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Old 17th February 2013, 03:38 AM   #1
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Default pl500 based integrated OTL amplifier

hi all,

i was recently having a bit of a clean out at in the garage and came across a few items that spawned the above idea, 12x phillips pl500 sweep tubes (some 27v heater, some 12v heater), 10x hitachi 400v, 680uf capacitors and two transformers, one a 230 - 230 300va toriod and a 30va, 40v ei.

Click the image to open in full size.

i have seen a guys video on youtube (i believe hes on this site somewhere) of his pl36 based otl

https://www.youtube.com/watch?v=ksBvKeN0u5o


i am looking to set these bits up i have as an integrated otl that has tone and balance adjustments all in the one unit, nothing is new on the preamp side of things,ill share the circuit i use for this later on....

im after a few opinions on how to go about this ....i have seen a couple of schematics using pl36 tubes in otl configuration and from what i read they are not too drastically different from the pl500 (i think the dissapation of a pl36 is 16w vs the pl500s 12w?)
so was thinking to follow this schematic....

http://bildarkiv.hififorum.nu/Lord/byggen/PL36_OTL.gif

i dont have any power goals, as i have no idea what this will net, however bare in mind there is enough room on the chassis for another 12 tubes and the power supply cap array is over the top even with 24 tubes! (not too sure about what HT current will be required for 12, let alone 24! however... a 100w + per channel otl amp would be great!

anyway, thanks for reading and any advice any of you gurus have would be great!


mike

Last edited by preludefan; 17th February 2013 at 03:43 AM.
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Old 17th February 2013, 11:29 AM   #2
Ketje is offline Ketje  Belgium
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Well,yes I think it could work.With some luck,depends on the condition of the PL500's,you have 500mA peak per tube.1A5 on 8ohm gives 9W sine,somewhat like you have to put in one PL500 heater :-( .
It woudn't be a bad idea also to have a speaker protection-circuit.If a tube shortens you get 300V on them.
Mona
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Old 17th February 2013, 02:58 PM   #3
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Quote:
Originally Posted by preludefan View Post
hi all, ..... i have seen a guys video on youtube (i believe hes on this site somewhere) of his pl36 based otl

https://www.youtube.com/watch?v=ksBvKeN0u5o


i am looking to set these bits up i have as an integrated otl that has tone and balance adjustments all in the one unit, nothing is new on the preamp side of things,ill share the circuit i use for this later on....


mike
Hi mike , yes this is the related video of my PL36 OTL amp , if you are interested more information you can find here My new Circlotron OTL tube power Amp. , as for the schematic that you posted , I think it will work , but in the 300V power supply you have to put an CLC filter to minimize hum , and if you can parallel the two sections of the 6N6P ( of course with the respective changes ) you will have better drive capabilities .
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Old 18th February 2013, 05:48 AM   #4
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thank you both for the replies, dimitris, you may recall my comments on your youtube video, just want to say that you have inspired me to undertake this....

i am looking to use possibly a 12au7 in the phase inverter stage, as i have a few of these at home, any idea how they would manage driving 6 tubes?
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Old 18th February 2013, 11:49 AM   #5
Doz is offline Doz  United Kingdom
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Quote:
Originally Posted by preludefan View Post
12x phillips pl500 sweep tubes (some 27v heater, some 12v heater)
mike
Aren't all PL500s 27V, 300mA heaters??
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Old 19th February 2013, 11:41 AM   #6
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Quote:
Originally Posted by preludefan View Post
thank you both for the replies, dimitris, you may recall my comments on your youtube video, just want to say that you have inspired me to undertake this....

i am looking to use possibly a 12au7 in the phase inverter stage, as i have a few of these at home, any idea how they would manage driving 6 tubes?
Yes I remember your kind words , and I am glad that my amp inspires you to start building your project , of course you can drive 6 PL36 with the 12AU7 tube , you have to parallel the two sections of the tube , I don't test it but it will work , sure it will not have the driving capabilities of 6N6P or ECC182 , but it will work quite good , the circuit is attached below .
In case you want more power and lower output impedance you will have to use another driver/spliter tube and you will need 10 or 12 PL36 or PL500 which is very similar to PL504 .
Attached Images
File Type: jpg 12AU7 spliter.JPG (68.5 KB, 360 views)
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Old 19th February 2013, 11:46 AM   #7
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Quote:
Originally Posted by Doz View Post
Aren't all PL500s 27V, 300mA heaters??
Sure all PL500 are 300mA 27v .
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Old 27th February 2013, 08:44 AM   #8
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thank you dimitris! am now looking for someone who will sell me 24x pl500!!!

stay well friend
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Old 27th February 2013, 10:59 AM   #9
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Ask the russians.
6П13С, 6П31С, 6П36С, 6П42С, 6П44С, 6П45С is what you want.
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Old 2nd March 2013, 06:53 AM   #10
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thank you manta, 24 are on their way already, from peru south america of all places!
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