[ARC5] BC-454-B tube question

[Kenneth G. Gordon]

On 2 Jul 2015 at 11:05, kg4kgl at gmail.com wrote:

> GM all,
> 
>  I have a question regarding the 12sk7 and 12sr7 tubes used in a BC-454-B
>  receiver. The tube specs show max voltage for heater with respect to cathode as
>  90v. 
> 
> How was this dealt with in the original installations?

As far as I can tell, the maximum difference in voltage between the cathodes 
and the filaments in the ARC-5 receivers was no more than about 12 VDC 
for half the tubes and 24 VDC for the other half.

The cathodes for some of the tubes are biased above ground in some cases, 
but only by a few volts

Why would you think that there was a greater differential?

> I built a SET amp

What is a "SET amp" ?

> that used 6sl7 driver tubes and a voltage divider (~83v) was
> created and fed to the center tap of the 6.3vac filament winding.

Again, "why" ? I don't understand what you are asking.

> Was any such
> thing done for these receivers? Should something similar be done if you are
> powering these from a B+ supply?

I am not sure what you mean by this: as far as the receivers are concerned, 
there is no difference between the dynamotor and an external AC supply as 
far as B+ input is concerned, and therefore no difference whatever as far as 
the cathode-to-filament differential is concerned.

Please clarify your question.

Thanks,

Ken W7EKB