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Title: Replacing A 5AR4 With Diodes? Post by: KN4SMF on June 20, 2024, 02:07:56 PM I have a BC-348 here that somebody had built a pretty nice 5AR4 power supply for. Problem is, voltage is a bit low for my taste, and the tube is too tall for the radio to slide into its cabinet without scraping the top of the tube. I don't want to buy one of those ebay plug-in rectifier modules, and I have some 1N4007 diodes right there. How do I solder them up to the bottom of the tube socket? Which pins to which, and proper way to turn the bands on the diodes? I'm not interested in breaking up an old tube for its base and wiring the diodes inside it. Surely it can be easily done by wicking enough solder out of the tube socket lugs to slip the pigtails of the diodes through, without changing any of the existing socket wiring. Thank you.
Title: Re: Replacing A 5AR4 With Diodes? Post by: WD8BIL on June 20, 2024, 02:37:42 PM The band on the diode indicates the CATHODE end.
For the 5AR4 cathode is pin 8. Anodes are pins 4 and 6. So, the banded end of each diode goes to pin 8. The other ends go to 4 and 6. Doesn't matter which ones. Now here's the rub; the peak inverse voltage rating on the 5AR4 is 1700V. 1N4007s have 1000V PIV. You'll need to string 2 in series on each leg. Title: Re: Replacing A 5AR4 With Diodes? Post by: KN4SMF on June 20, 2024, 03:17:53 PM Thank you very much. As for the diode ratings, the BC 348 is a pretty low voltage rig. 220-230V of B+, at most. I would think 2 diodes would work. The 5AR4 was overkill big time for what this radio needs. Right now I'm sitting at 195V of B+. The specs call for abut 220 or so. Although I doubt the diodes will get me that high, even if they get me to 210 or so, I guess I can call it good and button it up.
Title: Re: Replacing A 5AR4 With Diodes? Post by: KN4SMF on June 20, 2024, 05:52:08 PM Well I got the job done. It raided my B* from 195 to 203.4V. Anemic and disappointing. It should be AT LEAST 220. But I just recapped and re-resistored and aligned the radio just as it came to me, with the home made power supply that was in it. And it does indeed play quite well, for what it is. It's not a Hammarlund or a Hallicrafters. I guess I should be happy enough. Because to re-engineer and build a new power supply will likely give me pretty much the same thing.
Title: Re: Replacing A 5AR4 With Diodes? Post by: DMOD on June 20, 2024, 09:18:24 PM Here is a PS I use, depending on the rig.
Title: Re: Replacing A 5AR4 With Diodes? Post by: WD8BIL on June 21, 2024, 08:25:41 AM Good to hear, Henry! Enjoy. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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