The Rosenblit 6AS7 OTL

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Paul Barker
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#1 The Rosenblit 6AS7 OTL

Post by Paul Barker »

OK lets have a look at it.
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I once built it in mono and the memory of it was something which has always stuck with me. That nice sound of the 6as7's most people by now have heard, but with the overmushy 2nd harmonic quashed, and without the output transformers the sound is something you just have to hear. It is something I now struggle to describe. But an overriding memory is the soundstage was huge in size compared anything else I ever made. The 6em7 as an output valve comes second to it for imaging. But is less powerful.

I haver heard a couple of OTL amps which use other valves and they don't have the same lovely sound of the 6as7. Sorry.
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Paul Barker
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#2

Post by Paul Barker »

The 150v can be achieved from a builders 110v transformer. So I put a 110 commando plug on the power supply section and when I get in from work take my transformer indoors and plug in. More current capability than Rosenblit ever dreamed of.

Sorry no good, only gives you either the +150v or the -150v. Would have to use a 1:1 isolating transformer. Fortunately I have one.
Last edited by Paul Barker on Sat Mar 31, 2012 1:21 pm, edited 1 time in total.
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Ali Tait
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#3

Post by Ali Tait »

Yes Paul, if you recall the get together we had at my house in Leeds, I remember Clive's otl well, the main impression of which was the huge soundstage.
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Paul Barker
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#4

Post by Paul Barker »

Can't just find my rosenblit book. But you need a lot of different voltages.

You treat your output valve +/- 150v supply as a seperate entity, this is where the power comes from it is a high current supply, so it just has a large bank of capacitors on it.

Then you have your +550, +300 and +135, but non of those need a lot of current. You could start with 550v and pick off the other two with voltage deviders.

The bias is something like -60v if I remember rightly. So for the positive bank of valves you could also pick that of the above. So you just have a -60 (or whatever it is) supply for the bottom bank.
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Paul Barker
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#5

Post by Paul Barker »

Ali Tait wrote:Yes Paul, if you recall the get together we had at my house in Leeds, I remember Clive's otl well, the main impression of which was the huge soundstage.
Yes, I had already built mine by then and I recon the 6as7 one sounds better.

But the huge soundstage seems to be a family trait.

I always thought having heard the difference between this his original statement on OTL and what Clive brought, that Rosenblit felt he had to change the design into something which he could then patent, as this is far too close to original former designs such as Futtterman and Atmosphere. I suspect he had to come up with something different to bring it to market. I felt then that was not necesarily an improvement.

I may be wrong about all those thoughts it is only a lay person's perspective.

Similarly his most recent stuff which is different to what Clive had may be superior to the 6as7 OTL.
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Paul Barker
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#6

Post by Paul Barker »

The bad news is I can't find Rosenblit book.

The good news is I found my Electronic Universal Vade-Mecum, so if anyone wants a spurious valve looking up that they can't find the data on anywhere else pipe up.
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colin.hepburn
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#7

Post by colin.hepburn »

Paul Barker wrote:The bad news is I can't find Rosenblit book.

The good news is I found my Electronic Universal Vade-Mecum, so if anyone wants a spurious valve looking up that they can't find the data on anywhere else pipe up.
Hi Paul
Don't suppose you can shad some light on the true data of this Russian 6P3S/6n3C cant seen too fine a consistent spec on this valve

some say for example anode voltage is anything from 250/500volt and cathode anything from 44mA to 72+_18 Equivalents of 6L6 6L6GT they say but who knows any ideas :(
http://ussr-tubes.com/index.php?main_pa ... cts_id=307
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#8

Post by Neal »

I think Rozenblit change the cct from that original one Paul, certainly the one published in 'Audio Reality' has some changes, including 170v HT, a 'bootstrapped V3' and the use of EL509...apparently for reliability, he found the 6AS7 would fail occasionally.
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#9

Post by Paul Barker »

Neal wrote:I think Rozenblit change the cct from that original one Paul, certainly the one published in 'Audio Reality' has some changes, including 170v HT, a 'bootstrapped V3' and the use of EL509...apparently for reliability, he found the 6AS7 would fail occasionally.
You couldn't email me a copy of the page could you? v1505guyatgmaildotcom
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#10

Post by Neal »

Ah! Ignore that I hadn't fully read the thread! :oops:
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#11

Post by Neal »

Paul Barker wrote:
Neal wrote:I think Rozenblit change the cct from that original one Paul, certainly the one published in 'Audio Reality' has some changes, including 170v HT, a 'bootstrapped V3' and the use of EL509...apparently for reliability, he found the 6AS7 would fail occasionally.
You couldn't email me a copy of the page could you? v1505guyatgmaildotcom
Sure, I'll scan it later...
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Paul Barker
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#12

Post by Paul Barker »

Ta.
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Paul Barker
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#13

Post by Paul Barker »

colin.hepburn wrote:
Paul Barker wrote:The bad news is I can't find Rosenblit book.

The good news is I found my Electronic Universal Vade-Mecum, so if anyone wants a spurious valve looking up that they can't find the data on anywhere else pipe up.
Hi Paul
Don't suppose you can shad some light on the true data of this Russian 6P3S/6n3C cant seen too fine a consistent spec on this valve

some say for example anode voltage is anything from 250/500volt and cathode anything from 44mA to 72+_18 Equivalents of 6L6 6L6GT they say but who knows any ideas :(
http://ussr-tubes.com/index.php?main_pa ... cts_id=307
See Vade Mecum thread under Valves topic so all valave data related stuff can be easily found. I am sorry that I don't think I had anything to add to your quest but have a look anyway.
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#14

Post by Neal »

Paul, its 9mb inc the write up...hope it come over OK...
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Paul Barker
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#15

Post by Paul Barker »

Thank you it has arrived.

Just had a very quick flash at the schematic and it occurs at a very brief look that a hybrid of the two versions in which the 6as7 is used might be the best.
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