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Philco 37-630 question - Printable Version

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Philco 37-630 question - Hamilton - 04-19-2022

I just picked up a 37-630 and was looking through the chassis to see what caps/resistors I needed to order and noticed a couple of things that I hope the experienced members can clarify for me.

http://philcoradio.com/library/download/service%20info/wiring%20diagrams/vol2/split/Part21-Philco%20Wiring%20Diagrams%20Vol.%202.pdf

The first photo shows a .25 cap and what looks to me like a mica cap attached on top. I assumed from the base view of the parts list that these are, #34, a 400 ohm resistor and #35, a .05 cap. Both of these items look original so I’m confused as to how to proceed with replacing these two parts.

The next photo shows what I believe is #61, bias resistor, but the base view of the parts list show a wire wound resistor for #61. I’m new to this hobby so again I’m confused. I checked it and it read 230 - 10 - 38 ohms which compares well with the schematic. Again this part looks original so am I to assume that it wasn’t originally made with a wire wound resistor?

Lastly, #25 and #27 refer to “semi fixed” condensers. I haven’t come across this term before and I haven’t disassembled the radio far enough to locate these parts.  Can someone enlighten me as to what is meant by semi fixed?

My chassis is a Code 121. 

Thanks for your patience. I’m new to this hobby, just started on this radio and I know I’ll be back seeking advice again soon.?

RE: Philco 37-630 question - Mondial - 04-19-2022

The part that looks like a molded mica wired across the .25 uF cap is the 400 ohm wirewound resistor. Some low wattage wirewounds were made in that style in the 1930's. If the resistor measures near 400 ohms I would leave it alone. The original .05 uf was changed in later production to .25 uF to prevent oscillation of the IF amp as described in this service bulletin.

https://philcoradio.com/library/download/service%20info/service%20bulletins/Philco%20Service%20Bulletin%20Changes%204.pdf

The bias resistor shown in the photo is called a "candohm". It actually is a wirewound resistor which uses the chassis as a heat sink. Again if it measures the correct resistance its best left alone.

#25 and 27 are mica caps which are part of tuned circuits and affect the calibration. They should not be replaced unless definitely known to be bad.

RE: Philco 37-630 question - Hamilton - 04-19-2022

Thanks Mondial for the help. Very prompt as well, much appreciated! I'll surely be in need of the Phorum support later on.

RE: Philco 37-630 question - Hamilton - 05-04-2022

I’m in the process of updating some resistors and part #64 is a 9000 ohm 2 watt resistor. It’s out of value so I bought a 10,000 ohm 5 watt from Justradios. It was the closest I could find. Will that work as a replacement for me?

RE: Philco 37-630 question - Mondial - 05-04-2022

That should work fine.

Hamilton - Hamilton - 05-12-2022

I’m slowly working on this 37-630 but it may be beyond my limited schematic reading abilities. 

The speaker wire was destroyed when I got it so I have attached three wires, #1 black wire to Pin 3 of the 6F6,  #2 red wire to the 8 mfd #58 electrolytic and #3 yellow wire to the 12 mfd #62 electrolytic. 

I just don’t know where to connect them onto the speaker connection itself. The photo is there to show the positions I have them soldered too temporarily and I was hoping someone could tell me where each wire should be properly attached.

RE: Philco 37-630 question - MrFixr55 - 05-13-2022

Hi Hamilton,



You may have 2 connections reversed.

In these speakers, the field coil does double duty. It serves as the magnetic field and as a filter choke.

This is a little tricky but try this.

The point labeled 1 should be a terminal for primary lead of the output transformer. The black wire from the 6F6 Pin 3 (plate) goes here.

Terminal 3 on the speaker is a junction between the output transformer primary and the field coil. The wire that connects here should go to Pin 4 (screen grid) of the 6F6 and to a lot of B+ points in the Radio goes to this connection. This is typically also your 8uF cap (capacitor) but please trace your wires.


The last connection, #2 is the other lead of the field coil. The wire connected to this terminal should be connecting to the positive lead of the 12uF cap and also to the 5Y4 Rectifier cathode (filament) connection.

Inspect your connections at the Radio. If the Red Wire that connects to the 8uF cap also connects to pin 4 of the 6F6, the IF transformers and other points, then your connection has to be reversed with the yellow wire. If the Red wire that connects to the 8uF Cap also connects to the Rectifier cathode, then your speaker connections are good and your Cap connections are reversed.

If you got this wrong (# 2 and #3 reversed) and powered up the radio it will likely not smoke immediately, however, there will be 350V on the 6F6 plate and screen, higher voltage on the other B+ points and insufficient current through the field to develop the proper magnetism. The radio will likely hum and have low volume.

The cathode of the rectifier is usually at about +350VDC in most transformer powered radios of this vintage. This 350V connection connects to the first filter cap and to one leg of the field coil. The other leg of the field coil connects to the second filter cap, and is the source for B+ for the rest of the radio. The output transformer gets its DC B+ from this point. As the radio warms, this voltage usually stabilizes at 250VDC.

Finally, as the radio warms up, carefully inspect the 6F6. If you see a bright glow inside the tube that is not coming from the heater (filament) then shut down immediately. Your plate connection or output transformer is open and the screen is drawing so much current that it is glowing, can melt and short. This will be BAD.

Hope this helps.

Best Regards,

John "MrFixr55"

PS, Read on, I have corrected this entry after Hamilton's response, I had the numbering wrong but the concept is correct.

Hamilton - Hamilton - 05-13-2022

Thanks John but I may be even more confused now.

#1 black wire does go to Pin 3 of the 6F6.

You mentioned “Terminal 2 on the speaker is a junction between the output transformer primary and the field coil. The wire that connects here should go to Pin 4 (screen grid) of the 6F6” which it does have that connection to both the 8 mfd cap and Pin 4 of the 6F6. 

But later you write “Inspect your connections at the Radio. If the Red Wire that connects to the 8uF cap also connects to pin 4 of the 6F6, the IF transformers and other points, then your connection has to be reversed with the yellow wire.”

Why would I reverse them if they are connected where you said they should be. Please don’t take offense but I find that confusing.

#3 does go to the 12 mfd cap but I can’t check the cathode connection because I don’t believe a 5Y4G has a cathode. There is dark wire, can’t tell the colour, that is connected to the 12 mfd and it does go directly into the power transformer.

RE: Philco 37-630 question - MrFixr55 - 05-13-2022

Hi Hamilton,

No offense taken! No problem!! I misread your numbering. I am scheduled for cataract surgery next week.

Take 2!

I do think you have the wires switched.

In your picture, the connection labeled #3 is the junction that I described between the output transformer primary and the field coil. This is the connection that the wire to the 8uF cap, the 6F6 Pin 4 and the B+ bus should be connected to. In your text, you say that the red wire connects to the 8uF cap, the 6F6 Pin 4, et al, and the yellow wire is connected to the 12uF Cap and Rectifier cathode. If this is the case, swap connections. Connect the red wire to Point 3 and the yellow wire to Point 2

For a 5Y4 Rectifier, the filament is the cathode. This is referred to as a directly heated cathode. The use of the term filament or cathode are both correct.

Let me know if this helps. If not, I can draw a pictorial, but it will take me time, as I will have to scan and e-mail. I am retiring, but still working, getting eye surgery, have Church commitments, have to put grab bars in a bathroom for an elderly neighbor and have to fix my car, all this weekend and upcoming week, but will be happy to do the drawing if you need it. As they say, a picture is worth 1000 words (or 4000 of my words).

BTW, the other 2 wires coming out of the field coil are known as the "hum bucking coil. This is in series between the output transformer secondary and the speaker voice coil, and is phased to e 180 degrees out of phase with any AC component in the field coil.

Best Regards,

John, MrFixr55

RE: Philco 37-630 question - GarySP - 05-13-2022

John, best of luck with your cataract surgery. I had mine done last year... nothing to it! Take care and BE HEALTHY! Gary

RE: Philco 37-630 question - MrFixr55 - 05-14-2022

Hi Hamilton,

I have corrected my original post. In addition, the following may be helpful.

In the Link to the schematic for this set from the Philco Library, there is a page showing the speaker connections. The wire color is different from your present colors, and the originals are likely faded to non-recognition anyway.

The wire labeled green connects to the 6F6 plate. The wire labeled white goes to the 8uF Cap, 6F6 screen grid and other B+ points. The wire labeled green / white goes to the 12uF cap and the 5Y4 cathode (filament).

Based on you description in your post that the red wire goes to the 8uF cap, 6F6 screen and other B+ points and that your yellow wire goes to the 12uF cap and 5Y4 cathode, you need to reverse your red and yellow wires. Your black wire is in the correct connection.

Hope that my correction to the original post, next post and this post clarifies the situation.

Good luck. This should be a nice radio when you finish restoring it! Amazingly, in the 17 years between the introduction of broadcast radio and 1035, the circuits that this radio uses became sufficiently mature, that it is the basis of most radios and other than style of tube (Standard, Octal, Loktal, Miniature, etc.), and the elimination of the power transformer and field coil, the circuit is substantially the same until the end of production of vacuum tube radios in the late 60s.

Best Regards,
John "MrFixr"

RE: Philco 37-630 question - Hamilton - 05-14-2022

Thanks John. Much appreciated and best of luck with your surgery!

RE: Philco 37-630 question - MrFixr55 - 05-16-2022

Hi GarySP and Hamilton,
Thanks for the wishes, prayers, etc. And Prayers to Ron and all who are fighting illnesses, old age and other pain.

Kindest Regards,

John "MrFixr"