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Author Topic: SB200 Amp  (Read 1404 times)
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KS4QF
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« on: September 05, 2022, 01:05:27 PM »

I recently rebuilt a Heath kit SB200 Amp.  As long as the amp is in standby mode the receive is normal.  When I take it out of standby and apply the HV, the receive goes down.  I've been building amp since I was 14, I'm now 67 and never faced this problem.  Any ideas of what might be the solution to fix this problem?

Max/ KS4QF
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w4bfs
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« Reply #1 on: September 05, 2022, 02:29:40 PM »

try removing the amp key line from the sb200 and carefully measuring the dcv on the center pin to ground.  on an unmodified sb200 this is 100Vdc or maybe a bit more.  if there are modifications to the amp - fess up
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KS4QF
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« Reply #2 on: September 05, 2022, 05:07:44 PM »

Bought this amp from a silent key.  It has a soft start circuit and I installed a soft key board to be able to use my FT991A.   I'll keep digging,. Thanks for the reply.
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KD6VXI
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Making AM GREAT Again!


« Reply #3 on: September 05, 2022, 10:03:02 PM »

Unplug the key line from the back of the amp, see if the problem goes away.

Guy just had a similar problem on eham.  Turned out the key line from TX to thr amp had a short in it.  New rca cable fixed him up.

Maybe you'll get lucky!

If not, I'd double check the wiring on the soft key.  I built a soft key using a resistor, diode and an Irf640.


--Shane
WP2ASS / ex KD6VXI
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KS4QF
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« Reply #4 on: September 06, 2022, 07:01:09 PM »

Thank you, thank you, thank you.  I got my receive back.  The Harbock Soft key circuit was causing my problem.   I also am using a Ameritron 704 softkey circuit.  I took the Harbock unit out of the amp and she is working like a real champ.  I didn't need both keying circuits.  I am now keying the SB-200 amp with the 704 keying circuit only.   Thanks for bringing it to my attention.   

I appreciate everyone that responded to my question. 

Max/KS4QF
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