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Old 23rd April 2013, 04:29 PM   #691
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hi Felipe,

The 9351 will work with a 307A, if your load is somewhere around 600/300/150/40 ohms specified for Sowter 9351.

The 9351 offers around 5W - if that is enough. I assume you are not working with the 'Difficult' headphones, that Regal is aiming for.

Beware of running the 307A at 400V+. Ale's curves seem to suggest it will have lower distortion at nearer to 300V.

You could try to plot a 5K load line on 307A curves and see how they look. Or you could just build, since you have the 307As already!

If it doesn't work out, the transformers can be used with many other triodes, including 300Bs: 325V to 350V will work with these, also - but 45mA max dc though.
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Old 23rd April 2013, 04:37 PM   #692
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Hi Rod,

Thank you for opt advice.

I don't know how I can plot a 5K load line on 307A curves.

About power transformer how much power? how many secondaries one for 4p1l and one for 307a or only one for both tubes?

What about the power transformer & psu necessary for your heaters reg for 4p1l, wich transformer: voltage/power necessary for 307a heaters?

A big thanks for your support Rod.

Last edited by merlin el mago; 23rd April 2013 at 04:41 PM.
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Old 23rd April 2013, 04:47 PM   #693
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Wow, total cost for 2 Sowter opt incl. shipping 450€ near the 500€ Bartolucci asked, now I doubt wich one to purchase having in mind that Bartolucci are custom made and Sowter not.
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Old 23rd April 2013, 06:17 PM   #694
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Hi Felipe,

If you are sure that the 307A wll meet your Power demands, you can just build it, but I recommend 300-325V dc for this tube, unless you can get better information. Many other triodes work with 5K loads, even EL84 in triode mode - so you can use the OT with confidence.

For PT, you can achieve 325V dc with this trafospec.:

0-350V 75 to 100VA
EI-structure of core, with split bobbin (= dual bobbin)
choke-input filter
choke 5H 100mA

If using SSHV, then trafo is 370V rms 100VA-rated.

Please use a private transformer for the filament heating (important!)

Have you considered the Tribute versions of OT, also?
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Old 23rd April 2013, 06:20 PM   #695
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Please model the PSU with PSUD2, to fine-tune the transformer specification!

use choke-input filter.

You can see the demand on the trafo by looking at the rms-current column in the PSUD2 output.
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Old 23rd April 2013, 06:27 PM   #696
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How much cost the Tribute?
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Old 24th April 2013, 09:49 AM   #697
regal is offline regal  United States
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Quote:
Originally Posted by merlin el mago View Post
How much cost the Tribute?
The Tribute I ordered one is of nano-tech non-amorphous core (finemet), its fairly experimental for this application although has been done with the Japanese Feastex Takatsuki 300B commercial amp.

I would recommend contacting Tribute thru email for pricing, but he has a lot of business, so since this is a developmental OPT you may want to wait till it is a standard product.

I will be building my DHT SET headphone amp with 2A3 output tubes after Ale's not so good measurements of the 307A. I think the new JJ-2A3-40 and Chinese 2A3-C's which are basically 300B's with 2.5V filaments are ideal (the sims show much better linearity with 300B than an other DHT short of the HV transmiters.) Would be interesting to see Ale's measurements of these modern 2A3's-300Bs.

I plan on IDHT drivers in order to keep it 2 stage, just not enough gain from small signal DHT's for 2-stage.
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Old 24th April 2013, 05:45 PM   #698
mogliaa is offline mogliaa  United Kingdom
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Hi Regal,
I don't have any JJ-2A3-40 or Cs unfortunately. I do have 6C4C and classic 2A3 and recently someone gave me an EH 300B which I will trace as soon as get some time
Cheers,
Ale
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Old 24th April 2013, 05:54 PM   #699
iko is offline iko  Canada
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The good side effect of this is that the price of 307a has dropped significantly.
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Old 24th April 2013, 06:01 PM   #700
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The JJ 2A3-40 does not inspire confidence, for working above the usual 2A3 voltages.

compare the published curves:

http://www.jj-electronic.com/pdf/2A3.pdf


And, to keep the comparison fair - intramural, even - please see their 300B:

http://www.jj-electronic.com/pdf/300%20B.pdf

And see how the 2A3's behaviour goes bad, much above 400V.

The 40W thermal rating is deceptive. It's the internal geometry that makes the 300B the beauty it is (when well fed, and watered).

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