Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Robert,

That sounds like a hum or buzz.

Even though the caps have been changed, I'd scope the power supply to the BFO especially.

Scope the BFO signal or listen to it on another receiver.

Or try a new BFO tube.

73,

Gary

WB6OGD

 

On 01/18/2024 9:06 PM PST Jacques Fortin <jacques.f@videotron.ca> wrote:

 

 

Robert,

 

It seems to me that your AGC system is in trouble in this 51S-1.

I once had a similar trouble in my own 1967 WE when I bought it.

What I found suspect is that your S meter pegs to the max at all times (or almost).

In my own 51S-1, I found that the root cause of the problem was the 6DC6 RF amp tube: despite it tested good on a tube tester, internal leakage (gas ?) prevented the AGC line to go negative enough to control the receiver gain and everything received in SSB mode sounded as yours.

It take me two full weeks to finally find it !

I just swapped an other NOS tube and all became OK.

 

That could be the AGC line capacitors also causing this if they are still the original ones (leakage…).

You need to probe the AGC line when it is working.

 

Keep investigating !

 

73, Jacques, VE2JFE in Montreal

 

De : Amateur-repairs@groups.io <Amateur-repairs@groups.io> De la part de Robert Lonn WA6PHN
Envoyé : 18 janvier 2024 22:34
À : Amateur-repairs@groups.io
Objet : Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

 

Thanks Jim, Well everything you mentioned has already been checked, Even though the diodes of the bridge were good, I replaced all of them and before I installed then I verified them on my curve tracer. Resistors are all close to specification, All electrolytic were replaced, and checked before I installed them. I reviewed the schematic again to be sure I understand what is going on.

I have worked on JRC, Hallicrafters, Eddystone and other tube radios and was always able to figure it out and get them working. The owner was aware of the issue with the radio, he never tried to fix it other than changing some tubes…

He said give me $100 and the radio is yours… Naturally I jumped on that deal back in Late 2021…

I did get advice last year that the person had the same issue. It was related to a bad filter capacitor that filters several filaments on several tubes… But that lead to a dead end as well…

 

This is a link to a YouTube video of the problem with the radio, when I switch to 40 meters into the video… Hope the link comes through…

 

https://www.youtube.com/watch?v=v593yNskhO4

 

Robert WA6PHN