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|    rec.audio.tubes    |    Tube-based amplifiers... that go to 11    |    52,877 messages    |
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|    Message 52,596 of 52,877    |
|    johnnhelen4@gmail.com to All    |
|    Re: Replace plate load resistor with pla    |
|    22 May 17 03:38:12    |
      OK Jim, I found a copy of the schematic. The cct is a variation on something       somewhat common with old guys like us back in the day, convert down to the BC       band & use an ordinary receiver to do the tuning. I did two of them, one for       my old Ford car.              So the front end does a block conversion in this case & the 2nd IF does the       tuning, a slick way to get good image rejection. The preselecter completes the       job.              Given the cct constants a B+ of 180V seems unlikely, 140-150V is possible. The       first filter cap is shewn as 50 microF & is a problem for the PT. The peak       currents are limited only by the PT wdg R's. Better stuff in something like       100R in series with the        PT HV secondary to limit the peak charging currents. It is the RMS current       that heats & kills transformers, not so much steady currents.              I noticed somewhere on line 5W audio mentioned. I think one Watt more likely.       Rather then surgery to do a triode output & driver,if there is space there       should be some kind of suitable OPT that would improve the sound. Hammond has       several designed for SE        output. But rather expensive now.              If the NE2H neons are still working keep them in the cct as is. The B+ will be       about the same as original, no need to complicate with Zeners. My own       experience with zeners as the voltage increases so does the change with       temperature. As the zener heats        up the voltage drifts with it.              Looks like a very good radio.              Good Luck, John L Stewart              --- SoupGate-Win32 v1.05        * Origin: you cannot sedate... all the things you hate (1:229/2)    |
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