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In Reply to: Re: Well, I figured out that 'Zpri' must mean 'resistance of the primary'... posted by Poindexter on August 14, 2005 at 16:35:43:
The amp is an Antique Sound Labs Explorer 805 DT, the most-current version AFAIK...definitely store-bought. There are no obvious makings I can see on the OPT; it's bolted to the chassis and the bottom of the windings is not visible.
Follow Ups:
I worked it backward from your power rating. Your power spec is 50w; but let's be conservative and say 25w. Since P = V²/R, V = √(25×8), or 14 Vac, so your amp will be producing 14Vac into your 8Ω load at 25 watts. Your output transformer is specced at 4.6K : 8Ω, and since N (the numerical turns ratio, which is also the voltage step up/down ratio) is the square root of Zin / Zout, it will be √(4600 / 8) or 24. Therefore, your parafeed cap is dropping a possible maximum of 360Vac, or 480Vpk in addition to the 860 DC volts. This would, of course, seriously overvolt your 1200V caps.I say possible because it's not so simple. In the first approximation, that AC voltage is not supposed to be on the cap, since it will pass that AC waveform on to the output transformer, which it is what it does for a living. The cap and output transformer make a series circuit of two reactances whose phase is 180° apart, however, and so there is going to be a lot of voltage being passed back and forth between them; the transformer having some mongo reactance (hundreds of Henries, I would say).
I would have to work through the AC analysis of this LC circuit to see what exactly is happening, and I don't have time right now; but I would suspect that there is at least a good chance that you were overvolting the 1200V Mundii.
Ain't 'rithmetic wonderful? What was the voltage rating of the caps that were originally in there?
This, by the way, is the reason I have never been tempted to fool around with transmitter tube audio circuits. The sourcing of even the most common components in the circuit can turn into a king-sized PITA.
Aloha,
Poinz
I now have 2/1500 auricaps there.King-size PITA indeed. I HATE the very ideas of PS caps in series AND 'lytics in the PS, I so I found some 40uF/800+VDC ASC oil-filled 'propylene caps for the 3rd pole of the main PS. They are neither small nor inexpensive!
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