Regen Cap Question

[Carl WA1KPD]

Picked up a sweet regen back in Oct. Came with full coils, headphones and had been built exactly according to the design in the 1941 How To Become a Radio Amateur. Finally getting to it and have one question.
C5 is called out as a 2 mfd 450 electrolytic. There is only 90 volts applied to the rcvr anyway. Is this because the only reasonable priced cap that was available at this level of mfd was 450 rated?
Can I go with a higher .mfd (I have plenty of room to stuff it in the exisitng cap case) Is this voltage needed?

Schezmatic attached

Thoughts?

Thanks

Carl
/KPD 

[WQ9E]

Carl,

A lower voltage rating wouldn't be a problem but if you go higher in value there could be some lag between changing the regen control and the actual screen voltage change for the tube element.   Since you should be providing pure DC to the receiver I don't see any advantage in additional "ripple" filtering here, I believe C5 is there to provide decoupling for audio on the B+ line.

I am surprised there isn't a lower value capacitor in parallel with that capacitor to provide RF bypassing since electrolytic caps are highly reactive at typical radio frequencies. 

[KA2DZT]

Put a 200 volt cap in and it doesn't have to be an electrolytic.

Fred

[Carl WA1KPD]

Thanks to both of you.
Fred- What value would you suggest for the cap?

[KA2DZT]

Schematic calls for a 2mfd, I would put a 2mfd 200v cap.  They were made in paper type caps.  Not sure if you have any 2mfd caps that are not electrolytic but they were not that uncommon.

Fred

I just took another look at the schematic,  it looks more like a screen by-pass cap rather than a B+ decoupling cap.  Running the set from batteries, filtering is not an issue.  Hard to say why they arrived at that value cap.  May be more to do with what was more commonly available at that time, especially when you consider the 450 volt cap in a set that runs on 90 volts.

[N3GTE]

Hi Carl
Methinks that cap is there to keep the regeneration control quite. If a wire wound pot is used it can be pretty noisy. 450v is a bit of an overkill. I'd experiment around with the value I suspect it isn't very critical.
Terry N3GTE