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6C33B-C push pull with output transformer

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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?
 
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.
 
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.
 
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
 
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
 
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.
 
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
 
hy ,
i am from romania, and for me is too expensiv to bye an output transformer and i have to build one.
for this i need a schematic.... whith google i found one but i am not sigure if is working.
if you have a trafo pp for clas ab... i need dimension of wire (CuEm) and nr of spires , tole dimension and section of the core.
thk.
 
Alain Dupont said:
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.

There was a pretty recent thread where someone asked for a PP design using this output transformer. I know people here were scratching their head thinking how to apply this trafo...it has a reflected impedance of jut 150R. One person sent mr. van der Veen an email asking what kind of schematic or application he had in mind when designing this tube...as reply he got the datasheet from the 6C33C :xeye: Well, I would not buy it.

Sowter also have two trafo's, one with 600R and the other with 1200R. But I wouldn't dare to ask for their prices.

I have Morgan Jones valve amplifiers book, where he explains how to build a PP driver stage with a swing of 100V RMS. He uses it to drive two 13E1 tubes, but I think it would do a very good job driving the 6C33C. Just pay close attention to the adjustment for mains variation

Erik
 
I hate to sound like a stuck record, but here goes.
Mains toroidals make excellent PP output transformers for low output impedence applications. This is because their relatively low primary inductance is still plenty enough with the low output impedence of tubes like the 6080 and 6C33-c. Also the low reflected impedence required by these tubes is relatively easy to source in standard mains transformers ranges.
The only real issue is that they don't like DC and finding balanced pairs of 6C33-c (which stay balanced) is nearly impossible. So turn this to your advantage and place CCS in the cathodes of each 6C33-c and force them to stay balanced for ever and a day. There are also many huge sonic benefits to putting CCS in the tails of any tube.

The great advantage overall is that you can use transormers costing €30.00, rather than ones costing €120.00
I have done this in a 6080 amp and it is the best sounding amp I have built so far (and it goes down to 10hz).

Shoog
 
Shoog,

Thanks for the ideas. I am going to try a conventional OPT, but might also try a mains tx too. The CCS in the tail is a good idea.

FWIW, I did some digging when I was looking for a suitable OPT, to see what there was available. I didn't look into Sowter, Tribute or other European sources, but for US and cheap Asian sources there is James for SE operation only and Lundahl (guess both EU & US) makes the 1627 that will work for either SE or PP.

I went with O'Netics, because Bob Purvine is a great guy and has really given me a lot of time and energy since I first expressed interest in the Karna project. I still do plan to build something like that project, but I need to cut my teeth on something simpler first. At least it was meant to be simple and inexpensive, but when all is said and done, neither are turning out to be so. But, I'll have learned a lot I hope.

For front ends, I am considering something like the glass palace front end (probably with 6N6Ps instead), an Aikido split load phase splitter with differential aikido style cathode followers (you have to put two and two together from his articles), or use CCS loaded C3g in triode strap in an Amity style config (with requisite iron). Too many choices...but I may just have to build this module enough to try all three front ends and see what I like.
 
Shoog said:
I hate to sound like a stuck record, but here goes.
Mains toroidals make excellent PP output transformers for low output impedence applications. This is because their relatively low primary inductance is still plenty enough with the low output impedence of tubes like the 6080 and 6C33-c. Also the low reflected impedence required by these tubes is relatively easy to source in standard mains transformers ranges.
The only real issue is that they don't like DC and finding balanced pairs of 6C33-c (which stay balanced) is nearly impossible. So turn this to your advantage and place CCS in the cathodes of each 6C33-c and force them to stay balanced for ever and a day. There are also many huge sonic benefits to putting CCS in the tails of any tube.

The great advantage overall is that you can use transormers costing €30.00, rather than ones costing €120.00
I have done this in a 6080 amp and it is the best sounding amp I have built so far (and it goes down to 10hz).

Shoog

Shoog

Can you explain the CCS for the 6C33C in a bit more detail? Would I be able to use it in my 6C33C single ended amplifier?
 
I can't really see to much of an advantage in putting CCS in the cathodes of a SE amp. You have to ask - what is the problem you are trying to solve. In my case its current imbalance in toroidals and thats it. Its the toroidals which bring the sonic benefits and the fact that I can configure my 6080's as differential pairs. There are no such advantages to be gained with a SE amp

I tried it in a version of RH807 and it worked fine, but was there a sonic benefit - NO as far as I can remember.

Shoog
 
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