[Heathkit] SB220 and IC7300 problems

[Jim Jim]

Marty,
I have both the 7300   and 220 ... and knowing both of them fairly well at this point I would say it is fairly obvious that something has compromised the input circuit of the amp.  Now I take it you have the soft key feature on the amp so that you dont kill your nice new 7300's keying circuit with 120v but if you dont then I would start looking at your transceiver first and then the amp... because switching the amp correctly could cause just the problem you are talking about. Also these amps are known for burning the band switches when the tube arcs over.  Have you had a bang or pop while using the amp recently? I would start looking at the input tuned circuit and then the band switch for black marks. 

If you have a signal generator and scope ... disconnect the amp and and open it up. make sure the interlock shorts out the HV for sure dont just guess...  then force the relay into the transmit position and hook the signal generator in place of the radio.... and using the scope probe trace the input thru to the input to the tube.. taking note of signal levels .. more particularly losses .. and there should not be much if any losses 

Please drop me a line and I can help you can not find it and I will give you my phone number and we can trouble shoot it over the phone or by email

Jim

Message: 4
Date: Mon, 13 Mar 2017 21:34:57 +0000
From: Marty Bluhm <w8aks55 at gmail.com mailto:w8aks55 at gmail.com >
To: heathkit at mailman.qth.net mailto:heathkit at mailman.qth.net
Subject: [Heathkit] SB220 Problem
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Good afternoon,
You may remember I had a problem with my SB220 not loading into the antenna
(dipole) on 40m.
I am driving it with a ic7300. Tuning into the amp would be flat but when I
keyed the amp, the swr reading on the 7300 would spike.
At the time, I didnt have a dummy load for a 1.5kw , I purchased one but
health issues reared its ugly head and I am just getting back to
troubleshooting. So please bear with me.
I ran the SB220 into a 1.5 kw dummy load with 60w cw from the 7300.
This is my readings:
Band Plate Amp Grid Rel Pwr
80 .7 200 140
40 .4 50 20
20 .5 250 240
15 .4 130 240
10 .5 220 160

There is obviously something in the 40m circuit.
Any suggestions on where to start looking
Also Availability of parts, such a coils, etc.

Appreciated all the previous help and double that now.
Thanks & 73
Marty