6v6 plexi-ish build questions

[donzoid]

Thanks for clarifying the mv control too...

[donzoid]

Huh. I just re-checked the grid mV and they are both at 16. I think it changes after warming up. Coupling cap???

I'll let 'er warm for an hour and re-check.

EDIT: Jeez, it's only been 15 minutes, and we are at 30/98mV. Shutting it down to cool. I'll re-check the tubes but I would bet this has something to do with the coupler there on V4, or the resistors.

[matt h]

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[donzoid]

Thanks Matt! So, if I wanted to see how many mA were passing across the screen, is it as simple as measuring the screen pin 4 with respect to ground (with my DVM set to mA of course)?

[donzoid]

By Golly the problem is following the tube. After only 5 or so minutes, its 50/20 so I'm going to:

Swap in a pair of known good and well-matched tubes
measure the cathode resistor for an exact figure. If I wanted to get closer to the 70% I would want to run a higher value there, correct? Starting with say, a 300R.

[matt h]

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[matt h]

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[donzoid]

Thank you for explaining all that Matt.

I'll work on the schematic and hope to get the PS side of it revised, maybe even hopefully the pre side too. The last one posted by Colossal is pretty close tho methinks.

The low-value cap across PI plates, does it matter if its ceramic or s-mica? I think I have a SM that's close to that if that is the preferred type. If not I can certainly find a ceramic.

I put my original set of startup tubes in, and after sitting here for half an hour they are at 46/59 mV...much closer.

[matt h]

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[donzoid]

Here are my voltages across the string measured with all the tubes in, and standby "on" - I think what was on there before was with the rectifier only. Hopefully this makes better sense?

[matt h]

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[donzoid]

Good points, all - thanks Matt.

The 20uF at the beginning of the chain was so I could "safely" go to a 5Y3 if I wanted even more voltage drop/sag (or, I have several 5u4G's though and was thinking of just staying with the 5u4GB's and going to 2/22's for increased filtering at start of the chain). I had a few days ago also considered adding another 20 at the end of the chain, also for increased filtering, less noise etc.

The resistor is for voltage drop as the spec for the PT secondary was way higher and unloaded the tranny produced in the neighborhood of 480 or 485 volts and that was too high not to be a tube eater. Not necessarily for the sag factor, more for getting this PT into the right range. So, suggest away - I'm all ears/eyes this is an edumacational process for me...as I'm sure you and Dave can tell.

[matt h]

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[donzoid]

And....based on my revised voltage readings, no dropping resistor if added to the end of the power string (for the preamp section) correct?

...I should have one lying around here...then the issue is placing it, but I know where in the circuit, and thankfully there's quite a bit of room in this chassis. I'll look at it after a bit. Thanks.

[matt h]

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