I have what I beleive to be an "Automatic Radio manufacturing co" model 245 radio/phonograph with an unmarked tube that needs replacing. I found the schematic on this site (Thank you!!), and it identifies the tube only as a "resistor tube". I'm limited in my electronic & tube set knowledge, and am not familiar with what resistor tubes are (I can guess, but that's not always a good idea). It has a 5 - 7 pin base (forget which) with a keyed center post, and no ID on it at all. Can someone help fill me in on what exactly a resistor tube is, are they standard or are there different values, & can 'substitues' be made up out of modern components. I need to get past this obviously n/g component (glass cover is cracked around the base so that it can be lifted off the base) so that I can move on to the next step of repair. Thanks.

:I have what I beleive to be an "Automatic Radio manufacturing co" model 245 radio/phonograph with an unmarked tube that needs replacing. I found the schematic on this site (Thank you!!), and it identifies the tube only as a "resistor tube". I'm limited in my electronic & tube set knowledge, and am not familiar with what resistor tubes are (I can guess, but that's not always a good idea). It has a 5 - 7 pin base (forget which) with a keyed center post, and no ID on it at all. Can someone help fill me in on what exactly a resistor tube is, are they standard or are there different values, & can 'substitues' be made up out of modern components. I need to get past this obviously n/g component (glass cover is cracked around the base so that it can be lifted off the base) so that I can move on to the next step of repair. Thanks.

Hi Ned,

If your radio has this resistor tube then it is probably a 351 as the schematic states the resistor tube used in 351. It could be in series with the tube filaments to drop any excess line voltage. The 245 uses 5 tubes and the total filament voltages add up to around 122 volts so I don't think it would use a resistor in the tube filament circuit. What are the tube numbers in the set? The 245 shows 12SA7, 12SK7, 12SQ7, 50L6 and 35Z5.

Radiodoc

My mistake. Yes, I should have indicated model 351 as it does have the resistor tube. I will check to see what tubes it has when I get home tonight (I'll also check on how many pins the resistor tube has). Thank you.

:My mistake. Yes, I should have indicated model 351 as it does have the resistor tube. I will check to see what tubes it has when I get home tonight (I'll also check on how many pins the resistor tube has). Thank you.

Ned,

If the first number(s) on all the tubes add up to less than 117 or so volts then the resistor (ballast) tube will drop the excess voltage. It may be possible to use wirewound resistor to replace it.

Radiodoc

Is the glass broken or has the glass bulb detached from the base? A lot of people make the mistake of thinking that the bulb is broken simply because it has become detached from the base. The glass bulb is a sealed unit all by itself. You can remove it from the base after unsoldering all of the wires, and it will function perfectly all by itself.....you just won't have the convenient plug base. You should find a schematic for this tube--the ballast tube, and figure out what its pin connections are. Then make resistance checks between these pins with your ohm meter. ....Or you can simply replace all of the other tubes which are burned out with known good tubes. If you have replaced all bad tubes with good ones, and they still don't light, then the ballast is bad. If you don't have a tube tester and you want to test the heaters of all the other tubes, their heater pins are 2 and 7 except for the 12SQ7, which uses pins 7 and 8. Use your ohm meter to check for continuity. Then, once all faulty tubes have been replaced, be sure that they are in their proper sockets. Be sure that all wiring is fine. Be sure that the power switch is fine. If the ballast tube is then bad, the tubes won't light and you'll see 120 volts AC across where the current goes into and out of the ballast. As was suggested, a wire wound resistor will substitute well for the ballast.

If you wish to glue the ballast bulb back to its base, you can use a small amount of J-B Weld...found at your hardware store. With cooler operating tubes I use super glue. With this tube the super glue may not last long. You can try it anyway. Keep in mind that super glue will give off a nasty fume when heated to a certain point. This fume can burn your eyes. It won't last long, but it smells bad. Otherwise try J-B Weld. Don't bother epoxying the bulb to the base unless you know that the ballast is good.

Thomas

:Is the glass broken or has the glass bulb detached from the base? A lot of people make the mistake of thinking that the bulb is broken simply because it has become detached from the base. The glass bulb is a sealed unit all by itself. You can remove it from the base after unsoldering all of the wires, and it will function perfectly all by itself.....you just won't have the convenient plug base. You should find a schematic for this tube--the ballast tube, and figure out what its pin connections are. Then make resistance checks between these pins with your ohm meter. ....Or you can simply replace all of the other tubes which are burned out with known good tubes. If you have replaced all bad tubes with good ones, and they still don't light, then the ballast is bad. If you don't have a tube tester and you want to test the heaters of all the other tubes, their heater pins are 2 and 7 except for the 12SQ7, which uses pins 7 and 8. Use your ohm meter to check for continuity. Then, once all faulty tubes have been replaced, be sure that they are in their proper sockets. Be sure that all wiring is fine. Be sure that the power switch is fine. If the ballast tube is then bad, the tubes won't light and you'll see 120 volts AC across where the current goes into and out of the ballast. As was suggested, a wire wound resistor will substitute well for the ballast.
:
:If you wish to glue the ballast bulb back to its base, you can use a small amount of J-B Weld...found at your hardware store. With cooler operating tubes I use super glue. With this tube the super glue may not last long. You can try it anyway. Keep in mind that super glue will give off a nasty fume when heated to a certain point. This fume can burn your eyes. It won't last long, but it smells bad. Otherwise try J-B Weld. Don't bother epoxying the bulb to the base unless you know that the ballast is good.
:
:Thomas

Hey Thomas,

Good job. I haven't found a schematic for this radio either yet. When Ned checks the tube numbers on the radio we should have a better idea about the resistor in question. Without a schematic it is possible that the resistor may be used in some circuit other than the filament string.

Radiodoc

Thank you for all the help. Unfortunately the glass is broken, with a fairly clean crack right around the top edge of the base. I was able to carefully lift the glass off, the filiments & mica card inside look intact, but a good bit of white powder poured out, LOL. I have not been able to find any markings on the glass or base (other than the base mfg. info on hte bottom by the pins). I wish it had been as simple as glueing the glass back to the base, oh well.
I have no problems with the 'mechanics' of working on this radio as I used to manage a small circuit board assembly shop years ago (PCB asembly, wave soldering, hand soldering etc) so I'll have no problems doing the work, I just never got into the theory of circuitry to much, much less understanding vacuum tubes.
I'll check what's in there & post it tonight.

You will enjoy them once you get to know them. It would take a long page to explain the basics here, but tubes are pretty easy to work with and are nice to listen to (if the circuit is built properly...quite a few aren't, or not enough effort is put forth to make a basically good circuit nice). If you want me or someone else to explain some basic details, ask.

Thomas

I would be interested in learning some of the basics. We have just acquired this radio/phonograph that has been in my wife's family probably since it was new, and a week earlier a neighbor gave me a "Musette" cathedral radio from about 1933. The Musette had a couple of wires torn off & about 50 years of 'basement dirt' in it. I disassembled it, gave it a good cleaning & put it back together. I have turned it on and it works very nicely (on for about 20 minutes), however after doing a bit of reading I'm wondering if I should have concern about using it with the original components in it. Are there components that should be replaced out of precaution? Some time way back when the power transfromer was replaced and there are some large replacement caps that have been installed in parallel on the underside of the chasis. Maybe I shouldn't have trusted my luck & turned it on, but so far so good.

Hi Ned, welcome to the old radio hobby, its a great way to spend your free time. Get all the books you can find about the subject and read up, that has helped me to no end! The absolute very least that you should do to a radio is replace the filter capacitors and I mean disconect the old ones from the circuit and install new ones, DO NOT parallel new across old, that is a very bad practice. You should replace all of the paper caps in any radio you want to listen to for anything more than turning it on for a friend for a minute. If they arent bad at this moment its just a matter of time and they WILL fail. Enjoy

Greg

:I would be interested in learning some of the basics. We have just acquired this radio/phonograph that has been in my wife's family probably since it was new, and a week earlier a neighbor gave me a "Musette" cathedral radio from about 1933. The Musette had a couple of wires torn off & about 50 years of 'basement dirt' in it. I disassembled it, gave it a good cleaning & put it back together. I have turned it on and it works very nicely (on for about 20 minutes), however after doing a bit of reading I'm wondering if I should have concern about using it with the original components in it. Are there components that should be replaced out of precaution? Some time way back when the power transfromer was replaced and there are some large replacement caps that have been installed in parallel on the underside of the chasis. Maybe I shouldn't have trusted my luck & turned it on, but so far so good.

Leaky capacitors can cause trouble, too. Capacitors should have no leakage...not even in the millions of ohms. I'll give details on capacitor function later.

Thomas

I appreciate the help & suggestions, Thank you. I have checked the tubes & with one exception they all match the scematic that is in the 'resource' section of this site (under "Automatic Radio MFG corp", model 245). They are 1)Philco VT-104 (in place of the 12SQ7 indicated on the schematic), 2)50L6, 3)35Z5, 4)12SK7, 5)12SA7.
I looked at what the VT-104 and 12SQ7 are and they do seem to be crosses for each other.
Do I understand correctly that a 'resistor tube' and 'ballast tube' are the same thing, and that it is there to sort of balance the resistance of the other heater filaments to 120V nominal? Also, am I correct in thinking that the fist numers of a tube number are the heater filament voltage ie: a 12SK7 has a 12volt heater filament?
Sorry for all the questions, and I do appreciate the help. I think the next thing for me to do is to do some chasing of wires under the chasis with the schematic so that understand & make sure where the resistor tube is located onthe schematic (not sure I have that correct).

I just checked the schematic (Riders 14-1) and it seems this tube is a current regulator for the B+ and has 1000 ohms resistance (it takes the place of a field coil) A 3 watt 1000 ohm resistor should replace it just fine.

A current regulator is different than a ballast tube as the ballast tube is usually just a wire resistor. A current regulator is usually a sealed glass tube with a filament and filled with a special gas, this will actually regulate the current.

Dave

:I just checked the schematic (Riders 14-1) and it seems this tube is a current regulator for the B+ and has 1000 ohms resistance (it takes the place of a field coil) A 3 watt 1000 ohm resistor should replace it just fine.
:
:A current regulator is different than a ballast tube as the ballast tube is usually just a wire resistor. A current regulator is usually a sealed glass tube with a filament and filled with a special gas, this will actually regulate the current.
:
:Dave

Way-to-go Dave,

When Ned posted the tube lineup and it added up to 120+ volts I definitely decided it was not in the filament string. I suspected in an earlier post that it may be located in another circuit.

Radiodoc

I will pick up a resistor & give it a try. I will also make up a list of all the caps & work on replacing them. (Any thoughts on what the original Current regulator tube would be?)
Thank you.

Dave:
Are the complete riders schematics available on-line?

:Dave:
:Are the complete riders schematics available on-line?

Yes, they are on this site

Dave

Dave.. thanks..
I guess that makes me look kinda dumb ... no?
...I do and did realize that the schematics here are Rider's ... but I just didn't think it was a panoply, because oft times when I cannot find a print here and have had to locate it at Radiomuseum.org or elswhere.
so...I was refering to a Rider's 'specific' and complete index site...