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In the Forum: Melquiades Amplifier
In the Thread: More 6E5P-6C33C amps.
Post Subject: To regulate or not regulate 6C33CPosted by Romy the Cat on: 10/26/2010
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 Cosmos wrote:
Anyway, as the description on our site on second paragraph says, the third 6C33 located at the back, is used as the pass element of the regulator (controlled by solid state circuitry) providing 220V with 100uV of random noise & Hum at full load with very low and uniform, across the audio band, output impedance.
 
I see, you regulate outs tube. This is interesting. The best SET I heard with 6C33C (Lamm ML2.0) also use regulated output stage. There were a lot of debates on Russian forums about a need to regulate 6C33. I did not use 6C33 as regulator but I was trying to power 6C33 from a regulator on 3 paralleled 807 triodes along with a fast pentode areal amplifier. I experienced a slight improvement in low level details and more interesting lower end harmonics but I did lose a bit dynamics. At that time I was trying to improve over ML2.0 dynamics, so I figured the regulation is not my direction and went for choke regulation that I feel is faster. Can you express your view over regulated 6C33C vs. unregulated?
 Cosmos wrote:
On the other hand, 7721 was chosen amongst many other driver tubes tested including 6E6P-DR and 6E5 too. To tell you the truth I really liked 6E6 but the gain was lower than needed and after 1 year on the test amp it started to degrade in sound and characteristics. Also 7721 (specified for 10000hours service life which is good for a commercial design) seem to my ears marginally more analytical than 6E6, though 6E6 had marginally better articulated bass. 7721 is not a small tube at all and at 170V(at anode) and 14mA (triode strapped) provides very low distortion even at full power. In any case the circuit can easily accommodate 6E6 with very minor internal adjustments (though no soldering is needed).

The 7721/7788 are a wonderful tubes, my favorite high mu penthodes I use a single 6E6P to drive my tweeter (107dB sensitive ribbon via 1:175 transformers) and I did tried in there 7721.  It is 200V and 35mA. Do you feel that you do not need power in your driver? Gains is fine but gain without power is not good. Are you sure that your driver stage dose not clip. The reason I ask is because my 7721 had around 2.5V of bias with grounded cathode. This is very low bias as today DACs will out 5-6 V at 0dB. I would also disagree with your sentiments about the long service. Yes, the 7721 will live for very long time but they are long out of production and they are around $30. The 5E5P/6E6P are dirt cheap. Yes they will not last more than one year but frankly speaking so the 6C33C… Anyhow, I am not trying to convince you in anything o it is your amp. BTW, if you feel that 6E6 has more articulated bass then try Melquiades type of bias – what it make with bass will make you to lough…
 Cosmos wrote:
You are correct though that frequency response is not at full power and you can be assured that I am not at all evil minded as I am not stating that the response is at full power. The frequency response stated is measured at 8W@8Ohm done just for ease of measurement as the 8V mark on my millivoltmeter happens to be right above the 0db mark. For your information, I just measured the actual full power bandwidth at 15W and it is -3dB from 9Hz to 122KHz  which is not bad and not very much different from what it is stated at our site and very respectable for a zero feedback SET amplifier. This good bandwidth is the product of good old transformer calculation and construction execution using a total of 10 primaries and 5 secondaries carefully layered. The core is of type E120 with 8cm of laminations providing a total of 10H gapped for 250mA. 

Panos, to specify frequency response of 15W amp and to use 8W as referent is as use as measure sensitivity of loudspeaker but use an arbitrary distance for microphone. It must not be doe under any circumstances and I wish you manufactures get it. Do you know that my car get 150 miles per gallon. Oh, I forgot the say that my mile is 3 inch and my gallon is 54 litters… How is it useful? Also, with all due respect I do not believe that you have -3dB from 9Hz to 122KHz  at full power. Absolutely imposable!!! The best you can get is juts under 20Hz and somewhere around 20kHz -22kHz. If you deny it then you do not measure properly.

Rgs, Romy the caT

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