[ARC5] Audio stage impedances.

[Kenneth G. Gordon]

On 24 Jan 2013 at 1:17, WA5CAB at cs.com wrote:

> Although they are pin for pin compatible (have the same apparent
> basing), besides the significantly different heater requirements (you
> can't parallel any of them with the other tubes in a Command Set
> receiver because you would be putting 12 volts across 6 volt heater
> tubes),

Yes. That is why I said that all the filaments had to be wired in parallel. 
Furthermore, ALL the tubes would have to be changed to their 6.3 volt 
equivalents.

> the other three tubes will require at a minimum a change in
> cathode resistor and probably screen dropping resistors.

Yes. In any case, I do not plan to substitue any tubes.

I did find an interesting thing last night, though:

Just to check (and because I am intensely curious about most things), I took 
the time to measure the AC filament voltage at each tube socket: in no case 
whatever was the 24 VAC source evenly-divided across any two sets of 
seriesed tubes: it would be 11 volts on one tube and 13 volts on its partner, 
or 11.5 V on one and 12.5 on its partner, etc.

I found that interesting, but not particularly important.

Ken W7EKB