Princeton Reverb clone treble cap leakage

[M Fowler]

Never had a treble cap leak dc like the 500pf silver mica I originally used.

Replaced it with this 1000v 500pf cap large but working.

Freaking scratching pots and other noise all gone.

Mark

Fowler 68 Princeton Reverb Clone treble cap leakage.jpg

[joeboo88]

Hey Mark I had that exact thing on my Express, the cap was new and obviously a dud...

What’s the story on this amp. Is it yours? Or are you just fixing it?

[Colossal]

Mark,

Is that one of the new SoZo 500pF 1000V micas? Or the standard issue CDE 1000V 5%? I got a couple of those new SoZos for an upcoming build; thought I would try them out given the positive reception 'round these parts.

[Stevem]

I have had a few new bad ones right out of the bag over the years so I now test everything before it goes in!!
It only takes half a minute to solder one lead on to a V+ circuit and test of leakage!

[M Fowler]

Mark,

Is that one of the new SoZo 500pF 1000V micas? Or the standard issue CDE 1000V 5%? I got a couple of those new SoZos for an upcoming build; thought I would try them out given the positive reception 'round these parts.

Dave, yes the new cap is the large Sozo 250pf/1000v cap and I use the larger 500pf version in my hot rodded Marshall builds.

The cap I removed was a new black color SM 250pf/500v cap. Had scratchy pots and snap crackle sounds going on. First I replaced the .1 and .047 caps but got smart and lifted one end of the treble cap
and had over 200vdc. Replaced that cap and the amp was back to beautiful PR tones.

Mark

[M Fowler]

I have had a few new bad ones right out of the bag over the years so I now test everything before it goes in!!
It only takes half a minute to solder one lead on to a V+ circuit and test of leakage!

Your right that is something a guy could do, so I need to build that low voltage cap tester Mr Carlson's Lab patreon channel has to offer.

[gldtp99]

I recently also built a BF Princeton Reverb clone------ but with a cab cut for a 12" speaker from Mojotone.

I used one of these for the Treble cap in the tonestack:

https://www.ebay.com/itm/220pF-2000V-Ce ... 5889460229

Some blowhard on another forum tried to tell me that "Ceramic Disc caps have no place in an audio path". He was very serious in his opinion------ I didn't bother to respond to him----- seemed like a snobbish fool to me.

60's Fenders and 70's Marshalls used lots of ceramic Disc caps in the audio path----- I use them frequently------ I also have and use new CDE Silver Mica caps sometimes. And sometimes polystyrenes.

Why the backlash against Ceramic Discs ?

These are guitar amps--------- not deep space probes.

I get tired of the "High Horse" snobbish builders sometimes.

[pompeiisneaks]

There are some ceramics that will sound horrible in the signal path, you just need to choose the right type, I think its like X5F or something like that quality work great, Dumble used them extensively as did fender, marshall and vox I believe. Just use the right quality/type for the use case. I also read the books by the valve wizard and he talks about different types of caps and resistors and noise etc, and he mentions something very similar, some types are great others will sound horrid.

Edit: removed my name duplicate lol

~Phil

[gldtp99]

I know you're an admin here but this doesn't make sense to me.

Do you think Fender used only "Special High End" ceramic discs in the 60's amps that most builders fall all over themselves trying to duplicate the tone of these days ? And tone that the average player worships ?

Do you think Marshall did ?

What about the original Valco/Supro amps that have suddenly become popular again ?

Let's not forget the Danelectro made Silvertone amps------- they really used cheap parts.

I've used plenty of cheap Z5U disc caps and the amps sounded wonderful.

Reminds me of the old story, "The Emperor's New Clothes"

I'd be the guy saying, "All you people are nuts----- He isn't wearing a stitch !!!"

[pompeiisneaks]

I'm not special because I'm the admin

I have heard plenty of horror stories of the cheaper caps being used. The reason they're not optimal in these amps is that they are often very prone to microphonics. That makes them sound horrendous. Likely the quality of the caps that were made back in the 50's were different than they are now, but I welcome data that counters that, also, I may have misunderstood some part of this and am grossly misstating it.


~Phil

[sluckey]

Take a look at this. It's a well respected R2R recorder from the early '60s.


And I used some discs in my final project just because they look right.

[pompeiisneaks]

Ahh yeah that's the type, Z5U, I see them in that old one and in yours sluckey, got my letters all jumbled lol!

~Phil

[M Fowler]

Hey Mark I had that exact thing on my Express, the cap was new and obviously a dud...

What’s the story on this amp. Is it yours? Or are you just fixing it?

Joe, yes I built this amp first I tried building the silver face 68 custom PR but didn't like the sound so I converted back to stock 65 PR circuit and sold the amp.
Owner said it isn't sounding right and brought it in for inspection and he was right dc on all the pots.

Mark

[TUBEDUDE]

Wow, 200V of leakage, i'll bet those pots were scratchy. I've replaced my share of leaky pots, but they all had less than 10 Volts of leakage. Are you sure it was leakage and the cap wasn't just shorted?

[M Fowler]

I threw the cap away so I can't test it anymore but possible it was shorted 500pf/500v silver mica cap.

The amp sounds great now the customer said.

Mark