Tad

[bob orbell]

Hi all, has anyone used Tube Amp Doctor valves, German design made in bloody China , they do seam to get some good review's. BOB

[Ardee]

Rather a delayed reply but, yes, I have used the 6922. This is Russian, physically identical to EH, but internal matching not as good as the EH Gold.

[Greg.]

Originally Posted by Ardee

Rather a delayed reply but, yes, I have used the 6922. This is Russian, physically identical to EH, but internal matching not as good as the EH Gold.

.....and your thoughts on the sound, please?

[Ardee]

Greg,

If you run the valves at low current and low bias voltage, any slight difference in the valve's characteristics is likely to be audible. I am running them with reasonably high current and bias voltage, and with low signal levels. I cannot honestly say that I can hear any difference between two valves which have matching curves, even if they are a different brand.

I plot the curves of any small signal valves I use, so those that are poorly matched or obviously not linear don't get listened to. I find that a good TAD sounds the same as a good EH or a good NOS. NOS are more of a gamble, as TAD and EH Gold are selected, whereas NOS E88CC and ECC88 vary wildly. You need a large batch of these to find a couple of good ones, probably because the same batch has been picked over several times in the last 50 years.

The Russian valves tolerate higher cathode heater voltages than NOS, so are less likely to go noisy.

I think TAD aim to serve the guitar market, where AC gain is more significant than DC matching. EH seem more interested in the HiFi market, and I have not found any bad EH Gold valves, other than one which was clearly damaged by a dealer (Hot Rox) who admitted having no idea how to use a valve tester. I would advise buying from a dealer who does not try to test small signal valves which are already factory-matched.

[bob orbell]

I don't think that this was the answer that Greg was asking, most members here will want to change one valve for another to see if they get an improvement or not in sound, not rebuild the circuit that the valve is going into , as for Hotrox, I have had only good results from them as have many others. BOB

[andrew ivimey]

Nevertheless I would agree wholeheartedly with Ardee. And as a guitarist too I never buy my valves from Hotrocks who appear to use anything cheap (Chinese, Russian and JJ re-branded) I'm happier taking potluck on eBay myself for e.g. ecc83s and el84s and match them myself and then happy to use Russian valves rejecting a few on the way.

oh yes and EH valves are sovtek - Mike Mathews bought the factory in Russia.

For HIFi although I have a fair sprinkling of Chinese and Russian output valves I try to use ancient english and american valves where I can.