5879 operating conditions question

[dwinstonwood]

Hello all,
I'm looking at pg. 2 of this datasheet, in the maximum voltage gain table: http://www.r-type.org/pdfs/5879.pdf

In the image I've attached, I'm unclear about what the highlighted text means.
Is that the 5879's grid stopper?
What does "of following stage" mean?

Thanks!

[passaloutre]

It’s the grid leak resistor of the next stage, Rg in the attached diagram. My understanding is this forms an AC load essentially in parallel with the plate resistor.

Source: http://www.tubebooks.org/tubedata/hb-3/Receiving_Tubes_Part_1/Resistance-Coupled_Amplifiers.PDF

[dwinstonwood]

Thank you passaloutre!

I've been buying NOS RCA tubes of the "less-ordinary" types, and plan to build something with them. So far, I have a 6AT6, a 5879, a 6SL7GT, two 7C5's, and a 5Y3GT.

David

[passaloutre]

Same! I’ve been buying up a lot of junked old radio and hifi gear and doing my best to make use of those tubes. The Resistance Coupled Amplifier charts in that link have helped a lot in making sense of the unusual tubes.

Currently working on an all loctal 5E3 with 7C5 output…

[passaloutre]

This has also been a really helpful site in helping to compare uncommon tubes against the ones with which I’m more familiar: https://www.angelfire.com/electronic/funwithtubes/tube_select_guide.html

[j-b-c]

A good comprehensive and condensed guide for types and data is the MK-RT compiled by Radio Bulletin by De Muiderkring N.V.

It is extremely terse (at 339 pages) but it has all the most important data.

https://frank.pocnet.net/other/docs/MK-RT.pdf

[tubenit]

maybe this will be helpful?

[dwinstonwood]

Thanks tubenit! That's very useful.

[dwinstonwood]

I'm going to follow tubenit's practice and Blencowe's advice and place the 5879 at the end of the preamp chain. I want to overdrive the pentode for its special quality.
The other night I ran my AC15 through my Weber MiniMass attenuator, and even dimed I could not get distortion with single coils. Nice sizzle, but not grind. A pentode in the first position is a waste, as many have said.

I'll start another thread when I begin working out a 6AT6, 6SL7GT, 5879, 7C5, 5Y3GT concept. There's a Hammond PT that can supply enough current while delivering only around 280VDC with a 5Y3GT. 7C5's will be safe.

TBC

[tubenit]

A pentode in the first position is a waste, as many have said.

   


Two of my current amps that I play regularly.


with respect, Tubenit

[tubenit]

Two others I previously built.  I guess I didn't get the memo about where the 5879 was supposed to go? 


with respect, Tubenit

[dwinstonwood]

Thank for posting your schematics tubenit! I've been looking at you Carolina Overdrive Special for a while. I hope my post didn't offend.

Since I've built two amps with pentode inputs, I've been wanting to try one at the end, right before the PI.

And, thanks j-b-c for that great link.

David

[sluckey]

Since I've built two amps with pentode inputs, I've been wanting to try one at the end, right before the PI.

Look at the Matchless Clubman.

[HotBluePlates]

... dimed I could not get distortion with single coils. Nice sizzle, but not grind. A pentode in the first position is a waste, as many have said. ...

Consider the bias voltage of your tube.  Unless severely mis-loaded, a tube with 2v across its cathode resistor accepts 4x the input signal before distortion than a tube with 0.5v across its cathode resistor.

Turning down the screen volts reduces plate current; it also reduces bias voltage dropped across the tube's cathode resistor as a byproduct.  The follow-on effect is the tube distorts with a smaller drive signal, because the tube will absolutely distort when peak input signal exceeds the bias voltage.

   - The challenge here is balancing "Easy dirt" with "clean when I want it."

   - The 60s Vox AC10 had a Tremolo Amplitude control that altered the screen volts of the EF86 tube.  That also made it easier to distort the EF86 when the trem was turned off.

With your new low screen volts, and low plate current, you might now need to bump up the value of the plate load resistor to get a large enough voltage swing at the output.


There's an awful lot to play with here, though you might still decide that having the pentode later in the preamp & a Volume control before it (and maybe after) allows easier control of Dirt vs Clean.

[bmccowan]

I've built circuits using the 5879 in the first position and also further down the chain.
As Sluckey suggests, it works great in the Clubman substituting for the ef86 or 6SH7.
I built a Z-28 circuit using the 5879 and years later added a dual triode in front of the pentode - adjusting the gain as needed. Both worked out really well, just different.
The Gibson GA-40 circuit uses the 5879 to good effect.
Also - any circuit using the 6SJ7, and there a dozens, can be amended to use the 9 pin 5879.
And I've built some of Tubenit's circuits - they are really good and he is generous with his advice.
6SL7 is a favorite dual triode. I built an all Octal Clubman 6SL7>6SH7>6SL7>2x6V6 - very cool amp.

[dwinstonwood]

Well...

I feel like a complete idiot.

A while back I went into my AC15 and changed the EF86 resistors. But, when I did, I connected the plate resistor to pin 1 which is the screen, and the screen resistor to pin 6 which is the plate. 

Anyway, I got those two wires sorted out and I'm now trying the DC30 values in the table below with a .01uF coupling cap (Cc).

Thanks for all the input!