Peavey PA-200 Powerup With Dim Bulb Tester and Variac

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Dirttracker73

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Joined 2010
Sorry, it's different. It says PA 200 on the front but the back says 240 power module and the board it completely different. No interstage transformer.
 

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indianajo

indianajo

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Joined 2010
In terms of mono mixer amps, there are acouple of MMA-81502 for $70. Architectural Acoustics Peavey MMA 81502 Modular Mixer Amplifier Never *Used* | eBay
and Architectural Acoustics Peavey MMA 81502 Modular Mixer Amp-8 Channel Ports | eBay
They are entirely different technology, and not apparently broken. I have one, it worked 2 months before a cap audibly buzzed & I turned it off. 150 watts with a fan. No tools or caps right now, all those were stolen September.
There is a 75 watt MMA-875t mono mixer for less. I have 2 of those, since my cs800s was stolen and replacements are so expensive. I paid $60 with freight for each. All these MMA architetectural amps have transformer outputs, so a wiring short that blows the amp doesn't put DC on your speaker. They sound pretty good but my SP2 speakers were stolen too so I'm listening on a low fi organ speaker now.
 
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wg_ski

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Joined 2007
It really sounds like you have a short between windings. Somewhere around here I saw a tutorial about making one of those interstage transformers - from a small (20 watt) power transformer. It does work, I made one a long time ago to drive a pair of PNP Ge’s. Impedance ratio is somewhere in the neighborhood of 600 to dual 20 ohms, or about 5:1 to maybe 6:1. You wind it pri-sec-pri-sec-pri, and add all the primary pieces in series. Use insulating tape between interleaving. I use the yellow Mylar stuff they use on SMPS trafos for rewinds of all sorts. Something like 32 turns on each sec, maybe 72 on each primary piece, on a core from a 12 or 24 volt 1 or 2 amp power transformer. The only thing really critical in the winding is making sure you have the same number of turns on each secondary. If the primaries are off it does not matter. It takes really fine wire for the primary and the usual 24 ga or so on secondaries. Hammond makes one that almost works - impedance ratio is right- and costs about $22. But it is TOO SMALL to support the roughly 50 mA DC bias in the primary without saturating. A 20 VA power transformer core is big enough. I’ve tried the Hammond, it doesn’t work. *Capacitively couple* the input signal in and it does. But that’s not what you have.

If you could find it in the Peavey documentation what the impedance ratio is, you could take out the guesswork of the primary turns. 32 on the secondary is as good a starting point as any on that size core.
 
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indianajo

indianajo

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Joined 2010
I've tried rewinding a transformer. Big failure. short to core. The internet hadn't been invented to explain about mylar tape.
It was a lot easier placing 72 wires on a bare board to make an AX6 driver board. Kynar or teflon wire helps where you can't burn the insulation. Who needs eagle or windows98XP710 update right now!!!? That 3"x5" board would fit in here.
One doesn't need to understand electronics; one just has to buy the parts and download the datasheet to know which pin is E, B, or C. Labels written in sharpie on the board help. Also a yellow pencil to mark off the wires on the schematic as one installs them.
 
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prasi

prasi

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Joined 2014
sites.google.com/site/analogdesign1234/
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indianajo said:
Yes. Sorry about my mistake in post 82. I think a guitar head from that era may have interstage transformer too, but I don't play guitar so I've never had one apart. Advantage of old peavey mastodons, you can get the schematic diagram from the model number without buying the product. The look for an interstage transformer before you put in a bid on ebay or craigslist or gumtree.
Since PA200 has a npn input transistor, the interstage transformer can be replaced by some parts of a tgm8. https://www.diyaudio.com/forums/sol...ased-rod-elliot-p3a.html?highlight=tgm8+bigun
You can reuse the power transformer, rectifiers, can cap, speaker cap, output transistors case, jacks, heat sinks, volume pot, all that niddlety stuff. TGM8 board less output transistor part should fit in same space as interstage transformer. Reason for the transformer, in 1972 transformers were $4 and the 3 TO5 transistors, the VAS & the 2 drivers, were $5 each, the round heatsinks about $1.50. Now incredibly superior MJE15028/29 transistors are about $1.20, the flat TO220 heat sinks are about $.80.
If you download the tgm8 schematic, he favors wimpy drivers & VAS like BD139/140, which is fine for one pair 2sa1943/2sc5200 output transistors @50w but you have two pairs npn & 200 W. I see no reason not to use MJE15028/29 with heat sinks for a lot more drive current to the output transistors, to drive the pair of them. One liability of tgm8, he uses pnp upper output transistors, which in your case would be MJ15025. More $$.
Cheaper is AX6 which uses npn output transistors exclusively, but you would need a pnp input transistor like MPSA56. Fits on a 4"x4" board and that is with output transistors on the board, which you don't need. I have my output transistors physically located away from the driver board, 6" by wire and 3" by physical distance, and my unit doesn't oscillate. Downside to AX6, you can't buy the PCB. Prasi in India made some but I never found a way to pay him; he won't use e-bay so he doesn't drown in government paperwork. My computer is not new enough for pay-pal India's requirements for payment that way.
PCB's you can buy from ebay/alibaba are 99.999% split supply amps, which is not the kind of power transformer you have.
Happy shopping & diy modification.
Click to expand...

Hi Indianajo,
I understand the situation , I might have a few left. tell me your address by PM and I will send the PCB free of cost. along with some other pcbs that might be with me.
 
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