Portadyne RC75,

[Ukulant]

I am a complete novice, and have wanted a radiogram, to remind me of my youth!
I bought the first one I found....a 1952 Portadyne/Garrard RC75. The radio is S/M and Long wave only....should have thought about that one! And the turntable only worked on 78. Removing the turntable I found no speed belts present, so made a couple from some heavy rubber gloves, however 45 and 33 are slightly slower than they should be, to my ear, and I have no 78’s as yet to try. Could the drive wheel be worn down slightly? Or is there another common fault on these decks? Also is it possible to fit a stylus to suit my stereo Lp’s and singles, as I suspect the mono cartridge may be detrimental to my vinyl !
Sorry for all questions....it’s excitement!

[Michael Maurice]

First and foremost, you should not be using this radiogram until certain components, mainly capacitors have been replaced.

Second: That deck needs a proper strip down, clean and relubricate. The idler if worn will not cause it to go slow but will stop the autochanger from working.

[Audio1950]

Originally Posted by Michael Maurice

The idler if worn will not cause it to go slow but will stop the autochanger from working.

No idler on this deck, Michael, it uses rubber belts, which the OP says he has replaced.

[Ukulant]

Thank you for your reply and concern. Where do I found out which parts should be replaced before use, as am keen to progress with this project. The auto changer works fine, so that must mean that idler is ok. I suspect slow speed may be a more involved solution then.
There appears to have been an earth fitted to the unit recently, and luckily unit appears to have been well kept. Is the turntable strip down within a the scope of a novice, or should this be entrusted to an audio engineer?

[Edward Huggins]

The RC75 is a complex deck and a service sheet can be obtained for an RC75A from this Site - see the top RH Box on this page. You will need to fit a stereo (or ideally a stereo-compatible cartridge). These cost c.£35-40. The tone arm is pre-Stereo so you will need to adjust the tracking weight to at least 5 grams. You say an "earth has been fitted". Do you mean a 3 core earthed mains cable?

[Techman]

Sorry to disagree regarding the idler wheel, but this deck most certainly DOES have an idler wheel - it also has two small belts. The diameter of the idler wheel will NOT affect the speed. The condition of the idler wheel may affect its ability to 'drive' the mechanism.

Your made up belts could be too tight - use a larger thumb from the glove to make some that are less tight or use a section of small bike inner tube. Proper re-manufactured belts used to be available from 'The Voice of Music' in America, but they won't be cheap what with shipping etc.

The deck will need lubricating on all its moving parts, particularly the motor bearings, the two belt pulley bearings and the idler wheel bearing. These will be dry after getting on towards seventy years and will be running metal to metal and will soon be ruined if you keep running it like this - it'll also make it run slow. There are no spares available after all this time, so look after it and take note of the positions of ALL thrust washers and split pins etc. when dismantling, which you'll have to do to oil it properly. Use only clock or sowing machine oil and don't get any of it on any of the driven surfaces.

When cleaned and lubricated, these decks have a tendency to run very slightly fast. The adjustment method directly from the manufacturers instruction book is to move the idler 'pull-on' spring into a different locating hole (there's a choice of two), less pressure faster, more pressure slower - yes, it really is that crude! The down side of the less pressure hole on a worn deck is that it may cause the idler to slip during autochanging. Be very careful when autochanging 7" 45 rpm singles with these decks - you'll soon see what I mean after you've ruined one!

The next step will be looking at the electronics and possibly locating a couple of capacitors which will need replacing to prevent serious damage being caused by their leakage. These components can be obtained cheaply. Have a look at the link at the top of the forum page to see if a service sheet is available for your gram. There's a manual for the Garrard record deck which is the same as the RC80. Be aware that a service manual is not a 'how-to' for a novice, but are produced for experienced and qualified service engineers, so you'll likely still need to ask questions. It's a nice looking gram, but as you say, shame it's AM only on the radio, which is to be expected on something that old.

Edit: As an additional note, it looks like the cartridge fitted to the pickup arm is a non compliant mono only type that will spoil stereo vinyl pressings, so will need replacing with a later type. As it is, don't play any stereo records on it and certainly nothing later than 1970. You need to check the make and model number of the cartridge you have - unfortunately it looks as if you have the deck type that doesn't have the removable plug in head shell, so it's going to be slightly more difficult for you in this respect.

[Techman]

The good thing about these decks is that just about everything is adjustable. The bad thing about this is that if you do too much dismantling and you're inexperienced with these mechanical wonders, then you can be in real trouble getting everything back as it should be.

I forgot to mention that the turntable/platter bearing will most definitely need lubricating on this deck - a little bit of grease on the bottom ball race and some clock oil run down the shaft on this one.

Edward, the RC80 manual is available from the link at the top and is about 40 pages long and basically covers this deck. I haven't checked out what's available for the RC75, but probably worth getting both.

[Ukulant]

That is of great help, I will instigate a basic strip down and lubricate, once I have consulted a service sheet, and try thumb size glove belts. Can anyone advise on a suitable stylus/cartridge conversion, and if the parts can be obtained in the uk? I have only tried out the deck with my wife’s Barry Manilow LP, so technically that vinyl pressing is already spoiled 🤭.
The earth fitted is 3 core, as pic shows.

[julie_m]

It's a common misconception, but the size of the idler has absolutely no influence on the final speed as long as it can contact both the inside of the turntable platter rim and the stepped motor spindle.

Over some number of turns, a point on the surface of the driven spindle will travel one metre; and the corresponding point on the surface of the idler wheel will also travel one metre. The idler will make fewer turns than the spindle because it has a larger diameter; the speed ratio will be the inverse of the diameter ratio. (For example, a 6mm. drive spindle pressing against a 42mm. diameter idler wheel will make 42 / 6 = 7 turns for every turn of the idler). Likewise, a point on the inside of the turntable platter will also travel one metre. Again, the speed ratio will be the inverse of the diameter ratio; if the turntable inner diameter is 210mm., the idler will make 210 / 42 = 5 turns for each turn of the turntable -- which requires 5 * 7 = 35 turns of the spindle, and indeed 210 / 35 = 6. So it is exactly as though the spindle was driving the platter directly, apart from the direction being reversed only once as opposed to twice

Notice that the 42 is on the top of the division line one side, and the bottom the other side; so when the two are multiplied together, it cancels out. The only thing the size of the idler affects is the speed of the idler, and nobody is paying any mind to that.

[Ukulant]

Thank you for that explanation,as I did share that misconception. I did have to read it twice though to allow it to filter in.

[Edward Huggins]

Originally Posted by Ukulant

Can anyone advise on a suitable stylus/cartridge conversion, and if the parts can be obtained in the uk? I have only tried out the deck with my wife’s Barry Manilow LP, so technically that vinyl pressing is already spoiled

Because the tone arm on the Garrard RC75 is only wired for mono, the easiest cartridge to fit is a BSR X5M stereo compatible-mono cartridge, that's if there are any left. If none are available now, then buy a full stereo cartridge and bridge it for mono. Available in the UK online. Your cost will be £35-40.

[Techman]

A thorough explanation from physics and engineering guru Julie

However;

Originally Posted by julie_m

contact both the inside of the turntable platter rim and the stepped motor spindle.

Sorry to say I'm going to have to disagree on a small part of that explanation: The Garrard RC75/80 doesn't have a 'stepped' motor spindle - they don't work like that on this model...just to avoid confusing the OP, as this is an important point!

As to the earth - it looks like a replacement mains lead has been fitted at some time in the past. It 'looks' OK, so using your test meter, just check for earth continuity from the plug earth pin to the metalwork, ie, the turntable spindle of the record deck, also check the tightness of the screws on that connector block, obviously all done with the gram unplugged from the mains. Make sure the mains lead can't be 'pulled' against that connector block when in use and that the lead is firmly secured with a clip to the cabinet.

[Techman]

You haven't told us what cartridge is fitted to the pickup head as requested in the last part of post #6 yet - we need to know, as it'll indicate what replacement you'll need, but it's likely to be a medium output type, which is lucky, as these are still available.

Also, spot my 'typo' - I meant 'sewing' not sowing machine oil

[Ukulant]

Sorry Techman,
Once I had cleaned the window above the cartridge I could read it.....Ronette 2.3 with ST250 one side and ST075 on the reverse.
Does the ST refer to stereo?

Needles look pretty tired anyway!

[Ukulant]

Sorry my son tells me it’s SA and not ST on the cartridge, which is a four pin, but only two pins used for soldered connections.

[Techman]

A quick search didn't reveal a lot about that particular cartridge, but you can pretty much guarantee that it's very old. All original Ronette cartridges will be non-stereo compliant and the copy versions that were manufactured later weren't much better, so best avoided. Basically, if the stylus has an all in one metal shank with no flexible bit where it mounts, then it'll spoil those stereo pressings. Seeing as it's still working it's worth keeping for playing old records, but a replacement should be fitted to the pickup head such as a BSR X5M or a BSR SC11 or 12M - you could also possibly adapt one of those very cheap Chinese red and black ones if you're never going to play any 78s, as they really are very good for what they are. Whatever you fit, you may have to make and fit a spacer to the pickup head, as more modern cartridges sit higher in the head and the flip under stylus flag (if fitted) may catch the side of the headshell.

[Techman]

A good, clear close up picture of the underside of the cartridge will soon tell us what we need to know about the compliance (or lack of it) of this cartridge.

The BSR X5M as recommended by Edward will be the easiest replacement.

Actually, these decks were nearly always wired with twin plus screen wiring, so could accommodate stereo, but it would be a bit of a fiddle to wire it all up even if it was wired that way.

Just to say, the gram isn't a Portadyne RC75, that's the model number of the record deck. You need the model of the actual gram itself to find the service information - it should be written on the back.

[Ukulant]

I have added a couple of pics of the stylus, hopefully they are good enough quality!
Once again thank you for all your help. Now of to work sadly!!

[Techman]

Looking at your pictures it looks like there may be four connections on that cartridge and it's been wired up for just one channel. If this is the case then it IS a stereo cartridge, but seeing as the stylus shank is a one piece metal shank, there'll be very little compliance for playing stereo records. In other words, it'll decode both channels for feeding a stereo amplifier, which you haven't got, but while doing this, the poor compliance will eventually damage good stereo records. Does it actually have four pins with only two being used? Will probably hear the answer after your return from work.

[Techman]

I did a very quick search now you've confirmed the correct 'SA' part number for the stylus and it seems that they're available in the USA with a lot of cross referencing going on for both the LP and 78 version.

I've had a thought that it's possibly not the original deck in your gram, particularly with that newer looking mains lead heading off upwards with an additional earth wire going along with it as shown in one of your pictures. There's a slim chance that the RC75 is the American version of the deck intended for 60Hz, rather than 50Hz mains and that would make it run much slower. I was asked to convert an American RC75 deck to run on UK mains a few years back. I got the owner to buy a scrap UK deck off ebay and I swapped over the motor (non-stepped) spindle pulley and reset the voltage tapping on the motor, if I remember rightly. I think the spindle pulley actually came off an old DC mains version of the deck, but fortunately the pulley was the correct type.