Coupling cap placement

[Cartman]

Is there any problem in mounting this cap directly on the tube socket between pins 1 and 7 rather than how it is usually mounted on the board?

[pompeiisneaks]

There's no schematic reason to not do that, but due to the size of the cap, having it on a board is a bit better for long term stability. Otherwise the large cap with flying leads may slowly cause the leads to break over time. Not 100% sure on that, but basically to me it seems riskier unless you put the cap down on the chassis and glued it down.

~Phil

[ChopSauce]

Is that a 22nF cap?

Yet Phil sounds right, these are not so big caps.

If you're using some modern CD/DME or any Panasonic cap with similar small footprint, there shouldn't be much mechanical constraints on its support. These are much smaller than orange drops, NOS caps or similar repro models.

I look forward to seing your circuit/know why you intend to depart from the original layout, though...

[Stevem]

Anything you can do even in a amp that is already built to lessen the lenght of grid wire runs will lessen possible tone sucking interactions between stages, so that's a good move!

Also do not run your filament wires like that with one leg ground to the chassis, power the filaments with two twisted wires and then take advantage of having a lower 60 hz noise floor by making a artificial grounded center tap for the filaments with two 100 ohm 1/2 watt resistors.

[Cartman]

Thank you. Here’s a quick photo to show roughly what I was thinking. Heaters behind and low to the chassis, and a small Panasonic cap (positioned away from the red heater wires as much as possible).

[pdf64]

I can’t envisage that causing a problem.

On a side note, for future builds with that type of heater wiring, I suggest to consider rotating the noval sockets 180°, to take advantage of the gap between pins 1 & 9, eg

[SoulFetish]

On a side note, for future builds with that type of heater wiring, I suggest to consider rotating the noval sockets 180°, to take advantage of the gap between pins 1 & 9, eg

Are you kidding me, pdf? When I saw that photo, I couldn't believe how much sense that made. In fact, after seeing it, it seems so obvious that I'm embarrassed it never dawned on me to just flip the MF tube sockets around. You deserve an 'atta boy for that one.

[Phil_S]

Is there any problem in mounting this cap directly on the tube socket between pins 1 and 7 rather than how it is usually mounted on the board?

I can understand that you might hesitate to make the change because there might be something you don't realize, so it is always good to ask. Remember, in the bad old days when that layout was done, the caps were barrel shaped, about 1/4" diameter, and about 1" long, and then the axial leads. It would have fit the socket badly. I applaud you for coloring outside the lines. Things change. We are free to adapt.