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Last Friday, a friend of mine brought over a couple of power amps that he wanted me to test. I do stuff like that, and repair work for him periodically. I've written a few posts about amps I've tested or fixed for him in the past. He buys and sells this kind of stuff as a business. This time, he brought me a Peavey CS-800 2 channel power amp, an older linear amp, and a Fender Princeton Reverb from 1979 or 80. The Princeton will get it's own post on here once I've gone through it and taken pictures of it.
I worked on the linear amplifier and the CS-800 on Sunday. I also decided that since I was testing amps, I might as well test my old Peavey CS-400 2 channel power amp. The first thing I put up on the bench was the linear amplifier.
This linear amplifier was built by someone using high quality components, probably as part of a university program. It's hard to tell how old this thing is, I'm guessing it was built in the 1950s or 60s. It had radio call numbers on it so it may have been used as a local university radio transmitter. It was mounted inside of a steel cabinet when he brought it over, we pulled the chassis out of the cabinet and this is what it looks like.
The only thing I could do to test it was to see if it would power up and to check voltages. This is a radio frequency transmitter that probably drove an AM antenna. It had an antenna hookup cable on the back of it. I had to replace one of the power switches and tape up the broken fuse holder before I could test it. I also tested the tubes before powering it up. It has three 807 power tubes and a 5U4 rectifier tube. All the tubes tested good. After inspecting the wiring to make sure there weren't any shorts, I was able to power it up and check the voltages. Everything seemed to be working the way it should, so that was about all I could do.
This thing has 2 transformers in it, a high voltage power transformer, and a heater transformer. The heater transformer has outputs for both 5 volts for the rectifier tube, and 6.3 volts for the heaters of the 3 807 tubes. Ihe high voltage transformer puts out about 450 volts, which surprised me, because the tubes can handle about 750 volts. This amp didn't work the tubes all that hard.
The dark boxes on the chassis are the transformers, the 3 boxes that look the same are oil filled capacitors, and the other 2 big boxes are filter coils. The brown tube in the back has a coil wrapped around it, it's part of the output circuit. My radio transmitter knowledge is not very good, so that's about all I can tell you about this amp. I can tell you that with the proper parts and wiring, 2 of those 807 tubes can put out 100 watts of audio power. After I finished working on the amp, I decided to weigh it because it was rather heavy. It ended up weighing about 50 pounds. My back was not happy with that at all.
The next amp I worked on was the Peavey CS-800 audio power amp.
There really wasn't much to testing this amp. First I checked the fuse to see if it was good, and it was. That's a good way to find out if the amp has a major problem, if the fuse is blown, there's a problem. Next, I took the top cover off to give the amp a quick inspection to see that all the transistors were in place, and all the wiring was connected. It's also a good idea to clean the amp out if it's full of dust bunnies and crap. This one seemed to be pretty clean, so I plugged in the power cord and turned it on. It came on properly, so I plugged a couple of my speaker cabinets into it, fed it music from my computer, and turned up the volume knobs a bit to see what happened. It seemed to be working properly at low volume, so it was time to turn it up. These amps can get extremely loud in an average sized room in a house. The Peavey CS-800 will put out about 400 watts per channel with a 4 ohm load, or almost 200 watts per channel with an 8 ohm load That much power will rock your socks off! You need a room bigger than this house to use the power in this amp and still be able to hear yourself think. After thoroughly abusing my ears for about a half hour, I decided that the amp was indeed working properly and shut it down. Did I mention that these amps weigh at least 60 pounds?
It was at this point that I decided to test my CS-400 amp, everything was already set up, and I hadn't used it in several years. Leaving electronic gear in the basement over the course of several years is seldom good for it, so I didn't quite know what to expect from the amp. I dragged the amp up out of the basement and put it on the work bench. The first thing I did with this one was to take the cover off to take a look inside.
The inside of the amp was full of dust bunnies and needed a serious cleaning. I got the vacuum and my trusty dust removing paint brush and started cleaning. I use the paint brush to move the dust and crud so that the vacuum will suck it up. I ended up having to take the cooling fan out of the case to clean it properly, which also gave more room to get at the dust crap inside the amp. After I got it all cleaned up, it looked a lot better.
The Peavey CS-400 will put out 200 watts per channel with a 4 ohm load and about 100 watts per channel with an 8 ohm load. Plenty of power for a small venue, or to abuse your ears at home, which is what I did for the next 45-50 minutes. This amp doesn't weigh as much as the CS-800, but it's still about 40 pounds or so, not something I want to haul around very much these days.
Well, that's all I have for this post, I hope you found it interesting!
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