[Amps] TV sweep tubes and 6146s

[Bill Fuqua]

      I once ran 4x   6AG7's with 1200 volts on the plates in grounded 
grid. They required conditioning but it worked and got 200 or so watts put 
PEP with a couple of watts drive on 20 meters. The tubes were  pressed into 
a heat sink made of a block of aluminum with fins cut into it.   I was 
young and did not know any better. But it worked.
    I also made an 2x  813 GG amplifier and one with two 250THs in it as 
well. I loved the glow of the 250TH plates. The only problem was that I 
destroyed a perfectly good Halicrafters HT-4 to make my 250TH amplifier. I 
regret not having it now. It is a real collectable item today. A friend 
sold the HT-4 to me for $20 with lots of spare tubes.  The 250TH amplifier 
had somewhat low gain and I had to apply some negative bias on the grids 
but it worked just fine driven by my 20A exciter and a homebrew amp with a 
pair of 6146Bs.

6146B tubes should be able to handle 1200 volts on the plates. In AM 
operation they suggest a max of 600 Volts DC on the plates and with 100% 
plate modulation this amounts to 1200 volts peak.  But can't say how linear 
they may be or how far you can push the plate dissipation.

I was looking an EIMAC 15E triode. It is listed in the handbook as 
producing about 100 watts output in class C.  This thing has a  plate about 
the size of a pencil eraser.  With 20 watts plate dissipation and 80% 
efficiency you should get 100 watts output. A 6146B only has 35 watts plate 
dissipation and produces only about 85 watts in class C. Its too bad we did 
not have little tetrodes like the 15E, maybe a small version of the 4-65 
would have been nice.


73
Bill wa4lav