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

 

From: Amateur-repairs@groups.io [mailto:Amateur-repairs@groups.io] On Behalf Of James Amos
Sent: Thursday, January 18, 2024 1:36 PM
To: Amateur-repairs@groups.io
Subject: Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

 

If you are seeing distortion in CW/SSB and not AM, I would start with circuitry that is used in CW/SSB, and not AM.    This includes the product detector, and the SSB/CW preamp.   The SSB/CW preamp in particular has some high value resistors that drop 140V down to levels suitable for the 2N2222A preamp transistor.   So, start with the 140V supply and work you way in from there. The number of parts to check in this area of circuitry is relatively low, so look for heat damage.   The resistors are 10% carbon comp and those can age and change value over the years.     There's also a electrolytic emitter bypass capacitor on the SSB/CW AF Preamp that should be checked, that and other electrolytic caps are probably starting to age.    As pointed out earlier, from a signal  point of view this can also be checked with a simple RF carrier injected at the antenna then tuned for the correct sideband reception.    You should be able to see a sine wave all the way through the receiver chain which you can also check for  where the distortion is introduced. 

Also, the signal for AGC is sampled ahead of the last IF Amplifier, so there is no AGC voltages that are part of the product detector or SSB/CW preamp circuitry.

I hope this helps,
Jim N8CAH