Sb-220 power output at about half..

[John]

I will double check the plate caps on the tubes. These 3-400z's are testing
full output for me in another amp. In this amp I was getting 800 out with
100 in until the condition which I described took place and the power is
reduced to half it seems. Have exchanged tubes from socket to socket etc..
Also if this will help.. The plate air variable was really sensitive to me
until this happened. Now it seems that the plate has to be turned quite a
bit off of peak tune position to cause the peak output to change a little.
The best tune position on the plate variable also seems to be with the
plates open, in other words I am saying they don't overlap any to me as it
seems to me it should.

John Godfrey
 



-----Original Message-----
From: Glen Zook [mailto:gzook at yahoo.com] 
Sent: Wednesday, May 23, 2007 9:20 PM
To: john at hughes.net; HEATH at LISTSERV.TEMPE.GOV
Subject: Re: [HEATH-TEMPE] Sb-220 power output at about half..


Sounds like one of your 3-400Z tubes has gone.  Also,
the SB-220 was designed with the 3-500Z tubes and
definitely will work better with that tube even though
the 3-400Z is capable of about 20% less power.

One thing to check is that the plate connection is
still good on both tubes.  Once-in-a-while the
connection between the wire that comes through the
envelope and the larger connector comes loose.

Glen, K9STH


--- John Godfrey <john at HUGHES.NET> wrote:

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.  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.









Glen, K9STH

Website:  http://k9sth.com


 
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