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day 28th July 2004 04:02 PM

want to make otl with 6 tung-sol 6336a
 
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Hi my name is DAY form Thailand. I have 6 tung-sol 6336a and 30 of GE 12sx7and i like to make OTL drive with 12sx7gt. can i use Andrea Ciuffoli version 8.2 but change 6c33 to 6336a
thank you
day

tubetvr 28th July 2004 10:48 PM

Hi,

6336 is quite a bit weaker than 6C33C so I would recommend to either use 6C33C or to use 2 6336 in parallell. If you connect tubes in parallell I would reconmmend to connect cathode resistors to each tube, 2 ohm minimum but higher value is better, the tubes also need to be matched carefully both static and dynamic.

Regards Hans

fdegrove 29th July 2004 12:13 AM

Hi,

Another option, using the 6336As, is the TAKI OTL which has been talked about briefly in this thread:

OTL

There's a corrected schematic in that thread as the original one had a mistake, showing a 500K plate resistor for the EF86 iso a 150K one.

Personally I wouldn't use 6336As in a OTL unless I could get lots of them really cheap.
OTLs can be rather demanding on tube quality so the much more appropriate and easier to come by 6C33-C would get my preference.
After all with just 6 powertubes you wil only have a few spares in case something goes south.

Cheers,;)

day 29th July 2004 06:21 AM

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thank every once
if i use that circuit. do i have to use fuse at output to SP?
this is my frist OTL coppy of Andrea Ciuffoli version 8.2 but drive is 12sx7. sound is very good.

Sch3mat1c 29th July 2004 03:28 PM

6336, should be easy as walkin' down the street.... 6AS7s are usually used in packs of 4 or 6, three of these per channel is about equivalent. If you're using all six for a monoblock, have at it with the 4 ohm speakers...

Tim

day 30th July 2004 01:50 PM

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i got a case now but still think about circuit what the best.

day 11th August 2004 03:33 PM

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My OTL is done sound is very very good

woody 11th August 2004 06:57 PM

Day, that is a real pretty amp. Thanks for the photo.
I have a question about tube matching in otl amps. Say
I wanted to run 12 6c19pi in parallel would I need to match
them? If so for what parimeters? or would just putting
a 100 ohm resistor before each plate and using a 5 ohm
cathode resistor be as good as matching?

Woody

fdegrove 11th August 2004 09:09 PM

Hi,

Quote:

I wanted to run 12 6c19pi in parallel would I need to match
For most OTL amps you would first have to select the tubes on a tester (emission).
Next you best select them again from a bunch in the amp proper after a few days of burn in by measuring current.

When I said for most amps I mean that some manufacturers claim that selecting isn't necessary for their particular topology.
I don't know how this turns out in practice.
I haven't heard any feedback about these amps yet.

Personally I find that for any given OTL amp I've built so far I need about 15 to 20% spares to keep the paralled tubes in line.
The 6C19-P should be easier to match than double triode such as the 6080, 6336A, etc.
Some circuits may be more forgiving than others yet I'd still recommend as much individual biasing as is feasable, especially when such large amounts of //ed tubes are used.

Quote:

or would just putting a 100 ohm resistor before each plate and using a 5 ohm cathode resistor be as good as matching?
You can put a 1 to 10 Ohm current measuring resistor on the plates of each tube together with testpoints.
However these resistors are only there for measuring purposes and won't do much to equalize current draw.
Moreover these values are best kept small as to not unduely increase the output impedance of the output stage.

Cheers,;)

day 14th August 2004 03:29 PM

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thank you frank. for my amp i use 1.5ohm at the cathode and 200ma meter on it.
woody i do not know 6c19pi and mr.frank did.


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