[regel_1999]

I bought a Philco 42-327 code 121 as a beginner's project. I've replaced all the caps to include the electrolytics and one tube because the heater element was opened. The trouble is this: I assumed the other tubes in the radio were either replaced properly or original to the radio. What I think now is that the tubes were not the original tubes because 1) all but one are not Philco tubes, and 2) the radio still only produces a loud buzzing sound with 170.3 volts dc at the speaker wires. Furthermore, I think the rubes were replaced with incompatible tubes.

My last problem is that the labels on the top of the tubes are rubbed off and I can't identify 4 of the six tubes. Two of them are supposed to be 7B7's and they don't look anything like each other and neither has a label.

My question is this: Could the incorrect tubes produce a steady loud buzz from the speaker and/or the 170vdc at the speaker terminal? If so, should I just break down and replace all the unknown tubes with new tubes, even though they work? Is there a good way to tell which tubes are which?

Thanks for your help in advance!

-Brandon

[Ron Ramirez]

Hi

The steady buzz is usually caused by bad electrolytics, but you say you have replaced them. Could you have installed them backwards? (It happens, even to us old timers occasionally.)

Do you have the schematic/service data? If not...this is something you must have, especially as a beginner. Contact Chuck for the best possible copy of this data.

http://www.philcorepairbench.com/schematics.htm

It can be difficult, and sometimes impossible, to tell what type a tube is if the numbers are gone. Try this: Rub the top of each tube on top of your head; the oils in your hair can sometimes make the numbers visible enough to be read under bright light. If you're bald, forget this trick.

Incorrect tubes in sockets can wreak havoc with the circuitry, but you shouldn't have 170 volts DC at the speaker, not even at the field coil wires. The field drops 25 volts across it, and an additional 5 volts is dropped across the audio output transformer primary.

Be careful! That is an AC/DC set (transformerless); you could be electrocuted if you do not know what you are doing! Of course, you could be electrocuted when working on a set that uses a power transformer; but in an AC/DC set, there is no isolation from the AC line so the danger of shock is even greater.

[Carl Travis]

Sometimes, the tube numbers can be made visible by breathing on the tubes, if you can't use Ron's hair method.

[BILL]

Disconect your antenna, If the buzzing goes away you've got something in your house causing interference, touch lamps dimers or ?

[regel_1999]

The hair tricked worked quite a bit. I was able to identify three of the four unidentifiable tubes. The fourth at least looks like the pictures on the internet of a 7c6 and it was in the 7c6 socket. the 7b7's were in not in the right place though.

I disconnected the antenna and the buzzing is still there, present with the 170vdc too.

I have the schematics and I definitely don't see any 170volts on this set. The highest voltage in the schematics is 108vdc across one of the electrolytics. I have no idea where the 170 is coming from. Maybe a ground somewhere? I can't find any grounds to the chasis and the I've replaces the wires that looked worn. I also rechecked all my soldering and all the connections to make sure there wasn't a short (at least as well as I could). The ol' ohmmetter doesn't register a ground either between the chasis and any connection I could find.

I'm going to recheck my electrolytics in hope that I put them in correctly. The foil caps don't matter which direction they go in, right? I did not check direction on the foil caps.

Thanks for all your help and I'll continue my pursuits and let you know what I come up with.

-Brandon

[regel_1999]

Alright, so this is what I know: There is a ground somewhere on the chasis. I know this because when I had the radio plugged in and turned on I received a large shock to my hand that was enough to make my hand fly back and hit me in the nose. This radio hates me!

I've also come to the conclusion that the ground is probably the significant reason for the loud buzzing I was hearing. The electrolytics were correctly installed, the other caps had been replaced, and the tubes all looked and (minimally) tested sat.

My dilemma is this: Do I take the whole D**n radio apart, rewire everything and put it all back together (something I'm terribly confident I can do well) or do I use the radio as parts and find another old radio? I've now got 6 vacuum tubes that are good and a handful of capacitors that should still be good.

[Ron Ramirez]

My dilemma is this: Do I take the whole d**n radio apart, rewire everything and put it all back together (something I'm terribly confident I can do well) or do I use the radio as parts and find another old radio?

No, and no!

I was thinking about something last night. The 42-327 requires a loop antenna. Is the loop antenna present, and connected, on your radio? If it is missing, or not connected, it could cause buzzing.

Forget about grounds. This being an AC/DC set, you do not want to ground the chassis at all, period.

What did you touch when you received the shock? You should not have received a shock from the chassis. If you did, something is miswired.

The Philco AC/DC sets of this era have the chassis isolated from B- (one side of the AC line) with a resistor and a capacitor, as I recall.

Where in Ohio are you located? I think you could use someone close by to help you out.

Finally, exactly where are you measuring 170 volts DC? Can you show a picture? You should not have that kind of voltage in this set at all.

[regel_1999]

Hey Ron,

The loop antenna is disconnected. The wires were cut when I bought the radio, but all I'd need to do is reconnect it. I think all I touched was the inside of the chasis, but then, honestly, the oaf in me may have touched something else. I thought it was the chasis but I can't find any bad solders or bare wires in direct contact with the chasis. I also can't find any voltage on the chasis with the multimeter. No AC or DC. I don't really know what happened.

I also meant to say that rewire-ing the whole radio was something I'm NOT terribly confident I can do well. I'll try to dig out my camera and put some pictures up of what I have and I'll reconnect the antenna and see what happens. I haven't been shocked from the chasis since my last jolt (thumbs up) so maybe I just touched something else and thought it was the chasis. Yet another lesson learned. At least I've been smart enough to only touch the energized radio with one hand at a time, with the other hand behind my back. I guess I did learn something from that electricity lab in college.

Also, the 170vdc was directly from the wires that would go into the speakers. The schematic says it's the BC (broadcast coil, I think), directly from the speaker transformer. The speakers picked up the loud buzz too.

I just thought of something... if the speaker transformer was shorted could a high voltage be sent to the speaker and produce a steady voltage? Maybe a loud buzzing? It wouldn't produce 170vdc, but it could at least produce something pretty steady. How often do transformers go bad in these old sets?
... I just measured the resistance on the secondary winding. The secondary winding has infinite resistance (it should be about 0 ohms, right?) and between the black wire on the secondary side and the primary winding I had 0 ohms (indicating a short in the transformer, right). Does this mean I'm looking for a new transformer? Also, the primary winding read a resistance of ~280 ohms, per the schematic.

I'm in columbus, OH. I'm teaching Naval engineering and Weapons design to the Naval ROTC midshipmen at OSU and I'm hopefully going to get accepted into the electrical engineering program. I can work my way through transistors, but I don't know much about these old tubes... the technology of these tube radios is absolutely amazing. Much cooler than transistors. I'd definitely love to find someone who can help me bring this old radio back to life.

Ron, how'd you get so good at these radios? I'm thankful you and the rest of the radio hobbyists are good with these sets. Hopefully one day I'll be answering questions instead of leeching off you Thanks for your help.

-Brandon

[Ron Ramirez]

A correction: If you were standing on a concrete floor, with no shoes on, you could get a shock from the radio's chassis if it was plugged in, either on or off.

Also, the 170vdc was directly from the wires that would go into the speakers. The schematic says it's the BC (broadcast coil, I think), directly from the speaker transformer. The speakers picked up the loud buzz too.

That doesn't make sense. The B+ produced by the set's power supply is somewhere around 90 VDC. It isn't possible to have 170 VDC anywhere in that chassis, if it's wired correctly.

How are you measuring? DC across the speaker field coil? DC across the audio output transformer? DC from one of these leads to chassis? Any measurements made between a B+ point and ground will not be accurate, since the chassis is isolated from B-.

Also...the radio has only one speaker, not multiple speakers.

Another thing...I don't understand how you can measure infinite resistance across the audio transformer secondary, yet the set buzzes. If the audio output secondary was open, you would not hear anything from the speaker.

I'm not perfect - nobody is - but I have been tinkering around with old radios for 37 years now, and I like to think that I have learned a few things along the way

[regel_1999]

Ron,

I'm thinking I'm going to take a few days off from this radio. I just got some old 1940's-era books about radios that will hopefully shed light onto what I'm actually doing. Maybe I can figure this thing out. And I was thinking about it... what if my multimeter was messed up? I have two and they read different values of resistance, even on the same setting - a solid indication that one is wrong. I did not measure the voltage with both multimeters so, maybe? Anyway, I think staring at this radio is beginning to drive me mad.

I read about restoring old radios before I began and I thought this was going to easy. A few caps, a little solder, a few pieces of wire and viola! I thought I'd have an awesome radio... alas, I was fooled and had little idea as to what I was getting myself into. But, what better way to learn than trial by Philco? Bring it on, philco, I'm not scared!

Signing out for a couple of days,
-Brandon

[regel_1999]

Ok, I got one more question because I can't stop thinking about this radio...

Would there be any other symptoms of bad electrolytics other than a buzzing? Everything I read about buzzing all ended up with bad elec caps. Should I replace those again? I wish I had a cap tester... is there any useful way to test a cap without a cap tester?

I remeasured the leads coming out from the field coil. my multimeter is incorrect. My cheap analog multimeter reads like I'd expect, looking at the schematics. My expensive digital multimeter seems to read off on all resistances and reads off from the wall outlet by about 20vac. (it's reading 103 volts instead of 120) and the cheap analog reads 120vac steady... go figure my multimeter would be throwing me off...

So, I'm going to rework this whole set with a GOOD multimeter and see where I get. I'll post my new findings in a few days. Thank you for you help and sorry for my inability to test my tools before starting work. That's lesson number 352 from this project. Hey, bright side though, I'm having a lot of fun and when I got the set it didn't turn on or make any noise. Now it turns on AND makes noise! Sorry if I'm giving you headaches but I really do appreciate the help.

Thanks again!
-Brandon

[DeckApe]

[offtopic] "Trial by Philco..." that, sir is a phrase WIN. [/offtopic]

[Ron Ramirez]

that, sir is a phrase WIN.

Oh no...not here too...

WINNING, anyone?

[Radioroslyn]

Ok, I got one more question because I can't stop thinking about this radio...

Would there be any other symptoms of bad electrolytics other than a buzzing? Everything I read about buzzing all ended up with bad elec caps. Should I replace those again? I wish I had a cap tester... is there any useful way to test a cap without a cap tester?

Hi Brandon,
To answer your questions Yes there are some other problems that will cause a buzzing or hum in your Philco. I think the easiest way to unscramble your problem is to go though it stage by stage try to find where it is coming from. First off make sure that the two 20uf filter caps are connected with the proper polarity. You will notice a + sign at one end and or a - at the other. It is very important the + end of the cap is connected to the field coil and the - goes back to the pushbutton off/on switch.
Next take a wire and connect it to pin 5 of the 50L6. Take the other end and connect it to the - side of the filter cap. If filter caps are bad you will still hear hum if not it's coming from elsewhere. One other possibility is a bad 50L6. A short internally between the control grid and cathode will cause hum also.

Report back with findings
and good luck!
Terry

[Glenn Roberts]

Sorry, I know it may not be the place, but Ron you started it... Had too!