Metropoulos Forum

No not rivers, or events, plate current.

I've read about the shunt method, which I like, but there is something that's confusing me.

I unsolder the wire to the #3 tag of one tube socket - I put my DMM in 200mA mode BETWEEN the wire and #3 tag. I get a reading of say 37.5 mA. I leave the other tube to do its thing.

So am I missing something here? I don't need to divide by the number of tubes if I do it this way do I?

Seems a little odd to me; to divide....

If you put it in between the OT and sockets 5 or 6 then I think you would. But not if your reading the current between 6 and 7 or 4 and 5. Ive been using the 1ohm resistor method for a while subtracting the screen resistor voltage drop but I think Im going to make a set of bias socket converters from Hoffman parts. He sells parts to make them.

Now I'm even more confused - I think you mentioned every number except 3

I'm looking at KT66s.

1 NC
2 H
3 Plate
4 Screen Grid
5 Control Grid
6 NC
7 H
8 K

I think Im confusing matters like usual. I forgot you have a 45. No you wouldnt have to divide it by 2.

Yeah, I thought so.

But, for the record, when do you get into a situation where you would divide?

When you can actually tap from the OT itself before it gets to ANY of the tubes?

Thats what I was saying. With a 100W amp using the shunt method you divide or doing what you did unsoldering the plate connection and taking the current reading between the OT and the inner 2 sockets since your reading the current draw for both tubes on each side. Then you would have to read the current for the outer 2 tubes and subtract the totals.

Seriously the Hoffman parts lets you buy a tube base and fit a sicket inside it so you connect all the like pins together accept for pin3 which you would have the connection to the bas pin and the sockets lug both go out of the base through a hole to a set of probe sockets so you can read the current without bothering with soldering. Youd just have to remove a set of tubes, put the bases in and plug the tubes into them.

Ok, now I get it.


In front of me is a 45 with only 2 output tubes, so their plate connections come directly from the OPT primary ends. I think that's what I was confused about; there is no "common" plate connection to speak of.

I will look into Hoffman. I want to build myself something for this, but not at some of the inflated part prices you see on the ol' interweb.

Cheers mate