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Soundcraftsmen PCR-800 recap job?

Patrick620

Patrick620

Audio Enthusiast
I've got one of these coming and I'm wondering if I would be wise to recap it. Actually, I enjoy doing recap jobs on my tube radios but it's more of a certainty that they need new caps. On those I replace all of the caps except for the ceramic disc's and the mica caps. On this amp I have coming, if there are no obvious signs that the caps are bad should I go with the "if it aint broke dont fix it" line of thought? Has anyone else recapped one of the with good results? I would like to find a schematic, too. Thanks for any replies.

Patrick
 
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Patrick PCR-800 are good Mosfet amps, most need the DC offset worked on.
These are not a pot adjustment type, but matched component replacement.
There is a scat floating around on the net.
 
What components are we talking about? Is there some info on what you're talking about?

I just found a thread that talked about adjusting the dc offset by installing new matching transistors. Does that sound right?
 
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Input differential pairs should be matched. Find the SM, we're talking about Q1 and Q2. Q3 should be replaced also with the same type of transistor, but it does not need to be gain-matched to the other two.
 
I will find a copy of the SM and schem and I'm sure it will be much clearer to me. I have a good idea of what to do. Thanks for the help. I will likely have a few questions once I get started. I need to buy a new meter, too. A true RMS meter.

Patrick
 
Ok. I found a copy of the schematic w/o any parts list. I will have to wait to get the amp and open it up. I will post more, then.
My bad, MPSLO1's for Q1, 2, and 3
 
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I would suggest increasing the capacitance on the Soundcraftsmen in question. They pretty much live off their capacitors based on the inappropriate sized transformer.

They're good amplifiers and are rated 450 watts per channel @ 2 ohms.

Best Regards,
 
How much of an increase are you suggesting? It is my understanding that depending upon the function of a specific capacitor in a circuit, that an increase of 20 or 30% wont hurt, but some caps should be replaced with the same value that the circuit was intended for. Are you talking about the power supply caps? I assume that you are.
 
Yes. I am talking about the power supply.

I don't have one open at the moment. If my memory serves me correct, each electrolytic (two in total) is 10,000 MFD 75 Volts.

The voltage rail is +/-70 Volts so, you can decide if 10,000 MFD per rail is enough for your needs. If you don't want your lights to dim whenever the bass note hits, I would suggest increasing the capacitance value.

In case you don't know, there are no relays in this version. Once you engage the power switch it is ready to go. You will hear something chaotic happening inside based on inrush current and the fan starting up. However that is standard procedure with that model. I own four of them by the way.

Best Regards,
 
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