RE: A question about vacuum tubes

["Hakim Madjid" <HMadjid@mindspring.com>]

Counsellor Ross Writes:

>I'm sure there are some people around here old enough to be familiar with 
>how tube sets work.  I have an old Zenith AM-FM radio with a rather nice 
>sound, but it's had some problems lately.  I diagnosed the problem as the 
>audio output tube, which is 35C5.  I had an old 50C5 tube, which was used 
>for the same purpose in AM-only radios, I substituted it, and it works 
>well (I seem to remember something about it being sort of OK to do that 
>if the substituted tube had a higher voltage, as represented by the 
>initial number.).  My question is whether there's any harm to the radio 
>in leaving it that way, or whether I really ought to look for a 35C5 from 
>somewhere.

Dear Counselor Ross:

You should be ok with that tube substition.
Mind you this one of those things where theoretical stands in the
way of the practical. In *THEORY* you should use the right tube,
but as a practical matter, if the radio works fine with the 50C5
then you're ok.

I can't think of anyway that this would damage the radio, in fact
the 50c5 might last longer, as it will be running below it's rated
heater voltage. By the same token, however, it might give you less
audio power output.

73, de Hakim (N1ZFF)