Philco 604C Electronic Restoration
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Here you go, Terry...
[Image: http://www.philcoradio.com/images/phorum..._volts.jpg]
Key:
P - B- = Plate voltage measured to B-, as per Philco 604 Service Bulletin
P - K = Plate voltage measured to cathode
S - B- = Screen grid voltage measured to B-
S - K = Screen grid voltage measured to cathode
CG - B- = Control grid voltage measured to B-
CG - K = Control grid voltage measured to cathode
K - B- = Cathode voltage measured to B-
Specs = Voltages given in Philco 604 Service Bulletin (measured with 1000 ohms/volt meter)
The Philco service bulletin calls for all voltages to be measured to B-, so all of the "specs" voltages are to B-.
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Ron Ramirez
Ferdinand IN
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I should also mention this: When I touched the positive lead of my DMM probe to the control grid of the 75, the volume increased.  Not by a huge amount, but noticeable.
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Ron Ramirez
Ferdinand IN
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Hmmm
Voltages look pretty good. I'd try two things. Would try an other source of audio to the volume control and then the CG of the 43. The other thing would disconnect the VC on the spkr and connect a PM spkr to see if volume improves.
Terry
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Okay.
* Tried feeding an audio signal from the computer at my workbench. Audio was very low and distorted.
* Tried disconnecting the 604's speaker voice coil lead and connecting a test speaker. Audio was very low and slightly distorted.
I'm at a standstill on this one, and I must confess that I can't figure this one out. Why the voltages are OK, the tubes are OK, yet the thing plays very low is quite puzzling.
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Ron Ramirez
Ferdinand IN
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How about the heater voltage on the 43 and 75? Up to par?? I'd try a test spkr with an output transformer. Disconnect the plate lead from the 43 and clip in the test spkr. Or a signal tracer to see where the gain drops off.
Terry
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OK, Terry (and anyone else interested)...
I measured the heater voltages of the 75 and 43 tubes.
75 - 6.7 VAC
43 - 24.1 VAC
Not bad.
I looked...I do not have a PM speaker with an output transformer attached to it.
Then I remembered my Eico signal tracer. This signal tracer allows you to use its output transformer and speaker as a test speaker with output transformer...and the signal tracer does not have to be on to perform this test. (A good thing, because both the signal tracer and the 604 are AC/DC...and the two connected together and powered up would certainly cause the GFCI in line with my basement outlets to trip.)
I disconnected the plate leads from the 43 tube. I then connected the signal tracer's output transformer to the 43 plate and to B+.
The 604 plays loud and clear...
[Image: http://www.philcoradio.com/images/phorum...4_0026.jpg]
If I turn the volume control about 1/3 of the way up, I get a normal listening level with the 604 tuned to my SSTRAN at 660 kc. Which is how it should be.
So, it looks like I need an audio output transformer. Which should be interesting...it will need to match a 5000 ohm load to a 0.89 ohm voice coil...unless I change the speaker, too...and then there is the problem of speaker mounting...
--
Ron Ramirez
Ferdinand IN
Posts: 7,286
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Joined: Dec 2009
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Just for grins you might want to hook up a
3.2ohm source to the 604 spkr just to see
if it works properly.
Glad you got it sorted out!
Terry
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Well...not quite.
I found a 37-602 audio transformer in my stash o'stuff over the weekend.
I checked it out with the ohms function of my DMM and its specs were very close to original.
So I installed it.
No joy.
The volume is still low.
And the kicker...I disconnected the audio transformer and ran it through my signal tracer, using its audio transformer and speaker as before... and the audio is still low. 
I checked voltages again...they are now higher than what I posted before. 
I've made an executive decision. I am going to tear this thing apart, gut it to the bare chassis (save for the RF unit), and completely rebuild it. New wiring and all.
I did find the 1st IF secondary's resistance was near zero, by the way...I'll replace that transformer in the course of the complete, radical rebuild.
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Ron Ramirez
Ferdinand IN
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I'm not real smart at this,,you know,,but ,,my 620 had a little problem like this,,,,it turn out to be 2 capacitors,,,one was shorted,,and the other was bleeding thru,,,,just saying,,,,just a pipe fitter
Posts: 13,776
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Joined: Sep 2005
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Good point, Kenneth...
However, I've already set a course on a total re-do of this set. The circuitry will be changed slightly, to match that of a 38-14 save for the front end.
The original schematic:
[Image: http://www.philcoradio.com/images/phorum...604_sm.jpg]
The modified schematic:
[Image: http://www.philcoradio.com/images/phorum...mod_sm.jpg]
Larger versions may be seen by following the links just below:
Original 604 schematic:
http://www.philcoradio.com/images/604.jpg
Modified 604 schematic:
http://www.philcoradio.com/images/604mod.jpg
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Ron Ramirez
Ferdinand IN
Posts: 13,776
Threads: 580
Joined: Sep 2005
City: Ferdinand
State, Province, Country: Indiana
Good afternoon, anybody, and Happy 4th...
I worked on the 604 some more today.
But first...Let me show you how I made a 602/37-602 audio output transformer fit underneath a 604 chassis.
You take the 37-602 audio output transformer...
[Image: http://www.philcoradio.com/images/phorum..._00027.jpg]
shine it up real nice... no, no, wait, getting carried away with a former wrestler and now action-adventure movie star's catch phrases. Anyway...
You have to remove the core from the shell. It's not too hard, really.
[Image: http://www.philcoradio.com/images/phorum..._00028.jpg]
[Image: http://www.philcoradio.com/images/phorum..._00029.jpg]
[Image: http://www.philcoradio.com/images/phorum..._00030.jpg]
Keep pulling the steel frame from the core until you are left with only the bare core:
[Image: http://www.philcoradio.com/images/phorum..._00031.jpg]
Now you will need to install the core into the frame of the original transformer. Notice how both are nearly identical in appearance? They also have identical electrical characteristics.
[Image: http://www.philcoradio.com/images/phorum..._00032.jpg]
Remove the core from the frame of the original 604 transformer...and install the core of the 37-602 transformer into the 604 transformer's frame.
[Image: http://www.philcoradio.com/images/phorum..._00033.jpg]
[Image: http://www.philcoradio.com/images/phorum..._00034.jpg]
Lengthen the leads as needed, and install in the 604.
[Image: http://www.philcoradio.com/images/phorum..._00035.jpg]
--
Ron Ramirez
Ferdinand IN
Posts: 13,776
Threads: 580
Joined: Sep 2005
City: Ferdinand
State, Province, Country: Indiana
So today, I made good upon my threat to completely re-do this radio.
After a couple hours of work, I had an almost bare chassis.
[Image: http://www.philcoradio.com/images/phorum..._00036.jpg]
[Image: http://www.philcoradio.com/images/phorum..._00037.jpg]
[Image: http://www.philcoradio.com/images/phorum..._00038.jpg]
I cleaned the chassis somewhat, and also removed the IF transformers. The 1st IF is suspicious - its secondary winding is reading near zero, and so that transformer will be replaced.
The next step is all new wiring under the chassis.
*****
In case you were wondering (or care) about the antenna terminal strip, I managed to glue it back together and I think it will be OK.
[Image: http://www.philcoradio.com/images/phorum..._00039.jpg]
[Image: http://www.philcoradio.com/images/phorum..._00040.jpg]
--
Ron Ramirez
Ferdinand IN
Posts: 384
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Joined: Mar 2015
City: Waxahachie, TX
Nice work Ron. I appreciate all the pictures too!
Crist
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Joined: Sep 2005
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Thanks, Crist!
And so the work begins (again)...
[Image: http://www.philcoradio.com/images/phorum..._00041.jpg]
This is what I managed to get done this evening before we left to go see a fireworks show...
--
Ron Ramirez
Ferdinand IN
Posts: 2,353
Threads: 92
Joined: May 2010
City: Clayton, NC
Frustrating when a relatively simple set kicks ones ______ (rhymes with "grass"). I feel your pain, as a model 3630 I am re-doing for the family "camp radio" refuses to work.
The re-do of your 604 should make it play!!
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