Problems with a Philco 5 tube radio

[tgunner]

I'm repairing one like this as a gift for someone, and I've run into a strange problem. Well first, I replaced all of the electrolytic's, including a bumblebee, and the C2 cap on the tuner. After this, the set would work faintly but then fade out. I found the 12BE6 tube to be the culprit and replaced it; no more fading after being on. Now the only way I can get good sound and reception from the radio is to use my fingers to bridge the chassis to the C-1A terminal on the tuner. The C-21 part is a mini-tuning capacitor for a "Special Services" station at about 3.2Mhz. Any ideas what could be wrong, or what I could do?

Update: I replaced another cap, C20 a .1uf flat plastic job which connected the B- to the chassis. Now, simply touching the C-1A terminal results in the best sound and reception. Whether or not the loop antenna is connected (where L2 meets the tuner) seems to not matter. Connecting the loop to the C-1A terminal sounds like it overloads the signal.

[Reece]

The loop is part of the antenna tuning circuit of the radio and must be connected. Be sure the loop has continuity. Did you replace all the paper caps?

C1B will adjust a station near the high end of the dial to read at the right number on the dial. Then C1A should peak reception of a weak station near the high end of the dial. Be sure to use a very weak station. There's nothing much on the "Special Services" band any more so maybe not worth doing much with.

If you have a signal generator the radio ought to be aligned per the procedure in NostalgiaAir for this set. If not, and if nobody has played with the IF transformers before you, then peaking C1B and C1A above just listening for max output ought to bring the set around.

[tgunner]

Originally Posted by Reece

The loop is part of the antenna tuning circuit of the radio and must be connected. Be sure the loop has continuity. Did you replace all the paper caps?

C1B will adjust a station near the high end of the dial to read at the right number on the dial. Then C1A should peak reception of a weak station near the high end of the dial. Be sure to use a very weak station. There's nothing much on the "Special Services" band any more so maybe not worth doing much with.

If you have a signal generator the radio ought to be aligned per the procedure in NostalgiaAir for this set. If not, and if nobody has played with the IF transformers before you, then peaking C1B and C1A above just listening for max output ought to bring the set around.

Thanks for reply. I checked the loop; it has continuity. I did replace all paper caps, as well as the multi-cap can, a bumblebee, and two flat plastic caps which had six dots on them.

I don't have a signal generator, so I'm kind of going blind here... just using local stations I know of. The set sat untouched for a long time, so I doubt the IF transformers have been adjusted. I tried adjusting the screw on C-1A and had no real change. C1-B did cause the tuning of a lower and higher stations from where I had it set ~1300khz. However, even after adjusting them, I still get no sound or reception unless I touch the C-1A terminal.

Update: I'm starting to think this might be a grounding problem. I tried the radio using a different plug, which I know was properly grounded unlike the first. Here, depending on which way I plug it in, I get different results. One way, the set works OK when I touch or bride C-1A and chassis and the other way, the sound is muddy and I feel a tingle if I try to bridge C-1A and chassis. I took a volt reading and came up with 5.5V AC.

[Reece]

Don't think the AC plug is the problem. C1A should definitely greatly peak a weak station at the high end of the band. Right now NostalgiaAir is down but schematic can be seen at

http://techpreservation.dyndns.org/s...53-561_80.djvu

Check that the loop is connected properly. Per the schematic, the outside winding of the loop goes through a 944 mmfd. (or pf) cap shown as C2 on the pictorial to the stator of the rear section of the tuning cap. Also through the bandswitch when in broadcast band position the outside winding gets a direct connection to the rear stator. The inside winding of the loop connects directly to the tuning cap rotor (frame.) On the pictorial attached to the schematic I don't see that wire shown, and wonder if the inside of the loop got inadvertently connected to the outer end of L2? It is connected there, but also perhaps through internal wiring to the cap frame? Hard to tell without tracing the underchassis wiring.

What were the two rectangular caps you replaced, and what values? The old ones may be OK.

[tgunner]

The two flat caps were C20, .1uf. B- to chassis, and C2 - 944uuf in the tuning area.

I see what you mean about the inside and outside loop of the antenna, but when I opened the set up for the first time, there was only one wire from the outside loop to the tuner terminal. The inside loop terminal appears to have never been soldered to, but I do see from the schematic that it should connect C-1B? I'll try that.

Update: Ahh! Connecting the outside lead to where it was, and attaching the inside loop winding to C-1A fixed all problems! I wonder how the set ever worked before I got it... Now, next task - attach a polarized cord.

[Reece]

Congrats!

Loop antennas are part of the tuned antenna circuit. It takes a coil and a variable capacitor connected in parallel to tune it, and the loop serves as the coil.

[tgunner]

Originally Posted by Reece

Congrats!

Loop antennas are part of the tuned antenna circuit. It takes a coil and a variable capacitor connected in parallel to tune it, and the loop serves as the coil.

I still find it weird that it was never wired like schematic shows.
Anyway, now that I have the signal strong, whenever there was bass in the sound, I heard a popping or clipping noise. I remembered that I had removed the original Sylvania 35C5 Audio Output tube, and replaced it with a spare Zenith one I had. Swapped in the original, and no more popping!

Thanks for your help, Reece!

[Reece]

You're welcome, now on to the next project! Have fun.

[Robert Grant]

That is one strange tube complement!

It looks like the typical "all American five-miniature tube" arrangement, only the 50C5 in the audio out has been replaced with a 35C5.

It use to be common to use the 35C5 in slightly more expensive radios with a three-gang tuner and an RF stage (usually another 12BA6).

Here, using a 35C5 in place of a 50C5 necessitates a ballast resistor whilst slightly reducing audio output - with no benefit!

[wa2ise]

Originally Posted by Robert Grant

Here, using a 35C5 in place of a 50C5 necessitates a ballast resistor whilst slightly reducing audio output - with no benefit!

Looked strange to me as well. It could be something as stupid as the guy in purchasing at the factory got a really good deal on 35C5s, that was so good that the extra resistor cost added was still less than 50C5s.

Or maybe this radio was intended for use in Japan around the time we were still occupying them after WW2. Their powerline is 100VAC vs our 120VAC, so a 35C5 instead of a 50C5 would work. If that's the case, I'd change the 35C5 to a 50C5.

[dieseljeep]

If you look at the schematic you'll find R12, which is a so called "tube saver resistor" .I'd get one of those in with the complaint that it takes too long to warm up. I would just jumper it out and install a 50C5.

[Reece]

Most tube and lightbulb burnouts are on initial turnon surge. Today probably nobody is going to complain about warmup time (how would most people know what's normal with a tube set, having no experience with tube equipment?) and saving the tubes is important now with no more being made, even though there are still lots of them around. You could put in a 50C5 anyway and thus run the tubes on a little lower voltage with the resistor still in, and the tubes would be happier still. I usually put in a CL-90 inlet surge limiter in sets which slows things down a little (20 second warmup) and cuts a couple of volts off the line voltage, which is generally a bit higher now than when these sets were young.

[dieseljeep]

What I meant on that reply that resistor would change value and not respond properly. It is a NTC resistor. 800 ohms cold, 100 ohms hot. After they got old they would have too high of a voltage drop. I worked on these when they fairly new and they belonged to the original owners.

[tgunner]

Originally Posted by Robert Grant

That is one strange tube complement!

It looks like the typical "all American five-miniature tube" arrangement, only the 50C5 in the audio out has been replaced with a 35C5.

It use to be common to use the 35C5 in slightly more expensive radios with a three-gang tuner and an RF stage (usually another 12BA6).

Here, using a 35C5 in place of a 50C5 necessitates a ballast resistor whilst slightly reducing audio output - with no benefit!

Yes, the Zenith radio I pulled that other 35C5 from was an early 60's AM-FM set. It had the two 12BA6's you speak of. Everything with this Philco is working nicely now though, and I plan to leave it be! It's funny, even the original dial lamp still works and comes on brightly after 20-30s. I guess those tube-savers do their job...

[Reece]

Aha, dieseljeep, now I get it!