300b dpa

[howard99]

It's been out for six years or so, just wondering if there is a schematic for Vacuum State's 300b dpa out there? Any changes since it was introduced. Also anyone with experience with this amp. Thanks

[gingertube]

It is a current commercial offering and so is covered by Commercial in Confidence LEGAL requirements.
So the answer is NO, there is no schematic for it floating around the net and anyone who does have it is required by law not to disclose it.

There is, however, probably enough info around that a skilled/knowledgeable person could work it out.

So what "everyone" knows (offered in the spirit of "what everyone knows is probably wrong").

Simple 2 stage Amp.
Cascode Diff Amp front end running significant current (15mA or so per side), probably ECC88 or 6H30, powered from a "Super Reg".
MOSFET based Current Source in the cathode/filaments of the 300B's to put them in strict Class A differential mode.
A little bit of DC idle balance adjustment applied to the grids.
Choke Input Power Supply with SS rectifiers and Polypropylene Power Supply Caps.
ElectroHarmonix EH300B and Lundahl Trannies.

I don't feel comfortable saying anything more - probably said too much already.

Cheers,
Ian

[dsavitsk]

http://nutshellhifi.com/VSAC2003.html

[kmtang]

After reading the articles in the Vacuum State's web site about the DPA300B differential power amp, the way I understand that basically it is a Push Pull amp with Constant Source common to the cathodes of the two 300B's.

My only issue is how to get the balance of the 300B bias current. I think we can add a 100-ohm potentiometer that the center goes to the CCS sink and the other two legs to the 300B cathode.

I am asking my friend to try this in their EL84 PP amp that employ cathode resistor self biasing to see how the CCS improves the sound as described in Vaccum State's web site.

It would be very nice having the best things of SE and PP in the same amp... wuhhh...


Johnny

[Blitz]

Is this not doing exactly the same thing, but fully automatic ? You set once the current and it biases the tubes autmatically, replacing the cathode reistor.

http://www.tentlabs.com/Products/Tub...24/page24.html

[Nelson Bass]

Originally Posted by Blitz

Is this not doing exactly the same thing, but fully automatic ? You set once the current and it biases the tubes autmatically, replacing the cathode reistor.

Tube bias control

I'll use Gary Pimms self bias CCS between the cathodes of the 300B tubes. I consider to make a negative bias supply for this to make this part of the circuit more versatile for adjustments.

Maybe the bias circuit from tentlabs is a relevant replacement for my thoughts so far?

But I'll use tentlabs filament supplies one for each 300B as I already use the Lundahl LL1651 power transformer for my PP1CS (6.3 Volt filament).

I ordered one for test purpose and guido confirmed my request that I could order it without the heatsink and FET mounted as it does not fit my cabinet design for the 300B clone.

But I received a complete module from tentlabs! I complained and got this answer from guido: "We shipped "as is" as we do not provide other configurations".
So I got mad and p*ss*d off as it was a hazel to remove the heatsink.
So I've re-engineered the filament module and make my own PCB design for my DPA300B clones...

And yes it's possible to find almost everything needed to build a clone of the DPA300B. It will never be an exact clone but something in the same class I believe.