Weak reverb, or...what's weak this week

[g1]

As far as the bias goes, the 6L6 (5881) versions of this (or most 6L6 amps) will usually have enough range to be able to use either 6L6 or EL34.
The EL34 amps usually do not have enough bias range to handle 6L6's, they need more negative voltage than what is available, so 6L6's end up running too hot.

[bassistbobby]

Plenty of range in this one. there's just a slightly different tone. I have several sets of both types in my reserve, and like being able to use either tube. But I've been getting into using EL34s this year. Since I figured out what tube the circuit was built to use. I just should have swapped out those grid resistors as soon as I knew about them being out of spec.

[bassistbobby]

I read something about jumpering the empty tube pin socket to ground in order to mod a 6L6 amp to accept and use EL34 tubes.

This statement you made leads me to a question,.... is that the regular way to make an amp bias, if it's bias pot reaches the max of it's range before the tube is running hot enough?,... to lower the R value or the Grid Resistors?
In other words,... if I can't get my EL34 tubes biased hot with the bias pot,... I could just drop the value of R31 and R34 to say,... 1K5ohm.

Is that true?

Thanks

[g1]

No. Any changes to the bias circuit are made earlier in the bias circuit, further back from the tubes, usually the resistor that is in series with the bias pot.
You are calling the screen grid resistors, "grid resistors". Usually that term is used for the control grid resistors that connect to pin 5 of the power tubes. So it is best to refer to the screen grid resistors as "screen resistors", they are usually higher power, from 2 to 5 W, where the control "grid resistors" are usually 1/2 W.
The grounding of the open pin is usually in reference to pin1. It is unused with 6L6's but must be connected for EL34's. So usually pin1&8 get connected together, then the socket will work for either type.

[bassistbobby]

I thought I had this figured out, now I'm confused again. So,... then what does the screen in these power tubes do? Is it that the screen and grid do the same thing, and the only difference is the grid is a variable circuit, and the screen is a fixed circuit?

And,... then if I want to run my EL34s a little hotter, I would need to raise the value of my grid resistors, R24 and R25? I can get the bias to about 63%, but would like to run them up as high as 70% if I like the tone better.

What would I do to make that possible?

Thanks, I want to get this stuff about tubes and bias circuits straight, so I know.

[bassistbobby]

I'm sorry Guitician, when I was talking about those 2K2 5 watt resistors, and the 470ohm 2 watt, etc, I was just describing the little return to spec job I did on my screen resistors, R31 and R34. I didn't mean to depart so far from the reverb circuit we were discussing.

Thanks for the tutorial on ohms law for figuring wattage, and for soldering onto circuit boards. I haven't done much of that yet.