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RCA R35, 39 & 57 Terminal Usage...
RCA R35, 39 & 57 Terminal Usage...
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Old 3rd September 2006, 06:50 PM   #1
mcelaj is offline mcelaj  United States
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Default RCA R35, 39 & 57 Terminal Usage...


As I have no technical know-how of how tube amplifiers work, I ask here, the following:

I have an RCA R35, 39 or 57 amplifier, not sure the exact model number, but on the Nostalgia Air website there is a schematic which coincides with all three models. This schematic perfectly matches the tube amplifier that I have and I am asking about.

The schematic can be viewed at:

Nostalgia Air

or more specifically:

Nostalgia Air RCA schematic

Now on the second page of the PDF file is the schematic. To the right is the schematic for the amplifier and power supply, which is in one chassis (the unit I have), and to the left of the schematic is the radio, which is on another chassis. The two chassis' are interconnected with a terminal strip which has 8 connections, as seen on page two of the schematic between the two units. I set up the amplifier and assumed that connection 4 is to be used as the positive input and either 5-8 as the negative input. I tried all combinations and only got music when either powering up the amplifier or turning the amplifier off. I don't have the field coil speaker that is in the schematic so i threw in a transformer (+/-2k ohm resistance) in its place and the voltage readings at the corresponding terminals where in order, as stated on the bottom of page one of the schematic. The output transformer measures 10 ohms and I used an 8 ohm speaker when testing.

Am I using the wrong terminals for input? Which terminals should I use. There is a 227 tube acting as the 1st Audio Stage (preamp I guess) in the Radio (left side of the schematic), perhaps I need a preamp before connecting to the amplifier? I tried connecting straight from my laptop output, whose output can be controlled through the laptops volume control. Maybe my tubes (245 tubes) are bad (don't own a tube tester)? The 280 tube must work as I get the DC voltage readings specified on the bottom of page one of the schematic. Maybe the 8 ohm test speaker is the fault?

I hope I did a good job of explaining my situation and hope someone can help me.

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Old 3rd September 2006, 11:14 PM   #2
anatech is offline anatech  Canada
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RCA R35, 39 & 57 Terminal Usage...
Hi Mehmet,
You have a pair of #45 tubes in push pull with a chassis mounted output transformer. You should use a choke instead of a transformer, but your voltages are correct (the transformer is okay to test with).

The original speaker may have been any impedance, including 16 ohm. That will not matter just yet. You should still get pretty good sound. Do you have the original speaker? If so, use it's field coil and use the other speaker if the cone or voicecoil is damaged. Off centered voice coils can sometime be adjusted by loosening the screw in the center, repositioning and retightening the screw.

The first thing I would do is test the tubes. Be careful as the 45's are expensive to replace. Replace the coupling caps and the filter caps and check the resistors are in tolerance (+- 20%), or at least in the ballpark.

By this point in time you should have the power supply, amplifier and radio working. Your MP3 will work once you get the rest working.

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