Ferrograph Re-capping

[untune87]

Morning all,

I've had a Ferrograph 633H for a few years that has been collecting dust since the play lever started refusing to hold, pointing to a solenoid/power issue.

A few years ago I swapped out a cap on the power supply, (a 5000uF 18v I believe, for a 4700uF 63v) but I wasn't particularly comfortable poking around inside it back then. I fired it up again recently and noticed that there appears to be an issue with the motors working intermittently. I decided to take it apart and found a couple of off-spec electrolytics, so I'm going to replace them all and see if I can get it back upto scratch.

1. There's a chunky 0.75uF/440V Hunts Therminol cap [C4] strapped to the motor that appears suspect - searching round seems to indicate it's a motor start cap, will a regular electrolytic do here (of the correct voltage of course)? It is marked as "450V (AC Working)" in the manual.

2. There are a pair of 0.1uF caps across a switch on the deck [C1 & C2] that are listed in the manual as "0.1uF 250V (AC Working)" but mine are Dublier 0.1uF 600VDC and are a half blue/half yellow plastic cap that I *think* I read somewhere are unreliable - are these worth swapping?

3. There are a number of dual can electrolytics - a pair of 16uF+16uF and one 50uF+50uF (all dated 1966!) and probably worth switching out. The problem is that the 16uF ones are 25mm in diameter whereas modern replacements are all 35mm. I don't think these will fit into the round clips on the chassis - I can try fitting bigger clips but I'm not sure the holes will line up. How do folks usually deal with these?

4. There is a 100uF cap [C47] That is listed in the manual as 100uF 250V but in mine, it is a 100uF 25VDC. Not sure if this is a typo in the manual or it has been put in at some point in its lifetime - I've not seen one before. It should be an electrolytic but it's a red, plastic case axial 'Elkomold'. It's hanging off the EL84 if I remember. Could this be a problem?

I'm just taking stock at the moment before I start sourcing replacements etc but if anyone could weigh in with experience, that would be much appreciated.

Cheers!

[unitelex]

Hi,
Your 0.75uF 440v capacitor on the motor can’t be replaced by an electrolytic, use a 450V or higher voltage rated non polarised cap, eg Polypropylene motor cap.

I would replace the two 0.1uf 600v blue/white Dublier caps with modern 600V rated polypropylene.

The 100uF is probably the cathode bypass for the EL84, if so, 25V is reasonable, I would replace that also

Best Regards
Chris

[untune87]

Thanks for your help with this info Chris!

Those 0.75uF polyprops seem hard to find, Cricklewood have a 1uF - would it be an acceptable substitute in this application? There are a few of the Hunts originals knocking about, but I'm not sure it'd be wise to swap out an aged one for another, as it were.

[ms660]

Capacitors in parallel to the nearest value if you can't find a suitable 0.75uF.

Lawrence.

[untune87]

Cheers Lawrence, been looking for lower values but stumbled on a "CBB61 motor fan start running capacitor" 0.75uF 450VAC which is non polarized polypropylene and should fit the bill. It's a block shaped but I might be able to empty the can and hide it inside to keep the authenticity!

[flywheel]

Hi, some comments from me in bold below.

Originally Posted by untune87

A few years ago I swapped out a cap on the power supply, (a 5000uF 18v I believe, for a 4700uF 63v) but I wasn't particularly comfortable poking around inside it back then. I fired it up again recently and noticed that there appears to be an issue with the motors working intermittently. I decided to take it apart and found a couple of off-spec electrolytics, so I'm going to replace them all and see if I can get it back upto scratch.

1. There's a chunky 0.75uF/440V Hunts Therminol cap [C4] strapped to the motor that appears suspect - searching round seems to indicate it's a motor start cap, will a regular electrolytic do here (of the correct voltage of course)? It is marked as "450V (AC Working)" in the manual.

Is there a reason this is suspect? I've never know one to fail yet. As said above, though, a replacement must NOT be an electrolytic!

2. There are a pair of 0.1uF caps across a switch on the deck [C1 & C2] that are listed in the manual as "0.1uF 250V (AC Working)" but mine are Dublier 0.1uF 600VDC and are a half blue/half yellow plastic cap that I *think* I read somewhere are unreliable - are these worth swapping?

Yes, if there's one capacitor that most certainly will need changing it's these blue suppressor caps across the deck motor switches - in my experience they usually blow up (possibly after years of moisture absorption - they don't seem well sealed).

3. There are a number of dual can electrolytics - a pair of 16uF+16uF and one 50uF+50uF (all dated 1966!) and probably worth switching out. The problem is that the 16uF ones are 25mm in diameter whereas modern replacements are all 35mm. I don't think these will fit into the round clips on the chassis - I can try fitting bigger clips but I'm not sure the holes will line up. How do folks usually deal with these?

I usually leave them be - I know in theory I shouldn't, and that they're decades past their life expectancy, but they usually still seem to work okay (something seems to have happened with electronic component manufacture in the early sixties to make things a lot more reliable - maybe military/space spending?). For longer term, though, it's probably time to source replacements (may be worth taking time to track down items that are an easy fit).

4. There is a 100uF cap [C47] That is listed in the manual as 100uF 250V but in mine, it is a 100uF 25VDC. Not sure if this is a typo in the manual or it has been put in at some point in its lifetime - I've not seen one before. It should be an electrolytic but it's a red, plastic case axial 'Elkomold'. It's hanging off the EL84 if I remember. Could this be a problem?

That is indeed a 25v capacitor, and these can be out of spec., though effect on performance might not be obvious. Modern replacements seem improbably small!

I have a couple of Ferrograph decks from around this time and find most components quite reliable, so I prefer to only change things if I have to. Other capacitors like those yellow Mullard caps in the amplifier should be fine (and are sought after on eBay even second-hand).

[flywheel]

Originally Posted by untune87

Cheers Lawrence, been looking for lower values but stumbled on a "CBB61 motor fan start running capacitor" 0.75uF 450VAC which is non polarized polypropylene and should fit the bill. It's a block shaped but I might be able to empty the can and hide it inside to keep the authenticity!

I'm not sure about the Hunts 'Therminol' brand of motor cap as fitted to the later Series 6 decks (and the Series-Logic 7s too), but the older and larger version contains a greasy gel that may very well be polychlorinated biphenyl or 'PCB' - a rather hazardous substance!

I have one in a sealed bag I was tempted once to open, as it came from a damaged deck, only to find this stuff inside. It's now in two sealed bags waiting for me to find out how to get rid of this particular kind of hazardous waste...

[DMcMahon]

Originally Posted by untune87

2. There are a pair of 0.1uF caps across a switch on the deck [C1 & C2] that are listed in the manual as "0.1uF 250V (AC Working)" but mine are Dublier 0.1uF 600VDC and are a half blue/half yellow plastic cap that I *think* I read somewhere are unreliable - are these worth swapping?

Have not seen a schematic for the 633 so unsure what C1 & C2 are, but if the switch in question is switching mains voltage, it would make sense if replacing them to use 0.1uF/100nF 275VAC X2 (safety rated) Polypropylene Suppression capacitors, for long term reliability of the capacitors.

David

[untune87]

@Flywheel
Thanks for the info there; in regards to 1. You're right, I've fluffed this one. Must have had my DMM set wrong because I did think the reading seemed odd when I originally checked. Did it again earlier just to be sure and got 0.77uF or thereabouts, so it's within spec. Saves me having to do any surgery.

In regards to 2. I always thought those Dubilier caps looked a bit out of place. Apparently they cropped up in Marshall amps all the time, so I've read. Either way, they're easy to get at and painless to swap out.

I'd much rather leave things as they are to be honest but given that things are playing up, it seems like a good time to change them before something gives out, assuming it hasn't already. I thought that the 25V would have been fine, maybe they were just being cautious with the manual! I think I have a spare 25uF and 100uF knocking around which werre cathode bypass caps in an old valve amp project actually.

Not too keen on opening something like that up so I'm glad it's turned out to be fine! There's a 16+16uF can and an 8uF in the power supply that are probably the first to look at, followed by the cans on the amp side. I actually just found the original 5000uF can I swapped out a couple of years back and tested it, and it comes in at approx 5300uF. Dated Jan '65!

@DMcMahon
I will try to get the schematic uploaded, I have a photo (no scanner anymore unfortunately) but it's clear and might be useful to others looking. Appreciate the advice on the caps, I'll look for safety rated polyprops. Cheers!

[untune87]

Schematic attached, if the quality isn't upto scratch I'll host it elsewhere

EDIT: Hi res version ********************A7XrEG7

[DMcMahon]

My eyes struggled a bit with the quality of the schematic but think I can see that the switch with C2 across it (for capstan motor) picks up full mains voltage from the mains transformer primary and the switch with C1 across it (for the fast wind motors) picks up a reduced voltage from the mains transformer primary, so X2 capacitors still recommended, they also will help to protect the switch contacts and reduce/eliminate any RFI/EMI induced noise into the amplifier stages when switches actuated.

David

[DMcMahon]

Had not spotted the link to the Hi-Res drawing, so capstan motor gets 245 volts and fast wind motors 150 volts.

[untune87]

Thanks David! I will source the 275VAC X2 caps here, sounds like the logical solution.

Also, apologies if anyone is looking at the hi res image on a mobile device; turns out it will only be hi-res on a desktop

This morning I have pulled a few caps out and measured them to see if they had drifted.

In the PSU, the 16uF + 16uF can is reading ~22uF + 22uF (one a little under, one a little over.)

The 8uF reads 9.35uF.

The two 0.1uF caps across the switch on the deck read 150nF and 142nF.

Any of these enough to be causing issues with the function of the solenoid holding or the motors having issues?

I haven't measured the cans on the amp side as I assumed these would be filtering the power to the valves and wouldn't likely have much impact on the operation of the deck, but correct me if I'm wrong there.

[untune87]

Another observation in addition to the above: According to the service manual, the power for the hold-on solenoid is derived from the 12.6v AC heater supply, rectified by MR2 (BY122) and then smoothed by C10 and R6.

C10 is the 5000uF 18V electrolytic that I replaced a few years back. I measure this one at 4575uF, within tolerance but a way off the 5000uF originally in there. Wondering if it might be worth strapping a 470uF in parallel to bump it closer to original spec. Also I tested the resistor, which should be a 2.2R, and it measures 3.35R. I'm not sure if this deviation from value will have any significant effect on the DC that gets fed to the solenoid?

[barrymagrec]

Electrolytics have such wide tolerances that it`s not worth worrying about.

3.35 ohms instead of 2.2seems a bit odd, I`d check your measurements on a known good resistor. If the original is a wirewound type it won`t go high, it`ll be O.K. or open.

[untune87]

Originally Posted by barrymagrec

Electrolytics have such wide tolerances that it`s not worth worrying about.

3.35 ohms instead of 2.2seems a bit odd, I`d check your measurements on a known good resistor. If the original is a wirewound type it won`t go high, it`ll be O.K. or open.

Noted re the electrolytics, thanks!

Just measured a bunch of wirewounds from the bitsbox and they're all fine, doubled checked the one next to the smoothing cap and again, getting 3R3 or thereabouts. It's a 1 watt carbon comp (red/red/gold/silver) and has no tolerance percentage against it in the service manual

[DMcMahon]

Is that R76 ? annoying that the schematic does not show the component values.

[DMcMahon]

Originally Posted by untune87

Thanks David! I will source the 275VAC X2 caps here, sounds like the logical solution.

Also, apologies if anyone is looking at the hi res image on a mobile device; turns out it will only be hi-res on a desktop

This morning I have pulled a few caps out and measured them to see if they had drifted.

In the PSU, the 16uF + 16uF can is reading ~22uF + 22uF (one a little under, one a little over.)

The 8uF reads 9.35uF.

The two 0.1uF caps across the switch on the deck read 150nF and 142nF.

Any of these enough to be causing issues with the function of the solenoid holding or the motors having issues?

I haven't measured the cans on the amp side as I assumed these would be filtering the power to the valves and wouldn't likely have much impact on the operation of the deck, but correct me if I'm wrong there.

Impossible to say for sure but I would say unlikely.

Due to normal wide tolerance of most electrolytics their absolute values are not normally important, more important is their DC level/stability (when smoothing/reservoir caps) and their AC ripple level.

[untune87]

R6 for the one which should be 2R2 but is reading 3R3 - it really is frustrating having no values on the diagram, everything is in tables. I'll upload for convenience, might be useful to others in future.

[barrymagrec]

If it`s a carbon resistor reading high it may actually be worse under operating voltage conditions - I`d definitely replace it.