Re: Bias for 6L6?



"Dave Curtis" <dbaudiotech@xxxxxxxxxxxxxx> wrote in message news:aktpk5pi6r0khh8du4rja9nmb01re4cqnj@xxxxxxxxxx
On Tue, 12 Jan 2010 14:05:41 -0500, "Phil_S"
<psymondsnospam@xxxxxxxxxxx> wrote:

"RS" <RS@xxxxxxxxxxxxxxx> wrote in message
news:ur9pk556s2qdhj2235k2m14ccroom415m1@xxxxxxxxxx
On Tue, 12 Jan 2010 09:18:46 -0500, "Phil_S"

Make space for the cathode resistors. They're not that big, Phil. <g>

OK, I think I figured out how to shoehorn them in. I will be removing the
plate wires to the tip jacks, so those transfer to the cathode on the tube
sockets. Is it also unsafe to have the cathode on the outside of the amp?

No, they are at a safe voltage.

I'm asking because obviously I did not recognize the danger of what I did.
You know I wouldn't have done it had I thought it through. This is simple
inexperience showing itself.

Can the two 1 ohm resistors share a common ground point?

Yes. Ideally, they should ground to the same node as C13 (OP tube
cathodes and speaker ground should both go here)

In doing the measurement, with external test points provided, does it make a
difference how far away the ground is? That is, do I actually need to
capture the reading from the lead at the resistor body?

No, you can use the chassis right next to the pin jack. You'll likely
not see a difference when measured directly across the 1R.

Thanks, Dave. This is good. I removed all the filament wiring (nasty blue hose) when I had a few minutes before dinner. With all that out of the way, I can get this done fairly easily and I prepped for it by removing the cathode ground wires and cleaning the tube pins. The filter caps are hanging on a pair of terminal strips. C13 and C14 share a ground point. I already have the speaker ground there (some things I actually do understand), and had the cathode ground there, then a wire over the main chassis bolt ground.

The resistor for V3 won't reach the terminal strip. If you take a look at the bottom picture, it shows output jack #3 of 3 with the buss wire going to the terminal strips. Both cathode resistors can reach the eye on the sleeve of that jack very nicely. It that an acceptable place to make the cathode ground? It is just a few inches upstream from where the wire meets the ground side of the filter caps. I don't wants some funky ground current rearing its ugly head when I've got a speaker plugged in. I might just do the terminal strip anyway, but it's good to have options.

There is a slim chance I can get the bleeder R34 in the amp, as well. This was also obstructed by the filament wires.

.

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