Re: {Collins} 75S-3 S-meter Issue



Chuck,

As Glen suggested, check the receive gain pot.  It may be dirty or defective.  The rec gain pot will interact with the S-meter zero adjust.  You'll need to inject a -70dbm (50uv) signal at
14.1mhz and set the rec gain to S-9.  After that go back and reset the S-meter zero.  Basically what you're doing is balancing out the bridge circuit.  You may have to make this adjustment a few times until you get S-9 with -70dbm and have the S-meter perfectly zeroed.

Steve N6HK
________________________________
From: Collins <collins-bounces+n6hk=hotmail.com@xxxxxxxxxxxxx> on behalf of Don Rasmussen via Collins <collins@xxxxxxxxxxxxx>
Sent: Monday, August 19, 2019 8:28:27 AM
To: Glen Zook <k9sth@xxxxxxxxxxxxx>
Cc: Collins <collins@xxxxxxxxxxxxx>
Subject: Re: {Collins} 75S-3 S-meter Issue

IS YOUR AGC WORKiNG ??

On Mon, Aug 19, 2019 at 11:23 AM Glen Zook via Collins <
collins@xxxxxxxxxxxxx> wrote:

> Check R-57 the RF gain adjust potentiometer.  It is a 1K in series to
> ground from the cathode of V-6.
> Glen, K9STH
> website:  https://k9sth.net
>
>     On Sunday, August 18, 2019, 07:09:14 PM CDT, Chuck Curran via Collins <
> collins@xxxxxxxxxxxxx> wrote:
>
>  Hello the Group:
>
> I received a S-Line for repair, all items not having been on the air for 20
> years.  I started to repair the 75S-3 receiver for the owner, and was
> pleased with the success, after replacing electrolytic's and the Sangamo
> coupling caps.  PTO was messed up, as far as end stops and pointer being
> vertical, but that was resolved too.  Alignment followed, with great
> success, all ceramic trimmers were NOT frozen, a real surprise!
>
> OK, now on to the issue.  S-meter was jumping all over, the zero pot was
> junk.  Found a suitable replacement and installed it after lunch today.
> That totally cured the jumping problem, when trying to set zero.  However,
> I now see that the S-meter response is way high.  The calibrator signal
> PINS the S-meter, without a problem.  I checked pin voltages on V6 and V7,
> both were within spec.
>
> All on the air signals I have listened to are also WAY high, crazy high
> S-meter levels.
>
> All tubes were checked on my Hickok 752, three weak tubes were replaced,
> V3, V8, and V11.  Supply voltages are to spec.
>
> So, any suggestions on where to go next?
>
> Thank You in advance,
>
> Chuck W9KR
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