UK Vintage Radio Repair and Restoration Discussion Forum

UK Vintage Radio Repair and Restoration Discussion Forum (https://www.vintage-radio.net/forum/index.php)
-   Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players (https://www.vintage-radio.net/forum/forumdisplay.php?f=35)
-   -   Ferrograph 4A: Restoration advice needed (https://www.vintage-radio.net/forum/showthread.php?t=151194)

Uncle Bulgaria 7th Nov 2018 9:50 pm

Ferrograph 4A: Restoration advice needed
 
4 Attachment(s)
Ahoy,

I've recently got the above from Freecycle and am trying to get it going. There's rust and a very tatty case, and as it's to go in my hi-fi setup I'd like to get it pretty nice and polished without entirely removing its character.

I have removed all the chassis and run them through the dishwasher which has brought them up a treat. I am about to start on the component checking, and replacing the Bulgin plug with the Bulgin-made IEC that fits the same holes (PX0579).

I have a few samples of material on the way to see if they will be suitable to recover the case. That '50s olive green is not my bag... I've powder-coated my Lenco turntable RAL Signal Yellow! I digress.

While I am relatively experienced in the practical side of things (valve safety, soldering, manual dexterity) and have a basic understanding of valve circuits, I have near zero experience of how to treat tape decks.

The top plate of the 4A is pretty good, apart from some rusty screws and general grime.

Questions (see pictures):

1 - What do you all think the best approach is to getting the top plate and controls cleaned up? Should I a) go wild: remove everything from below, replace the screws, clean the plate, disassemble and lubricate the motors and get everything shiny. b) remove a screw at a time to identify & replace, in order to avoid having to relocate everything on the top plate, but make it harder to clean?

2 - What to do about the grimy tape transport area? Should this be removed to clean or is it toothbrush and isopropanol? What should I be careful of touching/not touching in this area?

3 - The felt pads look shot. What should I do about it?

Thank you for any advice. I have got the Manual and a tape head cover from Ferrograph World already...

nutteronthebus 8th Nov 2018 9:42 am

Re: Ferrograph 4A: Restoration advice needed
 
1 Attachment(s)
There is a set of pads on e-bay for £4.99 plus postage


Dave L

Uncle Bulgaria 8th Nov 2018 12:22 pm

Re: Ferrograph 4A: Restoration advice needed
 
Thank you Dave - I don't know how I missed those last night when now they are the only result in a search for 'Ferrograph felt'!

BillDWVA 8th Nov 2018 6:11 pm

Re: Ferrograph 4A: Restoration advice needed
 
2 Attachment(s)
Hi,

I have been working on the restoration of Vortexion tape recorders with the same deck and can offer the following:

The deck components are all nickel or cadmium plated and if you strip it completely apart you may be able to either polish the parts or have them pickled and re-plated.

The mounting screws - which are BA thread - are nickel plated and will easily polish up nicely. I did one deck one screw at a time with metal polish with reasonable results.

The paint finish was of a good standard from the factory and so long as there is no actual rust or bubbling from below you can use ĎT -cutí or similar cutting compound to polish away the dirt and then car wax to bring back the gleam.

Pressure pads can be re-faced with felt. Search for ĎPiano tunerís feltí for suitable felt. I cut new cubes of felt and glued them to the existing backing wings after scraping away the remains of the old.

Your deck is a Series 4 and it is a fairly easy job to strip down, clean and re-grease the capstan spindle bearings. Unscrew and remove the top bracket before attempting to undo the nut holding the spindle from below the lower flywheel bearing. Ferrograph used thread lock on virtually every nut and screw.

Hope this helps.
Bill

Uncle Bulgaria 9th Nov 2018 6:26 pm

Re: Ferrograph 4A: Restoration advice needed
 
Thank you, Bill.

Did you polish rusty screws? I will try with one, but fear if you've confirmed they're BA then it may be easier to get some stainless new ones. If it's the bit one sees it's harder to excuse pitted parts than when it's inside the bowels!

As can be seen from the pictures, the paint itself looks good (apart from the rather of-its-time, mould-like greyish green colour) so will wash off quite nicely I think. Without removing the components it will be a little more tricky as I can't just sluice it off.

Thank you for the tips on the bearings. What's your opinion of the tape-head assembly? Does that come under the heading of 'stripping and polishing', or does it need to be treated with care separately?

Edit: I didn't see the pictures before - that felt is a good shout! I have already bought the previous eBay object though, so I'll compare when they arrive. It can always go in the 'spares' box...

SteveCG 10th Nov 2018 11:29 am

Re: Ferrograph 4A: Restoration advice needed
 
When you have got the mechanical aspects sorted out to your satisfaction then don't forget that the paper capacitors in the tape recorder almost certainly need replacing as they will be electrically leaky. Check especially those that are connected to the record/replay head as (if my memory serves me correctly) they can result in DC passing through the head. And this will slowly erase any of your recordings when you replay them. I would suggest you search for a circuit diagram of the 4A on the web to check.

Uncle Bulgaria 13th Nov 2018 5:15 pm

Re: Ferrograph 4A: Restoration advice needed
 
1 Attachment(s)
Thank you for the tip, Steve. I have the manual here, with a circuit diagram. I've attached it for future reference. The only one marked as 'metalised paper tubular' in the parts list is C19, which from my amateurish reading of the circuit appears to be something to do with setting the recording level. I'm confused as to what V5 does, as it seems to be after the output. Is C19 a bypass capacitor for the output from the second triode in the ECC83 envelope? Is the ECC83 providing the constant current (I think from the manual it is 1mA) that is the recording meter 'zero' point?

The other capacitors are marked as 'metal tubular', and one of these in the PSU (0.1mfd Metalmite Visconol-X) has measured badly.

barrymagrec 13th Nov 2018 5:25 pm

Re: Ferrograph 4A: Restoration advice needed
 
V5 is the rectifier / amplifier for the peak reading meter.

BillDWVA 15th Nov 2018 9:19 am

Re: Ferrograph 4A: Restoration advice needed
 
Hi,
You have identified the capacitor most likely to cause trouble; namely C19, which couples the anode of V3 (pre-amplifier stage) to the control grid of the output pentode via what looks like R22 (sorry the image is a bit blurred). Another one to check, and possibly replace on sight, is C20 the coupling capacitor from V2, in the previous stage. Modern axial polyester capacitors are OK as replacements and are not expensive.

These capacitors have a high DC voltage stress across them and if they become leaky affect the biasing of the following valve. At best causing distortion and at worse, damaging the associated valve.

Going back to a previous post regarding the screws holding the components to the deck plate; these are plated, domed, countersunk cross-headed and may be difficult to source replacements for. I have only been able to find plain steel screws in BA sizes when looking for new. If you need spares then Terry Martini-Yates at Ferrograph World is your best source of parts for these decks.

Hope this helps?
Bill

Uncle Bulgaria 17th Nov 2018 2:46 pm

Re: Ferrograph 4A: Restoration advice needed
 
Thanks Bill and Barry.

I'm sorry - I didn't realise the diagram had been so reduced as to be almost unreadable! Here is a Dropbox link to download the full-size diagram which is rather easier to interpret.

Bill - could I prevail on you to check the numbers of the components again when the image isn't so illegible? I can't see how C19 couples from V3, as my reading of the circuit has it only seeing signal voltage between the anode of one half of V5 and ground, with R22 just elevating the grid of the second half. Were you perhaps meaning C15, or have I got confused with the way the circuit's drawn? I can't see where the HT source would be for V5, unless there's something high from the anode of the oscillator via pin 4 of plug 5.

C20 is what I would recognise as a coupling capacitor, which is a 350V 0.05uF 'metal tubular' in the manual. This is another 'Metalmite Visconol-X'. I can't find what they're actually made of and thus whether they're likely to have dried out.

I have a stock of polyester/polypropylene 630V capacitors which I was thinking of using, so it's good to know that they're recommended by the cognoscenti!

Screws: I've found the majority come up nicely with a brass brush, apart from one from the tape-counter which has a stripped head. Coming across the same difficulty of finding such a thing, I propose replacing it with a new M3 (available in raised countersunk Philips) which from my tests is easily re-tapped to 6BA without much fuss.

I've already tapped up Mr Martini-Yates for a head cover and the manual - what a help!

BillDWVA 17th Nov 2018 3:22 pm

Re: Ferrograph 4A: Restoration advice needed
 
^^ Yes, apologies, with a clearer circuit image the components I was referring to are actually C15 and R23 which are in the signal path to the output valve V4.

V5 is the meter drive and it’s HT supply comes via pin 4 plug 5. It looks like it may only be energised when the set is switched to ‘Record’.

ms660 17th Nov 2018 9:52 pm

Re: Ferrograph 4A: Restoration advice needed
 
V5(b) anode path to HT in record:

V5(b) anode>
P5/4>
SK5/4>
P4/6>
SK4/6>
P1/7>
SK1/7>
P5/5>
SK5/5>
HT.
8-o

Lawrence.

Uncle Bulgaria 19th Dec 2018 5:39 pm

Re: Ferrograph 4A: Restoration advice needed
 
Thanks for the replies. I hadn't been notified of them, I'm afraid! I'll look into the electrics momentarily and trace that path.

The 4A is still having its grotty cabinet material removed, but the chassis are cleaned and I have replaced the old Bulgin with a new IEC Bulgin that screws to the same holes.

I'm still wary of attacking the tape head assembly to clean it. There looks to be some general gunk and possibly corrosion, at least on the plate they attach to.

Can I do any harm with a cloth and isopropanol for an initial go? Anything I shouldn't touch?

Uncle Bulgaria 8th Jan 2019 2:14 pm

Re: Ferrograph 4A: Restoration advice needed
 
I've decided to take the whole head assembly off as it's so gunky. That's meant I'm now cleaning up the great flywheel, I've removed half of one of the motors and all the ancillaries from the tape head.

On another note, does anyone know how to get into the tape counter? I don't want to force anything but need to take the front glass out for cleaning...

Uncle Bulgaria 26th Jan 2019 2:51 pm

Re: Ferrograph 4A: Restoration advice needed
 
4 Attachment(s)
It seems not!

I've removed the heads, and wondered if anyone could tell me what their condition is. I don't know what I'm looking for. They're certainly stupendously gunky, though I have brushed off the worst.

TIMTAPE 27th Jan 2019 12:11 am

Re: Ferrograph 4A: Restoration advice needed
 
In short, the record/play head needs a relap.

http://www.igoramp.it/wp-content/upl...MAGNETICHE.pdf

Uncle Bulgaria 28th Jan 2019 5:19 pm

Re: Ferrograph 4A: Restoration advice needed
 
Thank you, TIMTAPE. That PDF is very helpful, and the process appears understandable.

As far as this head goes, is the brass tripod screwed over the coils, with the hole to attach the head cover, part of the re-lapping process or do I remove it? I imagine the procedure is to sand down the whole of that front brass curved surface, but it's as well to check!

Does the square (erase?) head need the same treatment, and if so does it need removing from its alloy case?

TIMTAPE 28th Jan 2019 10:34 pm

Re: Ferrograph 4A: Restoration advice needed
 
Quote:

Originally Posted by Uncle Bulgaria (Post 1114997)
Thank you, TIMTAPE. That PDF is very helpful, and the process appears understandable.

It's great isn't it. Lots of practical information there.

Quote:

As far as this head goes, is the brass tripod screwed over the coils, with the hole to attach the head cover, part of the re-lapping process or do I remove it? I imagine the procedure is to sand down the whole of that front brass curved surface, but it's as well to check!
Yes the entire face is lapped. Obviously the base would need to be temporarily removed. Just be careful with lapping, especially if it's the first time for you. A little bit at a time, with frequent visual inspection with a magnifier in a strong light. There's only so much metal there before the fine head gap opens out and then it's a bin job. Ideally practice your technique on something that's OK to destroy!

Quote:

Does the square (erase?) head need the same treatment, and if so does it need removing from its alloy case?
I wouldn't attempt relapping the erase head. It has a ferrite core rather than permalloy and I believe special techniques were used to relap them.

ricard 28th Jan 2019 11:13 pm

Re: Ferrograph 4A: Restoration advice needed
 
I love that open head design!

TIMTAPE 29th Jan 2019 6:03 am

Re: Ferrograph 4A: Restoration advice needed
 
Yes, unusual compared to later heads which are usually potted in some sort of epoxy, making internal repair virtually out of the question.

llama 29th Jan 2019 10:06 am

Re: Ferrograph 4A: Restoration advice needed
 
Interesting that there's solder on the pins of the R/P head. I thought all these heads plugged into 4 pins of an octal base.
Graham

barrymagrec 29th Jan 2019 10:51 am

Re: Ferrograph 4A: Restoration advice needed
 
I think Ferrograph normally only fitted the scket where the head was an option, as in the case of the stereo replay head on the 4Ax.

Uncle Bulgaria 4th Feb 2019 10:06 pm

Re: Ferrograph 4A: Restoration advice needed
 
3 Attachment(s)
The head has a Cyberman hat that screws on the top.

I can't see how to get the base off. It appears to be riveted, but there are wires soldered to the top of the rivets and to the screws holding the coil cores down. I'm loath to tamper with this as it looks pretty major.

The pins were soldered to rings formed in the wires. The 'dummy head' (something to do with adding stereo) plugs into a socket.

I've finished covering the case, so pictures will be forthcoming.

I've been investigating the PSU filter/reservoir capacitors as they are probably out of whack after all this time. the 16+8mfd reservoir/filter dual can will probably be replaced with a modern 16+16mfd, and the same with the oscillator dual can. I haven't got a high voltage capacitor tester and haven't powered it up.

I was interested in the circuit so was calculating what changes would happen to the filter response if I changed the LC capacitor value, and this led me to checking the anode limiting resistance on the EZ80. There aren't any limiting resistors, so I was interested to see what limiting resistance was being provided by the transformer. I think I've done the calculation wrong so would be grateful for someone to point out the error. The datasheet where I got the calculation from is attached.

Rt = Rs + n2 x Rp where Rs is 1/2 secondary resistance, n is 1/2 ratio of primary to secondary windings [1 : (n+n)] and Rp is total primary resistance. As I understand it from that diagram.

I have:

Rp = 7R

Rs = 420/2 = 210R

n = (420/7)/2 = 30

From this I get Rt to be 6510, which is rather different from the 2 x 175R to 2 x 300R the datasheet plots show.

ms660 4th Feb 2019 11:26 pm

Re: Ferrograph 4A: Restoration advice needed
 
n will be far less than 30, n is the turns or voltage ratio not the resistance ratio.

Eg: Let's assume that the transformer is on the 245 volt tap with 245 volts going in, therefore Vp = 245, Total Vs anode to anode (according to the manual) = 480 VAC therefore divide that by 2 which = 240 therefore n = 245/240 = 1.02 therefore n = 1.02

Rt = Rs+n squared*Rp…..(+ R1) R1 is any additional surge limiter that may be fitted, that can be omitted because none is shown in the schematic.

Rs = 210 (420 as measured/2) Rp = 7 (as measured) and n = 1.02

So, Rt = 210 + 1.02*7 = 217.14 Ohms for each leg or 2 X 217.14 Ohms if you like.

So far as I can make out.

Lawrence.

Uncle Bulgaria 5th Feb 2019 3:53 am

Re: Ferrograph 4A: Restoration advice needed
 
Thank you Lawrence, that's very helpful.

I thought there would be a relationship between the resistance ratio and the turns. I got wildly varying and worrying voltages on the secondary when putting low VAC across the primary, so reversed it. with 2 - 12VAC on the secondary, the average ratio was 1:13, when I could get a reading on the AVOmeter. (sub 1V).

If that is correct, then Rt is about 553R, with n = 6.5.

However, that's still far too high as Vaa' will be about 3kV at 240V! Surely the ratio is absolute, regardless of there being no load? It remained constant over the applied voltage range, which has confused me. I checked I am measuring the right secondaries, that go to the right pins of the EZ80 socket.

Where did you get the 480V from in the manual, and why am I not getting a reasonably measured value? I am overlooking it in the Ferrograph manual I have, if that is the one you are referring to.

ms660 5th Feb 2019 11:46 am

Re: Ferrograph 4A: Restoration advice needed
 
The 480v anode to anode was an estimate based on the other voltages given in the manual.

I would double check the transformer primary and secondary connections you're using for establishing the voltage/turns ratio.

Lawrence.

Uncle Bulgaria 5th Feb 2019 4:45 pm

Re: Ferrograph 4A: Restoration advice needed
 
You were right Lawrence - my error was checking the secondaries, when in fact I was using the wrong primary windings as one is on the other side of the transformer.

New values are 46R5 Rp, and a 1:2.5 ratio (30V at 12V), which gives an Rt of 282R6.

If 240VAC is across the primary, and 600V across the secondary, then according to the datasheet that's 2x300V which needs a minimum Rt of 215R. So it's in tolerance.

Correct?

ms660 5th Feb 2019 5:18 pm

Re: Ferrograph 4A: Restoration advice needed
 
Download this and scroll down to book page 10 (section 13):

http://www.nj7p.info/Manuals/PDFs/Tu...art-4-1972.pdf

Lawrence.

Uncle Bulgaria 7th Feb 2019 1:20 am

Re: Ferrograph 4A: Restoration advice needed
 
Thanks again, Lawrence! Yet another PDF to add to my 'very useful' folder. I see the point of the calculation is to make sure the inrush current is limited, so it looks like all is in order now that I have the correct primary to meter. I'll take some more readings when I power it up, of course. It's good to feel one is gradually getting a handle on the hows and whys of a circuit.

Question to the floor - is there any idea of how the base comes off that head, or is it to be re-lapped with it in situ, off the edge of the lapping plate, perhaps?

TIMTAPE 7th Feb 2019 12:01 pm

Re: Ferrograph 4A: Restoration advice needed
 
It was me who suggested the head needed relapping. I assumed it would be easy to remove the baseplate from the head as many years ago I think I did, but it was on a Series 5 Ferro which may be a different head design. I no longer have the Ferro to check the head.

Even so without a relap the machine may still perform reasonably well. Relapping just gives the best, most consistent tape to head contact and means less head cleaning. It also allows adjustment of the azimuth without the tape riding up on the ridges of old the wear groove. The old Ferro's also used the felt pressure pads which created uneven wear on the head, were more suited to the earlier tape types and with modern plastic tapes became unnecessary. At least on the record/play head, I removed the felt pressure arm entirely, but without the head relapped you may have to retain the pressure pad for good contact.

Uncle Bulgaria 7th Feb 2019 4:55 pm

Re: Ferrograph 4A: Restoration advice needed
 
3 Attachment(s)
Thanks TIMTAPE. I read on here or Tapeheads yesterday about incorrectly zeroed tape paths causing the 'characteristic keystone pattern' of wear on the Ferrograph head, which is certainly what this one has. The thing would certainly benefit from a relap according to those instructions you sent, and from what I can see the base wouldn't get in the way of the process. I'll ask at Ferrograph World in case there is a method of getting the base off without destruction!

That's interesting what you say about the pressure pads. I was up too late last night reading about the motors providing inconsistent back pressure to keep the contact with the head, hence the pads. I wondered about reducing wear by removing them, in this age of irreplaceable heads, but didn't know this could be done by using newer tape types. When it's up and running I'll have to experiment!

Meanwhile, two of the motors have been dismantled, cleaned up and lubricated...

TIMTAPE 7th Feb 2019 5:17 pm

Re: Ferrograph 4A: Restoration advice needed
 
Quote:

Originally Posted by Uncle Bulgaria (Post 1118301)
Thanks TIMTAPE. I read on here or Tapeheads yesterday about incorrectly zeroed tape paths causing the 'characteristic keystone pattern' of wear on the Ferrograph head, which is certainly what this one has. The thing would certainly benefit from a relap according to those instructions you sent, and from what I can see the base wouldn't get in the way of the process.

Yes I guess if the base cant be removed, the head would need to be relapped with the base hanging off the edge of the table, and thinking about it, maybe that's how I did it on my old Ferro 5 head.

Quote:

That's interesting what you say about the pressure pads. I was up too late last night reading about the motors providing inconsistent back pressure to keep the contact with the head, hence the pads. I wondered about reducing wear by removing them, in this age of irreplaceable heads, but didn't know this could be done by using newer tape types. When it's up and running I'll have to experiment!...
Yes the back tension changes with the diameter of the tape pack, and the larger the disparity between the hub diameter and the max diameter of tape, the greater the change. The special Ferrograph larger reel (8.25"?) must have been the worst possible in this respect.

I compromised with the pressure pads. I removed the record/play head pad but retained the erase head pad for some constant back tension on the record/play head. I also recorded with LP tape which tends to have better head contact than SP tape. This was about 40 years ago.

Uncle Bulgaria 15th Feb 2019 11:27 am

Re: Ferrograph 4A: Restoration advice needed
 
1 Attachment(s)
News from Ferrograph World:

The heads are not designed to be relapped, so Mr Martini-Yates is not convinced there would be any improvement. It looks like it's a new(er) head that's needed, which he can supply. I'll endeavour to straighten up the tape path when I get it back together so the new one doesn't have the same 'keystone' wear.

However, as I'm impecunious at present, and not back to the head-reinstallation stage, I'll leave that for now. I would like to try straightening up the old one as an exercise as well, so I'll see how that goes.

For now, I have been going through the PSU checking values after the transformer calculations. There are a number of 'Visconol-X' capacitors, some of which test open-circuit so I am replacing them with some film types I have already.

Questions:
  • I have seen reference on here to testing capacitors with a 'Megger' type machine for breakdown resistance. I might be able to stretch to one of these as the older ones are cheap. Is this worth it? At the moment all I can do is test for continuity and/or turn on the machine with the capacitor I want to test and see if the smoke comes out.
  • I like dual cans, but the right values are not available. My calculations suggest replacing the (for example) 8mFd + 16mFd PSU filter/reservoir capacitor (C24 & C26) with a 16+16mFd would not adversely affect the filtering. There are a couple more of these. Could I use 16+16mFd in all these locations? (C9/C13 & C11/C12)
  • There is a 0.1mFd, 350V 'MICAMOLD' capacitor between the AC contacts of SW3, the motor switch. Is this purely to prevent arcing? As it is on a mains AC line, though the capacitor is not between LN or L/N and Earth, should this be an X/Y type?
  • C3 is marked as 0.02mFd 360V, but in the unit it is bypassed by a resistor and a 3100pF(? - value half illegible) 'Suflex' (picture attached). What is the reason for this not being on the circuit diagram? Is it a pre-calculated snubber circuit for the speed control switch?

TIMTAPE 15th Feb 2019 1:59 pm

Re: Ferrograph 4A: Restoration advice needed
 
Quote:

...C3 is marked as 0.02mFd 360V, but in the unit it is bypassed by a resistor and a 3100pF(? - value half illegible) 'Suflex' (picture attached). What is the reason for this not being on the circuit diagram? Is it a pre-calculated snubber circuit for the speed control switch?
From memory these are for calibrating the repro (playback) response for which components had to be individually selected in production, possibly because the tolerances on the record/play head couldn't be made tight enough to use standardised resistors and capacitors.

I think the Suflex caps are polyester and as I recall, unlike electrolytics were long lasting and reliable. I wouldn't be changing them without a good reason.

Silicon 15th Feb 2019 11:42 pm

Re: Ferrograph 4A: Restoration advice needed
 
The Suflex capacitors are probably polystyrene.

They have a good technical specification.
Apparently they are susceptible to damage if the heat from the soldering iron travels down the capacitor wire leads.

TIMTAPE 16th Feb 2019 3:01 am

Re: Ferrograph 4A: Restoration advice needed
 
Ah yes polystyrene. Thanks for the correction Silicon.

Uncle Bulgaria 17th Feb 2019 5:27 pm

Re: Ferrograph 4A: Restoration advice needed
 
Thanks both. It does look just like a bigger version of some modern polystyrene capacitors I have!

I fear the Dubilier Metal Mini-Cap it is paralleled with will not be as reliable. I have just finished replacing all the 'Visconol-X' types I can find. At least one measured as a short so I've not taken chances, as I have no other way of testing capacitors. This 'Metal Mini-Cap' is the same colour and design, but doesn't say 'Visconol-X'. Does that mean it is not the same construction, and perhaps a more reliable type?

What are your thoughts on my other bullet points?

ms660 17th Feb 2019 5:50 pm

Re: Ferrograph 4A: Restoration advice needed
 
Quote:

Originally Posted by Uncle Bulgaria (Post 1120721)
Questions:
  • I have seen reference on here to testing capacitors with a 'Megger' type machine for breakdown resistance. I might be able to stretch to one of these as the older ones are cheap. Is this worth it? At the moment all I can do is test for continuity and/or turn on the machine with the capacitor I want to test and see if the smoke comes out.
  • I like dual cans, but the right values are not available. My calculations suggest replacing the (for example) 8mFd + 16mFd PSU filter/reservoir capacitor (C24 & C26) with a 16+16mFd would not adversely affect the filtering. There are a couple more of these. Could I use 16+16mFd in all these locations? (C9/C13 & C11/C12)
  • There is a 0.1mFd, 350V 'MICAMOLD' capacitor between the AC contacts of SW3, the motor switch. Is this purely to prevent arcing? As it is on a mains AC line, though the capacitor is not between LN or L/N and Earth, should this be an X/Y type?
  • C3 is marked as 0.02mFd 360V, but in the unit it is bypassed by a resistor and a 3100pF(? - value half illegible) 'Suflex' (picture attached). What is the reason for this not being on the circuit diagram? Is it a pre-calculated snubber circuit for the speed control switch?

1) A megger is down to personal preference, myself I would not use one for testing run of the mill capacitors but might use one if it was a large can paper type and I wanted to know of any electrical leakage problem.

2) 16uF for the reservoir should be ok.

3) "MICAMOLD" capacitors are notorious.

4) Suflex types have been known to go open circuit or partly open circuit (very high ESR) and sometimes short circuit if there's a high voltage across them in my experience.

Lawrence.

Uncle Bulgaria 18th Feb 2019 4:41 pm

Re: Ferrograph 4A: Restoration advice needed
 
1 Attachment(s)
Quote:

Originally Posted by TIMTAPE (Post 1120755)
From memory these are for calibrating the repro (playback) response for which components had to be individually selected in production, possibly because the tolerances on the record/play head couldn't be made tight enough to use standardised resistors and capacitors.

I think I see now - by dint of being across the switch and the 4-pin socket, C3 is actually coming into play for the 3 3/4"/sec equalisation.

Uncle Bulgaria 18th Feb 2019 4:50 pm

Re: Ferrograph 4A: Restoration advice needed
 
1 Attachment(s)
Quote:

Originally Posted by ms660 (Post 1121456)
1) A megger is down to personal preference, myself I would not use one for testing run of the mill capacitors but might use one if it was a large can paper type and I wanted to know of any electrical leakage problem.

2) 16uF for the reservoir should be ok.

3) "MICAMOLD" capacitors are notorious.

4) Suflex types have been known to go open circuit or partly open circuit (very high ESR) and sometimes short circuit if there's a high voltage across them in my experience.

Lawrence.

1 & 2. I'm fearful of leaving one in that could overload a part that is harder to replace. However, if you agree the change in value is not too far out of spec. then I feel more comfortable bringing it up on a current limiter and checking the voltages in use. If any of the big cans are shot, I can then replace them.

3. That sounds ominous! I'm considering replacing this with an X2 type. Is that a reasonable idea, or I could lash up an RC snubber. It seems odd they didn't do this, with the quality of the rest of the construction.

4. I'll disentangle them and check for shorts as there are two conflicting opinions on how reliable these Suflex fellows are.

Here's a hint as to how the case is coming along...

ms660 18th Feb 2019 8:03 pm

Re: Ferrograph 4A: Restoration advice needed
 
I wouldn't test run of the mill usual suspect capacitors, by the time they've been unsoldered, tested and re-soldered might just as well replace them instead, having said that, each to their own.

I would replace C1 with a 1,000 VDC polypropylene type.

I've had suflex types give problems in radios, TV's, tape recorders and test equipment, just my observation.

Lawrence.

Uncle Bulgaria 4th Mar 2019 5:44 pm

Re: Ferrograph 4A: Restoration advice needed
 
Thanks again, Lawrence.

The power supply has been running all yesterday afternoon on a bulb limiter, with no ill effects and a steady 375V on the choke/reservoir capacitor junction. It is almost time to plug the amplifier section in...

I'm quite pleased with how well it's cleaned up! I've left the top plate in its original state to retain some of its history and I'm gradually reattaching parts to it. I've rebuilt the switches and re-soldered a number of broken connections in the plugs from over-flexed, work-hardened or corroded joints.

Uncle Bulgaria 8th Mar 2019 7:52 pm

Re: Ferrograph 4A: Restoration advice needed
 
4 Attachment(s)
I had to rather demolish the tape counter in order to get into it to clean it. There are two screws underneath the cardboard printed face - in heating it up to try to dislodge the press-fit body, as I thought, I melted the cover! Time to make a new acrylic dial glass. Out with the holesaw!

Then a nicely scrubbed-up switch, and a horribly dusty loudspeaker. There's been a lot of elbow-grease and hot water gone into this project so far! Don't worry, not on the speaker cone!

Friday night - time for the last motor lubrication, and :beer:

The other night I did start to pick up my jar of remarkably malt-looking ISO100 oil instead of my glass of whisky... I need to remember to put a lid on!

Uncle Bulgaria 12th Mar 2019 5:40 pm

Re: Ferrograph 4A: Restoration advice needed
 
2 Attachment(s)
I am confused as to how the new set of pressure pads fit. The new ones have short legs and came with three springs that don't seem to have any place in my 4A. There is no detent in the collars they mount on for the springs to pull against. I also presume I don't need the third, as it would be for the stereo head that in mine is the 'dummy'.

Are these a later model that aren't compatible? You can see from the picture that the new ones (top row) can't hook onto the springs supplied on the head mounting plate, whereas one of the old ones has a bend in the wire which I assume is for the coil spring to engage with. This surmise is illustrated in the second photograph.

TIMTAPE 12th Mar 2019 8:58 pm

Re: Ferrograph 4A: Restoration advice needed
 
They may be from the Series Seven which IIRC was the last Ferro model to use pressure pads.

Tim

BillDWVA 12th Mar 2019 11:31 pm

Re: Ferrograph 4A: Restoration advice needed
 
Quote:

Originally Posted by Uncle Bulgaria (Post 1128307)
I am confused as to how the new set of pressure pads fit. The new ones have short legs and came with three springs that don't seem to have any place in my 4A. There is no detent in the collars they mount on for the springs to pull against. I also presume I don't need the third, as it would be for the stereo head that in mine is the 'dummy'.

Are these a later model that aren't compatible? You can see from the picture that the new ones (top row) can't hook onto the springs supplied on the head mounting plate, whereas one of the old ones has a bend in the wire which I assume is for the coil spring to engage with. This surmise is illustrated in the second photograph.

Hi Uncle B,

Those little coil springs are used on Series 5 and later decks; you donít need them as youíve got the tension springs under the deck as youíve shown.

Remember that you can simply glue new felt to your existing arms; I bought some piano tunerís felt and use it on all my decks when the old pads are compressed hard or packed solid with oxide dust.

Cheers,
Bill

Uncle Bulgaria 13th Mar 2019 5:50 pm

Re: Ferrograph 4A: Restoration advice needed
 
1 Attachment(s)
Thanks both.

Yes Bill, I've had in mind your recommendation - unfortunately I bought the arms before your initial post on the first page! However, these longer wire pieces look crucial for engaging the springs so I'll have to re-felt them rather than use the new ones.

New problem: R35 burning.

Attached is the PSU circuit section. On 'record' the manual suggests I should have 240V on the anode of V6, the EL84 oscillator. Each time I've engaged 'Record', R35 starts smoking. I've replaced it but it was a symptom not the problem.

Could this be a valve fault, in which case are there any measurements I can do with a multimeter or AVO to check? Or where else in the circuit should I be looking?

The heads are not connected, if that matters.

Radio Wrangler 13th Mar 2019 7:10 pm

Re: Ferrograph 4A: Restoration advice needed
 
Anode to g1 short in the valve? otherwise you have a lot of oscillator power going on because the only power reaching R35 should be erase frequency AC via the secondary of the oscillator coil... or has the thermistor gone low?

This circuit should survive without the heads, otherwise removing the erase/bias link will do damage.

David

Uncle Bulgaria 13th Mar 2019 7:28 pm

Re: Ferrograph 4A: Restoration advice needed
 
Thanks for the wrangling!

The EL84 has no continuity except h-h.

The thermistor out of circuit reads 110k Ohm at room temperature. Am I right in thinking that the thermistor and R35 are a divider to keep the screen current constant?

There is no indication I can see for the thermistor's values in the parts list: "Thermistor STC. A1 522/100" is all it says.

ms660 13th Mar 2019 7:55 pm

Re: Ferrograph 4A: Restoration advice needed
 
Just to note, the resistor is connected to the control grid not the screen grid, try powering up with the oscillator valve unplugged and see if the resistor still overheats when switched to record.

Lawrence.


All times are GMT +1. The time now is 8:22 pm.

Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.