VAC 30/30 & Sophia 6SN7's

At least on the VAC Renaissance 70/70, the outer sockets are for the driver tubes, which must be the higher voltage GTA/GTB spec 6SN7's (450 volts vs. 300 volts for standard 6SN7's), while the two inner sockets are for the splitter tubes, which need only be standard-spec (low voltage) 6SN7's.

So if the 6SN7 array on the 30/30 is the same, one would think that hum problems would occur if you were running standard-spec 6SN7's in the high voltage driver sockets, not the other way around.

It could be that there is another issue - your tubes may be defective - but I suggest that you ask Kevin about this.

Raquel,

The Sophias are not standard spec 6SN7's. Their data sheet reflects that they are higher voltage equal to GTA or GTB prefixes.

I had read your post and forgotten what you and Almarg had written about the voltage of the Sophia 6SN7's. I was commenting mostly to point out that driver tubes used in the Renaissance amps must be the higher voltage GTB or GTA spec 6SN7's - this is not mentioned in the 70/70 or 140/140 owners' manuals.

While I'm at it, I will also mention that any 300B's put into the Renaissance amps must be standard WeCo spec 300B's - "super 300B" variants like the KR BLX 300B, as well as meshplates, will damage or destroy these amps.

Finally, any 300B used in the Renaissance amps must be carefully vetted to ensure that it can handle the stress put on 300B's by the circuit, specifically, as for transconductance, output tubes for the Renaissance amps should test in the 3,000-5,000 range. In addition, the plate-to-cathode voltage is approximately 430 volts dc, with idle current approximately 85 to 90 milliamperes in a self-bias (cathode bias) circuit. This is approximately 5% below the maximum rating for the WeCo spec 300B, meaning that the 300B's in these amps are run close to flat out. The milliamp and transconductance testing for purposes of matching and vetting 300B's must be done at those voltage levels, and anyone you buy 300B's from has to be someone you can trust to cull tubes to meet these demanding standards.

This information is likewise not in the owner's manuals, but will be confirmed by Kevin Hayes if you ask.

Returning to the issue you face with you Sophia 6SN7's, it sounds like Almarg has identified the problem. For whatever it's worth, I've been running Sylvania chrome tops since 2003 with my Renaissance amps and they've always been trouble free (although my VAC is no longer my primary amp and it's seen only very sporadic use since 2008). While some production out of Shuguang that is quite good, there is no reason, in my opinion, to purchase any current production Chinese 6SN7's, as there remains a large supply of high quality new-old stock 6SN7's available that are not really expensive (for example, $50 per tube).