[poulsbobill]

While researching hi main volts and remedies,  i had tried putting 3,  10 watt, 30ohm  wire wound resistors in parallel in the line cord, I figured that my set uses 
1.15 amp   and trying to get a 10 volts drop i would use  about 11 watts...so i thought my approximately 3x safety factor was enough.

The resistors hit 300 degrees after 15 min... maybe within derated values but still.  Dang.  More research and i decided to try and make   a bucking transformer
out of a wall wart. It  brought my voltage to around 110 now.  Much less heat.

So to my problem, i have read using the heater voltage is a good guide of mains voltage to use.  I measured the 6j5g AVC tube originally and went from 7.0 to about 6.5 volts .  Much better until i started measuring random others and they are all about 5.8 volts now.  I put in a  nos  6j5g and the heater is the same  about .7
above the others.

Why is one higher than all the others?  I know there is a magnetic tuning transformer and maybe this is part of that, but the tubes around it the 6h6g and the 6k7g are also at the lower voltage.

Any ideas?

Thanks

Bill

[Mondial]

There are two separate heater windings used on the 37-116 chassis. Some tubes are fed from one winding while others are powered from a second winding. Perhaps there is a higher load on one winding which results in a greater voltage drop and reduced heater voltage?

The main reason for the two separate heater windings is for hum balancing of the directly heated 6B4G push-pull output tubes. Each filament is fed from a separate winding with a balance pot in each. Because the filaments are directly heated with AC, there is a AC component generated in the output. By balancing the filament windings voltage to ground with the balance pots, the AC hum can be cancelled resulting in minimum hum. In the latest production of the 37-116, the 6B4G tubes were replaced with 6A5G's which are similar but have heater-cathode construction. Without AC on the cathodes the need for the balance pots were eliminated.

[poulsbobill]

I do see the hum adjustment on the schematic https://philcoradio.com/library/download...%20258.pdf

Pot 128. You refer to a balance pot on each though...where is this?

i have a code 121 unit.

Thanks

Bill

[Mondial]

Yes, the balance pot is the hum adjustment #128. It is a dual 60 ohm pot with each section across one of the windings. If you look at the the filament windings you will see two pots, one across each 6.3 winding but it is a single adjustment dual control. Only one section is labelled #128, but if you examine carefully there is a dotted line between the sections.

[poulsbobill]

So my adjustment is a balance of the two filament readings?  ie less hum but at the moment i am more concerned about a better balance of heater voltages and this will do that?

Thanks again for your interest

Bill

[Mondial]

The hum balance pot has no effect on the actual heater voltage applied the various tubes. It only affects the relative AC voltage as measured to chassis ground seen by the output tube filaments.

Looking at the schematic, it appears that there are more heaters fed by the Fil 2 winding than the Fil 1 winding. This would place a greater load on Fil 2, resulting in slightly lower heater voltage to those tubes. The tubes you mentioned are fed from Fil 2 and would consequently read a lower heater voltage.

This appears to be normal and inherent in the design. I would not be overly concerned, as 5.8 VAC on the heaters is still within the + and - 10% tolerance specified by the tube manufacturers.

[poulsbobill]

The hum balance pot has no effect on the actual heater voltage applied the various tubes. It only affects the relative AC voltage as measured to chassis ground seen by the output tube filaments

Can you expand on this please

Thanks

Bill

[Mondial]

The filament winding supplies nominally 6.3 VAC across its terminals. The hum balance pot is connected across the winding terminals while the pot slider is connected to chassis ground.

The pot serves as a virtual center tap of the winding so the slider can be set at half the filament winding voltage. Since the slider connects to chassis, when measured to the chassis 3.15VAC appears from chassis to each winding terminal. It acts as if there is a center tap on the filament winding, but since the pot slider can move, the location of the center tap can be adjusted to compensate for any imbalance. When I say imbalance I am speaking of the precise setting so exactly half of the filament voltage appears from each end of the winding to ground. It does not refer to any difference between the output voltage of each of the two separate filament windings.

Because the 6B4G tubes have a directly heated filament powered by AC, the polarity of the filament voltage reverses 60 times a second. This causes a 60 Cycle AC signal to appear in the output. But if the ground connection for the filament is connected to exactly the electrical center of the filament winding, the AC signal in the output cancels and no hum appears at the output. That's the purpose of the hum balance pot. It allows you to set the filament to the exact center of the filament winding so the filament voltages is balanced with respect to ground which causes the AC hum in the output to cancel.

This is all a bit difficult to explain, but in the end the hum balance pot has nothing to do with why you measure different heater voltages on the heater pins of different tubes.

Getting back to your issue, are you saying that only the 6J5G AVC tube reads a higher filament voltage. All the other tubes read lower?

Do both 6B4G tubes have exactly the same filament voltage, or does one read higher than the other?

[morzh]

Not sure what it is about but why not use a bucking transformer.

[poulsbobill]

I owe you an apology Mondial. Everything is ok now. I have not removed the chassis from the radio so i measure all the tube voltages with a small washer that fits over a pin and a wire attached to it. Sounds odd but it works but goes slow. The other day as i stated i had that higher voltage on only one tube (the 6j5 and the nos i replaced it with) and all the others were lower, 5.8 at the time, The few i checked.

I have been using a bucking transformer to reduce my mains voltage currently at 123 today and was trying to use the heater voltage as a guide as i have stated. My bucking transformer lowers voltage about 12 volts so 111 to the set today . You had asked me to check a few other voltages and to be honest i did not even know about where the other filament tubes were. Thank you. I made a list from the schematic and off i went ------ all now at 6.0 or so volts - both filament strings ...hmmmm... i rechecked the offending tube (6j5) and sure enough at 6.0 volts.

SORRY!!, i don't know what happened. I originally checked the other tubes within a few minutes of finding that 7.0 volt 6j5 the other day when i got 5.8 volts on the other tubes..

So i think i know what happened at least some of it. When i rechecked today with mains at 123 and no bucking transformer attached ALL my heater voltages were about 7.0. My notes also show when the mains were at 117 the other day with the bucking transformer on i had heater voltages at 5.8. ( so about 106 at the set) So... maybe the bucking transformer maybe it malfunctioned during that time, maybe by pulling the tubes i reconnected a bad contact ( that has happened before ) ...I dont know. But all are at approximately 6.0 now except the the 6b4g's are at 6.3 nd 6.25. The plate voltage is a little low at 210 on a few i checked but i suspect that is because of the lower mains now.

So again i am sorry. This junior member did not mean to waste your time. I did learn some things so thank you.
I hope you will help me again in the future if the need arises.

Thanks

Bill