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Vacuum Tube OTL power amp!!
Vacuum Tube OTL power amp!!
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Old 14th November 2011, 06:30 PM   #401
M Gregg is offline M Gregg  England
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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, 09:12 PM   #402
Alastair E is offline Alastair E  Wales
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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, 03:26 PM   #403
M Gregg is offline M Gregg  England
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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!

Regards
M. Gregg

Last edited by M Gregg; 15th November 2011 at 03:56 PM.
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Old 15th November 2011, 09:04 PM   #404
Alastair E is offline Alastair E  Wales
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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, 09:12 AM   #405
M Gregg is offline M Gregg  England
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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, 04:40 PM   #406
poynton is online now poynton  United Kingdom
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...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, 06:14 PM   #407
EssB is offline EssB  United Kingdom
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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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Old 19th November 2011, 06:39 PM   #408
M Gregg is offline M Gregg  England
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Originally Posted by EssB View Post
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
I have tried it a couple of times it depends on application..The only thing I did not see mentioned was that quite a high voltage can appear on the disconnected primary inder some conditions so they need insulating...
Just thought it might be interesting..

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M. Gregg
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Old 19th November 2011, 06:58 PM   #409
M Gregg is offline M Gregg  England
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Alastair..
Just thinking out loud here..

While after 4hrs listening to the OTL with Deadmau5 (for want of a better name)

deadmau5 "16th hour" - YouTube
Got to test the bass haven't you..

Shakes my laptop across the table.. and hammers the Alpairs into submission
Very deep bass....anyway..yes there are fuses and bypass caps just not on this pic...
Some discussion going on....
Sounds great!!







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M. Gregg
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Old 19th November 2011, 07:08 PM   #410
Alastair E is offline Alastair E  Wales
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Opening titles, 'Lethal Weapon III' also demo the bass capabilities fairly well....

The original Sting track doesnt contain the added LF portions, so it must be the film itself....
Its one of the items I use for checking....

Pretty sure as I recall (Will have to confirm...) That the CT of the mains Tx is connected to the centre-point of the caps, (ie--direct, no 1K resistor) in my amp...

Been thinking of trying those 12V 50VA tx I have as chokes on the two lines, although the hum isnt a problem with mine--Just out of curiosity....
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