Philco 37-650 Plate voltage

[Steve Dow]

Check these two voltages, to chassis:

1. Junction of Resistor 60, and + terminal of Capacitor 59A.

2. The plate of the IF AMP 6K7G (pin 3)

[Rick D]

Hello Steve
From the + end of #60 cap to where the terminal of the 9K and 10 K #60 resistor join
I got 105 volts and on the 6K7 form pin #3 and to the chassis I got 324 volts,hope this
will help you help me,and I hope I got you what you wanted,I have not changed the
#58 resistor yet ,I will pick one up tomorrow,thanks again Steve all the very
best Rick

[Rick D]

Sorry Steve
I may not have it right,from the + end of the #59A the 20UF cap and to the
chassi I got363 volts and from the junction of the #60 resistor 10K this is
where the 9K and the 10K join and to the chassis I got 205 volts ,thanks
again Steve all the best Rick

[Steve Dow]

What is the voltage from the + end of the #59A cap to
the center tap of the output transformer ?

Also, after the radio has been off for several hours, while unplugged from power,
measure the resistance from the + end of #59A cap ,
to the + end of #57 cap.

[Rick D]

Hello Steve
From the the 59A – 20UF cap + end to the centre tap of the output transformer is 39 volts.
The resistance from the + end of the #59A – 20UF cap to the + end of the #57 – 8UF cap is
412 ohms.Steve so far do these voltages seem right to you,the set works fine right now but
like befor I am sure after about 1 to 2 hours it will act up and I feel sure the voltage
will climb on the centre tap of the output transformer,I have had it as high as 358 volts
thats seems to be when the problem starts,I don,t want to run it that long any more
because I am afraid to ruin the power transformer,thanks for the help Steve.
All the best Rick

[Steve Dow]

With the radio off for 2 hours, an unplugged, what is the
resistance between the center tap of the output transformer
and the + end of 59A cap ?

Could you look at the name plate of the radio and
see what the voltage and line frequency is ?

The field coil cold resistance looks good
from the last test.

[Rick D]

Hello Steve
From the + end of the 59A -20UF cap to the centre tap of the output transformer
with the field coil wire hooked to it and the wire that goes to the radio to the
+ side of the 8UF – #57 cap,in other words with everything hooked up I get
416 ohms.
On the back plate of the radio voltage = 115 volts
Chassis = 37-3650
Code = 121
Cycles= 2540
Watts= 110
Steve I don,t see anything that is stamped or marked Line Frequency,
hope this is what you need,do you think this could be a transformer
problem.or is there a chance it could be that #58 resistor 19 and 109 ohms,I have
not changed that as yet,thanks for all your help,all the best Rick
PS-I had the radio unplugged at least 2 hours befor I did the test

[Steve Dow]

Cycles 2540

The set was made for Ontario and approved for 25 Cycles.

But assuming the radio worked properly
in 1948 when the power system was changed, this could be moot.

Also it may have been replaced with a 60 cycle type.
Ontario Hydro did this in some cases through Philco service.

A question about the Candohm.
Are the measurements of resistance to chassis ?

i.e. from chassis to tap it should show 19 ohms and from the other end to chassis. 19
+ 109 or 128 ohms.

[Rick D]

Hi Steve
I changed that # 58 resistor 19 and 109 ohms,I used some 5 watt resistors,put
two together on each, to get me to 20 ohms on one and 110 ohms on the other.
I did test the old ones befor removing and they tested fine, and after I took them out
I put it in a vice ,applied heat with my heat gun with the tester on them and
they did not change value,I was hoping they would but no.I am going to start the
set up now and let it run for 3 hours, with one voltage meter wire on the centre tap
of the output transformer and the other voltage meter wire hooked to the chassis.I have
at start up 320 volts and it sounds great,I will let it run with the meter on and see if the voltage
goes up, I have had it go to 358 volts and at that point is when the sound goes
bad,I hope that changing that 58 resistor will fix it,I have been told that those
Candohm resistors tend to drift,will let you know all the best Rick

[Steve Dow]

If the voltage rises and the sound distort, if you can,
try and see if one of 6F6 tubes get cool.

Tube pins have the leads soldered at the bottom, and it not
uncommon for the solder to need re-heating.

Each 6F6 uses about 28 % of the B+ current for the whole set.

[Rick D]

Hello Steve
First of all thanks for sticking with me ,I sure need the help,tonight
I ran the set with the volt meter hooked up and on,I had it on the
centre tap of the output transformer and the chassis.The voltage
held for 2 hours at 311 volts,no more 358 volts,but after 1 & 1/2
hours the speaker noise started,like I said with any volume and
music with any bass in it ,the speaker rattles like it had a ripped
cone or some thing leaning on the cone.At that time I hooked up a PM
speaker I had ,and the same thing,I do have a electromagnet speaker I could
try same size, but the field coil is 930 ohms and the one in the set is 420
ohms,I am afraid if I hook it up I might do some damage,Steve do you think
if I hook it up it would be ok,I have no idea why the original speaker
sounds so good for an hour and a half then goes south,thanks for all
your input Steve all the best Rick

[Jean Marcotte]

Rick,

I am still there and watching everything. One measurement I (or Steve) never asked is the voltage across condenser 59A. I still think that those higher than normal voltages you’re getting is the cause of your problem. At some point, some component somewhere in the radio can’t take it any longer and causes the distortion.

Best regards.

Jean

[Rick D]

Hello Jean
I put one of my tester wires on the positive side of the 20UF # 59A and the
other wire from my tester to the chassis and got 358 volts,Since I changed the
candohm resistor # 58 on the schematic 19 ohms and 109 ohms the plate
voltage on the 6F6 tubes dropped to 320 volts and holds there.I have tried three
other speakers now,two PM speakers and two with the field coil,also tried
three other output transformers two of them brand new a Hammond 125D and a Hammond
125E,still the same.The cone on the speakers is really moving back and forth,
I don,t think they should be driving that hard,when they do I get the noise.
I did notice cap # 30 in the black block there is no wire going to the last
terminal,I put in two of the 110mmfd caps in the block,but
there was nothing going to that terminal befor I started,I took photos and drew a copy of
everything I changed befor doing it,just in case I made a mistake,I put
everything back the way it was.I have trouble following the schematic
and do the best I can,do you think this area could be causing the problem.
I am going to bed now ,if you think of anything I should try please let
me know and I will try it in the afternoon thursday.
Take care Jean all the best Rick

[Jean Marcotte]

Rick,

358V across 59A is more than 50V above normal. It should be around 305V. The only two components between the 59A + terminal and the line cord are the rectifier and the power transformer. I can’t see how a faulty rectifier could increase voltage, but try another one to confirm. If you stll have abnormal voltages then I am back to my previous diagnostic of a partially shorted primary. Then you would need another transformer. As long as you cannot get correct voltages, it is useless to try changing all kind of other parts. It is like if your car battery in giving you only 9 volts, changing the spark plugs won’t help.

Regards.

Jean

[Steve Dow]

Rick,
What type/model voltmeter are you using? The voltage readings on the chart are made by a 1000 ohms/volt meter.
While the main voltages will not be affected, going forward, some other voltages will be wrong if you are using a DVM.

There is way around this. When your voltmeter type is known a resistor can be added to make it 1000 ohms/volt.

At this point it would be useful to know the voltages on the 5Y4 plates with respect to the center tap
of the transformer, and the cathode currents of the 6F6 tubes.

These are hard to get.

Below are two adapters to do this with. The first is a socket adapter with measuring pins on the top side.

The second is a pin 8 cathode current interceptor, It is a tube socket, on top of a tube base, with pins
wired strait across, except for pin 8. Pin 8 is split into the two clip leads, one goes to the socket 8 and the
other goes to the tube base pin 8. This adapter was made by W. Frederick, a TV technician long ago.

Attachments:

1. 

   Pin-8-CATHODE-CURRENT-INTERCEPTOR-VE7ASO.jpg
   

2. 

   SOCKET-ADAPTER-VE7ASO.jpg
   

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