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    Building, troubleshooting and testing of these amplifiers should only be
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6C33C-B. PP or SE ?

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#3
Consider going single ended, and most important of all, choose cathode bias. The 6C33 has a tendency to drift when operated in fixed bias and run away with cherry-red plates.

Another recommendation is the operating point: 200V @ 200mA is conservative, but sounds good and provides trouble free operation.

Here some reference cathode bias designs:

http://www.borbelyaudio.com/adobe/15wse.pdf

http://www.metaleater.narod.ru/6c33c.gif

Enjoy,

-- jose k.
 
#5
Thank you guys !

I saw yesterday the Borbely design after some searches.

Found this schematic in a romanian electronics forum:



l_9fe68fba8d90458c9d4a099e89f1470e.gif
 
#6
That schematic is very close to an early one by San-Ei in Japan, San_Ei was owned by Dakesue who was the one in Japan who "discovered" 6C33C in Japan and imported this tube and sold it as EC33C. The only differences I can find is that San-Ei used a 12BH7 as the 2nd tube and used local feedback to the cathode of the SRPP, see here http://www.tubetvr.com/se.html

I have one of these amplifiers myself and it gives a very nice sound.

As is evident the amplifier used fixed bias to the output tube and I can vouch for that the output tube current is very stable, it usually doesn't drift even over a year. IMHO 6C33C tubes that are burned in correctly and is not used with more than ~40W anode dissipation doesn't drift.

Regards Hans
 
#7
tubetvr said:
That schematic is very close to an early one by San-Ei in Japan, San_Ei was owned by Dakesue who was the one in Japan who "discovered" 6C33C in Japan and imported this tube and sold it as EC33C. The only differences I can find is that San-Ei used a 12BH7 as the 2nd tube and used local feedback to the cathode of the SRPP, see here http://www.tubetvr.com/se.html


Regards Hans
Click to expand...




You must be talking about this :

http://www.bonavolta.ch/hobby/en/audio/6c33c_5.htm
 
#11
#14
I'm about to start building a 6C33C (will try 6C41C also) SET. I'm using UBT-1 Tranformers.
Click to expand...

6C41C would be a better match for the UBT-1. Both current and impedance are pretty much ideal for 6C41C. Where as you would have to run a 6C33C very conservatively.

Speaking of UBT-1, I have one on my shelf collecting dust. It's a little dinged up, but I'd let it go for cheap. If your interested shoot me an e-mail.

Here is an experiment UBT-1 with 6C33C.
http://www.geocities.com/dmitrynizh/ecc99-6c33c-se.htm
 
#16
IMO that is the right choice for the wrong reason!😀

Keep in mind that the output transformer is a very special stuff....
I remember B.A. give some optionals as like
- inductive input power supply
- only mkp capacitors
- cathode output

very flexible design😎

Cheers,
Paolo
 
#20
Understood.

Time to search the address of B.A. ...............

In a old italian magazine ( SUONO) , BA write three articles about this amp. It is not simply and require custom Transf and coils.
I remember one stereophonic weight 40 kg!!

Cheers,
Paolo
 
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