Marshall Silver Jubilee capacitors

[Joe L]

Does anyone have a source or information on the axial ceramic capacitors in the Jub? They look like resistors but are definitely capacitors. I'm pretty sure they are rated at 100v from research I did a long time ago and the circuit design confirms this by only using them where the rating won't be a problem.

I've built a version with normal film caps and it does sound great but there is a certain high midrange distortion that I don't hear with mine.

Any info would be greatly appreciated!

[Chuck H]

Mouser has many different rod shaped axial capacitors. I can't say about finite identification for brand, ratings, etc. for the Marshall though.

[Joe L]

The only axial types I've found are multilayer ceramics. And in fact there are a couple in the Jubilee.

[tedmich]

lots of axial ceramic caps in Peavey amps, they are usually green or orange yellow and can have banding like resistors, can you post a picture? They are made by Vishay or AVX I believe. The common 470pF (paralleled with 470k resistor) into the 12ax7 grid is only a 50v rated unit, but it uses the NP0 (C0G, all with zeros) ceramic which has much better distortion and temp shift characteristics than crappy X7R or other ceramic types and costs accordingly.

Odd to get more distortion with films, maybe a bad cap or other issue?

[Pedro Vecino]

Silver jubilee uses eight or ten axial multilayer ceramic capacitors. Some like Peavey (mustard color) and others such as those used in Dual Reverb Marshall (with colored lines looking like 1/4 watt resistors). In essence they are the same: cheap low voltage capacitors.
Not all are critical in terms of contribution to the distortion. Basically important for this purpose are:
C26 - 4n7 High voltage ceramic - pre tonestack plate output
C5 - 1n - Bypass gain pot - intermediate gain settings
C8 - 220p - treble pot input

I would not change more than that (all standard radial ceramic). And would use a pair of Chinese 12ax7 in the first two sockets

[Chuck H]

Got a pic? I don't even know if rod shaped ceramic capacitors come in other than multi layer type. Do they?

[Joe L]

lots of axial ceramic caps in Peavey amps, they are usually green or orange yellow and can have banding like resistors, can you post a picture? They are made by Vishay or AVX I believe. The common 470pF (paralleled with 470k resistor) into the 12ax7 grid is only a 50v rated unit, but it uses the NP0 (C0G, all with zeros) ceramic which has much better distortion and temp shift characteristics than crappy X7R or other ceramic types and costs accordingly.

Odd to get more distortion with films, maybe a bad cap or other issue?

Actually Ted, my repro has less distortion and really does sound good. The distortion quality I'm talking about is an mid emphasis that can be harsh at times but with an EQ in the effects loop, it flat ass works in a band situation. I played with a guy that had one that he didn't like. I suggested the eq and plugged in one of mine and adjusted it for him while he was playing. The distortion quality didn't change but we were able to "tame the hump" (sounds like a good name for a band). From then on, that amp was the best Marshall live sound I've heard. It just sat perfectly in the mix without being loud.

And for Doug who asked for pictures, this one shows the mixture of cap types used in the Jub.

[Joe L]

Silver jubilee uses eight or ten axial multilayer ceramic capacitors. Some like Peavey (mustard color) and others such as those used in Dual Reverb Marshall (with colored lines looking like 1/4 watt resistors). In essence they are the same: cheap low voltage capacitors.
Not all are critical in terms of contribution to the distortion. Basically important for this purpose are:
C26 - 4n7 High voltage ceramic - pre tonestack plate output
C5 - 1n - Bypass gain pot - intermediate gain settings
C8 - 220p - treble pot input

I would not change more than that (all standard radial ceramic). And would use a pair of Chinese 12ax7 in the first two sockets

Thanks for that info Pedro! It sounds like you have some experience with the Jubilee circuit. I recognize the mustard color caps as cheap multilayer types. I can't believe they are using those as coupling caps.

I found this post with a pic of the Marshall 900 you mentioned. What a cheap ass board!

[gui_tarzan]

What's up with this disc cap?

[Joe L]

Silver jubilee uses eight or ten axial multilayer ceramic capacitors. Some like Peavey (mustard color) and others such as those used in Dual Reverb Marshall (with colored lines looking like 1/4 watt resistors).

What makes you believe the ones that look like resistors are multilayer types? I was thinking those might be single layer types similar to the "dogbone" ceramics used in the old marshalls.

[dai h.]

I would try non-temperature compensating ceramics. They have more distortion (versus NP0/C0G and other temp. compensating types from my understanding) but this may be exactly what someone wants for an effect or amp. I mentioned before that non-temp. compensating ceramics sounded more correct (in a couple of positions) in a SansAmp pedal (an early one I had which I used a lot had them but a later version had a mylar for the input 47n and I tried many "good" caps such as NP0 C0G for the 470p coupling cap coming after the 47n). (This wasn't a rigorous scientific examination, so I suppose I could be wrong, but did seem more "right".)

The type may be "monolithic" but my guess is that if you use the same type (class--such as "X7R", "Y5P", etc.--you will get the sound). There are lots of them in my Marshall SE100 spk. emulator unit (not sure what all the brands (brand probably doesn't matter as long as the parts are from a reputable manf.--I've read of cases where the supposedly "NP0"s weren't) are but some were Murata/Erie IIRC). Also I've never broken one to look at the internals, but some axial ceramics look like a small surface mount part embedded inside a glass case w/leads on the end (perhaps if you scrape the paint this is what you'll find?). As Chuck mentioned above Mouser had some listed in their catalog (two makers, one I forget (but they were the inexpensive resistor stripe kind), and the other Sprague? solid mustard yellow).

[Joe L]

What's up with this disc cap?

It's a decoupler feeding the majority of the tone stack and keeps the HV off the cheap, low voltage caps used in the stack. The Jub's tone stack is unusual and awesome sounding. I need to do a spice simulation and see what kind of response it has but I can tell you, the controls have more range and don't interact like the normal Marshall/Fender tone stack.

[tedmich]

Dai may be right, the cheap ceramics may give the "tone" people "like" in this amp. As a rule, in all-tube amps, I replace all signal path ceramics with film, with old low value polystyrene caps being my first choice for the pF range. Ceramics have there place, as do tantalums (in voltage regulators!) but I have never regretted replacing them in most tube audio circuits.

Yellow mustard ceramics are Vishay or AVX or maybe Kemet...

[gui_tarzan]

It's a decoupler feeding the majority of the tone stack and keeps the HV off the cheap, low voltage caps used in the stack. The Jub's tone stack is unusual and awesome sounding. I need to do a spice simulation and see what kind of response it has but I can tell you, the controls have more range and don't interact like the normal Marshall/Fender tone stack.

No, I mean it looks like it got hot on the back side where my arrow is pointing.

[Joe L]

No, I mean it looks like it got hot on the back side where my arrow is pointing.

Nay,it's just shiny and reflecting the brown resistor next to it.