5879 tube examples

[tubenit]

Been looking around to see what values are used by others with their 5879 tubes.  Found these and thought I would pass this on.

IF anyone has any more examples, I would really like to see them.

with respect, Tubenit

[sluckey]

Thanks. Very useful to see all that on one drawing.

[MakerDP]

 

Great resource! Thanks!

[kagliostro]

Here some 5879 applications





this is labeled IPC Preamp








Kay520 - 720 - 820 has the same value that you put on your image

Franco

[DummyLoad]

see attached.


--pete

[PRR]

I computed resistor ratios. I would expect some trend. I'm not seeing it.

[tubenit]

I computed resistor ratios. I would expect some trend. I'm not seeing it.

I noted the same thing and was surpised by it.

With respect, Tubenit

[silverfox]

What does it mean? No trend. I'll take a guess and hope someone clarifies: No trend would seem to indicate the tube will work under a broad range of circumstances. What would be the tonal significance of that? Or is it similar to a water system where a range of components yields the same P/V State. Lots of ways to plumb a system and they all, within reason, yield the same result.

silverfox.

[John]

Merlin talks about the EF86 in his book at some length. I've read it at least 20 times and still don't "get" how to figure out values. I end up using a roughly 10-1 ratio, screen resistor to plate. From what I can see, yes it does work under lots of different loads and R values.

[DummyLoad]

from the RCA 5879 RC charts we see mostly 1:3 to 1:4 Rp:Rg2 ratio: except highest gain example at 300V Rp:Rg2 is ~1:2.75 


none of tubenit's examples seem to have been derived from the attached RC chart - including the example labeled RCA Hi-FI - go figure.


a stomp box with couple of 5879 and a couple of depletion mode MOSFET source followers might be interesting.     


--pete

[MakerDP]

You choose the screen grid resistor based on how much voltage you want to drop from your B+ to your screen. No other resistor value chosen  affects your B+ supply value so there is no ratio pattern that will emerge whatsoever.

Your bias point depends on your screen voltage because you draw your load line and then choose your Ra value from the grid curves for your chosen grid voltage. So, once again, very little to do with any other resistor value and so no pattern will emerge here either.

So, properly setting up a pentode is a bit more involved and a whole lot less "cookie cutter" than our old familiar 12A_7 family of triodes. It's not at all like choosing your values from a simple triode where your choices are driven by your choice of B+ and Ra and how steep you want your load line to be. With a pentode everything depends on your chosen grid voltage and that value is totally dependent on how much voltage you need to drop from your B+ to get there and nothing else.

[DummyLoad]

You choose the screen grid resistor based on how much voltage you want to drop from your B+ to your screen.

not exactly. when running in pentode mode, you chose g2 resistor to set gain. the lower the supply to g2, the greater the gain.

there is a ratio. if you examine RC charts. typically 1:5 to 1:6 for most small signal pentodes. for the 5879 it's about 1:4   

--pete

[MakerDP]

Yes which is controlled by the grid voltage. You choose the value based on the voltage drop you need across it.

There is no ratio "rule of tbumb" because it all depends on the amount of drop you need. The fact that you are citing three different ratios only goes to prove that point.

[shooter]

I like simple math, how bout adding the 8Ra values then divide by 8, do the same for  Rg2, walla average

[kagliostro]

the lower the supply to g2, the greater the gain

May be yesterday I've drink a beer too 

Thinking to Power Tubes, the lower the supply to G2, the lower the power

so ... the greater the gain confuses 

Franco

[PRR]

Power is not the same as Gain.

[John]

So to put in terms I can understand...


If I like the tone I'm getting, but want less gain, I actually *raise* the voltage to screen, by reducing the screen resistor.


And, I should decide on (roughly) what screen voltage I want to run at, and then set plate and cathode R values from there?


For instance, the amp I'm finishing up now sounds great, but I'm thinking I may want a little less gain coming out of the 5879 since this is a harp amp, and I'm trying to keep the tendency for feedback reduced. I have 235 on the plate /56K resistor, and 115 on the screen / 470K resistor.


sch file is attached for any criticisms or comments. Or complaints. 

[kagliostro]

A related thread

(read all expecially the latest posts by Andy Le Blanc http://ampgarage.com/forum/viewtopic.php?f=6&t=30019&start=30#p371511)

http://ampgarage.com/forum/viewtopic.php?f=6&t=30019

Franco

[DummyLoad]

If I like the tone I'm getting, but want less gain, I actually *raise* the voltage to screen, by reducing the screen resistor.

yes.

--pete

[jojokeo]

Yes, higher gain also equals faster/easier distortion breakup. I like lower Rs for more headroom which also coincides for less tendency or sensitivity to experience microphonics.