I am not too versed in Philcos and could use some basic help. I just picked up a very nice 37-670 yesterday and have no plans to power it up until after a full recap/restoration, etc. But just going over the chassis during my initial inspection gave me a bit of worry.
The radio calls for a 5X4 rectifier. The tube in the transformer socket is a 5U4. I know these are wired differently, but since the tube socket is part of the transformer I can't go underneath to see if someone in the past modified the wiring to fit a 5U4 tube.
Can anyone tell me, off the bat, the right way to determine whether or not the socket's been modified. I know, a basic question but I'd rather ask than go full speed ahead and screw something up
I found already though that a few of the electrolytics have been swapped out and JOY who ever did it paralleled them right into the original electrolytics. Sweet.
Thanks for the help everyone.
Ted
Bristol RI
(This post was last modified: 12-31-2014, 09:01 AM by Diverted.)
You have more concerns than 5x4/5u4 substitution. You can check that out with a tube manual or Duncan Amp web site.
Your 37 has the philco wire problem, hidden caps in the bakelite and IF cans and bad electrolytics that may have been wired wrong.
I would check the continuity of all major parts, power transformer, output transformer, IF's, all osc. and ant coils. Then I would check resistors for opens and high values. Then I would replace all caps. Then I would make sure wiring is safe.
Much later, when you are ready to power up, I would use a variac or a dim bulb device and heavily fuse the power transformer. These things are hard to get and expensive.
The 5X4 and 5U4 are wired differently. They are NOT pin-to-pin interchangeable.
Just checked Sylvania tube manual on-line.
Chuck
(12-30-2014, 02:55 PM)Diverted Wrote: Hi folks,
I am not too versed in Philcos and could use some basic help. I just picked up a very nice 37-670 yesterday and have no plans to power it up until after a full recap/restoration, etc. But just going over the chassis during my initial inspection gave me a bit of worry.
The radio calls for a 5X4 rectifier. The tube in the transformer socket is a 5U4. I know these are wired differently, but since the tube socket is part of the transformer I can't go underneath to see if someone in the past modified the wiring to fit a 5U4 tube.
Can anyone tell me, off the bat, the right way to determine whether or not the socket's been modified. I know, a basic question but I'd rather ask than go full speed ahead and screw something up
I found already though that a few of the electrolytics have been swapped out and JOY who ever did it paralleled them right into the original electrolytics. Sweet.
Thanks for the help everyone.
I forgot, about the power transformer, some of them had the "rubber" wire and should be inspected, this may require you to remove the transformer from the chassis and sleeve or rewire it. You could check for socket mods at that time. My guess is that someone just plugged a tube in to see if radio powered up. I really don't know whether that is enough to short the transformer or maybe in combination with the electrolytic "redesign" took the transformer out. Best to chech the big ticket items first to see where you stand!
regards, millievolt
Thanks Millievolt. Maybe I should have been clearer. As I wrore in the original post, I do not plan to put any power to this radio until AFTER a restoration including electrolytics, caps, resistors cleaning etc. I wanted to know about the rectifier and transformer issues now so, on the chance the xfmr is bad, I wouldn\'t waste time starting a restoration on a dead radio. Rest assured everyone, I will do a a full work over; I just wanted some help on the 5U4 issue for now. Thanks!
(12-30-2014, 03:25 PM)millievolt Wrote: You have more concerns than 5x4/5u4 substitution. You can check that out with a tube manual or Duncan Amp web site.
Your 37 has the philco wire problem, hidden caps in the bakelite and IF cans and bad electrolytics that may have been wired wrong.
I would check the continuity of all major parts, power transformer, output transformer, IF's, all osc. and ant coils. Then I would check resistors for opens and high values. Then I would replace all caps. Then I would make sure wiring is safe.
Much later, when you are ready to power up, I would use a variac or a dim bulb device and heavily fuse the power transformer. These things are hard to get and expensive.
Not sure what "Philco wire problem is" but if it is the rubber insulation one, it is either not present in 1937 radios or is in very limited use.
Otherwise Philco cloth covered wire is as good (or as bad) as anyone else's and so far have not given me any grief.
Starting 1940 or around, yes, rubber insulated, badly cracked.
(12-30-2014, 05:27 PM)morzh Wrote: Not sure what "Philco wire problem is" but if it is the rubber insulation one, it is either not present in 1937 radios or is in very limited use.
Otherwise Philco cloth covered wire is as good (or as bad) as anyone else's and so far have not given me any grief.
Starting 1940 or around, yes, rubber insulated, badly cracked.
Thankfully, this radio has not a lick of rubber wiring It's all cloth, and not cracked. Generally in really nice shape. Thank God! I have gone through that stuff with the one other Philco I did (42-380) and a bunch of early 40s Zenith sets. Stuff's brutal!
Just took the radio out of the cabinet. So far, so good. Tested field coil, AO transformer, Shadow meter coil. All three good. Only had a few minutes before dinner, so I'll get to the rest when I can.
Ted
It should be easy to check if it's been rewired by checking where the filament pins are wired.
According to my book filament pins are:
5U4 has them on pins 2-8
5X4 has them on pins 7-8
The wrong tube shouldn't hurt anything here it just won't light up.
Just check with the tube out (no power), there should be pretty low ohms readings when you find the right ones. Remember these are only 5volt windings. But watch out if you power it up and check voltages there will be very high voltage too!
!!!!!!!!!!!!!!!!!!!RESISTANCE IS FUTILE!!!!!!!!!!!!!!!!!!!!!!
/\/\/\/\/\/\/\/\/\
(12-30-2014, 07:14 PM)OZ4 Wrote: Ted
It should be easy to check if it's been rewired by checking where the filament pins are wired.
According to my book filament pins are:
5U4 has them on pins 2-8
5X4 has them on pins 7-8
The wrong tube shouldn't hurt anything here it just won't light up.
Just check with the tube out (no power), there should be pretty low ohms readings when you find the right ones. Remember these are only 5volt windings. But watch out if you power it up and check voltages there will be very high voltage too!
Thanks Chris! I will wait a while before I start digging in; replacing out electrolytics at the very very least, and fixing some obvious problems (like a cracked resistor I found).
It's very very encouraging to know though that the wrong tube shouldn't cause any larger issues. To me that means that either (1) the last person swapped that in, didn't get anything and stored the radio or (2) the socket's been rewired. If that's the case I would like to wire it back to the appropriate 5X4.
One question: How do I access the underside of the rectifier socket? I've never dealt with a radio that had the rectifier incorporated into the transformer shell.
I have never worked on one of those transformers like that one. I would bet it's not been rewired. Too much trouble. looks like you would have to take the top cover off the transformer. Back in the day it would be a lot easier to find the right tube.
!!!!!!!!!!!!!!!!!!!RESISTANCE IS FUTILE!!!!!!!!!!!!!!!!!!!!!!
/\/\/\/\/\/\/\/\/\
No rubber to worry about in the 37 models.
If you wire pins 2-7, 3-4 and 5-6 you can use either tube so check continuity between those pins or just install a 5X4. They are the same electrically. You can remove the top nuts and remove the top transformer bell cover to get to the wires.
Sounds like the pin-out of a 5X4 is like that of a 5Y4, so 7-8 for the filament. I would not make the assumption that whomever put the 5U4 in there knew what they were doing, anybody can stuff a tube in a socket.
Regards
Arran
Hi again. This is an edit to a previous response I had about the filament not having continuity. Well it does; I pulled the cap off the rectifier and jiggled the socket and got ohms! So a little remedial soldering is in order.
MOVING ON to other things, my next question has to do with candohms and one particular resistor that appears to have been swapped out.
On the schematic, resistor 82 is listed as a 5K wirewound. On the chassis, it's a candohm-style resistor bolted to the chassis. it runs between the field coil and the 3mfd electroytic to ground. Looking last night, I noticed that the field coil side of the resistor was disconnected. ?? Ohmed it out and it read many megs. OPEN. So I looked around and the only other likely replacement resistor I could find was an aftermarket Ohmite 15K, 10W tied in on one end to the middle lug on bakelite capacitor number 58. The other end goes to ground. That middle is used as a tie in post to the field coil, so I'm thinking this resistor is a replacement and whoever put it in just found that to be a convenient spot to tie it in.
But it's a 15K! Three times what's called for on the schematic. Obviously I'm going to replace it with a five. But how many watts should I use?
Similar question for the five section candohm (part 82). Several sections are quite high so I'm going to replace it. But I don't know what wattages to use, and space is at a premium. Anyone have any idea what wattages I should use for each section? Thank you!
Ted
Basic ohms law comes into play here. looks like The candohm #83 is the one you are talking about
I just did the same thing on a 38-10 I have been working on.
It's being use to create the negative bias voltages and it's carrying all the current of the power supply.
This radio has a lot going on so it's going to use a lot of current with push pull output and driver tubes.
The book states that typical current for that rectifier tube is 250MA.
So the small resistor sections 22 and 18 ohm I would use 2 watt resistors and the 146ohm section I used a 20 watter. There going to get hot.
Once you get it up and running be sure to measure the voltage drops and figure the power being dissipated in each.
I was told to always double the size of the resistor for the wattage calculated.
I should defer here to the more experienced wizards of the phorum.
Good luck
!!!!!!!!!!!!!!!!!!!RESISTANCE IS FUTILE!!!!!!!!!!!!!!!!!!!!!!
/\/\/\/\/\/\/\/\/\
(12-31-2014, 08:03 AM)Diverted Wrote: Hi again. This is an edit to a previous response I had about the filament not having continuity. Well it does; I pulled the cap off the rectifier and jiggled the socket and got ohms! So a little remedial soldering is in order.
MOVING ON to other things, my next question has to do with candohms and one particular resistor that appears to have been swapped out.
On the schematic, resistor 82 is listed as a 5K wirewound. On the chassis, it's a candohm-style resistor bolted to the chassis. it runs between the field coil and the 3mfd electroytic to ground. Looking last night, I noticed that the field coil side of the resistor was disconnected. ?? Ohmed it out and it read many megs. OPEN. So I looked around and the only other likely replacement resistor I could find was an aftermarket Ohmite 15K, 10W tied in on one end to the middle lug on bakelite capacitor number 58. The other end goes to ground. That middle is used as a tie in post to the field coil, so I'm thinking this resistor is a replacement and whoever put it in just found that to be a convenient spot to tie it in.
But it's a 15K! Three times what's called for on the schematic. Obviously I'm going to replace it with a five. But how many watts should I use?
Similar question for the five section candohm (part 82). Several sections are quite high so I'm going to replace it. But I don't know what wattages to use, and space is at a premium. Anyone have any idea what wattages I should use for each section? Thank you!
Ted, Believe the 4 section candohm is 196+18+22+22 = 258 ohms total used for the (-) negative control grid biasing of the audio tubes, etc. Use a 200 ohm to replace the 196 ohn section. Will make very little difference. The schematic and associated info. from Nastalgia Air shows about -33VDC developed on the C.T. of the high voltage transfomer feeding the candohm at 115VAC in. So say at 120VAC may be worst case -35VDC. Since this is a series string resistor the current to ground is common thru the four sections. Once you know the I. you can calculate the power rating of the individual resistors...P=IxIxR. I=E/R. I = 35/(200+18+22+22)= ~.134 amps. or 134 mamps. For the 200 ohm section...P= (.134)(.134)(200)= ~3.6 watts. I would use a 200 ohm, 10 watt resistor. You can calculate the power rating needed for the other three sections. The result would indicate that 1 watt resistors should be sufficient. R82 is a 5600 ohm bleeder resistor in parallel with the 3 ufd filter cap. on the B+ buss to the driver tubes, 6J5's. The schematic data shows about 235vdc at 115VAC into the set. I would think that the value of this resistor is not critical as it looks to me to mainly be used for discharging the B+, and to minimize pops, at turn on and turn off of the set. The B+ is primarily determined by the filter choke, capacitors, field coil in the power supply circuit. Say you get 245vdc on this B+ buss at 120VAC. The power dissipated by R82 would be P=ExE/R = (245x245)/5600= ~10.7 watts. Holy Toledo no wonder in burnt out . A 5600 ohm resistor here would require at least a 20 watt rating. I can see why someone put in a 15K resistor which I feel would have essentially no effect on the circuit operation. A 15K would limit the current rating needed to 10 watts. If you wish to stay with original values then a 20-25 watt resistor is needed. I seems that R82 accounts for slightly less than 10% of the power dissipated by the entire set if my calculations are correct. Good luck, John
It's all cloth, and not cracked. Generally in really nice shape. Thank God! I have gone through that stuff with the one other Philco I did (42-380) and a bunch of early 40s Zenith sets. Stuff's brutal!
. A 5600 ohm resistor here would require at least a 20 watt rating. I can see why someone put in a 15K resistor which I feel would have essentially no effect on the circuit operation. A 15K would limit the current rating needed to 10 watts. If you wish to stay with original values then a 20-25 watt resistor is needed. I seems that R82 accounts for slightly less than 10% of the power dissipated by the entire set if my calculations are correct. 
Good luck, John![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
