[Mariusz]

I happened to own Electra Print 300b monoblocks (2 300b per side) and what I assume is UltraPath Line amp - preamp with 6j5 signal tubes and 5v4gt rectifier tube. Very nice amps and preamp - keeper.
link to pictures below:
picasa album - click to open

Amplifier and matching preamplifier sounds fantastic and I couldn't be happier, however. I am a bit worry with limited information about this particular amp. From what I gathered and read about, Jack Elliano’s Direct Reactance Drive Amplifiers and his products is that most of his work is custom and that he usually builds around specific tube(s). Circuitry is tweaked and optimized for that specific tube(s) and that's how my dilemma began. Simply speaking, I have no idea what 300B tubes are used in this amp and if I can swap those with other new production tubes or something more vintage like Svetlana Winged C ? These tubes resemble in construction cheap, Chinese imitations of WE 300B tube but have no markings other then "300B" right in the middle of the glass.

Another concerning issue was mentioned in Enjoy the Music review article of similar amp. Here is small fragment from that review describing that nitty gritty problem:

" The Electraprint  has one problem. Not with the sound and normal operation, but with the biasing. Because of its setup, biasing is done by moving a connector on a variable resistor and then measuring the voltage drop change across a 10 ohm resistor. Problem with this is found inside the chassis where it is difficult to reach unless the amplifier is turned over. Therefore it is difficult to do with the amplifier in the system. Second, the variable resistor also controls the voltage to the driver tube and the two interrelate. Thus as you change the output tube bias the driver tube voltage changes. "

If anybody has any info about these amps (and preamplifier), tips, etc. please share your thoughts.

(BTW other tubes used in these amps are small radio 6an4. Also, I emailed these questions to Electra Print, Jack Elliano but was referred to circuit page on their website. Unfortunately, I am not that advance and it really did not help me in any way)

Thanks
Mariusz

[2wo]

Hi Muriusz,

I have build a DRD, I think I can help. First you say it uses 2, 300b per side. we need to find out if they are individually biased or not. some photos of the underside will help, especially of the variable resistors and any bias set resistors (10 ohm ~5W probably) I clicked on your link but just got a log in page...John 

[Mariusz]

Thanks John

I'll post more detail pictures tomorrow.
Without those it might not move forward as I am in no position to tell you anything from technical point of view.

Best
Mariusz

[mgalusha]

I would call Jack and discuss it - 702-396-4909, who better to answer any questions. Looking at the schematic he has on the site I see the resistor in question but that schematic only has one 300B per channel. I agree this would be a fiddly adjustment for a non technical type.

[Pez]

Ya, but you gotta start somewhere! I'd love to hear your experience with this project. I say go for it.

[Scott F.]

Mariusz,

Although I don't have any experience with the PP version of the DRD, I use the standard Wellborne SET 300b DRD.

When it comes to output tube choices, the DRD isn't too picky. I've tried Sovteks, Shuguangs and the TJ or Sophia Mesh Plates with no issues whatsoever.

That said, I did try a pair of Sophia Carbon Plates and had issues. At low volumes they played fine when driving a pair of Altec VOTTs. When I turned it up, the reactive nature of the speakers gave the carbon plates fits while the other tubes worked fine. I would get popping and channels dropping out. I know that sounds a bit weird but I've got to believe that it was due to the design parameters differing too much from a standard 300b tube.

Oh, and on the tubes that worked fine in my amps, I didn't alter the bias resistor. I simply ran with the the one specified in the build.

I want to say that my DRD input tube is the 6N1P (going from memory). It could be changed out with the 6AN4 with some minor circuit changes (as I've read).

You might try going to Archive.org and look up the old Wellborne Labs Forum that AA used to host. There were a number of threads (as I remember) that explained which parts needed to be swapped out to accommodate a different driver tube. Keep in mind on that DRD circuit, the design parameters of the tube play a heavy effect on the overall circuit. Not all tube equivalents will work without circuit mods.

[2wo]

The more I think about it, if you have pairs of 300B's that draw more or less the same current . Plug them and let it rip. Keep an eye on things, no red on the plates. not likely, but watch.

You can ask your tube guy about matched pairs. Every good power triode  I have bought new, has had had a number and they have been pretty close...John