40s Philco 40-145 BUMMER!
 

We live and we learn. I lucked out and bought this rather nice art deco Philco several years ago in working condition for a song. Even if a radio works, I like to remove the chassis and blow the dust out and clean the tubes and pots, so I did. Well, like an idiot I did that and replaced the tubes with two in swapped positions! I am fairly certain that I had the 7Y4 rectifier in the 7B5 output socket and vice versa.

NOT a good result! The radio was only plugged in that way for a matter of seconds as all it did was produce a full volume hum. Once I realized what I had done I tested the tubes and put them in the right sockets, but the radio has never been right since. Back then I went ahead and replaced the filter capacitors hoping that what I was hearing was just a coincidental failure of the filters in a very old radio. New filters helped with the hum, but the radio still fails to pick up anything and often takes to loud motor-boating until I touch one of four or five antenna terminals which by the way are not connected to their spaghetti mess of wires.

I also found the .5 Meg volume pot to be open due to worn away carbon at both outside terminals, so I replaced that. What noise I it produces if I tamper with the antenna terminals does not seem to be volume adjustable. I guess swapping in a rectifier to where an output tube is could have done anything. Nothing smoked I will say, but that doesn't matter really, but without burning up a resistor or capacitor you would almost think that no damage was really done to the components.

I hope to get this one going as it is a really nice piece with the pushbuttons and all. I'm so mad at myself because I can remember trying it when I bought it and it played wonderfully on AM and Shortwave.....:tears:

Edit: You did say you tested them after the oops. For more than just emissions? I still feel like the output tube took internal damage in the process.

Have you... tested... the output tube after your lapse of cognizance? :scratch2:


Motorboating and lack of volume control could be a burnt up 7B5. ~200VAC (actually probably ~400VAC) applied across the grid and screen will arc or melt them... Plus ~200VAC grid to cathode probably has similar results...

Yes, I tested the tubes after my idiotic mistake. :sigh: LOL! In my defense, I just bet I'm not the first person to put a tube in the wrong socket!:scratch2: The 7Y4 rectifier tested odd in that it would go high on the scale initially, then back way off into the red or bad. A replacement not any other rectifier that I have tested ever tested quite that way. I am going to try it in the working set I borrowed it from just to note the effect. Also, I jumped a few small value caps as everything is original old waxies. No differences there...

Earlier I hooked up the two sets of antennas as I noted that they had trimmer capacitors on them and I knew that Philcos of this design are notorious for having issues without the antenna hooked up. I was startled by the sound (finally) of some evangelist screaming about the voice of God rushing from my speaker at full volume! So, I am getting somewhere.

Evidently I wired the volume potentiometer up wrong as its full volume all the time. I checked the pot of course and it's within specs. The old one was fully open as I cracked the lid in hope of repairing it, but the carbon was just eaten away at both ends. I created this post mainly to tap this wonderful pool of knowledge about what could or did happen in such a case. Also, having a few nice old Philcos' I thought that others interested in them might chime in with other good info., stories or whatnot.

I'll update as progress continues.....

Still more luck. I discovered that I forgot to ground the potentiometer. The radio now plays on AM. There is still "Police" and Shortwave that I have not really gone through much, but this set has come a long way.

Thanks NoPegs for the tips. I thought perhaps these radios would be more popular than the low feedback dictated here. Anyway, I am happy with all the results.

You'll find a whole lot more response for radio issues over at http://antiqueradios.com/forums/index.php

.

Yeah, I really have hardly ever used the radio forum here before. I would go back to audioKarma for that or another site. I have been more interested in television than my old radios for quite a while, but I started noticing more and more of my radios needing work when I do my occasional power ups and blow the dust out.

So that led me to doing several radio jobs, but this Philco was an old project put aside and it seemed to have a lot of issues, so I thought it was worth a thread. Now back to my Zenith "roundie" color TV.

Dump the 7Y4
 

A 7Y4 is like a 6X5 or an 84/6Z4, there is 300+ VDC on the indirectly-heated cathode, which is wrapped around the 6.3 V heater, one side of which is grounded. One arc across and these tubes will fry your transformer.:nono:

Disconnect and cover or remove the tube socket and add two 1N4005 silicon rectifiers and an appropriate wirewound resistor before the electrolytic caps and field coil.

I have two 1941 Zenith console radios, both had original thier power transformers smoked due to these lousy full-wave rectifier tubes. :sigh:

Just a thought on minimizing the risk of a bad failure, nothing more.

Another option is to disconnect the plate and cathode leads from the socket and add terminal strips for the 1N4007 (I like the 7s better) diodes so the above chassis appearance remains the same and you still have a glowing rectifier tube.

Yep, I have a Zenith 8S359 that uses the 6X5. Recapped but almost no volume. Gonna take another crack at it in the fall......

This is the best idea for turning your all tube rig into a sort of hybrid with obvious pros' and few cons' that I know of. You get to keep the correct appearance and you will not have to worry about getting a (the right) resistor to go where the heater used to be. Not such a big deal in a parallel arrangement type heater string, but in a series circuit all voltages dropped MUST add up the the source voltage or there will be a problem. I'm not sure what tolerance there is in a real world situation, but mathematically, by the use of Ohm's Law it is spot on.

In a parallel set if you delete the rect. tube leave the heater connection for that socket unloaded it will likely have no negative effects, and the power transformer will run cooler (which can make a big difference if it runs hot).

Well, I'm glad my old Philco has new life and that I made this thread because I never knew that certain vacuum tube rectifiers spelled potential doom for our old radios. Seems like I have a late 30s Silvertone working on almost all original parts including a 6X5. I have always been proud of my working original sets that I have a few of, but I can't risk losing a power transformer over pride.

Seems like I was researching that set a while back and someone mentioned potential trouble with the rectifier, but I didn't pay any heed as mine has worked fine since my grandmother was 20! Maybe time to rethink this now that she is 96!?!?!

Ehh, sneak a tiny axial fuse into the mix if you don't want to change the tube lineup. I can't blame you on that aspect of things.

Better make that two, one for each plate lead from the transformer.
If you want the look of a lit rectifier tube, just disconnect the plate pins 3,5 and cathode pin 8 leads from the tube socket and put the 1N4007s in there, and two 100 ma. fuses of course.

I think that NoPegs was supporting my desire to keep things original and have a working 6X5 and add a fuse. Would I use two fuses as you suggest at 100 mA. with the working tube and still be protected. I didn't know if you were suggesting 100 mA. for the semiconductors or if that would apply to whatever device is in that circuit.

I think that fusing on the tube plates would be the same, a 1/10 amp fuse.
If you measure the operating current on the 340 volt B+ supply, its about 70 mA.
In my profession, adding 20% and fusing at that value is standard design practice.

I just acquired another 1939 Zenith radio, chassis and speaker only, that has a 6X5 in it.
No testing yet, but the transfomer is physically smaller in comparison to a typical Philco.

I just had a brainstorm on the 6X5 issue, since I'm studying the schematic of my 20A1 chassis Admiral and it has the silly 6X5GT on the LV side...

Could I use the guts of a "brightener" (Or preferably the type designed to work-around H-K shorts without the whole voltage changing part.) to just float the heater supply to the tube? Alternative options are just find a small >600mA 6.3v transformer core and tuck it up underneath the lower chassis. (There's so much room that I feel like I could tuck an entire AA5 set in there too!)

For my 1941 Zenith chairside I'm probably going to go with the multiple fuses option, since that chassis is much more dense than the lower on the Admiral.

Getting the filament off ground potential solves the problem. Great idea