Re: A question about vacuum tubes

[Larry Weil <kc1ih@mac.com>]

At 2:21 PM -0400 9/2/02, A. Joseph Ross wrote:

>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.

There's no harm to the radio.  These radios have series filaments, 
wired directly to the AC input.  You will notice that if you add up 
the numbers from the start of each tube, they add up to approx 110. 
By subbing a 50C5 for the 35C5, you will lower the filament voltage 
and current slightly to all the tubes.  If it works, stay with it, 
the remaining tubes will last that much longer.
-- 
Larry Weil
Lake Wobegone, NH