[Amps] 4-250A question

[COLIN LAMB]

Bill said:

"This reminds me of a homebrew amplifier I got some years ago. I replaced
the missing parts and installed a good 3-500z only to find  the output was
very low. I assume that why the builder gave up on it and I got it cheap.
Come to find out that the filament voltage was low. The problem was that
the builder did use a 5 volt transformer but did not take into account the
drop across the filament choke. I installed a boost transformer in the
primary to set the filament voltage at the socket to 5 volts."

My first home brew rig was in 1959.  It was "The Sandwich Box Transmitter"
from an article in 1956 Popular Electronics using a 6AQ5.  Using my Howard
430 Receiver, I called CQ for over a month with no answer.  I just had
enough power to light a 47 pilot light.  I did not own a voltmeter so I
could just check the wiring.  Finally, my uncle bought me a Heath VOM.  I
put it together and measured the filament voltage.  It was 3.2 volts.  Then
I realized that filament transformers were described differently than high
voltage transformers.  High voltage transformers were commonly described as
the specified voltage each side of center tap, while filament voltage was
the full tap - with a center tap.  

When I connected the full filament voltage to the 6AQ5, I almost
immediately worked someone at the other side of the world (about 80 miles
away, actually).  So, based upon that experience, running a tube on 1/2
voltage is too low.  

Happy 4th of July.

Colin  K7FM