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I have a pair of Magnequest grid chokes, 3700 H (BCP16 GC HN)

Can these be used to replace R1?

It would easily pass DC to ground, and practicaly inert to AC at audio frequencies.

John C.

John, I don't know if we're looking at the same schematic, but R1 on mine is a 1K stopper resistor. If you subbed a choke at that point, you'd virtually eliminate any signal getting to the grid.

If you're talking about R2, which is a 475K grid leak resistor, putting a choke in its place would shunt the signal to ground due to the low (relatively) DC resistance.

The short answer is "No".

My mistake, I did mean R2.

Yes, low DC resistance. Signal is AC, so R2 is bleeding off signal.

3200 Henries sould not bleed any signal to ground, only DC.

John C.

One major risk with grid chokes is that they are very susceptible to picking up 60Hz magnetic fields from the power trannie or filter choke(s). Some serious mu-metal shielding is usually necessary, especially when everything is pretty close together on a compact chassis.

The high-inductance grid chokes are better applied to SET designs than for PP, anyway, and are probably best used with "fixed" grid bias. Needless to say, any grid current can cause additional serious problems, including blown chokes, the 3200H winding uses very thin gage wire (like human hair) which does not tolerate current (even an mA or two is too much).

/ed B

I removed R2, mounted the choke using one of the bolts for the input board(I'll reinstall it in beter location later) And wired it to the holes for R2.

Theres always a little anxiety flipping the power switch after any change, but it was unwarranteed here. No buzz or noise at all.

I've only done one amp for now. My first impression is a more detailed treble sound.

I'm going to listen to just this one for a couple of days before I dicide to do the other side.

John C.

Those V Caps must have cost more than the amp!


JD