stokes

So now you learned something today. Now go ahead and tell me how he's wrong. Lets see, believe a guy that I know is an accomplished builder, and has built a very succesful amp business, or a couple of wanna be's on the interwebs. Have a good day you ignoramus.

No, you guys are awful ignorant. This from Gerald Webers book Tube Guitar Amplifier Essentials. Although I learned about this outside foil thing over 40 yrs ago I knew I saw it somewhere since.

My heart bleeds for you.

OK, you win, I guess I should get all the amps I've built and repaired over the years and ground the cab shields via the power supply caps since they bleed off stray ac noise.

But its not a lower dc resistance. Put your ohm meter on the plate and then the grid and see. Again for the outer foil to ground we are only concerned with the dc resistance to make the outer foil a shield.

No school for me, I went to work at 14 yrs old in a tv,radio repair shop and have been inside amps ever since. I have run a repair shop since 1982 and was the go to for Mandolin Bros for the last couple years before they closed. This has nothing to do with the ac signal.It is all about dc resistance. If the filter cap, or in this case the decoupling cap has almost zero resistance to ground, how do you suppose the signal being amplified gets past the plate, by your thinking that stage wouldnt pass the signal, it would be grounded at the plate,no?

Damn, I been doing it wrong for the last 58 yrs? How did I ever get this far without you. I'm sorry but you are wrong, I dont know how else to explain it to you. Impedance, ac grounds, whatever you think that is has nothing to do with orienting the outer foil of a cap.

You are over complicating this. The whole idea of grounding the outside foil is to create a sheild. The shield does not get grounded thru a filter cap, has nothing to do with ac voltage its a matter of dc resistance, the plate has no dc resistance to ground, the grid does. This is basic.

If by "AC" ground you are talking about signal ground, the signal ground is the same as the DC ground. To measure the ac signal voltage one meter lead connects to a chassis ground, with the meter connected to the same ground, you switch to dcv on the meter and measure any dc voltage in the amp. There is no seperate "AC ground"

But that is exactly what the "outside foil" scheme is all about. you are overthinking this. The aim of orienting the cap with the outside foil closest to ground is so the outside foil becomes a kind of sheilding to reduce noise and microphonics. Yes, a cap is microphonic. Now you have a plate with somewhere around 250 vdc above ground on it and the grid of the next stage with maybe 1vdc above ground. Which is closer to ground?

If you say so.

The 100k plate resistor would be in series with the cathode-plate circuit, not parallel. If you put a meter between the plate and cathode of say, a 12AX7 there will be no resistance reading. The other end of the 100k is connected to ground via the filter cap much, much higher resistance. Now if you put the meter from plate to ground you will see about 6 to 10 meg. Grid to ground will be from 0 to 1 meg depending if you have a pot or fixed resistor on the grid.

Sorry for the loss. Seems to be a lot of these "sudden heart attacks" lately. Video was interesting, I like old pics of bands, brings back memories.

Very talented, but damn, that was creepy.

No, the plate is connected to the grid of the next stage via the coupling cap. The grid has around 1meg or less connection to ground, plate is much higher