Weird Capacitors! Need help determining replacement value

[SoulFetish]

Hey JPB, I was measuring them in the capacitance setting but was responding to mozz who asked what they measured in resistance (presumably to see if they're something other than capacitors).

Most multimeters won't give you any accuracy at all under maybe a few hundred pf of capacitance. I think there are many techs who would argue that testing capacitance on almost all multimeters to be a convenient approximation at best, and any reliable reading should be done on a calibrated instrument (and probably at the high end of its voltage rating).

edit: I think these are vintage "dogbone" temperature compensating type ceramic capacitors. "MN" might be the tolerance or something.

[Tom Phillips]

I'm wondering, during this whole thread, why all those parts were removed in the first place. I.e what troubleshooting pointed to them as "bad?"

[Pedro Vecino]

Ceramic tubular capacitors. Measurements are usually in picofarads, from a few to 5000. ItŽs very difficult to find them damaged.

[J M Fahey]

Yes, they very much look like old style (say the 50`s, 60Žs) ceramic caps.
If some factory was already set up to make them that way, they would keep doing so until dies or machines broke or wore off, they would be well amortized anyway.
Any new production line would be set up to make them the modern way, of course.

I read them as small value ceramics, visible value being from 33pF to 100pF, *very* hard to read on a multimeter since probably cable and test leads would already show more than 100pF.
And if user is holding probes with his hands, forget about it.

A proper LCR meter would have them attached to some terminals, no human hands nearby, and even so might show "parasitic" 10 to 50 pF, which would have to be substracted from displayed measurement

I have this very same model, faithfully working since the late 70Žs:


I think the caps shown are ceramics, value in pF is the printed number, and MN either shows voltage and tolerance or temperature coefficient or is plain brand indicator (Minnesota Capacitors anybody? )

[nickb]

I'm wondering, during this whole thread, why all those parts were removed in the first place. I.e what troubleshooting pointed to them as "bad?"

Me too! I would list bad semiconductors, electrolytics, then resistors as noise suspects in that order for a SS amp. Little caps like those would be last.

[J M Fahey]

Agree.
Ceramic tubular capacitors, number is capacitance in pF, no need to stablish units, MN may be voltage and tolerance or temperature coefficient code, donŽt expect any mystery data.
Or even plain Brand label.
They should never have been pulled, shotgunning is a terrible repair technique and in any case they would never cause noise as described, which is way more possible coming from bad active components, in general ICs or transistors.

[SoulFetish]

Yes, they very much look like old style (say the 50`s, 60Žs) ceramic caps.
If some factory was already set up to make them that way, they would keep doing so until dies or machines broke or wore off, they would be well amortized anyway.
Any new production line would be set up to make them the modern way, of course.

I read them as small value ceramics, visible value being from 33pF to 100pF, *very* hard to read on a multimeter since probably cable and test leads would already show more than 100pF.
And if user is holding probes with his hands, forget about it.

A proper LCR meter would have them attached to some terminals, no human hands nearby, and even so might show "parasitic" 10 to 50 pF, which would have to be substracted from displayed measurement

I have this very same model, faithfully working since the late 70Žs:

That LCR meter is a sweet unit, Fahey! I want one of those. I admit, I have a little bit of gear envy.
(But how obnoxious is it the i look over and see the "range multiplier" switches and think "Ew! I would have to do it?" #spoiledbyautorange)

[bob p]

I have one of these. current production, easy to find.



https://www.bkprecision.com/products...-with-esr.html

[waspclothes]

Agree.
Ceramic tubular capacitors, number is capacitance in pF, no need to stablish units, MN may be voltage and tolerance or temperature coefficient code, donŽt expect any mystery data.
Or even plain Brand label.
They should never have been pulled, shotgunning is a terrible repair technique and in any case they would never cause noise as described, which is way more possible coming from bad active components, in general ICs or transistors.

Hi JMF, point taken. I thought the shotgun replacing of the mystery capacitors would be a quick experiment before I go to replacing transistors and then IC's. I thought I was onto something when they wouldn't measure any capacitance with my multimeter (and a known .1uF cap measured fine). The transistors in this are unlabelled and I can't find a schematic, so I'm not sure how to approach that problem.

[Tom Phillips]

Hi JMF, point taken. I thought the shotgun replacing of the mystery capacitors would be a quick experiment before I go to replacing transistors and then IC's...

The usual troubleshooting technique is to isolate the problem to a certain area of the circuit. Granted, that is hard to do if you don't have a schematic and are not familiar with the circuit in your amp. In post number 1 you said the equipment was a Carlsboro solid state amp. I suggest that we start by getting the complete model number and photos of the amp so the group can try to find a schematic.

Once we know more about the circuit then we can do troubleshooting to determining if various controls affect the noises. In addition, we can do various simple things to interrupt the signal path and/or dump the signal to ground with a temporary capacitor in certain places in the circuit and observe how that affects the noises. (Caution: Don't try this until you really understand the technique) Other things are thumping, poking & prodding, freeze spray, heat gun, pot, switch & connection cleaning and detailed visual inspection. The goal is to narrow down the section of the circuit where the noise is originating and all this comes before shotgun parts replacement.

Cheers,
Tom

[J M Fahey]

Excellent advice and the way to go.

So far we know nothing, "Carlsbro SS amplifier" covers way too much, we need some focusing.
Post model, whatever is written on the backpanel, plus some pictures:
front and back panels, then pull chassis out and post preamp and poweramp pictures ... weŽll then ask for more

After we get some idea of what you have, weŽll suggest some tests.

I seem to have read no controls affect noise except Master Volume?

If so, you need to detect which is the last active section , based maybe on an Op Amp or perhaps a couple transistors, which feeds/drives that MV, I guess we wonŽt be far from the suspect.

Problem is Carlsbro was actually a very popular, widely sold and available British brand (I saw them all over the place in UK in Ž86, way more than Laney, Marshall or Vox, go figure) , but since "nobody famous" used them, they are ignored today.
HH was more famous, but also disappeared, was absorbed by Laney; another popular but obscure brand was Torque.

Sadly Music pages, IF they remember them somewhat, that applies only to Tube circuits, but never SS.

[g1]

I thought I was onto something when they wouldn't measure any capacitance with my multimeter (and a known .1uF cap measured fine).

This is what I was getting at. A .1uF is 100,000pF. You are trying to measure caps in the vicinity of what we think is 50pF. A lot of multi-meters with capacitance functions will not measure caps of such a low value.
I would guess that when you measure them, you get the same reading as when the probes are open and not touching anything.
If you were comparing to a known good 50pF cap, and the meter measured one but not the other, then you could suspect the cap.
Out of curiosity, what is the make and model of your meter?

[Gnobuddy]

Ceramic tubular capacitors.

I remember those! Thin-walled, hollow, ceramic tubes, metallized on the inside and outside of the tube.

This thread is giving me flashbacks to my childhood. I started tinkering with electronics when I was about 8 years old, and saw a few of these ceramic tubular capacitors (pulled from dead electronics that was already old then) during my first few years in the hobby. I haven't seen any of them in a very long time, though.

-Gnobuddy

[waspclothes]

Agree.
Ceramic tubular capacitors, number is capacitance in pF, no need to stablish units, MN may be voltage and tolerance or temperature coefficient code, donŽt expect any mystery data.
Or even plain Brand label.
They should never have been pulled, shotgunning is a terrible repair technique and in any case they would never cause noise as described, which is way more possible coming from bad active components, in general ICs or transistors.

Just a quick update. I replaced all of the LM741 and CA741 op-amps and the noise is gone. Thanks everyone for their patience on this.

[J M Fahey]

Glad to know