6AU6 in Push Pull: Opinions please

[kruesi]

The idea of using a pair of 6AU6s for a lower power application intrigues me... Honest-to-goodness tiny little beam tubes in a 7-pin base! The RCA manual says they're pretty much the same as a 6V6 within their ratings... I'm thinking a pair of these in ultra linear ought to make for a pretty good sounding output stage for a receiver I'm thinking of building.

I'm looking for low distortion, about 10W output, and a compact design. Could use 6BQ5s I guess, but the idea of true beam pentodes sounds better for some reason. I also found the 6973 (or was it 7369?) but my goodness, they want $30 a pop for these beauties- and it looks like they're a bit rare. 6AU6's are available everywhere, at bargain-basement prices (well, ALMOST...) I only hope there's not a good reason for that.

Strangely, there's almost a complete lack of information/results out there from anyone that's actually built anything using them- it's as if the world hasn't heard of this tiny little miracle...!

Or are they junk?

Anyone have any actual experience in using these for a 10W audio amp? How did they work out?

[Shoog]

I've used them as LTP drivers and they work well.

10W seems a tad ambitious.

Shoog

[rojoknox]

Greetings from FixitLand!

Originally Posted by kruesi

The idea of using a pair of 6AU6s for a lower power application intrigues me... Honest-to-goodness tiny little beam tubes in a 7-pin base! The RCA manual says they're pretty much the same as a 6V6 within their ratings... I'm thinking a pair of these in ultra linear ought to make for a pretty good sounding output stage for a receiver I'm thinking of building. <snip>

I think you've confused 6AU6 with 6AU5-GT...6AU5-GT is in fact a beam power tube (octal base) for TV H sweep applications with 10 W plate dissipation rating in that service. 6AU6 is a small-signal 7-pin sharp-cutoff pentode with 3.5 W plate dissipation rating -- nowhere near a 6V6 <grin>.

Or you're thinking of a 6AQ5, which IS a 7-pin near-equivalent of a 6V6. I used a couple 6AQ5s in P-P (not UL) in the homebrew radio I built a few years ago; sounds great.

Take care,
--
J. E. Knox 'The Victor Freak'

[Bandersnatch]

hey-Hey!!!,
The 6AU6 is a three-grid, signal pentode pentode. I don't think you'll get 10W; not enough plate dissipation. 2W should be possible.
cheers,
Douglas

[kruesi]

AAAUUUUGH!!!

I meant 6AQ5, not 6AU6

Yes, Shoog... 10W is a bit ambitious for a pair of 6AU6 pentodes designed for RF amp service...!!

And Rojoknox, tnx for waking me up! You did succeed at guessing what I was *really* thinking about!

<groan> Sorry for the confusion!!

[45]

Originally Posted by kruesi

I also found the 6973 (or was it 7369?) but my goodness, they want $30 a pop for these beauties- and it looks like they're a bit rare.

You could try with the EH 6973's. They are very good indeed.
You can buy a matched quad for 60$.
Cheers,
45

[TheGimp]

6AQ5 is a beam Tetrode (6BQ5 is a Pentode).

That aside the 6AQ5 should make for a nice amp with 8W (UL) to 10W(Straight Tetrode PP. If you need more than 10W you could go with a 5K p-p transformer and do a Parallel Push Pull, but getting tubes matched close enough might be an issue.

I'm working on a 6P1P-EV PP version with selectable UL or not.

[Geek]

Originally Posted by kruesi

AAAUUUUGH!!!

I meant 6AQ5, not 6AU6

6AQ5 == minature 6V6. Use any 6V6 schematic


Though when I was a kid, I made a modulator for a mini AM TX from a pair of PP 6AU6 and it worked OK

Cheers!

[kruesi]

Yes, I've got an H.H. Scott 299B amp with 6BQ5 pentodes... A nice amp, to be sure, but after designing with beam tetrodes, it seems I can do better on performance (notably distortion) than by using pentodes.

I don't need much power- I'm thinking of making an AM/FM radio but paying attention to getting the best fidelity possible (instead of the usual single-ended 50C5, use a pair of 6AQ5s, and instead of a diode detector, use a product detector, synchrodyne, or some such) etc. etc.

So a few watts is fine. Even 2-3 watts of really clean audio would be a vast improvement over what the All American Five typically offers.

The 6973 looks like a GREAT tube... I may give it a shot despite the cost... I just thought that if I could get good results from a pr of 6AQ5s, why not? -But if someone knows why not (if there's something fundamentally wrong with the idea) I'll go straight to something better- likely 6973s.

I'll have to look up the 6P1P-EV thing... not familiar with that. It'd be fun to be able to switch UL or not while listening (avoiding any big transients, etc). I made measurements and convinced myself that UL would likely sound better, but there's nothing like actually LISTENING in a real A-B way to decide for real.

As Dan von Recklinghausen said, "If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you've measured the wrong thing."

[TheGimp]

The 6P1P seems to be a Russian equivalent of the 6AQ5, with a different pin out. I've seen a few sellers advertising it as a 6BQ5 equivalent which it is not (6P14P is close to 6BQ5).

I think the military (XXXXX-EV) tubes are supposed to be better quality than the standard tubes.

Low power + good speakers = pleasant listening