Not a single 12ax7 with 6922 SET mic/line preamp out there?

[reinw33]

Hello,
I just searched and searched online.
There seem to be no schematics of a preamp out there that use a two stage SET topology with a 12AX7 and a 6922.
There are some schematics that use 12ax7 and 12au7 as output.
The 12AT7 has a Mu of around 65 (Wow!) and the 6922 about 35 iirc.
The 12AT7's pin out is mirrored vs the 12AX7.

Does that mean that I have to come up with the design 12AX7 with 6922 all by myself?
I would love looking someone over the shoulder tho.
Is a 6922 so much worse in perfomance as mu follower vs 12AT7?

 

[Rob Flinn]

Maybe this ?

 

[Tubetec]

Thats push pull output though .

 

[pucho812]

Maybe this ?

What’s that?

 

[Tubetec]

Says RCA in the top corner

 

[Rob Flinn]

Actually now I look at it with the right glasses on both valves are 6072/12AY7.

 

[Accelerator]

Different continents ~ Different likes…

Although the EF86 ~ E88CC (6922 in American code) in single ended topology was the preferable vacuum tube-valve combination by the British -aka EMI REDD 47 pre-amp.- , the most of the “big” American manufactures (RCA, G.E., Putman-Universal Audio) preferred the 12AX7 with 12AY7, or even better with 12BH7-A vacuum tube-valve combination, mostly in a Push-Pull topology…

So, it is way too difficult to see a 12AX7 with E88CC (6922 in American code) vacuum tube-valve combination, in any topology and you have to come up with the design 12AX7 with 6922 all by yourself…

 

[ruffrecords]

Right tubes but not SET.

Cheers,

Ian

 

[rmburrow]

Most 12AX7's were noisy. 12AY7 or 6922 a much better tube...

 

[Disco Volante]

Just out of curiosity: Why do you need something like that?
No shortage of excellent preamps out there...

 

[ruffrecords]

Most 12AX7's were noisy. 12AY7 or 6922 a much better tube...

Actually a lot of 12AX7s are microphonic. I use the Sovtek 12AX7WA which is not.

Cheers

Ian

 

[reinw33]

Different continents ~ Different likes…

Although the EF86 ~ E88CC (6922 in American code) in single ended topology was the preferable vacuum tube-valve combination by the British -aka EMI REDD 47 pre-amp.- , the most of the “big” American manufactures (RCA, G.E., Putman-Universal Audio) preferred the 12AX7 with 12AY7, or even better with 12BH7-A vacuum tube-valve combination, mostly in a Push-Pull topology…

So, it is way too difficult to see a 12AX7 with E88CC (6922 in American code) vacuum tube-valve combination, in any topology and you have to come up with the design 12AX7 with 6922 all by yourself…

Thanks for the reply. Yes, different histories.
Just speculating here.
Could the underlying reason be, as to why there are no 12AX7/6922 combinations for a mic preamp, both tubes don't go well together (oscillation?)
Or that the single 6922 simply has not enough output current to drive speakers?
I'm not looking for drive power though, just line level is enough.
That means one hast to come up with a recipe for this combo and bake the cake and hopefully with some tweaking it'll be palatable so to speak.

 

[reinw33]

Just out of curiosity: Why do you need something like that?
No shortage of excellent preamps out there...

Already got the tubes, and matched. 6922. And 12AX7, 5751, 4 Tubes total.
Looking for a SE preamp that is DIY'able.
Do you have an excellent one to share?

 

[reinw33]

Different continents ~ Different likes…

...the British -aka EMI REDD 47 pre-amp.-...

REDD 47, made by chandler, as modern production today, is not cheap, at all. 3k5€
There are plenty EF86 being offered online where I live, they throw them at you basically as NOS.
Hmmmm, might give this a try.
Would be nice to have sth. to build, which should work just out of the box.
That hasn't to be guessed in components and tweaked so to speak too too much.

EDIT: Thank you for the reply and idea Accelarator.

 

[reinw33]

Right tubes but not SET.

Cheers,

Ian

Thanks for the reply Ian.
Yes, unfortunately, it probably has to be a SET project for mic because of crossover distortion, that I don't want to get into.

 

[ruffrecords]

Thanks for the reply Ian.
Yes, unfortunately, it probably has to be a SET project for mic because of crossover distortion, that I don't want to get into.

The design is 100% class A. There is no crossover distortion.

Cheers

Ian

 

[reinw33]

@Accelerator Thank you there is something that I really like about your good post.

The design is 100% class A. There is no crossover distortion.

Cheers

Ian

Hi Ian.
I some time ago listened to a DIY PP phono preamp, and an SE. I don't know weather it was your TLA twin, but it definitely sounded hifi and great.
I couldn't notice a difference,
I'm still undecided on this.
Am still waiting on those transformers, it's been about two weeks, and they haven't even shipped them yet. But it's paid.

 

[Cqwet Dbdfte]

Hello,
I just searched and searched online.
There seem to be no schematics of a preamp out there that use a two stage SET topology with a 12AX7 and a 6922.
There are some schematics that use 12ax7 and 12au7 as output.
The 12AT7 has a Mu of around 65 (Wow!) and the 6922 about 35 iirc.
The 12AT7's pin out is mirrored vs the 12AX7.

Does that mean that I have to come up with the design 12AX7 with 6922 all by myself?
I would love looking someone over the shoulder tho.
Is a 6922 so much worse in perfomance as mu follower vs 12AT7?

https://www.diyaudio.com/community/...a-thoroughly-modern-tube-phono-preamp.163570/
I made a design based on the above.
I used the lower FET source as output, this has very low output impedance and makes the tube follower obsolete.

6922, 6DJ8 are great low noise, medium gain, very linear tubes.

As gain and transconductance is much higher in a FET (DN2540) the performance as a follower is much better.
250V plate is also not needed, 180V works great for a very large output swing.
12AX7 is not a very low noise tube compared to D3a, or its equivalents.
A passive RIAA network is better than one in a feedback loop.
Preamps are rarely PP unless driving a 600 load, which is very unusual.

 

[merlin]

Could the underlying reason be, as to why there are no 12AX7/6922 combinations for a mic preamp, both tubes don't go well together (oscillation?)
Or that the single 6922 simply has not enough output current to drive speakers?
I'm not looking for drive power though, just line level is enough.

I'm confused. 6922 driving speakers? Is this a karaoke amp?

12AX7 makes a good mic input tube, low noise, super low distortion, low microphonics, but a lot of Miller capacitance because its gain is so high. It cannot drive heavy loads, so is not great as a line driver.

The 6922 has slightly lower noise (but higher microphonics), with lower Miller capacitance because it has less gain. Being high current and low impedance, it drives heavy loads well, so people like it because it can do both jobs.

Moreover, the 12AX7 work best with higher supply voltage (300V+), whereas the 6922 was not built for such high voltage, which makes them a slightly uncomfortable pairing with regard to supply voltage. Sure, you can compromise with 250V, but then why not pair the 12AX7 with a 12AU7 which has no problem with the voltage?

If you do want to try 12AX7 with 6922, there's nothing stopping you, technically speaking, just some design tradeoffs.

 

[Accelerator]

First of all I would like to say: You welcome and thank you for your very kindly words!..

Now, to answer back to your question, we have to put in our minds that we will not have to underestimate the “power of cost factor” aka “the desire for looking to get the most of the desirable profit from the product(s)”, for all the major commercial companies, especially in the designing of the power supplies for their tube equipment(s)…

The whole 12A*7 tube “family” valves runs at 6.3V/300mA in parallel heating, but you can also runs them at 12,6V/150mA serial heating…

Even the 12BH7-A tube runs at 6.3V/600mA in parallel heating, but you can also run it at 12,6V/300mA in serial heating…

So, if in any condition that we were “in their shoes & walking in their footsteps” of most of the “big” American manufactures (RCA, G.E., Putman-Universal Audio) or Pulse Electronics- Pultec and we are looking to get the most of the desirable profit from these products, we will choose something from the whole 12A*7 tube “family” valves as we had plenty of them in our hands & the 12,6 Volt serial heating, as this cuts down in half the cost factor of Amperage, for our power supplies…

In the same way your fellow German manufacture GmBH Telefunken-Siemens choose the EF804s tube(s) and the 6,3 Volts heating for their legendary V-72 SET microphone pre-amp. & of course the EF804s tubes with the E83F tube and the 6,3 Volts heating for their legendary V-76 SET microphone pre-amp. cause they had plenty of them in their hands…

The Aveliability of tubes and the cost factor was & is a major factor in choice for everyone, especially if you consider a tube pre-amplifier as a commercial product and the E88CC (6922 in American code) was mostly an "European" tube...

A much more “advancing” alternative combination of EF86 with E88CC (6922 in American code) to the legendary British EMI REDD 47 SET pre-amp., was the very “underestimated & unknown” German RFT Lorenz AG V241 - UV300 tube microphone preamp. back at 1957.