear into regular service, that mod is on the list. Currently its running the two 120v fans in series so they don't sound like a hair dryer.
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I didn't know you had to run fans on yours. Only PL amp I ever had that required a fan was a early WO rev B quasi-comp. I run my dual mono rev G 700 series II full throttle daily with no fan. I do keep my transistor covers off. Is your bias running above 350mV possibly? Your amp is already full comp so that's why I am wondering. You far smarter then me when it comes to electronics so just asking
 
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I forgot to mention, when I opened this up there were 7 screws, nuts, and washers rolling around in there. Minor miracle that nothing shorted.
 
Northwinds said:
I didn't know you had to run fans on yours. Only PL amp I ever had that required a fan was a early WO rev B quasi-comp. I run my dual mono rev G 700 series II full throttle daily with no fan. I do keep my transistor covers off. Is your bias running above 350mV possibly? Your amp is already full comp so that's why I am wondering. You far smarter then me when it comes to electronics so just asking
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Its a Pro 700, they came with fans. Two large ones that make obnoxious amounts of noise. It doesn't actually get hot even with them unplugged but since its an original feature I'd like to retain it in some fashion.
 
Willarado said:
I was recently given some PA equipment including a 1980's Peavey CS 800 power amplifier. This thing looks like it partied on tour with Keith Richards. The case is scratched to hell and both level pots were broken off. I was planning on giving it away but curiosity got the better of me. I opened it up and the inside looks pretty good, nothing is visibly fried or tampered with except one of the pots. The fuses were good.

After giving it a cleaning I plugged it into the dim bulb. The bulb lit up and then dimmed about 70% but stayed on. Would this be normal for an amp like this? I was using a 150-watt bulb. Should I be using a different wattage bulb?

Can anyone recommend replacement pots for the level controls?

I'll check the DC offset next. Thanks for any input.

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Check the bias, the bulb is normal is bias is pretty high on idle. I would make sure you can turn the bias all the way down and get a completely dark bulb.
 
Can anyone supply the schematic for a Peavey C S-800. I have one I am trying to repair - seems like issue is in the protection shutdown circuitry for 1 channel. The other channel works fine. All outputs look good on my curve tracer. I found a file with the schematic but I can't print it big enough to read the print. it needs to be at 300% mag or more to read it on my laptop. Any ideas ? I used to be able to print just a portion of the schematic on my widows machine. I would print about 4 to 6 sections then cut and tape those sections together to be able to read it. But with my Chromebook not liking my older HP laserjet I can no longer figure out how to print the enlarged schematic.
Please HELP !
Mr. Bill
 
Mr Bill said:
Can anyone supply the schematic for a Peavey C S-800. I have one I am trying to repair - seems like issue is in the protection shutdown circuitry for 1 channel. The other channel works fine. All outputs look good on my curve tracer. I found a file with the schematic but I can't print it big enough to read the print. it needs to be at 300% mag or more to read it on my laptop. Any ideas ? I used to be able to print just a portion of the schematic on my widows machine. I would print about 4 to 6 sections then cut and tape those sections together to be able to read it. But with my Chromebook not liking my older HP laserjet I can no longer figure out how to print the enlarged schematic.
Please HELP !
Mr. Bill
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i have cs 800s manual if any use ?
 
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Also a good idea to check the speaker protection crowbar Triacs that are connected across each of the amplifier`s output channels.
When the amp has had a serious malfunction that slams the full +/- PS rail to the amplifiers output jacks, the crowbar sensing circuit triggers the Triac to clamp to protect the speaker(s) until the main fuse blows, which almost always destroys the 15 amp rated protection Triac.
And this crowbar circuit can also be inadvertently activated when the mains is slowly brought up with a variac when the amp is not connected to a load and the PS` +/- rails become unbalanced sending DC to the output jacks, even if the amp is full functional with no circuit issues.
Just something to be aware of when servicing the 800 or 400 made in the late seventies ~late eighties.
 
elnaldo said:
The CS800 is one of the best sounding amps that ever powered my infinity speakers. Not just a "pretty good" amp. It's a tank that sounds really good. The only downside is the fan noise in a home environment. I suggest you to fix it and listen and judge by yourself.
Click to expand...
I've read somewhere (but I haven't compared the scats) that the Peavey CS-800 is the same basic amp as a BGW-750B, which has a reputation for being a very good sounding amp.
 
tarior said:
I've read somewhere (but I haven't compared the scats) that the Peavey CS-800 is the same basic amp as a BGW-750B, which has a reputation for being a very good sounding amp.
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The ORIGINAL CS800 (the four-rack-height version, with the silver and black cast aluminum faceplate) was indeed a fairly faithful rendition of the same design as the original BGW750. Both amps were designed by the same person, in fact.

A couple of the later CS800 versions-up to the CS800X, IIRC- were also designed by this same person, and had similarities to the BGW design, as a result. After that, they started diverging in design pretty comprehensively, over time.

Regards,
Gordon.
 
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