[Collins] 75S-3B receiver restore

Thu Nov 21 16:09:51 EST 2013

The CRA has these pots which are sealed.

For all your Collins needs, please contact the CRA at my email address

David Knepper - W3CRA/W3ST
Collins Radio Association
www.collinsra.com
Join the CRA today
-----Original Message----- 
From: Dr. Gerald N. Johnson
Sent: Thursday, November 21, 2013 2:36 PM
To: collins at mailman.qth.net
Subject: Re: [Collins] 75S-3B receiver restore

Its very likely that the S-meter zero pot needs to be replaced. I think
its a small pot so will be a little harder to find, possibly at Surplus
Sales of Nebraska who while ask a gold plated price.

You can try some fader clean from DeOxit, but I've not had really good
results with it.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association

On 11/21/2013 12:54 PM, Dick KF4NS wrote:
> Hi Guys,
> Sometimes this dementia is enough to bring on lots of foul language. Sorry 
> about the "SWR" error. It
> really hurts sometimes when I forget words I have used for over 60 years 
> and technical procedures that I
> knew better than the kids names hi,hi.
>
> Enough, the gentleman who brought the radio to me wanted it back as-is so 
> I only got so far as to clean
> the pot and work it, then swap out the V6 V7 (I think those are the ones). 
> It got worse, just touching
> the screw adjustment caused the needle to jump all over and now the 
> incoming signals no longer resulted
> in any movement and the adjustment was useless due to extreme sensitivity. 
> Just a guess without doing the
> voltage measurements or testing the resistor on pin 1 or resoldering 
> connections, I feel confident that
> someone is going to have to replace R13.
>
> Thanks for all the advice and I hope the guy he sells it to notices the 
> malfunction in the S-meter (GOT
> IT RIGHT THAT TIME, WHOOPEE)
>
> Best of everything to all and have a great Thanksgiving.
>
>
> 73, Dick KF4NS
> St Petersburg, FL 33714 USA
> Keep The Glow!
>
> ----- Original Message -----
> From: "Deric Affleck"<deric.vy2da at bellaliant.net>
> To: "Dick KF4NS"<kf4nsradio at verizon.net>
> Sent: Tuesday, November 19, 2013 2:48 PM
> Subject: Re: [Collins] 75S-3B receiver restore
>
>
> | Hello Dick,
> |
> | I think you are referring to the "S" meter, not "SWR" meter on the
> | 75S-3B. Have you tweaked the S meter "zero" potentiometer - R13?
> | It is located on the top of the chassis between V6 and L9 on the right
> | top side of the chassis. If the meter moves through zero when tweaking 
> R9
> | you should find a zero resting point.
> | If it won't settle down and remain at zero with no signal.
> | it may be dirty and need to be cleaned with some potentiometer cleaner.
> | The S meter circuit is in a bridge circuit configuration and
> | if either V6 or V7 is leaking it may be difficult for the circuit to
> | maintain a
> | zero setting of if related components (resistors) change value when 
> heated
> | up the S meter will also drift off zero. Try tweaking R13, the S meter 
> zero
> | control first and if that doesn't bring the metere down to zero then try
> | changing
> | V6/V7 one at a time and if that doesn't solve the problem then it 
> probably
> | require
> | a trial and error for other circuit components.
> | Good luck!
> |
> | 73, Deric, VY2DA
> |
> | 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> | ----- Original Message -----
> | From: "Dick KF4NS"<kf4nsradio at verizon.net>
> | To:<collins at mailman.qth.net>
> | Sent: Tuesday, November 19, 2013 3:28 PM
> | Subject: [Collins] 75S-3B receiver restore
> |
> |
> |>  Need a little help here on this RCVR that I was coerced into getting 
> up
> |>  and running again for a guy who
> |>  is interested in selling it for an old non-ham friend.
> |>
> |>  To make it short, I will just give the basics. It had been stored in
> |>  unprotected area for about 10 years.
> |>  What a mess! I managed to get everything cleaned up including all 
> contacts
> |>  throughout and the chassis.
> |>  Not an easy job. It did not work when I first started on it except 
> that
> |>  the tubes lit up. All tubes were
> |>  tested and 2 replaced. 90% of the trouble was the long resting period 
> and
> |>  corroded contacts.
> |>
> |>  Right now, after alot of tweaking, the receiver is working darn good. 
> One
> |>  problem observed is the SWR
> |>  meter which never reads UNDER 4. It appears to be giving a not too bad
> |>  sensitivity reading on signals
> |>  detected. It peaks on minimum rf gain.
> |>
> |>  How do I adjust the low limit on the meter? It works fine mechanically
> |>  with power off, going to zero..
> |>
> |>  Any advice will be greatly appreciated.
> |>
> |>  73, Dick KF4NS
> |>  St Petersburg, FL 33714 USA
> |>  Keep The Glow!
> |>
> |>  ______________________________________________________________
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