ceramic caps in Marshalls class 1 or 2? Identification hint

[dai h.]

was wondering what some of the unmarked ones were such as the red 500pF, (and thinking about this) I think it makes sense that those would be class 2 since class 2s are more volumetrically efficient (though very recently there seem to have been strides in making class 1 more volumetrically efficient but this was late 60s). Compared to the red 47pF, the red 500pF seen on Marshall boards are close in size (even though about x10 larger in capacitance). Looking at 250pF Murata class 1 (has purple mark) showing up on Marshall boards, those are rather large since it's easy to obtain 250pF 500V disk ceramics that are far smaller. Class 2 ceramic has more distortion than class 1 or mica. I think this is going to be more about taste than an absolute right or wrong. Could be useful when tweaking or cloning.

[Ben W.]

Is the red 500pf cap you're referring to the "dogbone" shaped silvered, ceramic one? Those sound really good, and I've wondered what a good modern equivilent would be for those.

[dai h.]

I don't know if they are silvered, but ceramic yes. As far as a modern equivalent, I would just try a disk cap (possibly something like an X7R or 'B' temperature coefficient--choose one that "looks cooler" to you if the appearance matters) for the small 500pF (a relatively small size should point to non-temperature compensating), and for the temperature compensating (Murata dogbone N750 500pF--the ones with a purple mark, or the Murata N750 disc ceramic), maybe an 'SL' (relatively "poorer" compared to NP0/C0G but the difference may be meaningless for this application--you can get disk 1kV ones inexpensively from Mouser---there were some Murata ones if memory serves in a not particularly vintage looking blue. Oh also, other maker ones may be available in tan, etc.--Panasonic does or did but I think quit making them recently). Another idea (for vintage amps where you want to try to not disturb things as much as possible) is to solder additional caps of the same type (don't necessarily need to be the same brand but similar temp. coefficient) underneath the board (only works for building up to values though).

Overall, (IMO) this can be very much a taste thing, so I wouldn't necessarily believe that (as far as temp. compensating vs. non-temp. compensating) one type is superior to the other in every situation, unless there was something very specific as a goal (say, a particular amp to be cloned). Things I would keep in mind is that with the non-temp. compensating, tolerances are typically poorer, values can change with DC and AC bias (DC and AC voltage applied--IIRC the higher the voltage rating, the less this is), plus very gradually over time, they can drop in value (a capacitance meter should be useful when experimenting to check the values of the caps). Also, they can be microphonic, so changing to another cap (that isn't or has less) or possibly gluing it down could be necessary.

Subjectively (not that I've done extensive scientific testing), I would choose the non-temp. compensating if you want coloration, and the temp. compensating if you want to pass the signal more cleanly. In some effects pedals and things I've tried swapping, the "better" temp compensating types have in some cases sounded worse to me.

[Ben W.]

In your opinion, do the NPO/COG class 1 caps sound cleaner in some applications like a silver mica? I'm looking specifically for a close equivalent to the old Lemco "Dog bone"caps in 560pf for the tone stack bypass cap. I have a silver mica there now. I'm guessing a class 1 NPO/COG ceramic would be a good place to start and I could move to a ceramic with more coloration if the class 1 sounds too sterile. The Lemco Dog bone caps seem a little cleaner to my ear than some of the cheap, disk ceramics I've used, but not as clean as silver micas and they're perhaps more rounded on the top-end and less glassy. I can see why many, including myself, like them; it's like you get just enough coloration without the "ratty, fizziness" that some ceramics can give. I'm totally splitting hairs, but I'm trying to clone a certain 1200 series amp with a very distinct sound, and those old Lemcos are hard to come by in anything above 100pf. Thanks for the help; I'll order up a few caps and just start from the cleanest NPO/COG and work my way to the other end of the spectrum.

[dai h.]

In your opinion, do the NPO/COG class 1 caps sound cleaner in some applications like a silver mica?

They do seem to be similar in that respect (cleaner, clearer highs).

I'm looking specifically for a close equivalent to the old Lemco "Dog bone"caps in 560pf for the tone stack bypass cap. I have a silver mica there now. I'm guessing a class 1 NPO/COG ceramic would be a good place to start and I could move to a ceramic with more coloration if the class 1 sounds too sterile. The Lemco Dog bone caps seem a little cleaner to my ear than some of the cheap, disk ceramics I've used, but not as clean as silver micas and they're perhaps more rounded on the top-end and less glassy. I can see why many, including myself, like them; it's like you get just enough coloration without the "ratty, fizziness" that some ceramics can give. I'm totally splitting hairs, but I'm trying to clone a certain 1200 series amp with a very distinct sound, and those old Lemcos are hard to come by in anything above 100pf. Thanks for the help; I'll order up a few caps and just start from the cleanest NPO/COG and work my way to the other end of the spectrum.

I would guess that if you have a mica for the tone stack treble cap now, and you put in a ceramic class 1 (of the same value), you would basically get a similar result. Possibly the Lemco (the small red 500pF10% ones which are probably *not* temp. compensating since they have a relatively small size) do sound somewhat distinct (I could be wrong but am somewhat sceptical of this), but I would want to measure the actual value to be sure that I wasn't just hearing a difference in capacitance (and if you are trying to match the sound of the smaller red Lemco 500pF dogbone I would start with non-temperature compensating--also who knows, maybe those were relatively crappy in terms of the technical specifications!). I would also try playing with the mixer bypass cap and not just the tone stack cap.

[Ben W.]

I found a few original Lemco 500pf caps...finally,and I'll see how they stack up against a few other ceramics in terms of tone, assuming there's any audible difference. Thanks for the help.

[dai h.]

cool. Try to report back with the outcome (and cap values if you're able to).

[EddyInChicago]

VERY, VERY interesting topic for me personally!! AND I'm glad someone is addressing it! Have you had a chance to compare these caps? Very interested as to a "modern equivalent" or as close as posible capacitor to a "dogbone".

PLEASE HELP ... thanks,

Ed