GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Melquiades Amplifier
In the Thread: Planning my DSET

Post Subject: The answers....Posted by Romy the Cat on: 5/29/2015

anthony wrote:
Do you have a “final version” of the schematic anywhere?

I think that the one you have might be recognized as final. The Rev2 was without DHT in MF and Rev3 was with it. I did not do anything else with the amp after that. The reality is that 5-6 or any “n” number of DSET are just a parallel implementation of the same amp with only biasing shared across all amps. The fact the biasing acts as filtration, loading and voltage divider at the same time make it somehow complex and confusing.

anthony wrote:
6E5P/6E6P resistor between plate and grid. Is this resistor influential to sound? I notice that at one stage you used a “high-quality” S102 resistor here but later on you are not necessarily using them.

Well, the purpose of this resistor just to rise a potential of one screen over another. You can use the S102 thought and it will not hurt as they are phenomenal resistors. I did them and I did the CMF55 and they both were fine. Did you heard any difference between Dales and S102 in the screen lifter? I honestly did not test them ONLY in this application.

anthony wrote:
Is the resistor in the Fundamentals Channel between the OPT and the S2? Apart from this resistor you run the S2 without any components between it and the OPT.

. Actually it is not a resistor connected to OTP, look closer. This is a regular screen lifter, like in your question above, it is juts drown perhaps not so friendly but as you see the red line goes from plate and directly to OPT.

anthony wrote:
.LPad for MF S2. Are you still running the LPad between the OPT and S2? I assume that the four resistors shown in the schematic at that position signify the LPad and not something else.

This is complicated question and I did cover it while I was dealing with it. I need to attenuate MF for ~2dB. In addition the S2 driver if it driver very “clean” has some very very minor metallic fanzines atop. My YO186 is very not neutral, it is sort of anti 10Y or anti type 45 tube. As the resole I have very interesting and I would say “simulated” MF but with very very very mild harshness atop. There are many way to deal with the mild harshness atop and one of the way is to put a very mild low pass filter before S2. It should be super low indictor that would hit the driver at 60-80Kz, wish at its low knee will hold S2 a bit at over 20Kz. Any indictors I trues combined with voltage dividers were detectable. What worked the best were not voltage dividers but the regular ugly wired attenuators, some sort of miniature rheostats. The problem is that they are hugely inductive, much more than necessary to deal with S2 fanzines. So, I found a solution to bypass the wired attenuators with two S102 resistors, kind of building a second divider with S102 and run it along with the wired one. The S102 have ultra-low inductance and if you connect the indictors in parallel then the summazing indictors will be less than the lowers one. As the result I have literally a problem free attenuation on my MF that at the same time do take care of my S2 “fanzines”.

anthony wrote:
Yellow circle with cross. On the schematic at the lower-right side there is a yellow circle with a cross next to a 33K resistor. I am not familiar with this annotation…could you please tell me what it is?

Well, from the annotation perspective it would looks like it was a lamp. I do not remember what it is and it looks like lamp but why the hell I took voltage to some kind of light emitting diode from B+ if I have a dedicated service 12V voltage running thought out all amp? I do not remember the answer.

anthony wrote:
Two sets of gas tubes. Have you considered more than one set of bias, say one for LF and one for HF? Do you think it could have any positive or negative effect? I have no idea.

It is possible to use as many gas tubes you wish, they are juts supple of negative bias. In my version I used one foe all channels. I do not know about sonic impact it has compare with own dedicated gas tube. I think own dedicated gas tube would shall be better but I made no practical experiments with it.

anthony wrote:
mV Meters on B+. Is their only purpose to check the plate voltage for the individual output stages? Would you consider leaving them out?

Sure, the mV Meters do not need to be there. You need to have 1R resistors and to access to left and right of them, the service points would be fine, and you then can you regular tester to measure it. I fine it is fine in a single full range but in case you have many 6C33C to deal with at the same time then it is very convenient to have the permanent meter.

anthony wrote:
Do you use an hour meter to monitor tube life? If so I imagine that it would be installed straight after the power switch. Is this true?

You can install the hour meter anywhere you wish. If it is low voltage devise then I would put it in service voltage. I was thinking to do it but for some reasons I did not make it. Now I feel that I do not miss it and I feel that it rather was my wishful thinking devise then the actually helpful tool. If you have multiple 6C33C for multiple channels then they will die with different tempo. Do you want to keep a chronometer for each of them? It is not to mention that knowing the tube hours is not necessary allow to know if the tube need to be replaced as some of them dies after 500 hours and some of them work for years and demonstrate no sign of aging.

Rerurn to Romy the Cat's Site