What 300B tubes are you using in your VAC amps?

I have a 70/70 MkII which I run with Sophia Carbon Plates.

To be honest I find them a bit of a disappointment - rather flat and lifeless (6SN7s are all genuine Russian milspecs - the ones with metal bases and 'OTH' on them).

The current consensus here in Australia is the the TJ Full Music Mesh Plates are the best all-round 300Bs at a non-insane price. BTW you can get GDs from Evatco (www.evatco.com.au).

One more thing - the VACs in unmodified form drive 300Bs VERY hard. I've had mine detuned to ~50 wpc. That's why I chose the Sophias in the first place. They are very ruggedly built.

Cheers

Alan

Alan....I was thinking about your detuning to 50wpc...could this effect the performance of the CP's. I ask because KH recommended the CP's over the mesh plates because he thought the carbon plates would be a better match with the Vac's push pull design. Did the factory detune the amp? My 70/70 does not have the tube sentry and I will have Kevin perform the upgrade soon. Kevin says it is a must for these amps. If you have talked to Kevin about this I would be intersted in his thoughts.

Wavetrader, I don't think 'detuning' has affected its performance. It's still delivering 50 wpc, which is very reasonable for two pairs of 300Bs.

The CPs are getting better, but it's a slow process if. like me, you don't listen for three to four hours every night.

I live in Canberra, Australia, so having factory mods done is out of the question freight wise, plus I think VAC's charges are OTT as well. Fortunately we have a valve genius here who's been able to trace the circuit and tidy things up at the same time.

Cheers

Alan

Hi Alan

About 90 or 100 hours and it should be WayWow time.

Enjoy

btw here in America Kevin does a fantastic job and has helped me tremendously....so we are lucky to have him right here.

"I ask because KH recommended the CP's over the mesh plate".

This suggests that Kevin Hayes might recommend meshplates as an option for the Renaissance amps in some circumstances -- he in fact warns people to never use them, as they cannot handle the plate voltage of the Renaissance circuit. Kevin speaks of one owner who has had success running meshplates, but it was against Kevin's recommendation and is to be viewed as an anomaly.

What the above poster states about the Renaissance amps running 300B's hard is true -- 95% of the WeCo spec maximum voltage. I've owned VAC Renaissance amps for eight years and they require carefully vetted output tubes. In fact, Sophia used to market a special set of the Sophia tubes for VAC Renaissance amps, which were the basic Sophia tube, but carefully tested at plate voltages that resemble the voltage that 300B's see in the Renaissance circuit. Generally, as for transconductance, 300B's for the Renaissance amps should test in the 3,000-5,000 range. In addition, the plate-to-cathode voltage for 300B's in the Renaissance amps is approximately 430 volts dc, with idle current approximately 85 to 90 milliamperes in a self-bias (cathode bias) circuit. Again, this is approximately 5% below the maximum rating for the WeCo spec 300B. The milliamp and transconductance testing for purposes of matching must be done at these voltage levels, or you will find out the hard way, when your amp starts imitating a popcorn popper, that your 300B's didn't make the cut.