I had no intention of obtaining another reel to reel machine as I already have a perfectly good Revox A77 installed in the hifi system.
However, this Ferrograph caught my attention as it is also a stereo two-track machine. It is a nice piece of British engineering and is in rather good condition.
It is complete with what I consider an essential user and service manual plus circuit diagram that applies to models later than serial number 50,000, which this is. Date wise, Jun/Jul 67 are printed on most of the visible electrolytics, so this is likely a later series 6 machine. I believe the Series 7 fully transistorised model came soon after.
Importantly, the heads appear to be in excellent condition and following below are a few pic's of the machine as received. I obviously anticipate some minor service work to be required, but as the vast majority of capacitors are of the polyester rather than paper construction, replacement en-masse will hopefully not be required.
The amplifier sections are valve, using ECC82's and ECC83's. The only exception to this is a small internal monitor loudspeaker that is driven by a transistor amplifier. The left and right outputs can be used independantly or summed into mono for the internal monitor.
I have given the machine a brief power up and run, all in all it seems to operate quite satisfactorily. It will naturally benefit from mechanical service as well as electronic, general cleaning and minor lubricating where needed.
Here is a pic of the transistor amplifier module. I have never seen this type of device before and neither is there a circuit for this part of the machine. It is just shown on the main diagram as a "module". Fortunately, it is working and I should not need a diagram for this. Plus, it is pretty simple anyway and could be drawn by hand.
It most certainly is ! Thanks Frank 👍
A type PC5+ Newmarket module.
Today, I have removed the main deck, amplifier section and PSU chassis. The purpose for this is to gain better access for minor cleaning and for mechanical service of the deck.
Here below is a couple of pic's of the PSU and bias oscillator unit. It is so nice not to have any nasty wax or Hunts capacitors to replace. Also, the HT rectifier consists of silicon diodes.
That looks like it's just left the factory!
That looks like it's just left the factory!
It does, and I have to say that is a rare sight these days. I mean it is 55 years old, but certainly not had heavy use.
The main deck had it's motors applied with one or two drops of sewing machine oil onto the felt pads around the bearings. I think they were pretty dry beforehand, as they certainly move more freely now.
One interesting item that could do with being repaired is the drive connected to the tape counter. This is similar to a bowden cable, consisting of a spring wire wrapped in an outer coiled spring. The whole thing rotates and is driven by a cog on the wind-on-motor, but it has broken at the counter end.
It is of similar construction, but in this case, the whole thing rotates. I am thinking about joining the broken ends together inside a very small spring that will give a good grip. There is very little rotational tension driving the counter, unless you grip the counter zero and force it to stop. It is this that makes me wonder if it is how it broke in the first place.
Here it is at the motor, and cable barely a mm thick.
The spring idea sounds good - something like that could be soldered together with the aid of a small sleeve and "Fluxite", which is an acidic flux.
"Fluxite" is my go-to for soldering the thin steel drive wires Bush had a fondness for just after the War.
As far as any electrical work on the deck is concerned, I am unsure about replacing these two mixed dilectric switch suppressor capacitors. They are 0.1uf 600vdc rated and, at certain times, can have 240vac across them. If either went short, then worst case the capstan motor or the take-up motor would run all the time. Not as dramatic as if there were raw mains across them, so I might leave alone.
Whilst I have the amplifier section out of the case, here are a few pics of it. As far as I am aware, there are no problems here. This will be confirmed later after more extensive testing with the machine as a whole.
I tried to repair the broken tape counter drive cord but it was not a success, so I bought a couple of replacements from ebay for a modest sum.
There are quite a number of other spare parts for these machines on there too, so always worth a look.
For instance, the pressure pads for the heads on my machine are slightly rotten and making the heads dusty with white powdery stuff from the felt. So again for a modest sum, replacements will be winging their way too.
A noise annoys.
Whilst I await the above parts, I continued testing the machine. It essentially works ok, but with the exception of an irritating crackling/frying noise on one channel. This was also recorded onto the tape and was present with just the amplifier set to "original" where you listen directly to an input. However, it was there with the main output towards maximum and the inputs turned down to minimum. But still noticable on the tape whilst recording.
To shorten a rather long boring story of tracing said fault, spread over most evenings of this week, it basically boiled down to one thing. Or several in fact. Noisy resistors. For the main crackling sound, this was solved by replacing R15,16 and 18 in the circuit below, all in connection with V2a. This was all very good and the channel was now quiet and worked normally. Yes, all three had to be replaced including the cathode resistor.
However, it was now much less noisy in general than the other channel ! Yes, you guessed it, I also had to replace the same resistors associated with that channel too. Furthermore, I also went ahead and replaced R9, a regular 220k V1b anode, plus it's partner in the other channel, along with R7 cathode resistor. This made the input stage noticably quieter with the input gain advanced. R5 for V1a, along with several others, is specified as a high stability resistor and was not replaced.
So, here is the circuit and a pic of the resistors that were replaced. You may notice the dark red type that are the better quality high stability types, extreme left, along with my lighter coloured replacements.
And finally, a selection of the noisy little blighters. Furthermore, their values were out of spec too, for instance a 220k was found to be over 300k.
Traditionally, high-stability resistors were denoted by a pink band after the tolerance band. The type of resistor to which you refer has led myself and a few others up a veritable garden path in the past: I recall a case where they were used in the line stage of a Philips '210' TV as part of the stabilising circuit. They were fitted as NOS replacements during the set's restoration and they had drifted off towards o/c which, in the set concerned, gave the appearance of a faulty line transformer and led to a *lot* of head-scratching and swearing.
Additionally, Chas Miller used to remark that for some unfathomable reason, 220k resistors fail more than any other when used as a triode's anode load. They've certainly given me grief in the past.
Compared with some of these faulty resistors, a piece of wet string would be more stable. Going around the chassis and testing at random some of the same type, they are typically 50% out of spec.
The "high stability" types, as specified in the parts list, all seem to be perfectly well within spec. These appear to be just a different make, but with the same 5% gold band as all the others.
The parts arrived today so I set about installing the tape counter drive. This now works well and I have refitted all items into the case. The machine makes good recordings and all functions are well.
On the scope both channels are equal, with reference to the level meter, and have a good response easily up to 15KHZ at 7.5 ips. It starts to tail off above 18KHZ, so well within spec.
The machine has been running for several hours and is quite warm. The monitor loudspeaker in the machine is making a low level rustling sound and driven from the germanium transistor amp module. The temperature of this becomes quite high, which does not help matters no doubt. The resistors on the module are the same type which caused me noise problems in the valved sections, but it could be a transistor causing the problem here.
It will be easy to remove the module and test it outside of the machine under various temperature conditions, which I may well do.
It was easy to remove the module and even easier to find the fault. There are two 47 ohm resistors associated with the output stage and one of these measured about 90 ohms. After it was removed, it decided to become a 350k resistor instead.
So I replaced this and the remaining few resistors, yes an over-kill perhaps, but as none of the transistors are marked (other than a single number), I don't want to run the risk of another faulty resistor causing possible damage.
Here is the re-fitted module and the old resistors. Most of them measured high of their 20% limits in any case. After using the machine most of the day, the rustling sound caused by the module has gone. It makes Victor Silvester on the pre-recorded tape sound much more enjoyable. 😊
Returning to the main deck and the consideration of lubrication, it is easy to see where on the reel motors they should have a drop or two of oil. On the felt sections where the rotor passes through the bearings.
The capstan motor in this model differs from the reel motors in that it has ball races enclosed and held in place by rubber and plastic surrounds. According to the manual, these should not require attention and are packed with grease. Obviously, applying oil here could attack the rubber and hard plastic housing. After nearly 60 years though, I thought at least an inspection of the condition of any grease should be made.
So, I dismantled the motor thus....
There was a very small amount of grease on the inner brass holding brace of the bearing, but the balls looked dry. I decided to clean away any remaining old grease completely. I dipped each bearing assembly in IPA and let them soak for a while. Old fragments of hardened black grease could be seen in the IPA so I gave them a good wash and rinse.
Here is one bearing, followed by the hard plastic case and rubber inner support....
I need to select a grease that will be safe to use with rubber and plastic as well as lubricating the bearings proper.
Just for a matter of interest, here is a close-up of a bearing. Made by Hoffmann of England. Sadly another long gone British engineering company. At one time, they employed more poeple than Marconi apparently.