Metropoulos Forum

Every Marshall build I see out there... they all typically use Allen-Bradley-style carbon comp resistors for the Phase Inverter plate resistors. Why? I've seen builds where every other resistor on the board is either a metal film or carbon film. But then the two V3 or PI plates are these carbon comps. Seems like it's a very deliberate decision to use them in that position. I figure there's got to be a good reason for it?

usually they are carbon film.

Roe wrote:usually they are carbon film.

Well, ok but why would someone choose to specifically use carbon comp then?

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The phase inverter plates have enough voltage swing across them to make use of the carbon comp mojo. I personally don't care for them in this type of circuit and stick with the standard carbon film.

In a practical sense, I don't understand why carbon comps are still used. I'll admit they look cool and have their share of vintage mojo history. Consistency and stability is much more of a priority.

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syscokid wrote:In a practical sense, I don't understand why carbon comps are still used. I'll admit they look cool and have their share of vintage mojo history. Consistency and stability is much more of a priority.

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That's what I was thinking. So I scratch my head when I see them still used in circuits that aren't really supposed to be 100% clones of that "vintage" thing. Now... that said, I have found new, modern production carbon comps that seem to be ok (Arcol). I wouldn't use them for an entire preamp section. But I guess a CC has its place here or there for some positions?

danman wrote:The phase inverter plates have enough voltage swing across them to make use of the carbon comp mojo. I personally don't care for them in this type of circuit and stick with the standard carbon film.

yes, but the nature of the phase inverter minimize resistor distortion. Not only is this a push pull power amp but it has negative feedback. CFs are better in this case imho

Well well well!!!!

This is exactly the kind of info I've been looking for and it answers my question: http://www.geofex.com/Article_Folders/c ... oncomp.htm

This is the reason why I see some builders use all Metal Film or Carbon Film in the amp. But always use CC for the PI plates. Maybe. No real way of knowing their motivations. But it seems to make sense if this article's information is accurate.

Ya they can add their own tone flavor any where high voltage is present.
Id just stay historical with compositions for my own builds IMO.

FourT6and2 wrote:Well well well!!!!

This is exactly the kind of info I've been looking for and it answers my question: http://www.geofex.com/Article_Folders/c ... oncomp.htm

Thanks for posting that article. It's interesting enough for me to try CCs again, and see (or hear) what happens. If I like them, I'll make sure I'll have some spares... ha ha!

Most Marshalls use carbon films in that position (most years). Only ones that did consistently were the early offset/prototypes.
You some times see the 100k cc throughout an amp but I think that was availability issues.
The Geofex article has been around for some time and I will often use a cc or two in the B+ line and have used them on V1 plates but to be honest never really noticed a difference. The best sounding amps I have (built or restored) seem to ones where I have used Piher (Made in Spain) resistors and mustard capacitors. I think that the over all tone is the sum of the parts rather than an individual component. Things like ceramics vs silver mica is a clear difference and mustards vs orange drops.
I will be interested to hear how this Ceriatone based hi-gain amp turns out with these expensive components as it certainly looks the part.

neikeel wrote:Most Marshalls use carbon films in that position (most years). Only ones that did consistently were the early offset/prototypes.
You some times see the 100k cc throughout an amp but I think that was availability issues.
The Geofex article has been around for some time and I will often use a cc or two in the B+ line and have used them on V1 plates but to be honest never really noticed a difference. The best sounding amps I have (built or restored) seem to ones where I have used Piher (Made in Spain) resistors and mustard capacitors. I think that the over all tone is the sum of the parts rather than an individual component. Things like ceramics vs silver mica is a clear difference and mustards vs orange drops.
I will be interested to hear how this Ceriatone based hi-gain amp turns out with these expensive components as it certainly looks the part.

I'm going to be building a few of them. Maybe 3-4. This first one is more for me to tinker with and figure everything out. Then the next few will hopefully be solid. The plan is to use the Beyschlags in the next one and compare to whatever else I use.

I'm going to ignore carbon comps and just go with metal film in most positions, if not everywhere.