EAB VE12 Tube Preamp Dual Power Supply Question????

[leadbreath]

Hi All,

I have a EAB VE12 Tube Preamp/Channel strip on the bench and not sure about the Power supply requirements?
I see a 320V/3mA Supply and it looks like another just above it at 200V/0.7mA??

Am I right here? I have posted the Schematic, with the second one indicating the second supply in question, any help will be greatly appreciated as always!!

Mick

 

[leadbreath]

Sorry for the crappy schematic its the only one I have....

 

[DerEber]

I think your right here.
It may only be 0.6mA, but thats roundabout it.

 

[DerEber]

Whats your plans with this unit?
I ask because it has Hi-Z output.
beste greetings,
Stephan

 

[leadbreath]

Hi Stephan

Thanks, unit is to racked up for customer, busy sorting out the PSU.
Its the first time I've seen one with dual supply???

 

[leadbreath]

What is significant about the high impedance output??

 

[DerEber]

Thanks, unit is to racked up for customer, busy sorting out the PSU.
Its the first time I've seen one with dual supply???

If I remember correctly the original PS had better filtering for the voltage going to the first stages.
Imagine to provide proper voltages on a bigger desk was another challenge back then, then it is now.

 

[leadbreath]

Ahh yes that makes sense!

 

[DerEber]

If your planing to calculate and add proper output transformer please keep me informed about your outcomings.
Also before doing anything else I'd check if the input transformer. Mine were broken on every unit.
Greetings from Munich!

 

[leadbreath]

Hi DerEber

Greetings from North London!!
Yes I heard about the inputs Transformer issues luckily this one checked out OK!!
The problem is how they are mounted with that sponge that perishes then transformer is loose in enclosure, not good!!
For output TX we have a few to play around with (V72/UTCA24/Sowter) etc.
Will let you know what works best...

 

[leadbreath]

Hi Stephan fyi, we finally settled on an original V72 tx for output. Was the best sounding of all units we tried(UTCA24/ Sowter/Tordarson).

 

[corgan4321]

Hi Stephan fyi, we finally settled on an original V72 tx for output. Was the best sounding of all units we tried(UTCA24/ Sowter/Tordarson).

Hi leadbreath,

I have a VE12 as well. And need to get it racked up! What did you settle on for the power supply? I was thinking about using the JLM scorpion but it only goes to 300VDC.

Did you hook up the V72 Output transformer directly to the output? I am not sure if the preamp alone can drive a transformer?

Have you measured good THD?

Thank you.

 

[corgan4321]

Also, I will add that my schematic is from 1963 and has lower current draws written on it. 320V/2ma and 200V/.5ma

Haven’t studied if your older 1961 schematic is different otherwise.

 

[leadbreath]

Hi Corgan

For power we used 2 seperate psu's one for the 320V and another 200V/ heaters.
We had these prebuild and are based on Ian (Ruffrecords) HT PSU schematics thst can be found on his website.

 

[leadbreath]

Thanks for schematic, have noted that the one we have is quite different to schematic I posted earlier. Only really used it for PSU requirements and figuring out I/O's.??

 

[leadbreath]

As for output, yes direct out, only testing we really did was comparing waveforms on scope onOutput, there definitley was some distortion to waveform but listening test were good!!!

 

[leadbreath]

Customer has some hispec transformers on order (think Jensen/Cinemag) tgat hw wants to try, but will be shocked if they sound better than the V72 output tx!!

 

[corgan4321]

Hm yes distortion should be very low. My spec sheet says below 1% so I don’t imagine you should see anything on a scope depending on frequency.

I really don’t believe this channel strip is meant to directly drive a transformer. I would love to have the input of a tube designer like Ian - what type of output configuration would be a good match for this topology?

 

[leadbreath]

Hi, Corgan as mentioned our unit was very different to the schematic, wanted to trace it out but didnt have time. Not sure if this unit was modded after production but all caps were old german types and solder looked original so suspect it was EAB build but cant be 100% sure...

 

[leadbreath]

Also when I mentioned distortion I meant sine wave was slightly distorted on output, no THD figures as such...