[Guest]

I Have recently found a philco model 20 although every picture that I have seen they show that these model only has 3 knobs on the front. Where as the one that I have has a fourth knob between the 2 lower knobs and im wondering if this is a standard add on or something very odd and what the extra knob would control.

[Chuck Schwark]

You don't have a Model 20 then. You are correct about only three knobs on a 20; Tuning, On/Off and Volume.

Similar looking cathedral cabinets are Models 35, 70 and 90 from that same year - 1931. All three are superhets. The Model 20 is aTRF circuit.

Please list a tube complement to help identify. Since you're in the Great White North , you may have a Canadian version; 35-A, 70-A, 90-A.

[fabignoli]

Hello,

first, sorry for my poor english and I'm new here ;-)

I've bought a Model 20 on ebay and I've got the fourth knob too.

I plan to restart this radio at the end of 2006, I will see what this knob is made for... Probably it's an add-on....

Here it is.

http://cfp.radio.free.fr/dispo/philco%20model%2020.jpg

It's not a heterodyne but a king of TRF receiver.
There's 7 tubes:
2 Rf amplifier with type 24
detection with type 24
type 27 for AF and a push of 2 tube type 71A

It's written philco model 20 on the back, I'm sure of this. but it has 4 knobs

I will have a lot of work on it. There's lot of rust, 2 knobs are missing, the grid cloth (don't known if it's the right word) have a small hole.
The 2 71A are out of order but I've got 2 new one somewhere.

I hope the transformer will be OK, especially the one before the 71A....



best regards
Frederic ABIGNOLI

[Ron Ramirez]

Welcome, Chris in Canada and Frederic!

Frederic, thank you for the photo. (And your English is fine.) Can you and/or Chris in Canada share larger, more detailed, photos with us, please? It would make it easier to document these and determine if they are factory variants or changes made later.

I bring this up because I have seen Model 20 chassis with the extra hole where your set has a control, Frederic. I have often wondered if Philco considered putting a tone control on the 20 initially, then backed off to save money.

Can you two tell us what kind of control that is? Would you mind removing the chassis and taking under-chassis photos of the front area where the controls are?

Then please tell us if there are three trimmers mounted on the side of the tuning condenser gang, or if there are only one or two, with one possibly under the chassis?

Thank you for your help. This could be quite interesting...

[fabignoli]

Hello Ron,

Actually I'm working on a small 2 tubes RF generator project. I will finish it this week or next week. After that, I will try to re-start the philco . Lot of work I'm afraid Lot of rust inside, the 71A are out of order (I've not received the new one, but before I can take 2 of the in an atwater 46), I've got 3 ou 4 24, so for the tubes its OK.

I hope that the AC transformer is ok, because it's long to rewind but if it's not, I will do it. I pray for the 3 RF coils but they are not difficult to rewind.


SO, for the photo it's ok, but Iif you don't mind, please wait one week or two. Many thak's Ron. Your forum is great....

best regards
Frederic ABIGNOLI

[fabignoli]

Hello,

It's a tone control. It is made with a 6Mohms pot and a 50nF condenser. The whole thing is between the plates of the two 71A.

I've written a small page to show you.
http://cfp.radio.free.fr/restaurations/ron/ron.html

Have a nice day.

Frederic ABIGNOLI

[Chuck Schwark]

Looking at your 4-Knob Model 20 page, that wax-paper cap (yellow) I don't believe would have been comtemporary for the model 20 in 1930-31 as available parts. Appears that this "add-on" tone control was added not long after the set was new.

That capacitor would have to have a voltage rating of 1200 volts to safely withstand the audio AC peaks on those plates.

Intersting find.