Bias Diode Boards

[brandon7861]

I think I will hold off on making large numbers of these until I get a chance to test a few other diode arrays. I can make them as is for anyone wants some, but as I showed in the video, 4148's on the back of the original board will do the same. I will get a sample of different diode arrays with my next order and see if I can get them closer to the originals..

 

[N8YX]

Thought this was going to be about a different subject.

Several amps I have here (in particular, the L7 and L75) can benefit by having their bias circuitry revamped slightly. There was an EU seller of a kit which also incorporated meter protection and a few other nice-to-haves onto the same board.

Due to tariffs he won't ship to the U.S. - so I'm left to fabricate my own or come up with another pre-made source.

 

[nomadradio]

I sell a pc board that simulates a zener with a string of forward-biased rectifier diodes. Has the advantage of being a bit less fragile than a zener in the face of a surge current. Its main appeal is to AM operators who ignore the factory's advice to select "CW/Tune" to operate AM. Cuts the power too much, so they flip to "SSB" and melt the solder out of the tubes' filament pins, and ruin the sockets. A higher bias voltage reduces the amp's idle current and allows the use of AM on the amplifier's "high" side without the suicide effects.

https://www.ebay.com/itm/1158114738...pid=5336136228&customid=&toolid=10001&mkevt=1

But it's a bare-bones widget and doesn't protect meters or such. The listing says "L4", but the L7 is more or less the L4 repackaged in an aluminum chassis.

And if your main interest is sideband, a series string of eight or ten of those diodes will calm down the amplifier's idle current without compromising sideband signal quality. Just pull the filament trasnformer's center-tap wire loose from the relay. The anode end of your diode string goes to the centertap wire, the cathode end to the relay circuit.

73