Anyone done a PI driver with 6V6's?

[LeftyStrat]

I posted this link a while back:

https://tubeamparchive.com/viewtopic.php?t=17830

It was suggested to me ages ago, by who, I don't remember, that this was similar to the Winterland. It certainly shares some similarities to the Odyssey.

Again another case of anode followers.

[vibratoking]

I think the term 'anode follower' is silly, but I also know of papers that have been written using that term! I thought it was silly many years ago.

'Anode follower' is ridiculous IMO. A cathode follower is technically known as a common anode gain stage. Cathode follower came about in a slang sort of way because the output taken at the cathode 'follows' the input - same phase and approximately a gain of 1. In the 'anode follower' case, the output taken at the anode does not 'follow' the input in any way whatsoever. This makes 'anode follower' misleading and incorrect IMO.

This is not a tomato tomahto thing. This is really about using language that is descriptive, accurate, and not misleading.

[talbany]

I think the term 'anode follower' is silly, but I also know of papers that have been written using that term! I thought it was silly many years ago.

'Anode follower' is ridiculous IMO. A cathode follower is technically known as a common anode gain stage. Cathode follower came about in a slang sort of way because the output taken at the cathode 'follows' the input - same phase and approximately a gain of 1. In the 'anode follower' case, the output taken at the anode does not 'follow' the input in any way whatsoever. This makes 'anode follower' misleading and incorrect IMO.

This is not a tomato tomahto thing. This is really about using language that is descriptive, accurate, and not misleading.

+1

The term follower ie," cathode follower" is used to quantify identical phase relationships..Hence the term follower.


http://www.freewebs.com/valvewizard/accf.html

Have a Good One!!

Tony

[LeftyStrat]

Yeah, that term always confused the heck out of me.

But it seems the two configurations; post-pi driver vs post-pi cathode follower have different goals?

The DC driven CF eliminates the coupling cap, and thus the associated blocking distortion, whereas the post-pi driver is to hit the power tubes harder.

Correct?

[LeftyStrat]

Here's a design that uses pentodes as post-pi cathode followers:

http://ken-gilbert.com/the-big-ass-guitar-amplifier

600 watts!

[Max]

Advantage of the CF arrangement is ... increasing overall amp clarity.

On paper this might be correct (I don't know). But AFAIR my personal perception it was exactly the other way round: A Dumbleland Special 150W kind of power amp e.g. with some version of such a kind of "non-CF" 12AU7 / 12BH7 configuration was in my personal perception clearer and purer sounding than some SSS 150W with the 7025 / 7025 "CF" power amp version (12AU7 /12BH7 versions of the Steel String Singer 150W exist, too) in direct comparision. Exactly as Alexander Dumble statet: "silky clean" - at least without the filters set up for a more "glassy" tone and without intentionally driving the preamp into distortion: ("I actually started making a series of amplifiers called the Dumbleland in about '66...it was a design way ahead of its time. It was too much power and too silky clean for people. It's perfect for Stevie Ray, though." ) http://personalpages.manchester.ac.uk/s ... /Articles/

Cheers,

Max

[FUCHSAUDIO]

Interesting Max. Not having tried both circuits (especially not side-by-side in the same amp under the same conditions), I was only speculating. Might be fun to make a chassis up with both circuits and do a direct comparison.

[talbany]

A Dumbleland Special 150W kind of power amp

Max
I believe at one point you mention your desert island amp as being such a Dumbleand..Does your DI Dumbleland have this driver circuit in it you mention..

On paper this might be correct (I don't know). But AFAIR my personal perception it was exactly the other way round: A Dumbleland Special 150W kind of power amp e.g. with some version of such a kind of "non-CF" 12AU7 / 12BH7 configuration was in my personal perception clearer and purer sounding than some SSS 150W

Thanks..

Tony

[Max]

Does your DI Dumbleland have this driver circuit in it you mention..

Tony, if you buy one for me and carry it around (and the shoes of plus one?) on the island along with a 4x12" - Yes!

- "this driver" in the sense, that I'm sure that the plates of the 12BH7 are cap coupled to the grids of the power tubes. But all the other details might be more or less different from what is shown in this Odyssey schematic.

BTW: If a Dumbleland Special 150W shouldn't be available, a SSS 150W with a 12AU7 / 12BH7 configuration might find a taker, too. And in a pinch perhaps even a 300SL.

Cheers,

Max

[LeftyStrat]

I think might be the guilty party for using the term 'anode follower.' Upon further reading:

http://www.aikenamps.com/anode.pdf

An anode follower always has negative feedback, which is not the case with these post-pi plate coupled drivers.

I also found an interesting discussion of the post pi cf in the SVT here:

http://music-electronics-forum.com/t23357/

The most enlightening quote:

"I think the cathode followers in the SVT are there mainly to drive the bias feed resistors, which have to be a low value to avoid thermal runaway of all those paralleled tubes."

Of course, that wouldn't explain why it was done in an amp like the Heathkit W6M, which has a single set of 6550's.

[vibratoking]

Lefty - I saw that article many years ago. What they are describing in that paper ain't a follower. Their terminology is incorrect IMO.

[LeftyStrat]

Lefty - I saw that article many years ago. What they are describing in that paper ain't a follower. Their terminology is incorrect IMO.

So exactly what IS an anode follower?

[vibratoking]

IMO, an anode follower cannot not exist. The anode part indicates that the output comes off the anode, so it MUST be inverted compared to the input at the grid. The follower part indicates that the output has the same amplitude and phase as the input i.e the output is exactly the SAME as the input. The term is an oxymoron.

[Max]

AFAIR you'll meet "inverter / driver" circuits at least in these Dumble amps:

12AU7 / 12BH7 Odyssey (Concert, Bass, Special):
https://tubeamparchive.com/viewtopic.ph ... 153#219153
https://tubeamparchive.com/download/file.php?id=13132
https://tubeamparchive.com/download/file.php?id=17340
https://tubeamparchive.com/download/file.php?id=15536
https://tubeamparchive.com/download/file.php?id=13170

12AU7 / 12BH7 Winterland:
http://personalpages.manchester.ac.uk/s ... 20%230003/
https://tubeamparchive.com/viewtopic.ph ... 443#219443

12AU7 / 12BH7 Dumbleland Special 150W

12AU7 / 12BH7 Dumbleland Bass 150W

12AU7 / 2 x 12BH7 Dumbleland 300SL

12AU7 / 2 x 12BH7 8 x 6550A Winterland power amp

12AU7 / 12BH7 SSS 150W:
https://tubeamparchive.com/viewtopic.php?p=66244#66244
https://tubeamparchive.com/viewtopic.php?p=66426#66426

7025 / 7025 SSS 150W: https://tubeamparchive.com/viewtopic.php?p=66244#66244

7025 / 7025 "Silver Alligator" EF 86 Dumbleland

7025 / 7025 SSS 100W: https://tubeamparchive.com/viewtopic.ph ... 738#204738

7025 / 7025 ODS 150W

And AFAIR sometimes the feel and timbre of the clean sound of two specimens of the 7025 / 7025 amps is less similar than the timbre and feel of two other specimens - one with some 7025 / 7025 version, and one with some 12AU7 / 12BH7 version. So the 7025 / 7025 configurations all might be more or less different in technical detail and perhaps all the 12AU7 / 12BH7 configurations, too?

So IMO generalizations like "7025 / 7025 Dumble power amps sound like this" and "12AU7 / 12BH7 Dumble power amps sound like that" might be inappropriate.

But as sometimes it's known what kind of Dumble amp has been used for a live performance or a recording (some examples: https://tubeamparchive.com/viewtopic.php?p=66244#66244 ) you all can get a personal impression in regard to what differences you perceive between the overall sound of some original Dumble amps with different "inverter / driver" circuits.

Cheers,

Max

[tictac]

In the Odyssey schematic the one plate load for the 12AU7 is not 4.7k; looks more like 17k or 27k...

TT