I have a unit whose filament wire seems to simply be a single strand runing to each filament and then the "ground" side is simply attached at the cathode ground. Would it be better to twist two wires together for the filament voltage so that it would reduce hum?

i dont think so. i think that twisting wires is more for noise induction on low level signals that get amplified in a differential fashion which cancels out in the circuit. the filaments are ac already. but that is my thinking. others may know better then me.

:I have a unit whose filament wire seems to simply be a single strand runing to each filament and then the "ground" side is simply attached at the cathode ground. Would it be better to twist two wires together for the filament voltage so that it would reduce hum?

Twisting the filament wires would be ideal for hum reduction (hum that is induced in other circuitry by the filament wiring). It would be most effective where the filament transformer winding did not have one side connected to the chassis, but rather a center tap. It probably wouldn't be too effective in a set where one side of the filament winding is already connected to the chassis. If hum is being picked up from the filament wiring in a radio where one side of the filament winding is connected to the chassis, and a single wire is strung about for the other side, several things can be done. One would be to shield tubes better, shield grid wires and capacitors (and possibly resistors). A second method might be to shield all of the filament wiring that isn't connected to the chassis. Be sure that shields don't touch the actual conductor, and also that the shields are connected to the chassis. The third would be to rewire the filament wiring so that two twisted wires were brought to each tube (you could start at one tube and go on to the next). With that you'd want to disconnect the filament winding from the chassis. If necessary, two 50 ohm resistors could be connected to each end of the filament winding. Join their other ends and connect the joint to the chassis.

Other hum problems could be caused by power transformers and motors being mounted too closely to the output transformer, or inadequate filtering. Revision of transformer mounting or filtering methods would help the problem. For instance, a small AC/DC Majestic that I've been working on lately was inadequate in just about every way. The power supply had way too much hum, even with all new components. Addition of a 68 ohm (what I had at hand) resistor between the rectifier and the output stage did the trick, and didn't reduce output power any. Of course I also added another filter condenser so that there'd be one on each side of the resistor.

T.

Excellent. Now on to the avc question. There must be something Im not understanding about the basic fundamentals here because no one is answering. If you would be so kind as to look at my earlier post about my AVC in the Howard and tell me what I am asking that is wrong I would love to know. There is something Im not understanding about this forum that is causing undue distress on my part. I dont expect immediate or expert answers, nor do I expect to be spoonfed. This filament question was answered inside of two hours, its been two weeks and no actual answer on my AVC question. HELP!

:Twisting the filament wires would be ideal for hum reduction (hum that is induced in other circuitry by the filament wiring). It would be most effective where the filament transformer winding did not have one side connected to the chassis, but rather a center tap. It probably wouldn't be too effective in a set where one side of the filament winding is already connected to the chassis. If hum is being picked up from the filament wiring in a radio where one side of the filament winding is connected to the chassis, and a single wire is strung about for the other side, several things can be done. One would be to shield tubes better, shield grid wires and capacitors (and possibly resistors). A second method might be to shield all of the filament wiring that isn't connected to the chassis. Be sure that shields don't touch the actual conductor, and also that the shields are connected to the chassis. The third would be to rewire the filament wiring so that two twisted wires were brought to each tube (you could start at one tube and go on to the next). With that you'd want to disconnect the filament winding from the chassis. If necessary, two 50 ohm resistors could be connected to each end of the filament winding. Join their other ends and connect the joint to the chassis.
:
:Other hum problems could be caused by power transformers and motors being mounted too closely to the output transformer, or inadequate filtering. Revision of transformer mounting or filtering methods would help the problem. For instance, a small AC/DC Majestic that I've been working on lately was inadequate in just about every way. The power supply had way too much hum, even with all new components. Addition of a 68 ohm (what I had at hand) resistor between the rectifier and the output stage did the trick, and didn't reduce output power any. Of course I also added another filter condenser so that there'd be one on each side of the resistor.
:
:T.

I was going to answer the AVC question, but didn't really have a good answer for you. I'm not sure that anyone has ever calculated the noise threshold for the RF tubes. The AVC circuit just makes sense and works. I'm not sure if anyone who designed it calculated for noise threshold. I do know that in some radios there is a slight distortion on distant stations--when the grids approach zero volts. With some I've found that biasing the AVC circuit slightly positive helps. I'm not sure why. I use a network of resistors to feed positive voltage to the low terminal of the volume control from the output tube's cathode. I also filter it so that the two circuits cannot affect eachother. I've only had to do this to a few radios, but got the idea when I saw it in a couple of Zeniths.

Regarding grid voltage, when there is no reception, and nothing to create AVC voltage, the grids will essentially be at zero volts, or whatever they are biased at with respect to the cathodes (sometimes resistors are put on the cathodes). I suppose that the noise of the tubes might create an ever so slight voltage, and so the grids might be ever so slightly negative. It would be an almost immeasurable voltage, however.

T.

Thank You. Thank You. Thank You. you have no idea how much i appreciate that.
I have alot of tube theory. I have alot of radio theory. Just not with the two together. In any ss arrangment(where it is obviously AGC and not AVC) is actually a delayed one. At least in a voltage sense. So there is always some forward level on the active devices. Its not really the AVC im concerned about, its the static current draw and voltages I really want. I would like to draw loadlines for everything and see if i cant simplify it a little more. I would like a seperate screen and load resistor on each tube, at least where they have it
I would also really like to know about the audio portion because i am DEFINITLY redigning it. To hell with the way they did it. What i mean by this is that i understand the inverter stage and the signal attenuation prior to the inverter stage as it will add gain and unbalance the signal. But the whole way they develop the tone controls and the fact that the output tubes are different plate voltages and both have screen voltages higher than the plate voltage just destroys everything i know about audio sections. I know this is long and i know it is a lot of ill definied questions in a short space but i would like to get this thing running for my dear old grandmother before she kicks the bucket. I think she has more than a year left but it might take me that long to get the damn thing working. I appreciate any help I can get with it because I really am lost. Thank you in advance

:I was going to answer the AVC question, but didn't really have a good answer for you. I'm not sure that anyone has ever calculated the noise threshold for the RF tubes. The AVC circuit just makes sense and works. I'm not sure if anyone who designed it calculated for noise threshold. I do know that in some radios there is a slight distortion on distant stations--when the grids approach zero volts. With some I've found that biasing the AVC circuit slightly positive helps. I'm not sure why. I use a network of resistors to feed positive voltage to the low terminal of the volume control from the output tube's cathode. I also filter it so that the two circuits cannot affect eachother. I've only had to do this to a few radios, but got the idea when I saw it in a couple of Zeniths.
:
:Regarding grid voltage, when there is no reception, and nothing to create AVC voltage, the grids will essentially be at zero volts, or whatever they are biased at with respect to the cathodes (sometimes resistors are put on the cathodes). I suppose that the noise of the tubes might create an ever so slight voltage, and so the grids might be ever so slightly negative. It would be an almost immeasurable voltage, however.
:
:T.