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RCA Victor T-55 AM radio - Printable Version

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+--- Thread: RCA Victor T-55 AM radio (/showthread.php?tid=15035)

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RE: RCA Victor T-55 AM radio - vecher - 07-30-2016

Ok, Here we go again.. I was replacing caps and found one cap marked .01 on schematic C15 was really a .0025 at 700 Volts. It goes from Plate of the 6SQ7 to grid of the 6F6.

C13 marked .0025 from Resistor R5 to switch was really a .001 at 1000 Volts.. Question should I change them back to values on schematic? Also do I really need 1000 volt caps. Would 630 Volt work..

[Image: http://i292.photobucket.com/albums/mm38/wb4yvo/t-55%2044%20004_zpsf0v6tr87.jpg]

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RE: RCA Victor T-55 AM radio - Radioroslyn - 07-30-2016

Value is not very critical .0025 or .003 is fine. Not very much voltage there either 200v or higher is good.

RE: RCA Victor T-55 AM radio - vecher - 07-30-2016

Terry, Ok thanks So I can use a 630 Volt cap on them and that would be OK.. I kind of thought so.. But wanted to be sure..

Thanks
Again...

Skip..

RE: RCA Victor T-55 AM radio - Mitch - 07-30-2016

C13 and C15 are DC blocking caps and passing the audio only.  You'll notice these caps are between the volume control and the speaker.  

Lower value capacitors in this part of the circuit will tend to pass only the higher audio frequencies, taking away that 'rich tube sound'.  I'd stick with the values on the schematic.  The caps you've got in there now were probably replaced way back when and whoever did the repairs used what he had on hand.  

600V caps are more than sufficient as replacements.  

Mitch

RE: RCA Victor T-55 AM radio - vecher - 08-02-2016

Ok, Here is another problem.. It seems that the switch on the volume control and the volume control is bad.

Its a 1 MEG Pot with switch..Does any one know how to get it apart??

Here are some pictures..
[Image: http://i292.photobucket.com/albums/mm38/wb4yvo/rca%20008_zpsib5inwkr.jpg]

[Image: http://i292.photobucket.com/albums/mm38/wb4yvo/rca%20009_zpsyksawtml.jpg]

[Image: http://i292.photobucket.com/albums/mm38/wb4yvo/rca%20010_zpsacsnqzef.jpg]

[Image: http://i292.photobucket.com/albums/mm38/wb4yvo/rca%20011_zpshrga4teh.jpg]


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RE: RCA Victor T-55 AM radio - Radioroslyn - 08-02-2016

Bend the four black tabs up on the front.

RE: RCA Victor T-55 AM radio - vecher - 08-02-2016

Terry, That worked great . I was able to get it apart and repair the switch. Can I use contact cleaner on the pot and switch? Weird looking on inside. Really smooth on sides where wiper goes around.

Picture of inside..

[Image: http://i292.photobucket.com/albums/mm38/wb4yvo/rca66%20004_zpskoocyx6d.jpg]
[Image: http://i292.photobucket.com/albums/mm38/wb4yvo/rca66%20003_zpscf9fp5q7.jpg]

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RE: RCA Victor T-55 AM radio - vecher - 08-03-2016

All, Ok I put the switch back together. Installed in radio.

Hooked to Variac and brought voltage up to normal with no problems.

However.. I only get a hum out of speaker. Hum gets louder with volume.. But no noise just hum.. No stations heard. I have a really strong AM station about 1 mile from me and cannot even hear that..

So unfortunately my schematic has little to NO voltage readings on it. So I guess my next step is to put 455 KHZ signal in and see what I get. Or should I try something else first..

Here is schematic.. Very hard to read.. http://www.nostalgiaair.org/Resources/821/M0015821.htm


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RE: RCA Victor T-55 AM radio - vecher - 08-03-2016

All, I hate to admit this but I found a wiring error I was missing a ground.. So tomorrow I will go thru all again to make sure I didn't make any other mistakes..

The way I found it was by measuring voltages. Some didn't match..

I should have been more careful.. But at lease I found it..

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RE: RCA Victor T-55 AM radio - vecher - 08-04-2016

OK, Added ground that was missing. Still has a slight hum when no stations are being received..However I can now receive some stations.. Not many probably around 3.. I will check tubes again.. Then I will attempt alignment next... Found the 6SA7 tube Bad only reading 40% on my tester..Its the 1st det /Osc tube..

Volume is not really loud.. I have new output tube in it a 6F6..

Need to order some tubes I guess..

Skip...

RE: RCA Victor T-55 AM radio - Radioroslyn - 08-04-2016

Hi Skip,
I take it you haven't looked at the last page in the Rider's manual. You can find the pin voltages there.

GL

RE: RCA Victor T-55 AM radio - vecher - 08-04-2016

Terry, I only have 2 pages from Nostalgiaair. On one page it does show some voltages. but not many.. That's how I found I had missed a ground connection. Had 161 volts where I should have had 95 volts..

But after that fix radio did start to receive.. but not real great. picked up only the strong stations. maybe the loop antenna is either not hooked up right or is bad..???

I did find a very weak tube a 6SA7 Had one in a different radio and substituted it sounds better.. but not as I would expect?? Maybe its the best it can be?? Maybe these 5 tube radios are not that great to start out..

Did I miss some pages of the riders ?

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RE: RCA Victor T-55 AM radio - vecher - 08-07-2016

All, Radio is recapped.. Plays pretty good for a 5 tube set.. .. NOW my problem is does anyone know who does cabinets? I do not want to spend a lot on it but would like to make it look semi nice for display.

I have never done wood working so I do not want to start..

Thanks

Skip...

RE: RCA Victor T-55 AM radio - Radioroslyn - 08-08-2016

(08-04-2016, 10:47 PM)vecher Wrote:  Terry, I only have 2 pages from Nostalgiaair. On one page it does show some voltages. but not many.. That's how I found I had missed a ground connection. Had 161 volts where I should have had 95 volts..

But after that fix radio did start to receive.. but not real great. picked up only the strong stations. maybe the loop antenna is either not hooked up right or is bad..???

I did find a very weak tube a 6SA7  Had one in a different radio and substituted  it sounds better.. but not as I would expect??  Maybe its the best it can be?? Maybe these 5 tube radios are not that great to start out..

Did I miss some pages of the riders ?

Skip...

Yes you are correct  there is just two pages in the Rider's. At 1st I just gave it a quick glance and didn't see the voltages on it Thought you might have missed them too.

The loop is easy enough to check with an ohm meter, just check for continuity and it should read a few ohms. As far as the connections it isn't shown on the schematic. In most cases it would be connect in parallel with rf side of the tuning cap. Some times the frame of the tuning cap is at chassis ground and sometimes it isolated from chassis but is at rf ground though a paper cap. This set up allows the antenna circuit to be part of the avc system.
If your chassis has L-9 in it the loop would connect in parallel to it's primary.

For best performance you'll need to break out the signal generator and give a good alignment. Connect the generator the ant post and ground. Set it up at 455kc w/ modulation and keep rf level turned down so you can just hear it. Adjust the trimmers in the IF cans for max signal. It's not uncommon for the trimmers in the plate of the mixer tube and the plate of the IF amp circuit to have HV on the adj screw. Disconnect the generator and use 1440 to do the rf alignment. This involves adjusting the two trimmers on the top of the tuning cap. The one on the left is the osc so set in so that 1440 is at 1440. The right one is resonates the loop so set it for max signal at 1440.

During your servicing you've changed some of the electrical characteristics by replacing caps with slightly different lead lengths, replaced tubes, and such. All this can affect the alignment. So it's always good practice to do an alignment to get the most out of your set.

RE: RCA Victor T-55 AM radio - vecher - 08-08-2016

Terry, Ok thanks.. I did try alignment. but probably didn't do it right.. I will try again..

When I put my hand near the loop it receives much better.. There are 4 wires coming from loop. one goes to tuning cap. one goes to bottom of L3 1st IF transformer.. Other 2 looks like a loop around the other loop. for external antennas? When I hook up a antenna to those leads it makes the signals disappear instead of getting better.. Weird..

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