Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Need some help with an old PHILCO radio.

I've gone to a local flea market and picked up a 1942 Philco Model A-361. It was humming like mad, the volume control didn't work and it had no reception. I recapped everything which fixed the humming but now it just doesn't make any noise at all (Just a very low dull hum that's barely audible, volume control doesn't do anything). I've double checked all of my solder connections and reviewed the schematic. I also kept the tolerances for the new caps within +/- 10% and tested before installing them. I've also checked for b+ voltage from the transformer, the heater filaments in all of the tubes all light up. What else could I be missing? Could it be some of the tubes themselves?

Thanks In Advance -Ray, KD2JID
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Yes it could be a faulty valve, or faulty resistors, or anything else - but valve radios are pretty easy to repair (they are pretty crude things).

Basically all you really need is a multimeter and a finger :D

Being careful of live chassis or anything, touch your finger to the volume control pins (with the volume turned up) it should buzz loudly - you've now cleared the audio stages.
 

Buk

Active Member
touch your finger to the volume control pins (with the volume turned up) it should buzz loudly - you've now cleared the audio stages.

The E.Tech equivalent of the mech's "Press point of screwdriver to the cylinder head and your ear to the handle. You shouldn't hear..."
 

danadak

Active Member
Probably out of IF alignment.

First you verify all the grid/plate voltages are what SAMs schematic are. If you
cannot find that signal grids coming from IF transformer usually close to 0 V, maybe
slight negative bias.

Tubes very much could be bad, you will need to check them, but if above voltages
at tube pins are correct they might be good, but thats still not enough, they need to be
checked. Their gain can be quite low, tube could be gassy....


Then do an IF alignment. Checking local oscillator first for its frequency.


Regards, Dana.
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
Probably out of IF alignment.

Why would you imagine that?.

First you verify all the grid/plate voltages are what SAMs schematic are. If you
cannot find that signal grids coming from IF transformer usually close to 0 V, maybe
slight negative bias.

Tubes very much could be bad, you will need to check them, but if above voltages
at tube pins are correct they might be good, but thats still not enough, they need to be
checked.


Then do an IF alignment. Checking local oscillator first for its frequency.

You seem to have somewhat of an IF alignment fetish? :D

I've already made a simple suggestion in post #2 - which is absolutely free, requires no equipment, takes seconds - and instantly reduces the potential problem by half. The 'half split' method is a standard and sensible way of servicing - and while the volume control isn't 'quite' half it's such a convenient and easy point that it's always considered as such.

In 46 years as a TV/Radio service engineer I don't recall ever having to relign the IF in a radio, and only once in a TV - that simply because the idiot of the customer took the back off and "tightened all those loose screws down".
 

danadak

Active Member
I regularly work on legacy Amateurs radios and they universally all
need IF alignments. I just did a HQ170 and it was significantly off, radio
virtually "dead". I did a SX101 a month ago, and my "fetish" served me well,
restoring that radio to performance.

I also have a "fetish" to realign bands and antennae tuned circuits, otherwise
the frequencies are off as readout by the dial indicators.

Spend a lot of time replacing plate and cathode R's as they run hot and carbon comp
over long periods of time typically rise by 50% or more. Another "fetish".

Also have a capacitor "fetish", in particular electrolytics, black beauties, occasionally a
ceramic, rarely a mica. Except for micas in certain radio IF cans.....I have one now I have to do.

Yes, lots of "fetishes". Anything else you would like to illuminate Mr. Goodwin ?


Regards, Dana.
 

unclejed613

Well-Known Member
Most Helpful Member
ok 1942, SHOULD be all octal socketed tubes. https://archive.org/details/RCA_RC-16_1950 the book will give you pinouts of the tubes, some clue what the working voltages on the tubes should be, and at the back of the book, are circuit diagrams for various radios, amplifiers, and i think maybe even some TV circuits... one little secret... Philco often ripped circuits from RCA's reference schematics, so you might actually find something in the RCA book that matches that Philco by 90% or better...

one note of caution, if you only have one iron core transformer in the radio (connected to the speaker), then you have a transformerless power supply, (also known as an AC-DC or "hot chassis" design)... if this is the case, make sure the radio has it's original polarized power cord, and your outlets are properly wired before working on this radio... the chassis ground is hard wired to the neutral side of the plug, and if you plug it in backwards to an outlet, or to an outlet that's miswired, you will have raw line voltage on the chassis ground, which is dangerous.... it's actually best to use an isolation transformer to work on such radios....

if the radio has a power transformer AND an audio output transformer, then it's ok to work on it without an isolation transformer...

a couple of hints: all of the tubes should have a slight positive voltage on the cathodes (measured from ground) if they have cathode resistors, and 0 to a few volts negative on the grids MEASURED FROM THE CATHODES. if the cathodes are grounded, then there should be a slight negative bias on the grid measured from ground. there should be a pretty reasonable voltage drop across plate resistors for each tube. for a B+ (power supply) voltage of 150V, there should be about 100V on the plate. if there's a screen grid, it's voltage should be about 10% or so higher.

it's mainly the voltage drop across the cathode resistors and the plate voltages, and the plate resistor voltage drops that will tell you if a tube is operating properly.

if there's a blue or pink glow in a tube, it has some gas in it, and should be replaced. if the silver coating on the inside of a tube is missing or looks like a white powder, there's atmospheric pressure air in the tube and must be replaced...
 
Last edited:
ok 1942, SHOULD be all octal socketed tubes. https://archive.org/details/RCA_RC-16_1950 the book will give you pinouts of the tubes, some clue what the working voltages on the tubes should be, and at the back of the book, are circuit diagrams for various radios, amplifiers, and i think maybe even some TV circuits... one little secret... Philco often ripped circuits from RCA's reference schematics, so you might actually find something in the RCA book that matches that Philco by 90% or better...

one note of caution, if you only have one iron core transformer in the radio (connected to the speaker), then you have a transformerless power supply, (also known as an AC-DC or "hot chassis" design)... if this is the case, make sure the radio has it's original polarized power cord, and your outlets are properly wired before working on this radio... the chassis ground is hard wired to the neutral side of the plug, and if you plug it in backwards to an outlet, or to an outlet that's miswired, you will have raw line voltage on the chassis ground, which is dangerous.... it's actually best to use an isolation transformer to work on such radios....

if the radio has a power transformer AND an audio output transformer, then it's ok to work on it without an isolation transformer...

a couple of hints: all of the tubes should have a slight positive voltage on the cathodes (measured from ground) if they have cathode resistors, and 0 to a few volts negative on the grids MEASURED FROM THE CATHODES. if the cathodes are grounded, then there should be a slight negative bias on the grid measured from ground. there should be a pretty reasonable voltage drop across plate resistors for each tube. for a B+ (power supply) voltage of 150V, there should be about 100V on the plate. if there's a screen grid, it's voltage should be about 10% or so higher.

it's mainly the voltage drop across the cathode resistors and the plate voltages, and the plate resistor voltage drops that will tell you if a tube is operating properly.

if there's a blue or pink glow in a tube, it has some gas in it, and should be replaced. if the silver coating on the inside of a tube is missing or looks like a white powder, there's atmospheric pressure air in the tube and must be replaced...
It uses 'loctal tubes', not sure if those are the same as octal. Also this radio uses a car radio in a full size cabinet.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
It uses 'loctal tubes', not sure if those are the same as octal. Also this radio uses a car radio in a full size cabinet.

There were a great many different valve bases used - Octal and B9A are the two 'modern' styles.

Loctal 'might' perhaps mean 'little octal'?, a miniturised version of an Octal base perhaps?.

It seems quite strange, a car radio in a larger box? - I would have thought it's a pretty expensive way to make a home radio?, as valve car radios were fairly expensive and more difficult to make and service.
 

JimB

Super Moderator
Most Helpful Member
Are they interchangeable?
No not at all, they both have eight pins and are more or less the same size, but the diameter and length of the pins is very different.

JimB
 
  • Like
Reactions: Buk

Nigel Goodwin

Super Moderator
Most Helpful Member
Interesting it's a locking base, intended for car radios etc.

I presume such radios weren't 'standard' car radio size, as such large valves would be difficult to fit in a car radio slot. I repaired a number of valve car radios over the years, and at one time had a Blaupunkt valve car radio that even had short wave on it - can't remember where it came from, can't remember what happened to it, but I do remember never using it (other than powering it up to test it).
 

unclejed613

Well-Known Member
Most Helpful Member
Loctal 'might' perhaps mean 'little octal'?, a miniturised version of an Octal base perhaps?.
it's an octal tube with smaller diameter pins and the locator pin on the base locks into a spring clip in the socket. the tubes are otherwise identical in dimensions and pinout to a regular octal tube.
 

unclejed613

Well-Known Member
Most Helpful Member

Nigel Goodwin

Super Moderator
Most Helpful Member
it's an octal tube with smaller diameter pins and the locator pin on the base locks into a spring clip in the socket. the tubes are otherwise identical in dimensions and pinout to a regular octal tube.

Already explained in post #13 by danadak.

Not good for squeezing in a car :D

Where I used to work the previous chief engineer used to be a policeman in Manchester long ago, and one of the things he was involved in was early experiments with radio transceivers in the police cars - pretty large back then. Two souveniers he had from his police days were a set of brass knuckles, and a huge great knife - standard Police equipment back in those days in Manchester :D

so, it must be using a power transformer...

You'd like to think so?, I gave up trying to find a schematic as all the ones I tried wanted to charge you for them, but the postage stamp sized pictures seemed to show a mains transformer, and as you'd expect it looked a fairly bog standard valve radio.
 

Latest threads

EE World Online Articles

Loading
Top