Heathkit SB-200 audio distortion

[Tom Buchanan]

Here is a bit more detail for everyone.  The exciter/transceiver I am using
is a Yaesu FT-840.  The received audio in the FT-840 sounds clear until I
turn the amp "ON".  It attenuates the signal somewhat and the audio sounds
raspy. I have moved the radio away from the amp and in close proximity with
no change in poor audio.  Turn the amp "OFF" and the signal in the FT-840
comes back up and is clear.  

I bought the amp in a non-working condition and it included an unassembled
power supply filter board with 6 new HV caps along with a soft start module
which may be from Harbach Electronics. Initial testing, the amp has a little
over 2400 HV and idling current 50 mA.  Idling current is a bit low.  

Two paper caps C3 & C19 on the bottom of the chassis were replaced with
modern electrolytics.  I installed a Harbach soft key to connect it to the
FT-840.  Disconnecting the keying interface has no effect on the audio in
the FT-840.

Tom
KG4KGY



-----Original Message-----
From: Heathkit Owners and Collectors List [mailto:HEATH at LISTS.TEMPE.GOV] On
Behalf Of Tom Buchanan
Sent: Saturday, February 28, 2009 5:24 PM
To: HEATH at LISTS.TEMPE.GOV
Subject: Heathkit SB-200 audio distortion

Hi,
 
I am working on a SB-200 for a winter rebuild project.  I have the amp
working with full output, but the problem is the receiver audio.  The amp
has a new power supply board, soft start and soft key interfaces plus 2 new
electrolytic capacitors under the chassis.   When I turn the amp on, the
radio audio is somewhat distorted and fuzzy. I turn the amp off and the
receiver audio is clear and clean.  Could it be picking up noise from the
fan?  Any ideas?  Thanks.
 
73,
 
Tom
KG4KGY

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