coupling caps AC15h1tv

[nekkio99]

hello guys, I am looking to replace coupling caps for my AC15h1tv. I have a friend who can do the soldering for me, but I am supposed to find out which ones to change, and I don't understand much about this. The schematics for my amp are at

www.*blue*guitar.org/new/schem/vox/ac15htvh1_handwired.pdf

can anyone help me out and tell me which ones i should replace? (e.g.c1, c2 etc)

many thanks

andrea

[Torquil]

Great amp! But why change them?

Usually one replaces the electrolytic capacitors in an amp when they are getting very old. But not the coupling capacitors, unless you need different values to modify the tone?

[FYL]

Why would you want to change coupling caps? Are they defective?

[ampgeek]

Welcome aboard Andrea!

The "why" is none of my business. I can only assume that you are chasing a tone like the rest of us.

However, you might want to discuss that a little more here just to make sure that you dont get into any not so obvious pitfalls that are likely about. The much more experienced folks than I here are a wealth of information and are always willing to share.

To your question, coupling caps, as the name implies generally (and I will use that term alot as some areas are not so black and white as we would like), connect multiple stages of gain. Each tube, generally, represents a gain stage in your plan. They pass the signal (AC) and block the DC from the previous gain stage. You will also notice, generally, that a tube plate load resistor(s) precedes a coupling cap. It is that plate load resistor that creates the AC that you want to shuttle along to the next stage.

So...for your schematic and plans:

V1 plate load resistor R6: coupling caps C7 and C9
V2 plate load resistor R26: coupling cap C20
V3 (cathode follower stage): C19 and C20. Typically referred to as tone caps in this configuration. A little different than your typical gain stage.
V4 (phase inverter) plate load resistors R3 and R4: coupling caps C5 and C6. This stage feeds the power amp (PA).

Good luck,
Dave O.

[lumox0013]

in order to know which ones to change one would need to know what purpose you are wishing to accomplish by changing the caps?

[dehughes]

Speaking as one who tinkered with the various cap value permutations found in the many AC30-ish amps....I can say that I vastly prefer the "stock" AC30 cap values. My goodness...I replaced the .047uf power section coupling caps with .01uf caps, and yes indeed...I have an AC30. Wow. What a difference.

But yes, it depends on the location of the caps, nekkio99, and your intentions.

[nekkio99]

hey guys, thanks so much. Yes, I am changing them as other people were suggesting that in other forums. They were saying the caps used by vox are very poor quality, and that replacing them made a huge difference in their amp.

So why not try and see if they are right? Same values, just better quality.

[FYL]

I am changing them as other people were suggesting that in other forums. They were saying the caps used by vox are very poor quality, and that replacing them made a huge difference in their amp.

Vox uses standard metallized poly coupling caps, which are OK for the application.

[dehughes]

So why not try and see if they are right? Same values, just better quality.

Yes, the quality of the cap is important and can certainly make an audible difference....I'd do the same thing if I were you.

[JamesHealey]

What are you intending to replace them with? sozo are an ideal choice for vox, as are mallory 150.. be careful of high voltages in amps if your friend hasn't worked on amps before i'd suggest finding a qualified tech. good luck and enjoy