Posts: 12
Threads: 3
Joined: Mar 2020
City: Lewistown
State, Province, Country: PA
Hi All, I just finished up on the restoration of a Model 20 Philco radio.
I successfully restored one of these about 5 years ago.
I have a few dumb questions, first of all I replaced all block capacitors
and also the ones in the big can, using the 630 V yellow jackets, like I did
before. Also replaced any resistors that were out of spect's..
I just fired her up this morning...No smoke  But nothing else 
Here is what I done before. This set was physically in bad shape, very rusted.
The cabinet I had to rebuild the grill work.
Also the output transformer, the primary was open, and the speaker was toast.
So I got a new output transformer, the P T 291 from AES. I am using the old
field coil winding which reads 3115 ohms. I hooked the 71-A plate's from each
71A tube to the new Primary to an 8 ohm pm speaker, and the center tap to one
side of the field coil. Now the schematic says I should be getting around 190vdc.
Now is that 190 vdc to ground or to each plate of the 71A's? If it's to ground
then I'm getting about 50mv ?? Also where it the best place to get the B+ voltage
I get on the 80 rectifier and am getting 5.45VAC on the filiments and 525vdc accross
each small pins and nothing to ground. Where is the best place to read B+ voltages?
Thanks for any help,
Gary
Posts: 7,294
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
https://philcoradio.com/library/index.ph...chematics/
>If it's to ground then I'm getting about 50mv ??
Not so good. All of the wires connecting to the fc and the pri of the opt should have HV.
I would measure the HV from the 80 filament (+) and terminal 6 (-)on the power transformer. Should see several hundred volts there.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 03-27-2020, 03:02 PM by Radioroslyn.)
Posts: 12
Threads: 3
Joined: Mar 2020
City: Lewistown
State, Province, Country: PA
Ok, Just checked, 505 VDC From 80 filament to pin #6 on power
xfmr. Should I use pin #6 to check for all B+ voltages. #6 as the most Neg.
point?
Posts: 7,294
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Yup. You'll probably find that the choke is bad or bias resistor has an open section.
Happy hunting!
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 12
Threads: 3
Joined: Mar 2020
City: Lewistown
State, Province, Country: PA
Ok, here is some readings..
Tubular resistor, Pin's 5-6 900 ohms, should be 2470
Pin's 6-7 757 ohms, should be 975
All others spot on.
#24 plate 250 vdc,other #24 250 vdc
#27 plate 317 vdc...should be 120 vdc
#71A plate 3.5 vdc should be 215 vdc
#71A plate 4.0 vdc should be 215 vdc
Choke # 23 418 ohms dc resistance
Oh yes, all cap's replaced, including the can cap's
used all 630V yellow jackets...As before in last working model 20.
Gary
Posts: 1,475
Threads: 69
Joined: Nov 2012
City: Kansas city, MO.
See what voltage you have where the center tap of your new opt. trans., choke, and field coil connect. point d on schematic.
https://philcoradio.com/library/download...l.%201.pdf
Posts: 1,407
Threads: 72
Joined: Oct 2007
City: Linn Creek, MO
It sounds to me like the choke is open.
Steve
M R Radios C M Tubes
Posts: 1,475
Threads: 69
Joined: Nov 2012
City: Kansas city, MO.
I was thinking same thing but he did show a reading across the choke. Maybe could bypass the choke.
Posts: 12
Threads: 3
Joined: Mar 2020
City: Lewistown
State, Province, Country: PA
Ok, Can't do anything more to day...
Will hook everything back up tomorrow including the new o p
xfmr and a 4 ohm speaker. I'll re check the voltages and if nothing I will
bypass the choke.
will report back tomorrow...
Gary
Posts: 7,294
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Check the ground connection on #25
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 26
Threads: 7
Joined: Dec 2011
City: Eagle,
State, Province, Country: ID
Gary, I restored a Philco 20 a few years ago and I had an open choke. I replaced is with a Triad C-7X. As I recall if fit perfectly and is still working to this day. So in case you need a new choke here is a link to the one I used:
https://www.mouser.com/ProductDetail/Tri...aP3g%3D%3D
Posts: 12
Threads: 3
Joined: Mar 2020
City: Lewistown
State, Province, Country: PA
Thanks Joe, I have already checked the choke for DC resistance
ohms out at 418 ohms. I know this isn't the way to check chokes,
It's impendence. But thanks anyway, I'll write down that info in case
it is the choke. This is the 2nd model 20 I have restored, didn't have
any trouble with the first one.
Gary
Posts: 7,294
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Replace the resistor from terminal 6 to ground (abt 200 ohms).
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
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