need help with ailing sb-101

[Mark V. Johnson VE3DJU]

I have the same problem with my SB-301/401 Combo...The receiver is slow to
"recover" after coming off transmit. I have not isolated yet BUT I found
that the problem seems to be in the RF Amp stage. The bias is going
negative 5 volts (cutoff) to zero, a bit too slow. Here's the interesting
point, if I put my hi impedance VTVM probe on the input grid pin (pin 1)
the voltage decays to zero in a snap and the receiver recovers normally. If
I go from transmit to receiver with the VTVM probe on the grid (pin1) the
receiver functions normally. Even more weird, it only happens on the higher
freq bands. 80 and 40, no problem. 20, 15, 10, it has the problem. My guess
at this point is I'm getting RF into the input circuit (rectification??)
and its charging up the cap on the input. The VTVM is enough "draw" to pull
it down normally... Have more checking to do.....What say ye, experts??
Thanks as always!!

Mark V. Johnson
Service Delivery Branch Manager
Metro Banking & DPM Profession
416-718-2726


---------------------- Forwarded by Mark Johnson/Ontario/IBM on 03/26/2000
09:41 PM ---------------------------

Steve & Anne Ray <sbralr at WORLDNET.ATT.NET> on 03/26/2000 05:35:48 PM

Please respond to Steve & Anne Ray <sbralr at WORLDNET.ATT.NET>

To:   HEATH at LISTSERV.TEMPE.GOV
cc:
Subject:  Re: need help with ailing sb-101




See Dale's page KB9JJA and my mod sheets on the HW-101.  If you need a copy
of the article on receiver recovery scanned in let me know.  The problem
you
have is very common and the fix is very easy.

73,
Steve Ray K4JPN ex K1VKW HW-101, HW-8, OHR-100A, SWL 30-40 and NC 38S
HeathKit fan
Warner Robins GA EM82fp



----- Original Message -----
From: Mike Hammer <mhammer at MISSLINK.NET>
Sent: Thursday, March 23, 2000 8:09 PM
Subject: need help with ailing sb-101


> Im in the process of resurrecting an old
> SB-101. Ive got most of the problems worked
> out but one remaining problem has me stumped.
>
> This unit has VERY slow receiver recovery
> from transmit. After a lengthy transmission
> it takes a couple minutes to recover fully.
>
> Ive made the usual changes. Ive replaced
> diodes D101, D902, D903, and D905. I replaced
> them with 1n4005s.
>
> This didnt seem to help.
>
> I also have a Hw-101 with the exact same problem
> and I know of another person with a HW-101 with
> the same problem. Is this a common fault and
> is there a fix anyone knows of?
>
> Thanks...
>
> TTYL!
>
> Mike Hammer
> mhammer at misslink.net
>

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