Well I just got done fully recapping this one and wow a total of about 25 caps including 5 ecaps. I can not figure out from the schematic where the negative ends of the 40/40/70 marked C103 on the schematic go. I am used to the negative ends going to chassis ground on the other radios I have worked on. Can someone tell me exactly which wire to connect it to in the chassis please?
After all that recapping I sure hope it works. I used up most of my 0.01 caps doing this one
thanks
Chris
Hi Chris,
On some sets there is a common B- line. or as some say, a 'floating ground" one that is not in contact with the chassis.
You can see that some caps have the ground symbol, that would be the chassis. If you follow pin 7 I believe from your 50A5, there will be a 220 Ohm resistor (R204) paralleled with a 25uf cap. The negative end on that cap (and the resistor) is your B-.
There are other points you can trace this line going to, such as the other end of the 120 Ohm resistor onpin 2 of your 6BJ6, (R307) .
Some manufacturers use a chassis symbol that looks like a rake, and their B- is the common ground symbol.
Someone can correct me if I am wrong on this particular set , but I just had to deal with a isolated B- on an RCA I recapped last week.
Take care,
Gary.
Gary,
I did find the "floating" ground. I finally got to power it up. I did recieve some garlbed stations on AM but nothing on AM. I have the troubleshooting guide for the audio sections. Is there something obvious I should look for? It was motorboating also.
thanks
Chris
Hi Chris,
I am not sure about the motorboating issue someone else may have an idea. I did have one set than had that low rumble and added capatitance to one of the filters cleared it up.
On issues like this I take out the highlighter and trace the circuit again, in case I made a mistake or someone else "worked on" with the set before.
Check the resistors also, if possible lift one side of those you suspect to get a more accurate reading.
http://www.nostalgiaair.org/Resources/675/M0013675.htm
You had said that there was signal on AM and not AM, maybe you meant FM
I had a Truetone a couple months ago that would not receive FM, AM was fine. The bandswitch actually turned on current to the "FM tubes" when the switch was changed. Good cleaning of the bandswitch cured that issue.
I would run thru the test they suggest in the guide. I see they have it broken up in to the stages. If you are able to receive audio then I assume that section would be ok. Touching the center of the volume control with something should make a nice loud buzz. (Make sure you use safe procedures for doing this).
I also see there are some good voltage checks to perform. I would do those. But I must warn you that I am not that good on diagnosing oltage readings, and if the tube is at 'cutoff' or if the grid volts are right. etc...
But it might give an indication of what section does not have the correct voltages, the go from there.
Did you get anything on the FM band? Is the antenna system connected correctly? Some of the old FM sets needed an good antenna for reception. A length of wire, maybe 4 or 5 ft long should work to bring something in.
OK Will check back later, good luck.
Gary.