Sb-220 power output at about half..

[John Godfrey]

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. 

  

-----------------------------------------------------------
Products bought, sold or traded here is the responsibility of the
parties involved.  This list and the City of Tempe are not responsible
for losses or misrepresentations of any kind.  Buyer beware!

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.aspx?list=HEATH
To post - HEATH at LISTSERV.TEMPE.GOV
Archives - http://listserv.tempe.gov/archives/HEATH.html