E.A.G preamp - interesting design?

I've been asked to rack a pair of these - they are labeled EAG EB022/a (schematic attached)
made in the 60's in Budapest(?)

I'm trying to better understand the circuit for adding some more gain and a continues gain knob.
things i managed to understand so far:
- a cathode follower push pull design
- the switching is very hard to decipher , but i think that the lower 3 gain settings takes the input TX out of the circuit ,
  and the 3 upper settings takes out V1 and V4 out of the circuit(cutting off the filament power).
- components value is not shown on the schematic, but V1 & V2 are 12AX7 and V3 & V4 are 12AAU7 and B+ is 300V.

any insight into this is highly appreciated..
Thanks.

Pretty interesting, I can't think of anything else quite like it.  I would assume line amp with that sort of output current drive.  Fast track might be to draw out the various switch conditions on fresh paper for clarity. 

could that be called 'push-pull cathode follower'?

might this be portable gear where filament current is rationed so?

I can't think of anything else quite like it.

Click to expand...

- the sellers pitch was "just like Telefunken V72,V76"
i did not see any similarities apart of the mechanical construction which does resemble Telefunken.
actually i think its very well built..

-definitely a line amp .question is how to suck some more gain out of it..
-I'll have to draw the switching from scratch as emrr suggests, to understand whats going on ,but i think gain is managed by padding before the input TX..
both input and output transformers are heavy duty.

might this be portable gear where filament current is rationed so?

Click to expand...

i dont think its portable - a pair of modules weighs 10 Kg...!

here is another pic, thanks for your help

Hi ,
I have added some values to the schematic , and the first 3 position of the gain switch from top (1=36db , 2=30db, 3=24db)
as you can see, in the first 2 pos. the signal in going unbalanced into the input tube, and the third is using the input TX and removing the first tube from the circuit.

the impedance switch has both output tubes operating in the '200' position, and removes V4 in the '600' position.
and i thought its an input impedance switch...

That output impedance switch is the first I'm aware of. 

Anyone know more about the system these were designed for, and used in? 

EB022 is a part of old mixing console.
It was used as line amp and mixing up amp.

PS: I pmed Mich if he had any documentation on this block, it must be in Russian, need to see.

Thanks ungifted,

unfortunately, i only have this schematic and no other info...

anyway , i'll investigate some more with these and update this thread.

Hi, if the case is still actual - I've got full EAG SA010 mixing console docs.
Need some time to make a scan.

ungifted said:

Hi, if the case is still actual - I've got full EAG SA010 mixing console docs.
Need some time to make a scan.

Click to expand...

That would be a welcome addition to the Technical Docs section!  We are always looking for interesting vintage designs to learn from.

Just wanted to ask if there are any updates on this project?
I have a pair of EB022a's sitting on my bench, so any input is warmly welcome..

Cheers

No, but I can say I just recently inspected a 'portable' 12 channel EAG console from 1961, fantastic construction quality.  It's being installed locally, hope to hear it soon. 

Cool, this makes me even more excited to get these guys up & running

Just got 4x of these.  Any pointers?  How'd your rack up go?

Anyone have any info on the power requirements for these?

Yes, I will post EAG SA10 PSU characteristics after holydays (10.05)

Here is the scan of EB022 summing amp with PSU - TA042-I, TA042-II modules.
http://diyfactory.ru/forum/index.php?act=Downloads&do=download&id=200
It's in Russian, ask me if you have any questions.
In a nutshell - EB011, EB031, EB022 needs plate PSU: 300v (plus 10v max) 30mA (for EB022), filament 6.3v (plus minus 5% 1.2A)
EB011, EB031 (line and mic preamps) are more interesting than EB022 imo.
There's tranformers datasheets, please let me know if it's needed.
Update:
EB022 and EB022a are a bit different, EB022a has additional input transformer, if anyone have it, please let me know how it's labeled.

Thanks for your scanning efforts, found EB031 mic amp too and it is more interesting in a sense that not many need tube summing amp. ECC85 was used in East as output tube quite often, if compared to West. Don't why this was so because 6N1P existed, maybe it was meant for Russian market and others wanted something for radio and audio.
I would be interested in seeing signal transformer datasheets. Some of them are toroids which are potentialy cheap line levels and can be wind with GOSS, same as power toroids. This is why i'm in search for datasheet that would show the structure, local winder can only go to 20kHz at -3dB. I guess it would at least require different separated sections because of interwinding capacitances.

If I'm not mistaken these tube modules transformers are not toroid. I will scan the docs, input trafo of EB031 is not so simple, here is EB031 docs:
http://diyfactory.ru/forum/index.php?act=Downloads&do=download&id=169

ungifted said:

If I'm not mistaken these tube modules transformers are not toroid. I will scan the docs, input trafo of EB031 is not so simple, here is EB031 docs:
http://diyfactory.ru/forum/index.php?act=Downloads&do=download&id=169

Click to expand...

Those transformers don't look like toroids, i just wanted to say they were often used as outputs and not only in East. Pikatron made them, i think also Haufe. If you find similar datasheet to V72 input (obviously not toroid), it wouldn't be hard to figure out how they are winded and work on that.

Mjrippe suggested saving scans in docs section, one of older posts already has EB031 from you. All of it is interesting, i've added some RCA schematics which were deleted and replaced by another guy with the same schematics at the same place. So it seems i'm not the one who is going to do it, although i'm willing to search for your older scans if there are more. Maybe others will save them "properly".