Teaberry Model T 40 Channel CB Base Station

[danmcclain]

I've been working on this cb radio for awhile now. Replaced all the electrolytic capacitors, all the tubes are good. The problem I'm having is when I turn it on, and once it heats up, the signal meter slowly moves down to zero and stays there. I've been told it could be a resistor problem. My next move is to replace all the red resistors (flameproof). Is there any other area that I should check? The receive is fine, by the way.

Thanks, Dan

 

[DoctorAudio]

Does the signal meter still work on TX and if so does it read the same as the radio warms up?
Check the squelch when it's cold (with no signal) and note on the knob rotation where it just squelches the static. Does that squelch point change as the radio warms up?
The S-meter and the squelch circuit are on the same AGC line is why I ask.

 

[Dmans]

I owned one of those long ago and if I remember correctly, when first turned on the S Meter moves to full scale then slowly drops to the low end as it warms up.
(Or was that the Browning???)

73
David

 

[DoctorAudio]

Dmans is right, lots of tube radio's do that at first for a short time as the filaments come up to temperature but I was assuming you meant it was a slower process over several minutes.

 

[danmcclain]

I owned one of those long ago and if I remember correctly, when first turned on the S Meter moves to full scale then slowly drops to the low end as it warms up.
(Or was that the Browning???)

73
David

This radio does that, when turned on the meter needle would go all the way to the right, then settle at about 6-7 pound signal. I was monitoring channel 6 for the strong signals, after a few minutes it would slowly back down to zero, no matter if people were still talking.

 

[danmcclain]

Does the signal meter still work on TX and if so does it read the same as the radio warms up?
Check the squelch when it's cold (with no signal) and note on the knob rotation where it just squelches the static. Does that squelch point change as the radio warms up?
The S-meter and the squelch circuit are on the same AGC line is why I ask.

I will check that out tonight, thanks... Dan

 

[Dmans]

Above from the Robyn T240 manual.
Have you checked the meter adjust pot on the rear?

73
David

 

[danmcclain]

View attachment 58774

Above from the Robyn T240 manual.
Have you checked the meter adjust pot on the rear?

73
David

Yes I have David....It's reading zero when no signal is applied... Dan

 

[Dmans]

Assuming you have the S-9 setting done as well?

I would check the 2-1N34 diodes connected to the meter circuit for forward voltage. Should be very closely matched.

73
David

 

[danmcclain]

Assuming you have the S-9 setting done as well?

I would check the 2-1N34 diodes connected to the meter circuit for forward voltage. Should be very closely matched.

73
David

I checked the one diode close to the meter, the other one I couldn't find... Dan

 

[Dmans]

These 2 are from the Robyn T123B and T240 schematics. Same basic Panasonic chassis as your Teaberry.

73
David

 

[danmcclain]

These 2 are from the Robyn T123B and T240 schematics. Same basic Panasonic chassis as your Teaberry.

73
David
View attachment 58847View attachment 58846

Thank you David, just remembered I have the Sams for this radio...will check the pic to get a location... Dan

 

[danmcclain]

Thank you David, just remembered I have the Sams for this radio...will check the pic to get a location... Dan

Found it, both test good....been told it could be a resistor.... Dan

 

[Dmans]

Dan,
It just occurred to me that the Teaberry has a switch under the meter for "S" signal or "RF" reading (where the Robyn is a "Range Expand" On or Off). Perhaps the switch is a bit flaky??

73
David

 

[danmcclain]

Dan,
It just occurred to me that the Teaberry has a switch under the meter for "S" signal or "RF" reading (where the Robyn is a "Range Expand" On or Off). Perhaps the switch is a bit flaky??

73
David

Sprayed the S and RF switch didn't help.... Dan