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Old 13th August 2019, 09:18 PM   #11
knarfor is offline knarfor  United States
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Quote:
Originally Posted by Monte McGuire View Post
R19 overlaps C12. Even if they are mounted on opposite sides, the pad of R19 cannot be within the courtyard of C12.

In general, you have a bunch of meandering traces - straight traces between pads are preferable. The current trace widths are nice - I'm not a fan of thin traces and see no benefit to them, except when you need to reduce capacitance, but you have no copper planes so the point is moot.

There's a DECOUP GROUND trace that winds under SX5, through the pins when it could clear that socket completely by routing it to the right. Or, since it's a ground, you could convert that into a copper pour and it will act like a ground a lot better than a thin, windy trace. You may want a star ground but I find that more copper is better than slicing it into tiny ribbons that end up not acting like ground at all. If you do a pour, set the software to give you a wide clearance, maybe 20 mil. Do not go right up to the design limits of space/trace. Designing to 7 mil space/trace is fine for low voltage stuff, and 20 mil is safer for tube voltages.
Is it desirable to clear the socket?

My rational for routing the returns (the grounds) was to keep each circuit's loop area as small as possible. So the return traces (grounds) track their circuits' respective supply traces.

Is my logic faulty?

If not, is making a plan a better way to implement it?
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Old 13th August 2019, 11:48 PM   #12
knarfor is offline knarfor  United States
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That should be "plane", not "plan" #ThanksAutocorrect
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Old 16th August 2019, 11:22 AM   #13
6A3sUMMER is offline 6A3sUMMER  United States
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knarfor,

You need a circuit revision. Simple, but important. Connect each output tube's individual cathode current sense resistor directly to ground. Do not connect those through the switch. Then use a 5 position switch to connect the meter and its dropping resistor to the switch rotor, and the 4 stators to their respective cathode current sense resistors. The 5th position is Meter off, so it is not subjected to the time varying DC when audio test tones, and music is applied to the amp (current changes with signal in Class A, and even more if it goes into class AB).

If you do use your current switch scheme, be sure it is a make-before-break switch. The last thing you want is the quiescent current of one tube going to zero as the switch contact opens before the other switch contact closes. That will sound bad, and may damage a tube, OPT, tweeter, or your ear.
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Old 16th August 2019, 11:26 AM   #14
nigelwright7557 is offline nigelwright7557  United Kingdom
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For my valve amp designs I use star grounding. Don't mix output grounds with input grounds. I also keep input signal short as possible and surrounded by ground plane. On input valves keep tracks and components as near to valve as possible, especially grid stoppers.
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Old 19th August 2019, 05:11 AM   #15
knarfor is offline knarfor  United States
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Quote:
Originally Posted by 6A3sUMMER View Post
knarfor,

You need a circuit revision. Simple, but important. Connect each output tube's individual cathode current sense resistor directly to ground. Do not connect those through the switch. Then use a 5 position switch to connect the meter and its dropping resistor to the switch rotor, and the 4 stators to their respective cathode current sense resistors. The 5th position is Meter off, so it is not subjected to the time varying DC when audio test tones, and music is applied to the amp (current changes with signal in Class A, and even more if it goes into class AB).

If you do use your current switch scheme, be sure it is a make-before-break switch. The last thing you want is the quiescent current of one tube going to zero as the switch contact opens before the other switch contact closes. That will sound bad, and may damage a tube, OPT, tweeter, or your ear.
Thanks for this! Yes, I thought that was a particularly weak/bad part of the design. Good to get confirmation and a road map on fixing it.

Quote:
Originally Posted by nigelwright7557 View Post
For my valve amp designs I use star grounding. Don't mix output grounds with input grounds. I also keep input signal short as possible and surrounded by ground plane. On input valves keep tracks and components as near to valve as possible, especially grid stoppers.
So would Version 2 be preferable to the scheme I posted previously?

Version 1:

"Source" traces in red, "return" traces in green"

board.jpg

Version 2:

"Source traces are the same as in previous versions, but the "returns" are in the form of planes for each section.

The large outer plane is for the drivers. The inner left plane is for the input section. The inner right plan is for the inverter section.

Everything still connects to the rest of the circuit as indicated in the first post.

Untitled-1.jpg

Last edited by knarfor; 19th August 2019 at 05:14 AM.
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