Airline-Ambassador Resistor Question

[Hi-Fi-Mogul]

What is the purpose of R11 ( 27 Ohm 5 watt resistor )
b/t the 120 house VAC to the plate of the 35W4 rectifier ?

Today this basic info eludes me.

[electra225]

To control current "in-rush". The idea is to soft-start B+. They can also run a higher-capacity input filter cap to control hum. Sometimes, you find that resistor after the cathode of the rectifier.

[Hi-Fi-Mogul]

To control current "in-rush". The idea is to soft-start B+. They can also run a higher-capacity input filter cap to control hum. Sometimes, you find that resistor after the cathode of the rectifier.

Oh yes, that's the location I was more familiar seeing.
Thanks !

[wparks]

Exactly. It does also provide a continuous voltage drop in operation to reduce the B+ somewhat.

Neat little record player. I dig the negative feedback coming from the audio transformer secondary winding back to the tone control in the 12AT6 cathode circuit. How does it sound? Pretty good I bet. I see all of the capacitors are in one can- Do they work? Have you tested those?

[Hi-Fi-Mogul]

Neat little record player.
I dig the negative feedback coming from the audio transformer secondary winding back to the tone control in the 12AT6 cathode circuit.
How does it sound? Pretty good I bet.
I see all of the capacitors are in one can- Do they work? Have you tested those?

I powered up the record player to make sure there was
no motorboating like in the AMC.
The usual bad e-lytic filter cap hum is present.

The 12AT6 tested weak, and I had a replacement.

I drilled out the rivet/band holding the multi-value
capacitor.
The 27 Ohm sand resistor is degraded as they do,
so it will be replaced.
Will check the resistors and wiring,
then on to the re-cap.

[electra225]

If you would care to have a tad more gain, replace the 12AT6 with a 12AV6. I would also replace C1D, the cathode bypass capacitor with one of higher capacity, probably a 50 uf at 50 volts. This tends to reinforce the "bottom end" of the amp, as far as bass response is concerned. I like using 50EH5 in record player amps in place of the 50C5. It takes less grid voltage to drive a 50EH5 to full output, but that's just me. This may be more important when there is no first amplifier tube.

[TC Chris]

If you would care to have a tad more gain, replace the 12AT6 with a 12AV6. I would also replace C1D, the cathode bypass capacitor with one of higher capacity, probably a 50 uf at 50 volts. This tends to reinforce the "bottom end" of the amp, as far as bass response is concerned. I like using 50EH5 in record player amps in place of the 50C5. It takes less grid voltage to drive a 50EH5 to full output, but that's just me. This may be more important when there is no first amplifier tube.

What were the design considerations that went into using the original tubes as opposed to the substitutes? You'd think the manufacturer would have aimed for making as much noise--music noise, that is--as possible.

Chris Campbell

[electra225]

The 12AV6 replaced the 12AT6. Possibly that some manufactures still used the 12AT6 for cost considerations. The 50EH5 is commonly used in record players with no first audio tube, since it takes less grid voltage to drive the tube. I like replacing the "C5" tubes with the "EH5" tubes because I think they sound better, have better tone and arguably more volume. But again, that's just me.

[Hi-Fi-Mogul]

I did a temporary wire up of the e-lytics, and upped the C1(D)
cathode cap to 47 mF.

It did help some on the mid-range notes. I'll use that value
when I solder it all up.

Interestingly, putting in a 12AV7 seemed to have no aural
change in the output volume.

I used 3 different 12AV7s, with the same result.

I need to put in a terminal mount strip for the caps,
so some mount hole drilling today.

Great news is that there is only expected very low hum !!!

[electra225]

I think you meant to type 12AV6. The 12AV6 was a new tube in 1953, IIRC. The 12AT6 appeared in 1946-'47. I read an article one time explaining why the AV6 was advantageous to the AT6. Higher gain, lower noise and something else that I forgot were the main differences, since they did the same job. I always try the AV6 and many times have found advantage to using it. GM car radios used a 12BF6 instead of the AV6 due to its tendency to have less microphonics in equipment that was subject to jarring, such as a radio mounted in the instrument panel of a car.

[Hi-Fi-Mogul]

Yes, 12AV6 was the tube used.

[electra225]

Also check R7, the cathode bias resistor. It needs to be right on value, 150 ohms. If it has drifted high, that may cause the output tube to conduct more heavily, which can put the audio output transformer in jeopardy. This may not be a huge deal on a small record player amplifier, but it is good general practice to check this resistor and be aware of it's purpose in the circuit.

[Hi-Fi-Mogul]

Also check R7, the cathode bias resistor. It needs to be right on value, 150 ohms. If it has drifted high, that may cause the output tube to conduct more heavily, which can put the audio output transformer in jeopardy. This may not be a huge deal on a small record player amplifier, but it is good general practice to check this resistor and be aware of it's purpose in the circuit.

Will do that check, thanks !

[Hi-Fi-Mogul]

1. The cathode bias R7 is right on the money.

2. Tonight I hand drilled two holes to mount the
terminal strips for the 4 e-lytic caps.

I added some electrical tape pieces on the
chassis' sides where the terminal strips will be
for added protection.

3. Tomorrow to solder the caps' leads onto terminal strips, then
solder on B- connection wire and the 4 wires
to the e-lytic caps' positions.

I'll also replace the 27 Ohm 5 watt sand resistor,
then hopefully have a successful power up test.

[Hi-Fi-Mogul]

Re-cap finished and all re-assembled in
the cabinet.

Sound is very good.
With the 5 inch speaker, it puts out more
than enough volume.

A couple of minor tweaks, and then I'll run her
over to the record shop for consignment.

This Ambassador is the same unit as a
Wards Airline GAA-954 from the same year, I have.
Will probably attend to her next, since I'm familiar with
the setup.

The V-M 954 changers are identical in both.
From the code I supplied, Gary at V of Music said
Audio Industries were the buyers of these V-M 954 changers.

[electra225]

The cabinet on that record player is a LOT like the one on the Magnavox TP-241D I have. The blanked-off corners on the cabinet are unique. I wonder if they were built by the same company.

Nice job! Somebody will enjoy it for many years to come.....