22-09-2018, 09:01 AM
Hi.
Yes I agree with Jeffrey.
On one amp I was playing about with a few years back I used a linear pot on the cathode of the follower, at the time I searched for a quality pot that would handle the little bit of cathode current and not sound scratchy, a hard task indeed and I was just about to give up, I then saw some pots on a Ukrainian site on E-bay and ordered a few of them. These were the biz, no discernable noise when adjusting the pot.
If you notice the value of the grid leak at 100k and the pot at 20k, the circuit can and does work with a much lower grid resistor and the effects of charging reduces but of course the bass response falls off too so although the circuit does work it can be a compromise, DC coupling is by far the best as phase shifts due to cap coupling are obviated but to get a good design to work all the way through a valve amp is challenging to say the least.
Yes I agree with Jeffrey.
On one amp I was playing about with a few years back I used a linear pot on the cathode of the follower, at the time I searched for a quality pot that would handle the little bit of cathode current and not sound scratchy, a hard task indeed and I was just about to give up, I then saw some pots on a Ukrainian site on E-bay and ordered a few of them. These were the biz, no discernable noise when adjusting the pot.
If you notice the value of the grid leak at 100k and the pot at 20k, the circuit can and does work with a much lower grid resistor and the effects of charging reduces but of course the bass response falls off too so although the circuit does work it can be a compromise, DC coupling is by far the best as phase shifts due to cap coupling are obviated but to get a good design to work all the way through a valve amp is challenging to say the least.
