Good replacement for ceramic caps in old Fender amps

[Bman]

Hi, I'm repairing a Bassman 50 and the 0.01uf ceremic cap that connects the preamp stage to the phase inverter has broken, not blown just the leg has broken were it connects to the cap, photo attached. I need to turn around the repair fairly quickly.

What type of cap do people recommend? I have Mojo Dijons on hand at the correct value.

In the past I think have used silver mica or polyester, but I don't have any of those on hand, will the mojo dijon be suitable or should I order something else and hope it arrives on time? The whole signal passes through this cap so I don't want to put something in that could potentially change the sound at all.

I would say i'm an intermediate/hobby builder having built several fender style amps and repaired some too. This one is a repair for a friend that I need to turn around quickly, as it is heading on tour next week. I can order something and just hope it arrives on time.

Thanks in advance for your help!

[sluckey]

What type of cap do people recommend? I have Mojo Dijons on hand at the correct value.

A bird in the hand is better than two in the bush.

[Bman]

Yes I like this answer!

I suppose my question should have be more like, is there any reason I shouldn't use a mojo dijon in this position?

[sluckey]

I suppose my question should have be more like, is there any reason I shouldn't use a mojo dijon in this position?

No reason not to use it, other than... Will it physically fit? That cap is 19mm x 7.5mm. I believe it will fit.

[Bman]

Yes it just about fits, so I have put it in.

Many thanks for your help!

So then is there any reason they used a ceramic in this position originally rather than the blue blob/turd/blue mouldeds? Would it just be a cost or availability thing?

[sluckey]

Those Z5 disc caps were cheap and plentiful back in the day that amp was built. Leo built great products, but he was also very frugal.

[acheld]

And they were extremely reliable, and small, and cheap.

[HotBluePlates]

... is there any reason I shouldn't use a ...?

No reason not to use it, other than... Will it physically fit? That cap is 19mm x 7.5mm. I believe it will fit.

... is there any reason they used a ceramic in this position originally rather than the blue ... mouldeds?

I have looked at a number of original Fender eyelet boards and noticed something about "capacitor choice":  the type that got used was whatever was the type that fit between the available eyelets.

   - There are a number of places where same-capacitance appears as a "brown blob" cap, and a "ceramic disk" cap, and sometimes even a "blue molded" cap in the same amp.

   - The only significant difference between these capacitors is how far apart the eyelets must be to have their leads fit.

   - I do not have any proof, but I have come to believe Fender bought capacitors of a certain type because they fit in the space allowed on the eyelet board.  Like the brown blob for Vibrato channel output to phase inverter mixing resistors, but blue molded for same-value in the phase inverter output. Or a ceramic disc for Normal channel output to the mixing resistors, when the brown Deluxe had the exact same value in a blue molded cap.


I don't perceive a "technical reason" Fender chose one cap-type over another, and I suspect it wasn't "price alone" because there are same-capacitance-value present in several different cap-types.  The only material difference I can find when the vales overlap in a single amp (or similar grouping of years) is the distance the cap must span on the eyelet board.

[EL34]

I stock .01 and .02 ceramic on this page

Capacitors-4

[tubeswell]

Those Z5 disc caps were cheap and plentiful back in the day that amp was built. Leo built great products, but he was also very frugal.

Leo knew that you don't need fancy caps!

[kagliostro]

My 2c

Avoid the use of esotheric components

https://partsconnexion.com/jupiter-capacitor-0-022uf-600vdc-ht-round/

Franco

[passaloutre]

I fell for the Jupiter trap once when restoring an amp I wanted to keep aesthetically vintage. I have no complaints about the actual product though, it does the job. I’d love to know if there’s an old man rolling foil caps in a workshop somewhere, or if they’re just rebranded something’s.

I might start using more ceramics though, they seem to be found in a lot of the 1950s junk amps that I like.

[acheld]

I've had great luck with modern ceramic caps.   When I first started choosing them, I paid a lot of attention to dielectric (to reduce heat related drift) but now not so much.   Like Leo, they are small, cheap and reliable.  I subscribe to the notion that there is a place for every part, but not every place is for every part.

[stratomaster]

Polystyrene and MLCCs are great if you're willing to heatsink properly and work hot/fast.

I'm particularly fond of using MLCCs in the tremolo oscillator for the two downstream caps and a stout 630V+ film cap for the one that sees the full plate voltage.

Also, you can get away with a relatively low voltage 10pF cap for the 3.3M bypass in most cases (but not on the Reissue Princeton Reverb, where they moved the cap to before the coupler for some reason).

[sluckey]

Also, you can get away with a relatively low voltage 10pF cap for the 3.3M bypass in most cases (but not on the Reissue Princeton Reverb, where they moved the cap to before the coupler for some reason).

Hmm, all the PRRI schematics I've seen show that 10pF after the coupler just as all the AB763 amps.

[stratomaster]

Also, you can get away with a relatively low voltage 10pF cap for the 3.3M bypass in most cases (but not on the Reissue Princeton Reverb, where they moved the cap to before the coupler for some reason).

Hmm, all the PRRI schematics I've seen show that 10pF after the coupler just as all the AB763 amps.

You're correct. Brain fart. I was thinking of the 500pF coupler to the reverb driver.

[pdf64]

Polystyrene and MLCCs are great if you're willing to heatsink properly and work hot/fast. ...

The 630V polyester caps made by LCR in Wales are pretty robust (and pricey, unfortunately) https://www.newark.com/lcr-components/fscex-390pf-1-630v/film-capacitor-390pf-630v-axial/dp/97K0274