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Old 13th November 2011, 06:25 PM   #401
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by Alastair E View Post
With mine, if you listen at the speaker-cone from 6" there is discernable hum.

Thats not really surprising, as I have only around 4,500uF on each of the main O/P stage rails.

At normal listening distance in a quiet room, I cant hear it though...

Have you tried 'biassing up' the heaters to around 40V on the input/second-stage valves?
I will look at biasing up the input tubes ...I think there at about 20V at the moment..

I know it made a big difference when I made the Aikido pre..

What values did you use for the divider?

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M. Gregg
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Old 14th November 2011, 06:19 PM   #402
M Gregg is offline M Gregg  United Kingdom
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Alastair,

I think you've done it again...

I guess the 20V lift was not enough for the 6SN7's.
So to keep to standard values and keep the current down because it's a ref voltage, I just used 680k and 100k gives me a lift of 42.5V on the DC heaters.
I did think about just using the cap to Gnd trick to allow the leakage to charge it but..
So there you go!
Few more tweeks to try..
Mainly component changes..
Did you ever try the Electronic choke?

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M. Gregg
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Old 14th November 2011, 06:34 PM   #403
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Ah--Good, glad to hear the hum--or lack of it!

Not tried the ripple-filter/eleccy choke on the rails yet...

What other tweaks have you got in mind...?
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Old 14th November 2011, 07:30 PM   #404
M Gregg is offline M Gregg  United Kingdom
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Just for interest,

I find this inspires me:

otl amp.handmade with 12 PL36 tubes per channel . - YouTube

Thinking about Maida reg on the pre/driver..
Just waiting to see what Mr Murre finds with his regulators..
Think he could have extruded the wire and wound a Tx by hand ..
perhaps he is!!

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M. Gregg
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Old 14th November 2011, 10:12 PM   #405
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Current-drain on the driver/pre rail is pretty low, and wont significantly alter with signal.

I very much doubt there will be any significant change in regulating that supply, providing its got good filtering to start with!....

That otl on utube, Looks to have a LOT more PL36 than 12!

More like 16 or 20 if you count 'em! There's 4 rows of at Least 4 valves under those fans...
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Old 15th November 2011, 04:26 PM   #406
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by Alastair E View Post
Current-drain on the driver/pre rail is pretty low, and wont significantly alter with signal.

I very much doubt there will be any significant change in regulating that supply, providing its got good filtering to start with!....

That otl on utube, Looks to have a LOT more PL36 than 12!

More like 16 or 20 if you count 'em! There's 4 rows of at Least 4 valves under those fans...
It’s interesting that the pre/driver supply can be heard through the speaker. I know this because HT off Heaters Off in power stage.. yes still very quiet but you can hear it pull the pre supply fuse and its gone. Not surprising because the supply goes via feedback through 150 Ohm and speaker coil. LOL And yes not significant gain to be had their me think's.

I think it would be interesting to look at the main PSU ripple. .Space may be a problem..Mr Murre lets hear the outcome....

Alastair, I can agree it is very rugged. Power off all heaters switch the HT pull the 6c33c's while warm plug them back in, pull them again..OK i had power off!
Switch in and out heaters one or two or none and back on again!
Might try bypassing the choke with a .1uF it worked well in the past!
Some different bypass caps on order!

And yes I am convinced OTL...No Tx!

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M. Gregg
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Old 15th November 2011, 10:04 PM   #407
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Default Decoupling filter-caps..

Using 0.1uF film caps to de-couple the filter cap supplying the pre stages should be a good idea, and if you have a larger value, up to 10uF may be good.

The two 'heavy' supplies for the O/P stage prob need around 25uF film-caps to amke any significant differences sonically....

--Even then, The effect will probably be minimal, but if you have them, might as well shove 'em in there...
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Old 19th November 2011, 10:12 AM   #408
M Gregg is offline M Gregg  United Kingdom
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Just for fun link..

Servicing of a Musician OTL Hi-Fi Amplifier

Normal service will be resumed ASAP
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M. Gregg
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Old 19th November 2011, 05:40 PM   #409
poynton is offline poynton  United Kingdom
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Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)
...an interesting use of the small transformers as chokes ......

I have a load of those but no chokes !



Andy

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Old 19th November 2011, 07:14 PM   #410
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Seems like a good idea but my gut reaction is there won't be enough inductance to be any real use. I've got a 12VA 12-0-12 very similar - I'll test it later when I get this sick pair of Quad II's off my bench. I did once use the 2 x 110V primaries of this same tx as a line level isolator - it worked surprisingly well.
Simon
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