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Re: MingDa MC805-AA Experience

152.163.101.6

"....do you think it is a good idea to use power tubes (like the 6L6) for drive? For SET design, using power tube as drive always hum I thought..."

If designed properly, this would not be an issue with the larger triodes such as 211, 805, 845 tubes. I have worked on at least a dozen of the Ming Da 805 based amps as well as the 300B driven unit.

I also have experience with other similar designs such as the Jolida Envoy and JD3000 mono blocs which use EL34's to drive each of the two 211 output tubes. These are also dead quiet.

One the biggest causes in the past for noise on the Ming-Da 805 amps has been the overbias of the 805 tube often causing an orange glow of the plates. They do not provide enough adjustemnt to compensate for this and the choice of driver tubes greatly effects the bias.(the bias is actually adjusted at the driver tube). I would recommend these amps only to well experienced DIY'er as I believe some circuit changes are needed in the bias stages.

These amps have the potential to sound fantastic but tube selection is critical as even the small input signal tubes can be a source of noise. Maybe a DC filiment voltage would be a better choice for input tubes of these amps.

They do sound great but can be problematic and one should proceed with caution when making a purchasing decision. You must also keep in mind that you are working on an amp with approximately 1000 volts at the plate of the output tube and you have to go inside to play with the bias pot or any other tweaks. One false move and you will feel it in your toes.

I have decided not to get involved with these amps anymore as you simply never know how any particualr unit is going to work out.

Bill
Response34


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