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RE: What !!!! ...........

Posted by FlaCharlie (A) on August 19, 2007 at 12:47:48

In Reply to: What !!!! ........... posted by drlowmu on August 19, 2007 at 10:38:29:

Jeff - Actually, I was the one who posted the schematic of the negative supply. It's not an Eico, by the way, it's a Scott 299B. I also posted an Eico HF-87 schematic and asked for comments on the viability of the 6SN7 portion of its input section as a possible input for the 6B4G amp since I want to use 2C22s (half a 6SN7) or 6SN7s or some combination of the two.

I have a rather large collection of vintage amps. The DIY interest came along with my doing restoration/repair on the old stuff. Out of all the vintage amps I have there are only a few that use fixed bias or some kind of negative supply - the Pilot 260, Dynaco ST-70 and the Scott 299B. I just posted this as an example of a negative supply, not with the intent of copying it.

The resistors are actually 18 ohm each and preceded by a 10 ohm, so don't these result in 64 ohms? That's a far cry from 1k, but as I said, the 1k was just an example. Hopefully I'll be able to come up with a combination of primary and secondary connections with the Signal transformer that will get me close enough for both the two B+ sections and the negative section that I won't have to use high value resistances. Mikeyb suggested previously that the Eico HF-87 input voltages could be adjusted and doing so I would need -125v to the cathode resistor. That's what the negative supply will be for.

I don't know what the Scott engineers were up to in this design somehow I don't think it had anything to do with "low DCR" since you'll notice in the Scott circuit there's also another leg with an 8.2k in it. So neither of these values are truly "low DCR" in your book. Correct?

I'll try to experiment with some heavier wire but, honestly, I wonder if 12 AWG wire will even fit through a standard tab on a terminal strip even by itself, not to mention on a tab that has other parts on it. I'm not sure if I even have any 12 guage around but I'll maybe try a pair of 16s or some 14 to see if it might fit.

I know there have been a couple of other guys who have built the "low everything" power supply. One, I believe you mentioned yourself, and you noted that he was pleased with the results even though he hadn't used heavy guage wire. Hasn't John Swenson (who I believe is a very experienced builder) built this PS too? Did he also employ your heavy guage wire strategy?

I'm going to be trying out various people's ideas in the process of building this amp, not building it according to, or trying to prove or disprove, any one person's theories. Sorry if that disappoints you. My purpose is to learn from it all and, of course, to hopefully end up with a great sounding amp. In the end, ALL of you guys will probably be able to call me an idiot and say, "There's NO WAY that could sound good because of . . . X, Y or Z." ;^)

. . . Charlie

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