Vox Caps

[fiftynine]

Gents, I've seen all sorts of value caps either side of the PI on Vox AC15's and AC30's. Anything from 0.01 both sides of the AC15 to Hoffmans choice of 0.047's and 0.1's on his AC30.


Why did Hoffman stray so far?

[sluckey]

Gents, I've seen all sorts of value caps either side of the PI on Vox AC15's and AC30's. Anything from 0.01 both sides of the AC15 to Hoffmans choice of 0.047's and 0.1's on his AC30.


Why did Hoffman stray so far?

I'd say he's right in the middle. I see two AC30 schematics from the '60s that show .047µF and .15µF.

[fiftynine]

Indeed. Vox changed all the PI coupling caps from 0.01 to 0.047/0.15 for the 1960 AC30. The DC30 uses 0.01/0.047.


I've messed with the online calculators and can see the smaller values rolling off substantially more bass. But I'm guessing in the real world the difference is subtle even with a 10x change in capacitance in places...........especially if those frequencies were not still present.

[HotBluePlates]

I've messed with the online calculators ...

If you have an amp-in-hand, just swap and listen. The caps before the phase inverter (going into the long-tail grids) will have little effect for a reduction in value. The caps between the phase inverter and output tubes will have much more effect on low end.

It's fastest to just try & see.

[fiftynine]

Yes, HBP. They would need to be on a switch though. In my experience, if there's considerable debate the effect is subtle.

[Willabe]

In my experience, if there's considerable debate the effect is subtle.

Depends on who's doing most of the debating. How good are their ears? How good are yours?


                           Brad