[ARC5] 24V B+ supply for "command" receivers.

[Bill Cromwell]

Hi John,

Well now you have a second hand answer from Robert Eleazer from the
folks at Fair Radio. They would know the answer pretty well as they have
seen a tube radio a time or two. They have said the tubes in your radio
are are ordinary HV B+ tubes in a radio *designed* to operate them at
the much lower B+.

Most of the replies you got from people like me were telling you that
most ordinary HV B+ tubes will operate well at B+ voltages and often
even lower than you 24 to 28 volts. It was left for you to infer that
your tubes would do the same. So your question really was addressed.

I can't speak for any others here but as for me - I do not have any of
the tubes your radio uses. If I did I would have whipped one into a
circuit and applied HV B+ to it to give you an answer. I don't often
have the pieces to directly answer in that manner but when I did I was
back within hours to report results. You could have a pulled a tube or
two and checked for that yourself. You obviously DO have some. You still
could do that if you wanted to be sure. It might be a poor idea to just
apply 200 volts to your radio. The tubes might be okay but other parts
might not survive!

73,

Bill  KU8H

On Sat, 2013-03-09 at 21:24 -0700, john rose wrote:
> I have read the responses to my questions with interest. None of them
>  have addressed my questions. I shall restate them.
> 
> The R392 uses a series of tubes designed to run at 24v on the filaments
>  and B+. However the tube spec sheets I have read all go out to at
>  least 200v. Question; will a tube designed for 24v B+ SAFELY run with
>  B+ at 200v or more? Question; if it does, then is this series of tubes
>  really 6/12v tubes "in drag" so to speak? Comment; obviously these
>  tubes run on 24v B+ and run very, very well. In my (not even close to
>  humble) opinion, the R392 as an SWL rig is very nearly the equal of
>  the R390. Collins designed both and if you lift the lids on both, they
>  very nearly look the same except for size. Oh, BTW if you compare the
>  selectivity graphs of the 85kc IF of the '453/R23 with that of the 392
>  at 2kc, they are virtually identical. 6 gain stages at 455kc will do
>  that.
> 
> This series of tubes is not "Space Charge" tubes. Space Charge refers
>  to the electron cloud that forms around a hot filament or cathode. The
>  'Space Charge Circuit' put + voltage on the grid closest to the
>  cathode (usually the control grid) of an 'ordinary' tube to attract
>  and accelerate the electrons in the general direction of the plate.
>  Circuit control is passed to the next grid in line. This series of 24v
>  tubes operates as you would expect from a normal tube. I.E. the first
>  grid is used as the control grid as any normal tube. What became
>  commonly known as "Space Charge Tubes" were developed by Tung-Sol in
>  the 1950's and had an extra grid (cathode grid) placed in front of the
>  control grid. They have a limit, as I recall, of 30v or so on the
>  plate or you will need to open your wallet.