In Reply to: Re: big resistors posted by rjm on March 01, 2002 at 08:37:22:
Hi,> Wouldn't those 10M and 22M resistors be extremely noisy?
Of course they are terribly noise. But the Impedance in the Grid Circuit is dominated by the RIAA Network, excepting VERY low frequencies, so these resistors are not what makes the circuit tick.
> Grid leak bias works, but because the leak current is unreliable,
> the operating point varies with tube sample more so than cathode
> bias.I have heard similar statements before and found them to be rather untrue in reality. In fact when servicing gear that used gridleak bias I was surprised how well the bias was held over a range of different valve brands.
> You might consider battery bias or just plain bypassed cathode
> as viable alternativesGrid battery bias is an alternative, but it requires rather low resistance grid leak resistors and as a result causes more losses in the RIAA network. The bypassed Cathode Resistor forces you to use a substandard quality electrolytic bypass capacitor in a rather critical position. There are applications where gridleak bias does not work that well, but they tend to happen at fairly high levels. In the second stage of a phonostage it is a really smart idea.
You should try it on your 6DJ8 Phonostage one day, you maybe surprised.... And while you are at it, add the 3.18uS 4th Timeconstant.
Ciao T
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