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 Post subject: Re: Philco 37-38
PostPosted: Jun Sat 08, 2019 9:38 pm 
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Location: Annapolis, MD
ken/sc wrote:
If I solder the resistors between the end terminals and the center one on the volume control
Will I still be able to control the volume or does that just bypass the control?

Sort of....

Here's how to analyze it: (Assumes that you keep the basic "potentiometer" configuration, which is a simple voltage divider)

The basic control creates a voltage divider where the input is on the high side, and the output is on the wiper. The setting of the control determines the voltage division ratio. Call the high side R1, and the low side R2. The total (for yours ) is 500Kohms, regardless of wiper setting. So maybe R1 is 400K and R2 is 100K---in which case the output voltage is 1/5 times the input.
If you now shunt either R1 or R2, two things happen: the total no longer stays constant, and the shape of the curve is altered. Same thing, but different numbers, if the control is partially open and you add a shunt resistor over that part.

For trouble-shooting, you simply need the DC path to be restored and have the resistances "in the ballpark". Once you have things working, you can install a proper control.

_________________
-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Philco 37-38
PostPosted: Jun Fri 14, 2019 1:35 am 
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Joined: Nov Sun 20, 2011 1:10 am
Posts: 384
Location: South Carolina
I bought a new switch off eBay. It looks identical to my old one, but when I wire
It in, the radio will not come on. I put the old one back in. (On left in picture) the
Radio comes back on, with the motorboating of course. I checked the new switch with
A ohm meter it seems to be good. Obviously it wires in differently.


Thanks for any help,
Ken


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 Post subject: Re: Philco 37-38
PostPosted: Jun Fri 14, 2019 2:23 pm 
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Location: Annapolis, MD
Not a switch!! These things are mostly called controls, but another common term is "pot", which is short for potentiometer, which is a 3-terminal variable resistor configured to control voltage (variable voltage divider)

To check the control, you need to check resistance on all 3 terminals. The typical method is to first measure end to end, and then from one end to tne wiper, while turning the control.

PS:
You said the radio "would not turn on"---this implies a problem with the power switch. Are the power switch and the volume control connected mechanically?

_________________
-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Philco 37-38
PostPosted: Jun Fri 14, 2019 9:07 pm 
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Joined: Nov Sun 20, 2011 1:10 am
Posts: 384
Location: South Carolina
there is one wire I see leading back to the audio transformer and from there back to a wire providing c- 3v.

I am attempting to replace the Philco 335165 volume control with a Philco 335157.m

They look identical except the new control has a plate on top that connects to the outer terminal
which I guess would be to ground the control when you mount the switch, that same terminal the wire from the c- comes to.. The old control does not have that connection. So that’s not gonna work.

Ken


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 Post subject: Re: Philco 37-38
PostPosted: Jun Fri 14, 2019 9:47 pm 
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Location: Annapolis, MD
I'm having trouble relating your last post to the questions I asked....

I wrote:
You said the radio "would not turn on"---this implies a problem with the power switch. Are the power switch and the volume control connected mechanically?

I wrote:
To check the control, you need to check resistance on all 3 terminals. The typical method is to first measure end to end, and then from one end to the wiper, while turning the control.


YOU wrote:
the new control has a plate on top that connects to the outer terminal
which I guess would be to ground the control when you mount

Whenever I find anything like that, it's removeable.
BUT: One side of the control is supposed to be grounded. Is it grounded in yours?

And--the volume control is not a switch.... :shock:

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-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Philco 37-38
PostPosted: Jun Fri 14, 2019 10:27 pm 
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Location: Mountains of Mourne. Ireland.
Ken old bean, you will have to forgive me as I haven't been following too closely... :)

--------------

Arcade repair tips. Checking potentiometers with a multimeter.
Watch edited clip: https://www.youtube.com/embed/R91mazXzd ... autoplay=0

--------------
Image
VC (volume control) 33-5165 and 33-5157 have the same recommended replacement.

The above notes only apply when using the IRC replacement control D13-133


Greg.


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 Post subject: Re: Philco 37-38
PostPosted: Jun Fri 21, 2019 2:21 pm 
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Joined: Nov Sun 20, 2011 1:10 am
Posts: 384
Location: South Carolina
I think I smoked it! I had removed the cover off the secondary if can to
Look at a bad looking wire to see if it was causing the motor boating and
When it turned the radio on with the intention of wiggling the wire, all the
Tubes got really bright and now it won’t come on. My power supply is still
Putting out the right power.

Oh well
Thanks for all the help, last battery radio for me,
KM


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 Post subject: Re: Philco 37-38
PostPosted: Nov Fri 08, 2019 6:45 pm 
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Joined: Nov Sun 20, 2011 1:10 am
Posts: 384
Location: South Carolina
I had more time to play with this one and attempt to resurrect it.

If you look at my earlier post I thought I smoked this radio. It’s such a neat
Radio I hate to junk it. The light works. But I measured all my voltages at the various tubes.
They are all very low and as your measure them they get lower. In my earlier post all the tubes got very bright
And it quit working. Could the electrolytic caps and other caps be bad or the transformer?


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 Post subject: Re: Philco 37-38
PostPosted: Nov Sun 10, 2019 2:42 pm 
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Joined: Nov Sun 20, 2011 1:10 am
Posts: 384
Location: South Carolina
Bttt


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 Post subject: Re: Philco 37-38
PostPosted: Nov Sun 10, 2019 6:33 pm 
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Ken wrote: Could the electrolytic caps and other caps be bad or the transformer?

It's up to you to pull and check the electrolytic capacitors if you have any doubts.
What transformer?
There are eight "transformers" in your set... :)

------------

Disconnect your power supply (completely) from the radio and confirm - List - all your output Voltages with no load applied.
Image
from page one of this thread.
viewtopic.php?p=3013805#p3013805

The Voltage divider network modification shown in blue above, should look like this.
viewtopic.php?p=3105839#p3105839

:) Greg.


Philco 37-38
Schematic: http://americanradiohistory.com/hd2/IDX ... e-0038.pdf
Layout: http://americanradiohistory.com/hd2/IDX ... e-0039.pdf
Changes: http://americanradiohistory.com/hd2/IDX ... e-0013.pdf


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 Post subject: Re: Philco 37-38
PostPosted: Nov Sun 10, 2019 10:26 pm 
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Joined: Nov Sun 20, 2011 1:10 am
Posts: 384
Location: South Carolina
A+,A- 1.5vdc
B+ 88.2, B+ 132
C- 3, 8.3

At power supply with radio disconnected.
I got it to play on a station earlier in the year,
But it was motor boating. I wiggled a wire and
All the tubes got bright. Now I am getting nothing.
But the dial light, tubes are not warming up. I
It has been recapped but not since the got bright and
It quit working.


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 Post subject: Re: Philco 37-38
PostPosted: Nov Sun 10, 2019 11:02 pm 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 10403
Location: Mountains of Mourne. Ireland.
Remove all power from radio, and...

Discharge any electrolytics with juice in them. Use a resistor or 100W light bulb. lol
fyi... Constructing a Capacitor Discharge Tool.
http://antiqueradios.com/forums/viewtop ... 6#p2318386

Look for an intermittent (break) in one or more of your wires.

Clip your multimeter to both ends of each and every individual run of wire - use the continuity (buzzer) setting or select a resistance range (analog meter with needle works best here), starting with the highest and working down. - - and wiggle for results.

Re-flow/re-solder (touch up) any suspect dry solder joints.

Greg.


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 Post subject: Re: Philco 37-38
PostPosted: Nov Sat 16, 2019 4:22 pm 
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Joined: Nov Sun 20, 2011 1:10 am
Posts: 384
Location: South Carolina
I went back and checked all my wires for continuity. All seem ok. Then I check the filaments pins 2 and 7
On the tubes, not one tube was good. I must have fried them all when they all got bright. What should I replace beside
The tubes $$. Do I recap it again?


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 Post subject: Re: Philco 37-38
PostPosted: Dec Mon 02, 2019 8:12 pm 
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Joined: Nov Sun 20, 2011 1:10 am
Posts: 384
Location: South Carolina
I replaced all the tubes with NOS or used tubes. I am getting several stations on the AM band and no stations on the shortwave band. I can only get AM stations with the volume control turned all the way up, if I turn it down I get motorboating. Ideas or suggestions?

Km


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 Post subject: Re: Philco 37-38
PostPosted: Dec Mon 02, 2019 9:24 pm 
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Joined: Jan Tue 31, 2012 1:55 am
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Location: Mountains of Mourne. Ireland.
If you have inadvertently applied reversed power to the electrolytics, try replacing them.
Don't forget to label the removed ones as suspect, or consign them to "file 13"

Greg.


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 Post subject: Re: Philco 37-38
PostPosted: Dec Mon 02, 2019 9:51 pm 
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Joined: Jan Tue 31, 2012 1:55 am
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Location: Mountains of Mourne. Ireland.
Image
from here: Changes 1939 I. F. Transformer (preventing oscillation).
http://americanradiohistory.com/hd2/IDX ... e-0010.pdf

See (run-4) filament changes here: Changes 1938
http://americanradiohistory.com/hd2/IDX ... e-0013.pdf

Greg.

Schematic pages... Rider 1937
7-17 http://americanradiohistory.com/hd2/IDX ... e-0038.pdf
7-18 http://americanradiohistory.com/hd2/IDX ... e-0039.pdf


Edit: 1C7G screen-pin-4
https://archive.org/details/Raytheon_19 ... s/page/n42
1D5G screen-pin-4
https://archive.org/details/Raytheon_19 ... s/page/n43


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 Post subject: Re: Philco 37-38
PostPosted: Dec Wed 11, 2019 1:51 pm 
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Joined: Nov Sun 20, 2011 1:10 am
Posts: 384
Location: South Carolina
I replaced the volume control and that took care of the motorboating.

I was getting several stations, I tried to do a realignment and now I get no stations.
I was able to peak the 470kc for the IFs, step 1 in the procedure. When i switch
The band control to the second position for step 2 to align the RF circuits it is not picking
My signal generator anywhere on the scale 2.3mc to 7.4mc. It is supposed to be picking up
The generator at 7.0mc and 6.0mc for this step.

For step 3 you switch the band selector back to position 1 and peak at 1600kc. i can hear the
Signal generator at 1600kc but it is very faint.

Thanks for any help.


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 Post subject: Re: Philco 37-38
PostPosted: Dec Wed 11, 2019 3:37 pm 
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Joined: Jan Tue 31, 2012 1:55 am
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Location: Mountains of Mourne. Ireland.
Have you serviced (cleaned) the band switch?

Philco ~1940
Image

image: Hallicrafters...
http://i836.photobucket.com/albums/zz28 ... 9f4f9c.jpg

image: Zenith...
http://radiorestorer.com/arcswitch.JPG


Greg.


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 Post subject: Re: Philco 37-38
PostPosted: Dec Fri 13, 2019 12:24 am 
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Joined: Nov Sun 20, 2011 1:10 am
Posts: 384
Location: South Carolina
I went back and cleaned the band switch again.
Still no stations.


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