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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 25th May 2024, 12:09 am   #1
daveone23
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Default Atwater Kent model 40

I rebuilt two model 40s and they both have the same problem: the volume is extremely soft. Both power supplies were rebuilt using the attached article, resistors and bypass caps replaced. All Voltages look good. Antenna transformers and volume pots look good. Connected to verified 80 foot long antenna. Any thoughts.
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Old 25th May 2024, 1:39 am   #2
Silicon
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Default Re: Atwater Kent model 40

I am not familiar with these sets but I have a query regarding the output circuit.

The AC output signal to the speaker has to pass through a 2,200 Ohm resistor as it returns to ground (chassis or HT negative).

This seems wasteful. What type of speaker are you using?
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Old 25th May 2024, 3:59 pm   #3
daveone23
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Default Re: Atwater Kent model 40

I am using a 1920's RCA 103 mechanical speaker.
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Old 25th May 2024, 7:37 pm   #4
Silicon
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Default Re: Atwater Kent model 40

The 2,200 Ohm resistor is the automatic grid bias resistor for the UX-171A power Triode.

It is a directly heated cathode type of tube (valve).

That resistor is effectively wired between the cathode and ground.

The 'Return' wire from the speaker is effectively wired to the cathode of the UX-171A.

This looks strange to me, I would have expected it to be connected to chassis.

You could try wiring a non-polarised film capacitor (i.e. polyester) across the 2,200 Ohm resistor to see if it would improve the volume.

What is the Impedance of that RCA speaker?

Last edited by Silicon; 25th May 2024 at 7:38 pm. Reason: more info.
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Old 26th May 2024, 12:16 am   #5
daveone23
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Default Re: Atwater Kent model 40

I tried a ground from the antenna connection to the mains and it helped the volume alot. Do you guys use grounds on your TRF radios?
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Old 26th May 2024, 10:47 am   #6
Silicon
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Default Re: Atwater Kent model 40

We need to be careful when we talk about the 'antenna connection to the mains'.
That sounds dangerous.

The terminology here can be different.

To me, protective earth, earth, ground, Antenna ground, chassis and HT negative are all different things.

In a 1950s AC radio they may all be connected together.

However in many other radios they are deliberately kept separate.

When I mentioned 'ground' in a previous post I meant 'signal ground'.

We need to know exactly what you meant in your last post.
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Old 26th May 2024, 1:29 pm   #7
paulsherwin
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Default Re: Atwater Kent model 40

Quote:
Originally Posted by Silicon View Post
I am not familiar with these sets but I have a query regarding the output circuit.
There are very few AK radios around in Britain, so expertise on this forum will be limited.

Generally speaking, 'earth' (UK) = 'ground' (US). There may be more subtle differences in terminology that I'm not aware of though.
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