Sb-220 power output at about half..

[R Johnson]

John:
I assume that the 3-400 tubes you refer to are really 3-500's !!!

All the SB-220'S I've used, repaired, or owned used a pair of 3-500's !!!

If not a TYPO and you really 3-400's in the amp, that's the problem.

A 3-400 has about half the Mu (Gain) of a 3-500 which may be your problem.

If it was a TYPO then you still have a problem, if not you need to spend the $$$
for a set of 3-500's !!!

Hope I'm not the "bearer of bad tidings".

73 es GL
Bob, K1VU


At 06:33 PM 5/24/2007, John Godfrey wrote:
>I do hope you guys can help me. I have been in the process of restoring a
>heath kit SB-220. I replaced all the filter caps - diodes in the doubler
>etc. all with new parts including a new air variable for the plate tuning.
>All was well and output was plenty acceptable on all bands. Then output just
>went to zero after a power-on condition. Meaning it was fine when turned
>off. Then after much investigation I found that the little bolt/nut that
>holds the output tuning 10/15 meter coil to the plate tuning capacitor was
>loose. After tightening and re-power up and tune. I just get half the output
>as before. Both tube filaments light bright and voltage to the pins on the
>filaments is 4.9 volts ac on my meter. Cleaned the sockets and pins in case
>of any resistance but like I said voltage seems to be correct. Zener diode
>seems to deliver exactly 5 volts DC through the center tap of the filament
>transformer to the tubes at transmit and the 117 volts dc at receive mode.
>Tubes do produce gain. With 40 watts in you get about 150 out. 100 watts in
>gives 400 watts out. Again about half what I was getting. Both tubes EIMAC
>3-400z l believe them to be full output because I tested them in another
>amp. Tested the high voltage on SSB mode and I have about 3010 volts DC.
>Input SWR is acceptable and I am driving it with tubes as well instead of
>transistors. 
>
>  
>
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