The set is showing correct voltage of 2.2v at the #24 & #45 filaments, the rectifier filament is 15v and should be 4.5v and the screen grids at RF & detector are only 3.3v and should be 90v.

There is a main transformer, a field coild under the chassis and then a third transformer/coil mounted on top of the chassis at the opposite side. (There is also a coil mounted to the speaker) Can anyone tell me what this third coil/transformer is and what its function is? It has an old resistor on it which was detached and it has the correct resistance.

There is a voltage-divider also with three connection tabs and a ground tab. One tab is connected to an electrolytic (with 315v on a target of 275v), there is a .1mfd connected to the second tab (which shows 315v with a target of 180v) and the third tab has a wire to it (which shows 0v with a target of 90v).

I know there is a relationship between high rect filament and no screen voltage. All of the caps have been replaced and all of the resistors have been tested except these block type ones that have a rating of .0001 and .001. They are rectangular shaped with one on top of each other.

Elements of Radio Servicing has the exact symptoms... no reception/no hum/B plus voltage normal (#45 plate to ground is 310v with target of 275v and the detector plate to ground is also 310v but with a target of 180v)... the abnormal reading is screen voltage zero, which is my situation, and the Look for is open voltage-divider resistor, short circuited scrrn by-pass condenser or both.

The by-pass condensor tested no resistance so it was replace with a same value normal resistor (I hope that is correct to do). If that was correct to replace with, them it is down to the voltage-divider. I included the transformer/coil info above incase the problem could be in those. Dim bulb test shows no short and rect filament to chassis is 15 meg resistance.

Sorry if this is too much info or not presented in a good format.

Thank you for any help you can give.

I thought I was understanding things, but

Make, model, schematic?

Steinite model 421... I was getting too understand schematics but this one confuses me again!

Thank you.

By "no resistance" do you mean that the ohm meter said Zero ohms when you tested the 0.1 mfd capacitor that connects to the screen voltage line?

I assume that is why you replaced it. Hopefully you meant that you replaced it with a capacitor (you said resistor, but I suspect that was an oversight).

If that capacitor was shorted it would be likely that the big voltage divider resistor with the two extra tapped connections now is broken (opened) between the 180 V tap and the 90 V tap and this would result in no voltage to the screens of the tubes (loss of the 90 volt line).

Apparently there is still a connection between the top of the resistor and the 180 V tap, which is why it is showing 315 V.

With the radio turned off and unplugged can you measure the resistance between the 275 volt tap and the 180 V tap and tell us what that is? Also, can you measure resistance between the 90 V tap and ground and tell us what that is?

You should probably also try to measure the resistance between the 180 V and 90 V tap and let us know what that is as well, but I suspect that is going to show very high.

Curtis Eickerman

That's an awful lot of information... When you say the rectifier filament voltage measures 18 volts, are you measuring between the filament terminals or to ground? I presume you are using an AC voltmeter. If you are measuring the AC voltage across the filament (pin 1 to 4), it's hard to imagine any way you can get 18 volts unless the power transformer is faulty in a very strange way.

I agree that there is something wrong with the measurement. If it was 18 volts the filament of the rectifier would have been burned out a long time ago (within seconds after being turned on), yet it is obviously running because of the reported DC voltages.

Curtis Eickerman

Thank you Eickerman and Alfred Corbin for replying.

Yes, I apologize, I stated the .1 mfd capacitor at the 180v tap incorrectly. One end was detached, tested on a cap tester and it was leaking. It was replaced with a .01 mfd cap.

The resistance values for the voltage-divider are:
275v tap to 180v tap - 2,600 ohms
180v tap to 90v tap - with VTVM at RX1 MEG setting, the needle moves to 100 meg and then moves back up ending at 200 meg
90v tap and ground - with VTVM at RX1 MEG setting, the needle moves to various points but repeatedly moves back up ending at 40 meg

The rectifier filament voltage was measured from pin #4 to ground. I am using a Heathkit VTVM on AC setting. The voltage from pin #1 to #4 shows 4.4v which is the target. Looking back at my notes from Elements of Radio Servicing, I should have measured the chassis to rect filament in DC and not AC. Measured in DC voltage is at 450v. Honestly, I don't know what this reading is used for yet but it is one of the normal voltage data it says to measure. I should have more accurately reported the AC filament to filament voltage in my original post.

Thank you for your help!

[A] The field coil is not under the chassis. It is part of the speaker. It is actually an electro-magnet and does the same duty as a permanent magnet in modern speakers.

The choke coil might be mounted under the chassis though. It will look like a small transformer.

[B] The transformer with the resistor is probably the audio interstage driver transformer. It serves to couple the last 24 tube to the two push-pull 45 output tubes.
Maybe this will help:

That definately helps me to understand!! Thank you.

The schem is drawn much different than the others that I have used so far. May I ask you... to the right of the field coil is the voltage-divider I believe and then following the line that ends above the #24 tubes, there are lines coming down and terminating with squiggle shaped symbols. That symbol appears in other areas of the schem as well (i.e. the upper right side of the audio interstage "driver" transformer). What does this symbol mean?

Thank you for your help!

An early way of drawing the grid of a vacuum tube. In this case, they put things is a funny order----eg for the type 24; control grid, cathode, filament, screen grid, and plate. (Build the tube that way, and it won't work very well....... )

I couldn't find that symbol in any of the old drawing symbol charts I have.
With your example, I can even see the whole tube now!

Thank you for your help!

Your second and third sections of the large voltage divider resistor are junk... open... in the pictorial drawing it shows a total of 22,440 ohms for all three sections of this resistor together. You have 2600 ohms in the high voltage end of it .. leaving something on the order of 20000 ohms total to be split up between the two bad sections of the resistor. Those replacement resistors for those two sections will need to be in the order of 10 watt resistors. It probably won't be exactly TWO 10,000 ohm resistors but something close to that.
John k9uwa

This may help you understand the drawing. The old way of drawing is on the left, the newer style that you may be more familiar with, is on the right.

Those strange symbols represent ohms. They really should be lower case Greek letter Omega which looks somewhat like an inverted u.

This might be a reasonable way to mount your replacement resistors (see below). Either 5 or 10 W resistors would be plenty big enough (dissipation is under 1 watt for each). You would just be making use of the terminals of the dead divider to attach replacements for the open sections and still use the part of the divider that is OK. Alternatively you could take the whole thing out, put in a terminal strip, and replace all 3 sections of the divider. You will probably start with 10K resistors for the blue items. You might have to increase or decrease values somewhat to get the 180 and 90 volt setting to come out right.If you decide to replace the 2600 ohm section and use a terminal strip, that resistor should be rated at 10 Watts (it dissipated 3.5 Watts all by itself).

Curtis Eickerman

Great drawing to have! Thank you Oldbear!

Thank you Eickerman! This forum can not get any better! I can not imagine trying to learn this art without the help of you and all of the members of the forum.

This will sound rookie I know... a 5w or 10w resistor is completely different than the radio repair resistor kit that I purchased from JustRadios correct (the kit items are rated in ohms and are all 1w resistors)?

Is this a resistor to purchase at a Radio Shack maybe?

Specifically, would I look for a separate 5w or a 10w? or is it one resistor rated for 5w or 10w?

Thank you for your help!

They might have them. I have not looked there recently. Each resistor would be either a 5 Watt or a 10 Watt device. Alternatively you might have to order them somewhere (Digikey, Mouser, other)

I checked Radio Shack online and they list the following possible candidate resistors in the approximately 10K 5 Watt devices. Unfortunately they are all listed as "Web Only" so they are probably not in local stores.

10K 5 W part number 5WR310 $2.45
11K 5 W part number 5W311 $1.09
8.5 K 5W part number 5W285 $1.09

I didn't see 10K 5W in the cheaper ($1.09) version. Not sure if I just missed it.

Curtis Eickerman

Solved the problem, provided the solution and provided the sources! Don't know what to say... hardly enough, given this amount of help, but Thank you!

I have 4 new Mallory 5HJ100 blue resistors and was trying to find what the ratings are for them in the Mallory RS Encyclopedia but can not find them.
They are too long for this application anyway.

Going to get them on order.

Thank you for all of your help!

To help in regard to your current difficulties: Below is a schematic that is a little blurry, but now contains reference designations (T2, R1, C1, L1, etc.) and tube pin numbers to help with tracking down remaining problems. This might also assist in locating wiring problems. Please let us know where the "sparking" occurred. For example, was it at the junction of L1 and C2? Have you visually inspected any solder joints in the area to make sure they are OK?Curtis Eickerman