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

Post Subject: Hello and Fullrange Melquiades schematics questionPosted by Welborne on: 5/24/2013

(sorry, this is supposed to be posted in the questions and answers colume but I must be so stupid to have it posted here and now I don't know how to move it there.)

Hi Romy,

How are you! This is Welborne, from far across the ocean, Hong Kong. I have known your wonderful blog for long time (because I am a big fan of 6c33 single end and owns a stereo amp with this tube) but only recently I bring myself together to make the fullrange Melquiades.

My loudspeaker system is a Bastanis Mandala Chrystal open baffle system with 100db efficiency. Right now I have a few different amps rollling (D3a-300B DHT, 71a DHT etc) and the one that stands out is a 6c33 single end stereo based on the little pentode 6ac7 triode wired driving 6c33c.

I have not had the chance to hear the Melq, but from my limited exposure to 6c33, there is a spooky realm in the presentation this tube brings about when compared to what other amp does. I am not a tech expert, but I think the unique sound of 6c33 may come from its high transconductance, low internal resistance (meaning very low turns ratio for output transformer), and high current ability (high damping/control over the movement of the speaker unit).

Anyway, charmed by my own experience, I decide to make the Melq. Here are a few questions after I have had a good look at the schematics:

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.

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 ^^)

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?

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?

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.

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.

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

Thanks for your help in advance.

Welborne

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