GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Melquiades Amplifier
In the Thread: Bias help

Post Subject: Answers.Posted by Romy the Cat on: 5/24/2013

Welborne wrote:
1) There are hexagons on the schematics marked with A, B, C ...M. What are these? Are they testing points or they carry some meaning? I can't find much info about these here.

Yes, the hexagons are test points. Do not worry about them. I have my reasons to make them available.

Welborne wrote:
2) Besides Schottky diodes, I seem to read somewhere that now you find something with better performance, and again I try to find them but got lost in the forum (your blog is huge ^^)

Yes, in 6-Ch Milq I used new at that time Silicon Carbide Diodes.

http://www.GoodSoundClub.com/TreeItem.aspx?PostID=6116

They are objectively better then any lower noise SS and run up to 1000V. However, I do not insist that they sound better. Also, it was years back, in 2007 and now something ease new might be available. Anyhow, you need to make some kind of test make and try to listen them or talk with somebody who know how they sound.

Welborne wrote:
3) I find two R23 in the schematics. I believe this is an error. The one linking the anode and the grid I believe is a grid stopper and can use a 1/4w carbon film I suppose?

I did not see two R23 but I remember somebody told me about it before. Anyhow, if it is the case then this is obvious a mistake. The one that links anode and grid of the driver tube is not a grid stopper but a resistor that slightly decuple the potentials of grid and anode. Yes it might be very very low power, 1/8W would be fine but I would not comment about the type of resistor. There are people who like carbons and they might be right. I comment upon something that I tried and likes. The RN-55 from Dale was my chose and I do like those resistors a lot. Again, it was back in 2004 what I made those experiments and the thing might be changed. I have see that large companies that made very good resistors started made them to sound like crap.

Welborne wrote:
4) Regarding C2 and C10, is there an advantage going over the stated 2000uf? and is there a ceiling on the value one should go?

Well, I feel the 2000uf is a minimum to decuple the PS from the tubes. In case of C10 that run might higher current it might be much higher. In my 6Ch version I went for36.000uF or something like that, I do not remember already. Yes, there are many advantages why the higher value of the last cap is better but they all purely intellectual. I doubt that blindly I will be able to say if Milq’s power tube is driven by PS with 2000uF or 3000uF. I think however that I will be able to say if it will be 470uF in there…

Welborne wrote:
5) Primary impedance of output transformer: I am going for a custom made transformer based on Finemet c core, and I need to decide on the primary impedance for the builder. In my own 6c33 stereo I am using 980 ohm.

Hm…. To load 6C33C with 980 ohm is somewhere near where I fill it has to be, at least with the acoustic systems that I tried. Some people swear by 600R but it too much load to 6C33C, they get more power but it did not work for me. Without knowing personally your speakers and a few other parameters it is very hard to guess how you will need to load your 6C33C. In initial stage I used the OPT with re-mapable coils that let me to play with loading variances. Perhaps you might try something like this.

Welborne wrote:
6) Here in Hong Kong I could not source Magecraft timer relay as they are all in 120v version (here the mains supply is 230v), so I am just going to use toggle switch to switch them on manually.

You can use any other timer relay that you mike and that sound good to you or you can build or buy a very simple SS timer relay. I think to use manual delay is kind of difficult. However, you can always add it later if you like the sound of the amp and decide to use it.

Welborne wrote:
7) Meter: Is there a difference using a 300mv and a 300ma meter in terms of calibration?

Nope, you can use voltmeter or ampermeter. There is no difference, and from a good company they are well calibrated. I prefer to use voltmeter as I would like to make sure that the voltage measuring resistor is the resistor of my chose and that signal current doe not flow over the ampermeter wires.

The Cat

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