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Philco 20 - variable capacitor tuning - Printable Version

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Philco Model 20 schematic by Ron? - winston763 - 02-19-2017

Hi, i was researching threads and Ron mentioned an enhanced schematic of the Philco 20 with '+/- ' in the filter condenser block etc.  I would appreciate this more detailed schematic but I can't find it,  the links are gone.  Can someone help me with this schematic? thanks in advance.  I remember using a nice Model 90 schematic (the numbers weren't "blurred") from here that helped me a lot. Rich

RE: Philco Model 20 schematic by Ron? - Radioroslyn - 02-19-2017

Hi Rich,
Probably not a good idea to use electrolytic caps in this power supply. Originally they where foil/paper caps which withstand the ripple current much better than the e caps. The modern equivalents would mylar or poly caps. These are non polarized.
The e cap tend to short after being in service for a relatively short period of time.

Philco 20 - variable capacitor tuning - winston763 - 02-20-2017

Hi, i've never encountered this. I completely recapped (everything) this Philco 20 (not 20A) since I started with no signal.  I have it working loud and clear but 1 major cavet. The only way i get a "loud and clear" reception is when I put my finger on the middle tuning screw of the variable capacitor.  this is rather inconvenient.  Otherwise i hear white noise.  I must have missed a grounding somewhere but just wondering if someone knew off the top of their head.  The cabinet is in great shape which i understand is not very common.  I followed George's advice and did not use electrolytics but rather 2 1MFD, and 1 2.2MFD non-polarized capacitors in the power supply (prior post).  Thanks, Rich

RE: Philco 20 - variable capacitor tuning - morzh - 02-20-2017

If this is the case, check the continuity of your RF transformers' windings; one of them could be open. You might have to rewind one or some of them. See which RF coil the cap section you touch goes to, that could likely be the one that is open.

RE: Philco 20 - variable capacitor tuning - Steve Davis - 02-20-2017

Rich, it sounds like transformer number 7 has an open winding. Check the plate voltage of the first 24 tube.

Steve

RE: Philco Model 20 schematic by Ron? - sam - 02-20-2017

rich
I think this is posts your looking for ? or not

http://philcoradio.com/phorum/showthread.php?tid=14994


http://philcoradio.com/phorum/showthread.php?tid=14990

if these are it.   please use other post as this is just looking for schematic post

sam

RE: Philco 20 - variable capacitor tuning - Radioroslyn - 02-20-2017

+1
Sound like a bad rf coil. Fortunitly the primary (the smaller winding) of these coil is untuned so the number of turns isn't super critical. It most of the time is the outer winding on coil. Original is most likely 38ga magnet wire but any thing from 38 to 30 will work fine. You can approximate the # of turns by the size of the original winding, it's probably 20-50 turns. Unlike the osc coil in the the superhet sets direction doesn't matter.
Obtw Is it a standard, deluxe or consolette? Doesn't matter for the repair just curious, call me George.

RE: Philco 20 - variable capacitor tuning - winston763 - 02-20-2017

I will check the coils and the voltage on the 24 tube.  I was hoping not to rewind coils but we'll see. this is a standard Philco 20 not a 20A.  i have a 20 Deluxe which works great.  thanks for the help, Rich. (sorry George - i assume from your quote)

RE: Philco 20 - variable capacitor tuning - Phlogiston - 02-20-2017

All that has been said is true but also check for corroded/bad connections on the 24 grid cap.

RE: Philco 20 - variable capacitor tuning - winston763 - 02-20-2017

I cleaned the '24' grid contacts (they were dirty but not corroded) and sprayed deoxit.  Then i decided to try and align at 140/1400 and the sound was just about as loud as you could ever want,  but no signal without my finger on the center variable condenser nut. 

I checked the plate voltage and it was 255 and conformed with the schematic - although i usually play my radios at 100 via the variac.  I don't want to burn tubes on these so i'm a little protective.

last, i touched my fluke mulimeter to the center coil at the lug from the grid (same as from the tuning condenser) and it plays loud and clear.

"All roads" point to that coil but i don't know why my alignment is not impacted.  Thanks for pointing to this - now i know which coil. Rich

RE: Philco Model 20 schematic by Ron? - winston763 - 02-20-2017

that's the one! Thanks !!! Rich

RE: Philco 20 - variable capacitor tuning - klondike98 - 02-21-2017

I merged your two 20 threads into one to keep the topic together.

RE: Philco 20 - variable capacitor tuning - winston763 - 02-21-2017

Great progress report.

I recoiled the middle coil as you predicted. My recoil job was not anywhere as nice as the original but i did as many turns as to match the original coil. To me it was sloppy but no overlapping. ANYWAY it works great!!

Thanks for the advice.  I wouldn't be done without it.  On to a model 70 at my next avaiable auction.  I'd like to have the threesome (I have Model 20, deluxe, Model 90 among others) I want 20/70/90). My Philco 52 still has coil issues but now i feel i can return to that issue.

"Sound like a bad rf coil. Fortunately the primary (the smaller winding) of these coil is untuned so the number of turns isn't super critical. It most of the time is the outer winding on coil. Original is most likely 38ga magnet wire but any thing from 38 to 30 will work fine. You can approximate the # of turns by the size of the original winding, it's probably 20-50 turns. Unlike the osc coil in the the superhet sets direction doesn't matter."

Thanks again!
Rich

RE: Philco 20 - variable capacitor tuning - Radioroslyn - 02-21-2017

(02-21-2017, 02:54 AM)winston763 Wrote:  Great progress report.

I recoiled the middle coil as you predicted. I did not do anythingl ike the original but i did as many turns as to match the original coil. To me it was sloppy but no overlapping. ANYWAY it works great!!

Thanks for the advice.  I wouldn't be done without it.  On to a model 70 at my next avaiable auction.  I'd like to have the threesome.

"Sound like a bad rf coil. Fortunately the primary (the smaller winding) of these coil is untuned so the number of turns isn't super critical. It most of the time is the outer winding on coil. Original is most likely 38ga magnet wire but any thing from 38 to 30 will work fine. You can approximate the # of turns by the size of the original winding, it's probably 20-50 turns. Unlike the osc coil in the the superhet sets direction doesn't matter."

Thanks again!
Rich

Hey Rich Your welcome!
If you keep fooling with these older Philco set ( pre '35 or so) better have a spool of magnet wire handy.

Glad to help out.