Philco 49-602; I are stymied - Printable Version

Philco 49-602; I are stymied - Printable Version

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Philco 49-602; I are stymied - Joe Rossi - 05-21-2026

I finished recapping and re-resitoring my 49-602. It initially fired up fine, but I needed to replace the 4PDT slide switch for battery/AC selection. Surgery went well, but when I plugged it in to the Variac I got nothing. No 120VAC. I checked the output of the Variac and it measures 120VAC at the output. I checked the continuity of the NEW line-cord, it is OK. I checked each individual connection to the new 4PDT switch to make sure the hook-up is correct. I triple checked it. It is correct and functions correctly measured with the DVM. The tubes check good. I replaced the selenium rectifier with a 1N5408 (overkill, I know) and compensating resistor. I checked the sets power switch (twice) and it works as designed. I checked every solder joint. No cold joints or loose or broken wires. There are no open circuits. Ay-yi-yi! Icon_crazy

I have attached the schematic for perusal. Any thoughts? Thanks folks! Joe

RE: Philco 49-602; I are stymied - morzh - 05-21-2026

Joe,

I will not tell you what else to check.
My personal rule is this: if something worked BEFORE I did something and stopped working immediately AFTER, I will keep investigating WHAT I'VE DONE until I prove to myself this is not the culprit, of which the chance is maybe 1%.
Either this, or something you touched along the way.
Retrace the steps.

RE: Philco 49-602; I are stymied - MrFixr55 - 05-21-2026

Hi Joe,

+1 on Morzh's statement. Try the following.
Radio unplugged, Bat / AC switch in AC. Power switch on. There should be continuity between one prong of the power cord and the anode of the rectifier. There should be continuity between the other prong of the power cord and the common negative of C101 A, B and C.

Next, plug the radio in. There should be 120V across C101A. Ther should be 65 V across C101B. There should be 7.5V between Pin 7 of the 3V4 Audio Output Tube and P1n 1 of the 1R5. If the voltage is high, then one or more tube filaments are open, the string may be interrupted by miswiring, etc. It is important to note that a tube may have opened due to hi voltage from the power supply.

RE: Philco 49-602; I are stymied - radiorich - 05-22-2026

Hello joe,
I also agree with Morzh's statement. I’ve been there more than once, taking plenty of photos, marking wires and boards, and making drawings to help. I always check and double-check everything before powering it back up.

Sincerely Richard

RE: Philco 49-602; I are stymied - Joe Rossi - 05-22-2026

Mike, Mr Fixr, & Richard,

I applied the ecellent advice given, and voila, no continuity between the line cord and the rectifier. So the last thing I did was replace the 4PDT switch (S101). Result was: The original Philco switch's detent must have gone bad at some point and 'someone' wired it so it would work on AC only. Oh, what a fool (or Phool) I am. I didn't follow the schematic and went by how it was wired. Once bitten, twice shy. I'll be working on the rewire sometime today and I'll get back with the results. A guy can't go wrong with friends like you'all.

Thanks, Joe

RE: Philco 49-602; I are stymied - RodB - 05-22-2026

Hi Joe,

One thing to be cautious about is that the filament voltage of 7.5 volts is derived from a voltage divider from B+ (R101A and R101B). If you replaced the selenium rectifier with a silicon diode (1N4007 or equivalent) the B+ will now be about ten volts higher. In addition, this circuit was designed for 117 volts from the mains and my house gives me 122. That's an additional five volts. You should consider increasing R100 to compensate for the increase. I also add a 1 watt zener diode to the 7.5 volt connection point to protect the filaments.

RE: Philco 49-602; I are stymied - morzh - 05-22-2026

Whenever a selenium rectifier gets replaced by a diode, there always should be a series resistor used.
If there has been one, it gets increased.

Increase of the resistor, considering the current stays more or less the same as it is defined by the total resistance which is all filaments plus that dropout resistor, will be accompanied by an additional power dissipation (proportional to the increase), so if you simply replace the old resistor with the one of a higher value, increase the power rating by the same factor (say you replace an 80 Ohm 3W resistor with 120 Ohm one, then the power rating of the 120 Ohm will be 4.5W (round to 5W)).
If all this resistor does is being the ballast for the filament, I would then not use the Zener, instead of picking the value such that the voltage across the filaments is right where it should be at 120V.
Of course, Zener is also an additional protection, so it is a judgement call.

RE: Philco 49-602; I are stymied - Joe Rossi - 05-25-2026

Sorry for the delay in getting back on this. Life and Memorial Day interrupted. The saga continues. I found I had a misconnection on the new switch (S101). I fixed that. But still no voltage within the power supply. I rechecked my variac (Mike, I have the same one you have). The variac output plug was bad! I replaced that, and it is all good. I now have 120VAC going to the radios PS. Per Mr. Fixr's notes I should have the following voltage:

C101A s/b 120V, measues 117V. OK
C101B s/b 65V, measures 69.2V OK
7.5V between Pin 7 of 3V4 and Pin 1 of the 1R5, measures 21V. Ay-yi-yi, Not OK

I turned the radio off to save the tube filaments. And it did not produce sound or hissing.

I also measured the voltage after R102. The schematic says it should be 90V, it measures 110V. Not OK
I replaced the Selenium with a 1N5408, and added a calculated 135 ohms. These are two 2-watt resistors in series.

R100 = 55 ohms (replaced with a 62 ohm 1W), R101 is a candohm. R101A = 1250 ohms & R101B = 1210 ohms. All other caps and resistors have been replaced with new. Well, I'm closing my workbench down and will look at it afresh tomorrow. Thanks for all the help! Have a blessed Memorial day. Joe

RE: Philco 49-602; I are stymied - RodB - 05-25-2026

Better check the tube filaments before going further. They weren't designed to handle much over 1.5v.

RE: Philco 49-602; I are stymied - MrFixr55 - 05-25-2026

Hi Joe,

A blessed and meaningful Memorial Day to you also.

Try this:

Remove all the tubes. The voltage across the filament string is 7.5V. Current in the string is 0.05A. If E=IR, then R=E/I. So 7.5V/0.05A = 150 Ohms.

Remove the tubes and tack a 150 Ohm resistor best to use at least 5 W. between pin 7 0f the output tube (3V4) and Pin 1 of the convertor (1R5). Plug the radio in and measure the voltage across the resistor and the other power supply points. They should now match the schematic. If the voltage across the resistor is 7.5V +/- about 10 - 20 %, then then replace the tube(s) that have open filaments. If the voltage is significantly higher 9V or higher), then troubleshoot the power supply.

I assume that this radio never worked since you had it and since someone tried to fix this before, then only the Dear Lord knows what happened beforehand.

RE: Philco 49-602; I are stymied - radiorich - 05-25-2026

Hello joe,
I have seen that switch bad in a Philco before and someone doing the exact same thing soldering a wire across the switch it's self .

Sincerely Richard
P.S. hope eveyone had good day !

RE: Philco 49-602; I are stymied - MrFixr55 - 05-26-2026

More on my previous comment:

I think that the high voltages for the 7.5V and 90V are due to no load. Remember, that the heater string is part of that "voltage divider" that the junction of that divider is where the 7.5V is measured from therefore with the heater string open, the voltage at that junction is much higher.

Because the heater string is open, the tubes are not conducting, therefore, there is no load on the 90V supply. The 90V supply is high because of the same "Voltage Divider" theory.

Morzh has a great point to have a Zener diode across the output of the 7.5V supply. (Zener diodes did not exist when the radio was built.) To protect the diode and prevent noise, consider using a 9V diode. remember that excessive voltage causes excessive current that will short the diode. This is my reason for using one higher than the desired voltage. This is significantly higher than 7.5V but likely not enough to blow the tubes if the voltage increases. If the diode shorts, the tubes are protected and nothing else will likely burn up.

The fact that the observed reading of the 7.5V supply is 21V and not something much higher, is because there is a 30 uF cap and a 680V resistor between the center tap pf the 3V4 filament and the negative "rail" of the power supply, meaning that at least half of the 3V4 heater is good.

The filaments for these 1.4V miniature tubes are pins 1 and 7 for all of them. Therefore, you can "Ohm" the tubes to determine if one or more are bad.

When the set is working, the "glow" of these filaments is so faint, it will not be seen. Even in a totally dark room, the glow of the filaments is such a dull red as to be almost invisible. I accidentally operated one of these tube in a tester at 3V. The filament glowed almost yellow but did not burn out for the 15 sec that I had it on.

RE: Philco 49-602; I are stymied - Joe Rossi - 05-26-2026

Richard, Bad switch, Bad! The replacement switch is a Switchcraft 50212LX, got it thru Mouser. Couldn't believe that the switch was available. So, the 150 Ohms is to replicate the filament string? I measured the resistance (with the power off!) and got 271 Ohms, I measured continuity on each tube filament, and there is continuity in each one. Also popped them in my tube tester and each showed good. Should I still tack in the 150 ohms? The closest Zener I have is a 1N4735 6.2V 1W or a 1N5340 6V 5W. Would that work? If not I could purchase some. Thank you all and let me know. Joe

RE: Philco 49-602; I are stymied - MrFixr55 - 05-26-2026

I'm very surprised that you got 21 Volts with the tubes in. Check wiring. I'm glad that the tubes tested good. With 21V across 5 tubes, that's 4V per tube. The filaments should have been glowing very brightly at that voltage until they burned out rather rapidly.

For those following along especially if new to the hobby, I calculated 150 Ohms based on the Ohm's Law Formula R= E/I, (where R = Resistance, E = Voltage and I = Current). Based on the fact that each tube in the string is rated 0.050 Amps, the current across a series string is the same for each resistance in the string, and a total voltage of 7.5V across the tubes (Three 1.5V 5ubes = 4.5V; one 3V tube + the 4.5V from the 3 tubes = 7.5V, then 7.5V / 0.050A = 150 Ohms. A nice little chart for the formulae for Ohm's Law is reproduced below:

I think that there is a wiring or socket issue. If you individually measure the resistance between pins 1 and 7 of each tube, It should not total 271 Ohms. In fact, it should be a lot lower than 150 Ohms as most filaments have a much lower resistance when cold.

Use a Zener diode above 7.5V. Not much above but above. 9-9.5V tops. If you can get an 8.5V diode, that should be great. It is there for protection, not regulation. Correct resistor and capacitor values should give you the regulation that you need.

I would still try the 150 ohm resistor substituted for the tubes. This way, you can measure and troubleshoot without totaling out one or more of these tubes. If you get 21V with the tubes in place but 7.5 V (or so) with the resistor in place, then check the sockets and wiring. Something is wrong.

Hope this helps! Don't give up!

RE: Philco 49-602; I are stymied - Joe Rossi - 05-26-2026

Mr. Fixr, There are only 4 tubes in this radio. 3 of the tubes are 1.4v fil @ the 3V4 is 2.8v, = 7v. After I get cleaned up I will review the filament wiring and the sockets. Thank you, Joe