I have a Mk2 Ferrograph F307 amplifier. The volume control is a dual concentric 100 KΩ logarithmic pot with one half serving the left channel and the other half serving the right channel thus obviating the need for a balance control. The bass & treble controls are also dual concentric pots.
As you turn the volume control(s) you get crackling from the speakers; other than the crackling (which only occurs when adjusting) everything works fine. I have been told that I should not use any form of cleaner or lubricant to clean the pots. Does this make sense or would it be safe to spray the volume control with Servisol Super 10?
As you turn the volume control(s) you get crackling from the speakers; other than the crackling (which only occurs when adjusting) everything works fine. I have been told that I should not use any form of cleaner or lubricant to clean the pots. Does this make sense or would it be safe to spray the volume control with Servisol Super 10?
to understand why 'cleaning' isnt a good idea, you need to understand how pots are made.
cleaning/treating will work, sometimes, but never for long.
best long term fix is to replace the pot.
Ahhhhhhhhh we used to have that exact same ferrograph.
selling it was the best thing we ever did..........
cleaning/treating will work, sometimes, but never for long.
best long term fix is to replace the pot.
Ahhhhhhhhh we used to have that exact same ferrograph.
selling it was the best thing we ever did..........
You must have a long, long history of doing some truly awful things then!
The F307 was the first amplifier I ever bought, over 40 years ago and still going strong in the kitchen with a DAB radio & CD player attached. Other than the crackling volume control it works well - EVERY day!
Sadly, I'm not convinced that I could locate a suitable replacement pot so cleaning is likely to be the only solution other than putting up with the occasional scary crackle.
If the crackling is caused by dust/dirt/gunk that got into the hole openings, spraying may help. After all, these are not sealed type pots.
If the crackling is caused by worn out carbon tracks of the pot, then replacing the pot is the surest way to fix the problem. Is the crackling only occurring on a specific portion/sector of the pot? Or all around?
You don't have to buy the same exact part, but get the value of your current pot (measure it, or look for any markings) and get the same value dual pot. You can get a sealed-type Bourns conductive plastic pot. That should be good for several million rotations.
If the crackling is caused by worn out carbon tracks of the pot, then replacing the pot is the surest way to fix the problem. Is the crackling only occurring on a specific portion/sector of the pot? Or all around?
You don't have to buy the same exact part, but get the value of your current pot (measure it, or look for any markings) and get the same value dual pot. You can get a sealed-type Bourns conductive plastic pot. That should be good for several million rotations.
Spraying just a little of this usually fixes things right up. Exercise the control a few times afterward. Caig Labs DeoxIT D5 (Part No. D5S-6).
So far as I can tell, the crackling occurs at any point - it is intermittent (doesn't always happen - i.e. it hasn't happened this morning when I was told to "TURN IT DOWN!".If the crackling is caused by dust/dirt/gunk that got into the hole openings, spraying may help. After all, these are not sealed type pots.
If the crackling is caused by worn out carbon tracks of the pot, then replacing the pot is the surest way to fix the problem. Is the crackling only occurring on a specific portion/sector of the pot? Or all around?
You don't have to buy the same exact part, but get the value of your current pot (measure it, or look for any markings) and get the same value dual pot. You can get a sealed-type Bourns conductive plastic pot. That should be good for several million rotations.
My concern over a replacement pot relates to the dimensions; I want to retain the external appearance and there is one shaft inside another - probably using measurements that are no longer used
As it happens I also get a thump through the speakers when switching on / off which I guess means that the capacitors should be replaced.
Is DeoxIT in some way superior to Servisol Super 10?
Why do people keep repeating this? It's not true. I deal with a lot of vintage equipment, and only once have I encountered a potentiometer that needed replacing - and it wasn't even worn out as I first thought - it was intermittent due to a crack in it. Potentiometers practically never wear out. Cleaning them might not work for long, but if that's the case - you're cleaning them wrong. First clean with alcohol or similar, then apply lubricant to keep the surfaces free from contamination. It'll take years for it to become scratchy again - if ever.
Power-on thump won't be fixed by replacing capacitors. It's normal and cannot be removed without modifying the amplifier.'
I don't know what Servisol Super 10 is, but it doesn't really matter what you clean with, as long as you lubricate it afterward.
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I had a Quad 303 power amp serviced by Quad (about ten years ago); before servicing it caused a thump on switch off, afterwards it didn't. I was told that this was down to the new capacitors - not true?
With what do I lubricate the pot -and- how? It is pretty much enclosed.
ps - many thanks for everyone's replies|.
Perhaps you haven't encountered sealed pots and those multiple gang types whose wafers have to be fully dismantled to access the front section(s) so you can flush them properly. From a service point of view, unless your clients have deep pockets, you don't have the time it takes to do this and reform the swaging that secures the wiper assemblies to the shaft + testing each operation. A new pot is usually the economical way to proceed.
People say that the use of solvent cleaner doesn't work for long because it simply doesn't when you can't access it properly and as you suggest, add some lubricant, though a fully cleaned carbon element shouldn't need this either.
Perhaps I should relate the cases where the wiper was worn off, the track was divided by wear or even delaminated - maybe some other time.
In this case, a dual concentric non-ganged pair, it may be possible to withdraw the rear pot with its shaft and also the front section rear cover if there is no hole large enough to flush each section properly.
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It appears from the pic. that there is quite a hole in the casings for the terminals that could allow flushing of the resistance element with a fine syringe or even the tube of an aerosol can. Solvents can be anything that evaporates easily without moisture or residue and is non-corrosive. Alcohol, isopropyl alcohol, white spirit. etc is suitable. A Lubricant may even be a light grease such as petroleum jelly (Vaseline). Doubtless there are many $$ specialised service products that work no better.
If you were looking for a 2 min. fix without tools or expertise, you may have to think about help for this as it does require some materials and tools that may be assumed by techs. and others who regularly do this kind of work.
If you were looking for a 2 min. fix without tools or expertise, you may have to think about help for this as it does require some materials and tools that may be assumed by techs. and others who regularly do this kind of work.
Why do people keep repeating this? It's not true. I deal with a lot of vintage equipment, and only once have I encountered a potentiometer that needed replacing - and it wasn't even worn out as I first thought - it was intermittent due to a crack in it. Potentiometers practically never wear out. Cleaning them might not work for long, but if that's the case - you're cleaning them wrong. First clean with alcohol or similar, then apply lubricant to keep the surfaces free from contamination. It'll take years for it to become scratchy again - if ever.
I'd side with the cranky one
As an ex service engineer I know from experience that crackly pots were the bane of the service engineers life. A good squirt got the engineer out of the house, only for the job to keep bouncing until the pot was replaced. I say replaced, another lasting repair was to open the pot and carefully re-tension and move (vitally important) the wiper such that it runs on fresh unused track. Do that and it was as long lasting as a new replacement.
The ferograph is old.
the pot is obviously the original.
back then they didnt have polymer pots, only graphite ones.
the wipers loose tension or wear the ends off.
the track wears through to the substrate.
the substrate can crack.
the graphite track gets hairline fractures.
all things that lead to failure.
at best 'spraying' chemicals into them only pushes a little carbon dust into the cracks.
at worst it will blow the little remaining dust and track material out of the pot making it worse.
after 30 years of working on electronics, I stand by my suggestions.
with the one we had, we replaced the pot with a std dual pot.
no more balance function, but how much pain are you going to go through to find an exact replacement ?
it was pretty to look at, but with bakelite boards, carbon resistors and pots, its had its day.
dont start me on leaky bakelite boards..
Yes, I'm old, yes I can be cranky.
But sometimes us old farts can remember why we do things a certain way
What ever path you choose to repair it, I wish you the best of luck.....
the pot is obviously the original.
back then they didnt have polymer pots, only graphite ones.
the wipers loose tension or wear the ends off.
the track wears through to the substrate.
the substrate can crack.
the graphite track gets hairline fractures.
all things that lead to failure.
at best 'spraying' chemicals into them only pushes a little carbon dust into the cracks.
at worst it will blow the little remaining dust and track material out of the pot making it worse.
after 30 years of working on electronics, I stand by my suggestions.
with the one we had, we replaced the pot with a std dual pot.
no more balance function, but how much pain are you going to go through to find an exact replacement ?
it was pretty to look at, but with bakelite boards, carbon resistors and pots, its had its day.
dont start me on leaky bakelite boards..
Yes, I'm old, yes I can be cranky.
But sometimes us old farts can remember why we do things a certain way
What ever path you choose to repair it, I wish you the best of luck.....
It's the best there is, but use as little as possible, and then turn the pot from stop to stop several times afterward.
Old gear is too often saddled with cheap (cheapest the maker could source : )
pots.
Carbon deposits on a pheno substrate are not durable.
These Time out. Even when unused.
Had similar issues on a Dynaco.. NOS parts (finally sourced a few) were only marginally better than the 40 + year old used bits I had.
Serious waste o' time/$$
In frustration I fitted a Cheap (clone 12$ delivered 'alps' blue box pot.
It fit Fine ! and the thing has Never worked better.
And I bought the Darned Dyna Brand new.
Quad 303 isn't a unit to worry overly about, frankly it ain't a great item.
pots.
Carbon deposits on a pheno substrate are not durable.
These Time out. Even when unused.
Had similar issues on a Dynaco.. NOS parts (finally sourced a few) were only marginally better than the 40 + year old used bits I had.
Serious waste o' time/$$
In frustration I fitted a Cheap (clone
12$ delivered 'alps' blue box pot.It fit Fine ! and the thing has Never worked better.
And I bought the Darned Dyna Brand new.
Quad 303 isn't a unit to worry overly about, frankly it ain't a great item.
Well, a couple of replies seem to think you were talking about the Quad 303 all along, surv1v0r. Apart from 303s not having any controls and sound quality being irrelevant, one wonders why folks don't read the OP.
If you want to try solvents as a temporary fix, it won't matter too much what you use as long as it's volatile and suitable for electrical applications. Any lubricant they also contain for that application, won't be such a bad thing and may reduce noise over a longer period. My experience over many years doing repairs too, is that they all work to some degree when used casually on carbon pots - for a time, depending on usage. The jobs then bounce and may cost the repairer rather than the customer. If that fix is actually effective, it's down to other issues such as shaft wear and contact, wiper tension, accumulated debris or track groove wear as Mooly explained.
Going to the next step of a complete teardown and reassembly, fitting adapted parts or assemblies from similar pots as necessary, may take days and considerable skill, yet not resolve the problem with any guarantee, so the simplest solution is a replacement dual gang pot. For me, a balance control is a once only setting when the system is installed. A preset pot, fitted internally and wired as per a standard balance control across both channels with the wiper grounded, can then be adjusted by removing the cover if ever needed. For appearance, the separate knobs could be lightly bonded together with the aid of a short, centre alignment pin.
One other realistic option is to add a preamplifier, which eliminates the need to operate any amplifier controls apart from the power switch and even that can be controlled from a single switch via the mains, if needed. Modern preamplifiers are often remote controlled and some are very good, whilst being inexpensive and having no pots or switches at all. This could also improve your noise levels and sound quality considerably.
You haven't commented on whether you are going to proceed with any suggestions yet so we still await developments.
Thank you for a most helpful response.
In reply to your question, I am going to "put up" with the occasional snap crackle and pop when I am adjusting the volume. I am not wholly reassured about spraying Servisol Super 10 into my volume pots and I am definitely not going to take a soldering iron my my Amp. If matters get worse I may have to revisit the problem.
Many thanks to you and unnamed others for some informative advice
well my suggestion might be to little to late.
when trying to determine whether a potentiometer is just too old and worn out and needs to be replaced or a new control is noisy i always look for the presence of any dc across the control a good many "noisy" pot is the victim of leaky coupling/interstage caps. i've been surprised at just how little dc leakage it takes to make an otherwise acceptable control appear noisy
at the age of the unit in question this could be the case.
when trying to determine whether a potentiometer is just too old and worn out and needs to be replaced or a new control is noisy i always look for the presence of any dc across the control a good many "noisy" pot is the victim of leaky coupling/interstage caps. i've been surprised at just how little dc leakage it takes to make an otherwise acceptable control appear noisy
at the age of the unit in question this could be the case.
You could be right as the issue is often raised here, though I have only encountered it a couple of times. The pots are 100k and impedances are fairly high for solid state, with JFET input semis too. On the positive side, caps are generally higher than necessary voltage ratings which IME, helps longevity.
It seems unlikely the OP will tackle the work though. Perhaps the work will wind up in professional hands when the problem becomes unbearable. Here's a schematic link: Ferrograph F307 Manual - Stereo Integrated Amplifier - HiFi Engine
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