[black85vette]

I appreciate this forum. In searching through all the past posts about audio quality on the model 20 I found several good bits of information. The first I did not have to worry about. The spider had been replaced at some point in the past and the speaker re-coned. Both were a pleasant surprise to me. The next useful part was about the detector circuit. I was getting distortion in the audio and read about the modulation levels of early radios so I dropped my transmitter to 25% modulation and cleared that up. Then the reminder about line voltages back in the 30's so I dropped my bench variac to 115 volts.

End result is a very acceptable sound quality. Not as good as some of my other radios but acceptable. I have been wanting to add a model 20 to my collection but so far just had a spare chassis that was too rusty. The spare came in handy by supplying the dial, an rf transformer and the speaker pig tail. It was very nice to have the parts on hand!

Thanks!

Rick

[klondike98]

Good to hear the phorum has helped you out and the radio is working well!

[morzh]

Rick

I have two 20s, a console and a Delux cath restored and a plain cath waiting its turn.
20 to me has more of symbolic value than it has performance value: plate detector an the speaker it uses won't let it be a superior musical instrument, but then like I said, it has its value for many of us, judging by how it s sought after.

Congrats on finishing it. Enjoy!

[black85vette]

A couple of additional notes on this radio;

1. I reduced capacitor 13 (detector cathode) to 250pf after reading several posts on dealing with distortion. There was some improvement.

2. This radio had previously been modified with resistor 20 (input to 1st audio) having another resistor placed in parallel to it. The original was not out of spec so it had to be changing the value. Curious, I put a 1 meg pot in place and varied it. It had less distortion at values below the 500k specified, also slightly less audio. But it did seem to improve sound quality.

3. When doing the recap I found that this was a model 20 but put in the caps for 20a and moved the B+ line to the low side of the field coil.

Not back in the cabinet yet but playing very nicely on the bench with my AM transmitter set to about 30% modulation.

Rick

[morzh]

Have to tell you about that cap in the detector: yes it will reduce the distortion. But it also will reduce sensitivity. Quite a bit.

[black85vette]

Have to tell you about that cap in the detector: yes it will reduce the distortion. But it also will reduce sensitivity. Quite a bit.

Thanks. I had read about this and decided it was an acceptable trade off. This radio will not likely be a daily driver so being sensitive and selective will not be a priority. Most of the time it will be playing music from my transmitter. So I am opting for better sound quality as the priority. Having the classic looks of an early cathedral in original condition and good sounding audio will make this a great addition to my humble collection.

So far I have acquired these Philcos; 41-221, 60, 20, 111, 38-7, 38-40 and 48-482

Regards,
Rick

[morzh]

Same is my 90 that I did the same mod to. It is not a daily player. I have 37-116 for that and now 38-690.

This said, 20 with the original speaker as a player of any music isn't the best chouce unless for now you have no alternative. Even when the speaker is reconed and the spider is changed. Though in this case it should be a decent player for sources like iPod if the connectors are installed.