Re: {Collins} 75S1 S-Meter not Sensitive after S-8



Thanks for sharing what you found Rich. We like to do that so that everyone can benefit, so I will copy the list on this email and they can read your findings below.

 

Good Job!

 

Bill

 

From: Richard Atwood [mailto:ratwood47@xxxxxxxxx] 
Sent: Thursday, December 06, 2012 9:19 AM
To: Bill Carns
Subject: Re: {Collins} 75S1 S-Meter not Sensitive after S-8

 

 

Hi Bill, well I found the problem with the S-Meter. R16 47 k ohm was to high in resistance. It measured 58K ohms and looked new but after 50 years it just got old, like me....lol R16 connects to pin 6 of V4's screen grid and to the meter. I did some playing with it prior to replacing the resistor with a 3meg pot in parallel with R16 and I could actually cal the meter to read correctly thru out the range of it. I want the receiver to be original so I just put R 16 back in as it should be. The resistor that I used was actually reading right at 46K ohms and all worked as it should. I hope this helps you with your 51s1. I'm going to do some work on my 51S1 soon and I'll take a look at the circuit when I get it apart. My unit is very low in sensitivity on 10 meters, say from 20 to 30 megs. I do not think anyone has been in it so will look for something failing with the coupling circuits  to start with..... Will let you know.... Thanks for your help and 73's Rich WD0BGO. 

PS. I'm not sure if I should put this out to everyone or not so If you would like to feel free. 

 

 

From: Bill Carns <wcarns@xxxxxxxxxxxxx>
To: 'Richard Atwood' <ratwood47@xxxxxxxxx> 
Sent: Tuesday, December 4, 2012 9:03 AM
Subject: RE: {Collins} 75S1 S-Meter not Sensitive after S-8





Good luck and keep us informed.

 

From: Richard Atwood [mailto:ratwood47@xxxxxxxxx] 
Sent: Tuesday, December 04, 2012 8:54 AM
To: Bill Carns
Subject: Re: {Collins} 75S1 S-Meter not Sensitive after S-8

 

Thanks for the info Bill. I will start looking for a Kwm2 case. The one I have is ok if you can not see the back because the back is missing.

Thanks again and I'm going to do some testing on the 75s1 that Don suggested. If I find anything out I'll let you and Don know. Thanks and 73s. Rich WD0BGO

From: Bill Carns <wcarns@xxxxxxxxxxxxx>
To: 'Richard Atwood' <ratwood47@xxxxxxxxx> 
Sent: Monday, December 3, 2012 9:28 PM
Subject: RE: {Collins} 75S1 S-Meter not Sensitive after S-8

 

Rich…  The 51S-1 case is a tough go. I do not know of any aftermarket ones at all. With modification, a KWM-2 case will work I think. You have to open more hole in the rear and then repaint.

 

There is an absolute dearth of 51S-1 cases because there were many 51S-1s in commercial service and particularly in the military and government service that were rack mounted. When those were surplused out, all the guys that bought them went looking for cases (and some still are) and sucked the supply dry.

 

About your only hope is to put out a want on the reflector, hope you get a nibble, and also watch for someone parting a 51S-1 and hope there is a case involved that can be saved.

 

That is about all I can offer.

 

Bill

 

From: Richard Atwood [mailto:ratwood47@xxxxxxxxx] 
Sent: Monday, December 03, 2012 9:05 PM
To: Bill Carns
Subject: Re: {Collins} 75S1 S-Meter not Sensitive after S-8

 

Thanks Bill, I also have a 51S1 not mint but real nice shape excet for the case. It has a case that is simular to Collins but there is no back to it. Do you know of a source where I might find a caes? After market will work for me. I have some collins equipment not acomplete setup. i'll list it as follows:

KWM 2

KWM2A in use now.

32S1, just got it and got it working

75S1, this is the one with the AGC/S-meter problem

2 ea. 312B4

2 ea. 516f2, only one has the speaker cabinet, need to get another one.

PM 2 power supply

MP 1 Power supply

30L1 

30S1, Had to rebuild it, works great now but needs painting. 

180S1 Antenna tuner

2 ea. crystal packs.

R388, real good shape, I use it with a Johnson Viking 2 that is real good as well.

51S1 Real god other than it needs a real cabinet and real weak on the upper end. haven not had time to get into it but been useing it below 20 Mhz,

2 ea. Collins carring cases.

 

I think that is it. I'm retireing on the 16th Jan. and plan on useing my Collins much. I do have some other gear but really like the old stuff. i still have my first readio that got me started in this. it was a Hallicrafters S38 , looks new and still will pick up Sputnik... LOL 

 

I want to thank you for your help.... 73's Rich WD0BGO..... 

 

 

From: Bill Carns <wcarns@xxxxxxxxxxxxx>
To: 'Richard Atwood' <ratwood47@xxxxxxxxx> 
Sent: Monday, December 3, 2012 11:05 AM
Subject: RE: {Collins} 75S1 S-Meter not Sensitive after S-8


Great posting and well done.  I may have the same problem on a very mint 51S-1 that I like to use. I have forwarded your posting to one of our members who is a real expert on ALC and AGC and asked him to comment. Let's see what he has to say ?  There are a number of things that could cause this. Your AGC source voltage supply is obviously good since the RF gain directs the AGC line correctly when it is applied manually. The detection circuit is just topping out. Let's see what Don has to say.


Bill Carns, N7OTQ
K0CXX, Trustee MRCCC
President Collins Collectors Association
Editor, Signal Magazine
Founding Member # AC94-0009
512 618 2762 (Cell + VM)
512 847 7010 (Home + Fax)




-----Original Message-----
From: Collins [mailto:collins-bounces@xxxxxxxxxxxxx] On Behalf Of Richard Atwood
Sent: Monday, December 03, 2012 10:21 AM
To: collins@xxxxxxxxxxxxx
Subject: {Collins} 75S1 S-Meter not Sensitive after S-8

Hi All, this is the first time to post on the Collins Group and not sure if I’m doing it correctly but here goes. 
I have a 75s1 receiver with a S-Meter problem. The S Meter works good up to S-8 then it becomes very un-sensitive after that. It’s so bad that a 220 micro volt signal will give me about a hair over S-9. The meter will swing all the way over to the right with the RF gain control and when it is muted by the transmitter (32S1). The meter seems to be ok and the voltages on V4 and V5 seem to be close to what the book says it should be. The receiver will receive a -120 db signal so believe the sensitivity is good. Any help will be greatly appreciated…. Thanks to all.... Rich WD0BGO. _______________________________________________
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