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Old 21st August 2004, 07:27 PM   #1
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Default se otl

Having built the Transcendent sound se otl and being very happy with it I want more power for some of the other speakers I have. I am now playing with some D101a Swans by T. Nagaoka and am very happy with them, I was using Jerico horns before. While the se otl can play the swans which are ~90 db/w/m they compress at higher volumes and so the need for more power.
I saw this while looking around the net http://www.tubebuilder.com/images/sc.../otl/otlse.gif
and was wondering a few things and hoping someone here will help me out.
I am assuming (never a good thing to do) that the 4 x 6as7 is 4 tubes (8 halves) and not 2 tubes (4 halves) since it is requiring 2A for the output stage.

Also, is that some form of a local feedback circuit within the output stage between the cathodes of the 6as7's and the output side of the 2uF coupling cap?

What are you looking for with the 5k 3W VR in that circuit in terms of adjustment? Square waves or when it sounds good

Has anyone seen the power supply for this amp? I am particularly interested in the 420v driver circuit.

Anyone here ever built / heard this circuit.

It seems simple enough to me to perhaps give it a try, any hints?

and.... what is the approximate power output, I would like around 10 or so watts.

Anyone else with a se otl circuit suggestion please let me know about it.



Thanks

Andrew
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Old 21st August 2004, 11:01 PM   #2
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I too have looked at that circuite and the 5k ww resistor is used
to set the bias. Now the 6as7 is rated at 125ma max per section
so 2 x 125 ma x 4 = 1A so I I expect that the 165v 2A power
supply rating is to supply this when the grid goes +

I have been playing with a 6c33c-b biased at 300ma driven
with a choke loaded 6sn7 with some good results.
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Old 21st August 2004, 11:13 PM   #3
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Hi,

Quote:
I am assuming (never a good thing to do) that the 4 x 6as7 is 4 tubes (8 halves)
You assumed correctly.

The circuit you link to has been discussed before here:

SE OTL

Keep in mind that most of these old OTL designs were developed with 16 Ohm speakers in mind.

As you built a Transcendent Sound OTL before, maybe you can try out BR's 25W/channel PP design that was published in GA, It would go well with the 90dB/m speakers IMO.

Cheers,
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Old 21st August 2004, 11:46 PM   #4
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Default se otl

Thanks for the link Frank, I did search but did not find anything, of course when I followed your link it did look familiar

I have considered Bruce's 25W PP but would like to stay with se if possible. The only otl I have heard is his se otl and lets just say I am converted. I am considering his 15W PP version but as you can read no decisions yet.
I did consider another pp and was looking at the old Counterpoint SA-4 hoping to get one for cheap, 150w per channel from 4 x 6LF6 but besides the valves being difficult to get and expensive I understand the amp had its fair share of problems.

I did come across someone on the web who wrote of a 6c33 se otl he had built but cannot remember where.

The (higher power) se otl quest continues.

Andrew
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Old 23rd August 2004, 01:01 AM   #5
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Hi,

Quote:
I did come across someone on the web who wrote of a 6c33 se otl he had built but cannot remember where.
Hmmm...I do recal having seen a webpage where someone had that in the project cue.
Last time I checked it still hadn't materialized.

Keeping in mind you'll need to run the amp in class A and 20W of power wouldn't go amiss on 90dB/m-ish speakers you could run a couple of 6C33-Cs in PSE.

You'll need a driver with a good amount of clout to kick the grids of these powerhouses though but it can be done.

BTW, being a religious OTL inmate...you wouldn't have a copy of the SA4 schematic for me? Would you???

Cheers,

P.S. Regarding PP and SE, I could sort of meet you half way by suggesting a White CF topology (PP) for the outputstage without you having to use a phasesplitter...
The richess of the even order harmonics would be greatly reduced but so would most of the distortion anyway....
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Old 23rd August 2004, 02:17 AM   #6
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Regarding the SA-4, no I'm sorry, I don't have a schematic but this guy should.
Michael Elliott

http://www.altavistaaudio.com/SA-4.html

I am looking around though and if I find come across it I'll let you know.

Andrew
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Old 23rd August 2004, 06:59 PM   #7
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Default was se otl

Frank,

Have you ever heard of / seen the "Clive Locke" otl circuit ?

Andrew
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Old 23rd August 2004, 07:08 PM   #8
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Hi Andrew,

Quote:
Have you ever heard of / seen the "Clive Locke" otl circuit ?
Sure. It appeared in Glass Audio in '92.

To my mind it's way too complex for what it should be....and it's PP IIRC.
I never heard any feedback from anyone so I can't tell if it's any good. YMMV.

Cheers,
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