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In the Forum: Melquiades Amplifier
In the Thread: A different breed of 6C33C amplifier.

Post Subject: The half life of 6C33C and 6C33C preamp.Posted by Romy the Cat on: 9/22/2011

KOTriode wrote:
The preamp has the classic tube regulated power supply using 5R4, 6AS7, 6SJ7. It is transformer coupled output and has no capacitor in the signal chain, the gain is about 8db, so it is not a buffer. For convenience, it does has a remote control. It is still in the work, but will be able to sing pretty soon.

The 6C33C preamp and amp has only one power switch, both has two transformers, one for just the heaters, the other for B+ and regulated supply. When plugged in, the heater will light up first, when flipping the power switch, the B+ will start slowly with the regulated power supply. Without hitting the power switch, I can burn in the new tube filament over night .

The rational behind using two 6C33C with one triode in each tube is that it will allow you to have a total of up to 90W plate dissipation for two tubes instead of 60W using single tube or for higher reliability (according to the spec) 3000h with 70W versus 45W two tubes. Another feature is that I will be able to use the amp with 1 tube and adjust the bias for 45W dissipation for less demanding speaker ( Quad ESL 57). Also my output transformer is rated with 350ma/30W so it should be interesting to squeeze more power out of it. For me it is a very convenient feature. By the way the preamp only use one triode instead of both. I always like using output tube in preamp, to me it is sonically superior to the small 9 pins and octal tubes, the only downside is the microphonic.
I will report the sonic quality of the preamp/amp in the future.

I see, I got confused with your using the phrase “6C33C with one triode”. I usually use this wording for pure double triodes what you can use them separately. Unfortunately it is not the case with 6C33C. The two half of 6C33C have separated contacts for heaters, but no ways driver separately anodes but cathodes. This is kind of bitch, I have no idea what they did this way. So, what we talk about use of half of 6C33C we do not use one triode but rather a half of triode by disengaging filaments from “other” side. BTW, if you like this type of operation then you might like to try 6C41C. You do not need to change anything with that tube and juts plug it into the socket that just drew the half of 6C33C. The 6C41C is a single heater tube with exact half of 6C33C. I truly do not like the 6C41C sonically in power amp but your mileage might wary and who knows, it might be in preamp it might work out. The preamp duty is not the same as power amp duty….

The microphonic 6C33C in your preamp? This is interesting. I never use the 6C33C in the line level situations and therefore I never had the situation that it might behave microphonic. Try to put a small rector before grid and put some ferrite bids before the grid pin. Also, try to shut down temporarily your fans that cool down the 6C33C from the bottoms (it would be noise to have a picture of it).

I also like preamps with very powerful drive but I am with the world of SS preamps with direct coupling. I found that it would be very interesting to listen the 6C33C preamp. What kind transformer you get for it. Also, I do not know where you live but if you in US’s East cost and ever come to Boston then I would very much do not mind if you bring that 6C33C preamp for a few hours to let me to hear the beast. I have no idea how it might sound but the notion to have 6C33C in preamp sound too absurd to pass the opportunity to hear it. Too absurd? Well, this is very much in my alley…

The biggest question would be if the half of 6C33C is as good at line level buffer as let say 2-4 of small 9 pin tubes. You also have that output transformer that is controversial aspect. I kind of do not feel at ease with line level output transformers, but it is me….

The Cat

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