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[email protected] johnnhelen4@gmail.com is offline
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Default Replace plate load resistor with plate choke

On Monday, May 22, 2017 at 9:51:03 PM UTC-4, Jim Candela wrote:
On Monday, May 22, 2017 at 5:38:13 AM UTC-5, wrote:
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


John, Thanks for the very thoughtful reply. The Mosley CM-1 has an interesting history. The designer, John Clemens, W0BD was interviewed in 2013 about his receiver. John was 90 years old then. Here is the video:

https://twit.tv/shows/ham-nation/episodes/129

Fast forward to 15:00 minutes...

Here is where I got to thinking about a triode audio output tube:

http://our-house.jp/6AW8/index.htm

Jim


THX for the 6AW8 running as a pwr amp, very useful info. I see they shew that the pentode section running as a triode at 1/2 W output while on the 200V PS. There are nomographs included in several of the RCA Receiving Tube manuals that allow estimates of pwr at other operating conditions. With the existing PT in the receiver I got 0.48 X 0.5W, about 240 mW, still very usable on a good speaker.

I didn't hookup to the video. Surprisingly, even tho we are in a major metropolitan area here, HS iNet has not yet come to this area. I'm on a rocket stick that communicates with the local cell phone tower close by on a 6 lane, soon to be 8 lane highway. Ridiculous & very expensive.

Cheers, John