6C33B-C push pull with output transformer - diyAudio
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Old 12th September 2006, 09:39 PM   #1
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Default 6C33B-C push pull with output transformer

I would like to make a push pull amplifier using 2 6C33B-C triodes per channel with output transformer, to get about 50W class AB and no feedback. A 50W push pull OTL would required too many output triodes.

I would use 6C33B-C for the mid bass-midrange to get sound same family as my 6C333B-C treble amplifier
(see http://vincent.brient.free.fr/otl3w_eng.htm).

Did you ever build a 6C33B-C push pull amplifer with transformer? Is it a good idea? Which output transformer can be used?
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Old 12th September 2006, 09:51 PM   #2
JoshK is offline JoshK  Canada
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Although not directly applicable to your application (I am designing for class A, not AB), I am currently working on a PP 6C33C amp.

I am having Bud Purvine of Onetics design the OPT. Having done a bit of digging and feedback indirectly from Romy the Cat, it seems a good operating point is 1200R @ 220VDC.

Apparently the main challenge with be with dynamic matching the triodes, so bias currents will be different. Do a search on "PP 6C33" and you should turn up a couple of breif discussions about this including my request for such schematics.

The German fellow's PP6C33C amp is the only one I've seen.....oh and the sketch by Dave Slagle.
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Old 12th September 2006, 10:32 PM   #3
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vincent,

There is a tranfo made by Plitron/Amplimo: PAT4144-00.pdf

http://www.plitron.com/
http://www.plitron.com/pages/Products/Audio/special.htm

Made for a push of 6C33C-B

A great one!!

Regards.

Alain.
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Old 12th September 2006, 10:39 PM   #4
JoshK is offline JoshK  Canada
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I'd be concerned with DC saturation with a toriod OPT and 6C33C, especially given that the 6C33 is so hard to match.
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Old 12th September 2006, 11:15 PM   #5
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JoshK,

True, but looking at the price of these baby's,
I payed less than 100U$ for 8 pieces, all from Ulyanov factory
I think it won't be a problem to make pairs...

If Plitron with Vanderveen made it 10 years ago and it's still availlable
that's fine for me.

There are probably some amateurs happy with a Push of 6C33C-B
specially those who own a BAT VK-55, lucky guy's.

Before starting the SE 6C33C-B ; The Push with the Plitron was my favorite.
At 55 watts it's only 28 watts out of 60 Nominal by tube.

Regards.

Alain.
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Old 12th September 2006, 11:35 PM   #6
cerrem is offline cerrem  United States
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I have designed and made P-P outputs using the 6C33C ...For both Class A and AB....
It is pretty straight forward....just a little bigger currents than usual..
Pretty descent tube....
As for toroids and saturating the cores... i wouldn't worry about it.. Depending on how you design the toroid it can tolerate imbalance... I usually don't use toroids for OPT's..for other reasons....Toroids choosen for OPT's are gapped cores and can deal with reasonable DC current imbalance without any problems..
If your worried about DC current matching....You can varry heater supply each valve to adjust the cuurent if reasonably close...
Heater's are the worst offenders in modern day tubes...they have big variance... Some designers are anal and say you MUST run the tube at the ratted heater voltage...It's not that critical as long as you have adequet space charge density...if not then you may strip a cathode.... Whats more important is heater POWER...Lets say you drove constant current into a string of 10 6C33C valves....you will notice that the voltage drops across each will be different due to process variation...So whats correct??? Proper heater current?? or proper heater voltage??? I believe it's proper heater POWER..

Chris


Chris
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Old 13th September 2006, 12:16 AM   #7
JoshK is offline JoshK  Canada
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Well I am a newb' so don't mind me...I am just going off what I have read. If it works, it works.
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Old 14th September 2006, 04:07 PM   #8
pusttiu is offline pusttiu  Romania
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hy , am new on 6c33c... and i make one pp whith 2 6c33 per chanel... (sorry for my bad englease...)
i need help whith a trafo for clas ab , on E+I suport,,,
am have tha power trafo on toroidal.
i use 6h9c and 6h8c for pre, and defazor...
if you hava an ideea plese help.
my mess id is : pusttiuc
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Old 14th September 2006, 04:26 PM   #9
protos is offline protos  Greece
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In my SECAD simulations for se operation I get an optimum combination of 1000R/260v for this tube.Now I guess in PP that would mean a OTP tx of 2000R.Perhaps 1000R is reasonable if you are going to cancel all that 2nd harmonic that is double what you get from 300B with this tube.
However with 2000R you will get a a lower output Z and better DF and lower overall distortion although you might lose 6-7 watts.
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Old 14th September 2006, 04:51 PM   #10
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I am using mains toroidals in a 6080 PP amp as output transformers. I started out with variable resistors in the cathode to adjust for equal current in the two windings. I later substituted a LM317 based CCS in each cathode to give perfect current balance. It works a treat and has presented no issues. Unfortunately it only works for pure class A operation.
This technique should work well wiith 6C33B, been a similar type tube.

Shoog
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