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The Fine Things are Always Hand Made

Area of B Voltage Divider - How should wiring look?

The wiring in the area of my B voltage divider has a few problems.

A loose wire is connected to the 100 V tap. There may have been a replacement resistor attached to this (broke away early on). The B+250V terminal attaches to a 'blob' of solder (blob-right) that joins several wires. There is also another blob to the left that is not attached to the B divider but is just a floating connection for several wires.

If anyone has a photograph from the same perspective as mine (see below) please be so kind as to post it. I just need a little help in putting this area back together again. I realize that I will have to trace everything but a photo of the correct physical layout may be helpful.

Thanks!

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Mouser sells 5K 50 watt units like Bill used, they are less than 20 bucks.  They come standard with one tap, maybe Bill can tell us where he got the extra 2 taps.

Trace all the divider wires where they go to and label them.  We should be able to tell you what each one is for. 

Ohmite part number: 2121E. Description, adjustable lug.

Think I got them from Mouser also. Make sure you bend the mounting tabs so the resistor isn't loose and tighten the lug just enough so that they don't move. The extra lugs will sit close to each other so put a piece of shrink over the solder tabs. I set them for resistance initially then adjust for correct voltage. Good luck.

That's my plan, tracing all the wires. Once I know where they all terminate I'll make my best guess as to where they go on the B Voltage Divider. I will report back here for confirmation.

I did several leads today. I also worked out all the leads on the floating solder blob that is not attached to the divider, but may have been.

It sure gets crowded in a few spots under that chassis. Once again, I appreciate the helpful dialogue here from everyone.

If still visible, the color combinations on the wires dictate the voltage tap to which they should be connected.

Norman

Ken,

Fortunately, the B divider is used exclusively for the pentode screens. All pentodes use pin 4 for the screen except the 6B8 tubes which use pin 6. You should have an easy time measuring continuity (1500 ohms or less) to these points:

100 Volt tap used for: 1st & 2nd RF, 1st & 2nd IF, S.S. & Expander tubes (4 uF bypass)

125 Volt tap used for: 3rd & 4th IF, IF AGC

150 Volt tap used for: Converter & RF AGC

Anything left should be for 250 Volts

regards, Bill

Norm ... The colors are all faded, unfortunately. Almost everything looks like brown with dull red or green tracers. Not reliable at all. I also must confess that I have no idea how to read these resistors other than un-soldering one end and using a meter. I use a color code lookup and it never matches the drawing value of a resistor. I think those colors have gone too. Thanks for the suggestion.

Bill ... So far I have one lead that went to pin 6 of the 6K7G 3rd IF, one to pin 6 of the 6L7 converter, and one to pin 6 (through a resistor) to the 6B8G RF AGC. 

Of the leads that were not attached (just floating) one did go to a 6L7 expander, pin 4.

I suspect some of these wires don't even go to the divider. It will take a while but I will get there. I will compare carefully with the data you provided. Thanks!

Ken,

When I mentioned that your continuity would read less than 1500 ohms, that is due to the screen limiting resistor used for most tubes. Pin 6 is also not used for the pentodes, so Scott used them as tie points. If you look, you will see that most of the time there is a 1K ohm resistor from pin 6 to the screen grid pin. These are indeed for the screen supplies.

The first lead you mention is for the 125V and the second is for the 150V. The lead going to the 6B8 should also be 150V unless there were screen grid voltage changes through production.

good luck

Ken,

Here is a picture of your set that you posted...the colors look fine to read.

The resistor on the upper left with the yellow band is read Brown-black-yellow.  So you have a 1 and a zero with 4 more zeros...you have 100K ohm.  The one below it is read brown-black-green which is a 1 meg.  The one with the orange is read orange-green-red which is 3500 ohm. 

You read the large body color first, then the band off to the side, then the band in the middle of the body.  The silver band is just the tolerance and does not play into reading the value.

It is a bit different than modern resistors and takes getting used to.

Scott..Thanks for explaining how to read the resistors! I was trying to read them as a straight sequence and getting nowhere. This is the first I've heard of an old method. I thought I was either color blind or worse.

Well, I have traced all the wires that went to my B+ Voltage Divider. As you may recall one of the two solder blobs was attached to the divider and the other was not attached to anything other than a bunch of leads.

Most leads I traced went to a 100 v, 125 v, 150 v, or 250 v supplies at various tubes. The details are below. If something looks suspicious, please comment:

100 volt, 4 wires total to:

            Both 6L7G expanders, pin 4

            To ▲ terminal on C42, electrolytic capacitor, 5 mfd (not 4 mfd as in Rider)

            6J7G scratch suppressor, pin 4

            Tab on front of selectivity rotary switch

125 volt, 1 wire total to:

            6K7G 3rd IF, to pin 6 tie point and then to pin 4 through 1K resistor (R9)

150 volt, 2 wires total to:

            6L7G converter pin 6 tie point the to pin 4 through 1K resistor

            6B8G RF AGC to pin 6 through 1K resistor

250 volt, 4 wires total to:

            Bass Choke supply

            Pin 2 of set plug

            RF-AGC diode assembly, by way of R9 (1K) resistor

            6J7G scratch suppressor pin 3 through 500 K resistor (R27)

 

I’ve ordered the 5K resistor and hardware that Bill recommended.

 

Regarding Bill’s photo, assuming the resistor has an even progression of resistance from left to right, would the connections be:

Ground (left end terminal) -- 100 V (tap)  --- 125 V (tap)  -- 150 V (tap) --  250 V (right end terminal)    ?

 

For now I am working on replacing capacitors. It takes me forever – I have a short attention span!

Ken,

I think you have it right. Take your time. Those who rush these things, spend more time correcting mistakes.

Good luck

Today was the day that I was finally ready to wire in the 5K 50 watt resistor to replace my burnt out B+ Voltage Divider.

I really needed some encouragement on this project so I hooked everything up with partial power through a variac and inline high wattage dining room light. I was taking no chances. I just wanted to hear some static so I could then shut it down and continue with the capacitor replacement.

To my surprise a local AM station came on full blast playing "Light My Fire"!  I thought that was appropriate. I ran to my camera and made a short video just in case it blew up. I needed to save the moment. Now I can continue to work on this radio knowing that the end result will be a nice sounding Philharmonic.

Thanks to all the people here who have been so helpful. I could not have done this alone!

I made a short video and the link is below. Please excuse the choppy movement. I think I was messing with the lens.

http://youtu.be/l9zO4eMjNdg

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