Wawasee style JB12 " no bias components"

[Danzik]

Hi there, I have this modulator that is alot like a JB12 that I am working on and recapping after opening the unit up I noticed that there is a pair of old camera batteries 22 1/2 volt that are being used for the negative bias LOL, I also noticed there is only 4 wires coming from the transformer and not 6 wires like the Wawasee's so with this being said is there any easy way around this can I come off from somewhere else to put my bias circuitry in safely? I find multiple places that have around 50 VAC but they are going other places. Thanks

 

[KneeBiter]

Hi there, I have this modulator that is alot like a JB12 that I am working on and recapping after opening the unit up I noticed that there is a pair of old camera batteries 22 1/2 volt that are being used for the negative bias LOL, I also noticed there is only 4 wires coming from the transformer and not 6 wires like the Wawasee's so with this being said is there any easy way around this can I come off from somewhere else to put my bias circuitry in safely? I find multiple places that have around 50 VAC but they are going other places. Thanks View attachment 70491

Why not add another small transformer?

 

[Danzik]

Why not add another small transformer?

If that's my only route I can take I may have to do that but there isn't much room to add another, would probably have to replace the one that I in it.

 

[Danzik]

I think I may have found a wire cutoff at the base of the transformer, I added wire to it so I may have my issue resolved hopefully!

 

[Shockwave]

Hi there, I have this modulator that is alot like a JB12 that I am working on and recapping after opening the unit up I noticed that there is a pair of old camera batteries 22 1/2 volt that are being used for the negative bias LOL, I also noticed there is only 4 wires coming from the transformer and not 6 wires like the Wawasee's so with this being said is there any easy way around this can I come off from somewhere else to put my bias circuitry in safely? I find multiple places that have around 50 VAC but they are going other places. Thanks View attachment 70491

Unfortunately there appears to be more than one issue here. Many of these designs only used a two pole relay and offer no ability to switch the bias on and off. They are tube killer's from day one as a result.

 

[Shockwave]

If that's my only route I can take I may have to do that but there isn't much room to add another, would probably have to replace the one that I in it.

I modified one for use with a 6LF6 tube that required more negative bias. I took a small 24 volt transformer out of a tiny "wall wart" and used a voltage doubler. This provides over -65 volts DC to work with. Usually enough to place a stock tube into cutoff. Although, I prefer switching the screen voltage off in RX on these units.