home bbs files messages ]

Forums before death by AOL, social media and spammers... "We can't have nice things"

   rec.audio.tubes      Tube-based amplifiers... that go to 11      52,877 messages   

[   << oldest   |   < older   |   list   |   newer >   |   newest >>   ]

   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)   

[   << oldest   |   < older   |   list   |   newer >   |   newest >>   ]


(c) 1994,  bbs@darkrealms.ca