Portadyne RC75, - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

electrogram · 17th Jan 2019, 1:48 am

The cartridge looks like an original ronette 105 stereo cartridge, definitely better than the 'repro' 105 that has been available for the last 20 years or so. As has been said only one channel of the two has been connected. You need to bridge - connect together - the two channels, connect the left signal to the right signal, left ground to right ground. Never solder directly to the cartridge pins, if you do the cartridge will be destroyed by the heat

Ukulant · 17th Jan 2019, 10:23 am

Hi Everyone,
Yes the existing cartridge does have four pins, with two being used currently.
I understand from the lady who sold me the gram, that her husband had an electrician friend earth this unit, following his advice to do so.
The deck has been out before, as a few wires have been tagged, new speaker wires fitted and mounting screws have been turned, so it may be a replacement.
I can find no make or model on the back, so would Portadyne have commissioned the unit, and bought in the Garrard deck? It is a cheaply made box, which needs a few veneer repairs. I wanted to make sure that all was working with the deck before I made a start on the outside. Once I know it’s all working, then I will strip it out and give the exterior some attention. Probably not the best way to approach the project, but if I know it’s all working well, then it will seem more worthwhile to finish well.

Techman · 17th Jan 2019, 1:07 pm

So it looks like it's definitely an original stereo Ronette 105 cartridge - not sure where the 2.3 number came from then. It's going to be entirely up to you whether you play your stereo records with it, as although it's designed to reproduce stereo, it's a very old design with rather poor compliance which can be seen in the construction of the stylus cantilever. These are exactly the same as the stereo version of the old BSR TC8, the TC8S, which is another example of a stereo reproducing cartridge which uses non-compliant mono engineering in its design. So it's up to you, but as you say, certainly good enough for Barry Manilow (poor old Barry) and you'll only be reproducing half of him due to only one channel of the cartridge being connected!

To find the model of your gram, you're going to have to go through all the listed Portadyne radiograms in either the list in the link 'up top', or go through all the ones listed on the Radio Museum website and see if you recognise it from the pictures. You've got the actual item in front of you, so you can check the valve line up against the description.

Portadyne, like most manufacturers, would not have made there own record decks, they were always brought in from specialist manufacturers such as Garrard etc. I'm now reasonably sure that the deck in your gram is not the original one, but a later modification. Looking at the radio/amplifier chassis shown in your picture and the type of valves, I would date the main unit as late 1940s, whereas the Garrard RC75 dates from the early to mid 1950s. When you remove the deck for service (if you do remove it), look closely at the woodwork of the motorboard that it's mounted on and see if there's evidence of some additional and non-original cutting on the left hand side where the speed change mechanism would pass through. Motorboard woodwork nearly always has to be hacked about in this position when one of these Garrard decks are used as a replacement, particularly for replacing an original Garrard single speed 78 rpm deck. There's at least two methods of fixing these decks - one is where the four mounts sit in spring wells with nuts which need removing from underneath. The other method is the same, but there are no nuts underneath. Sometimes the whole lot will just lift out if the holes have been made oversized in the wood by a DIY operator in the past, or the bolts are just unscrewed from on top and the unit then lifted out, leaving the spring mounts in place as in the first method - close examination will soon tell you the method required.

daveobuchanan · 17th Jan 2019, 1:12 pm

I had one of those when I was a kid, ( I had a lot of radiograms when I was a kid). The deck had been swapped out for one of those bronze BSR auto changers, I can see why now. Nice one, hope it works well for you.

Ukulant · 17th Jan 2019, 5:29 pm

Thank you,
I hope I can enjoy my record collection through it very soon.
I have learnt so much from this forum, in such a short space of time!
And yes, Techman was right about the inverted cone springs that this deck sits on, just lifts out, and I see that there are other mounting holes that were used for a different deck. I am not removing just now as need to study a bit more first, and clear an area in my cave!
I have seen a similar designed cabinet front from 1947, so it all seems to fit now, pity I can’t add Am/Fm to the unit!

17th Jan 2019, 1:48 am	#21
electrogram Heptode Join Date: Jul 2008 Location: Hereford, UK. Posts: 719	Re: Portadyne RC75, The cartridge looks like an original ronette 105 stereo cartridge, definitely better than the 'repro' 105 that has been available for the last 20 years or so. As has been said only one channel of the two has been connected. You need to bridge - connect together - the two channels, connect the left signal to the right signal, left ground to right ground. Never solder directly to the cartridge pins, if you do the cartridge will be destroyed by the heat

17th Jan 2019, 10:23 am	#22
Ukulant Retired Dormant Member Join Date: Dec 2018 Location: Diss, Norfolk, UK. Posts: 9	Re: Portadyne RC75, Hi Everyone, Yes the existing cartridge does have four pins, with two being used currently. I understand from the lady who sold me the gram, that her husband had an electrician friend earth this unit, following his advice to do so. The deck has been out before, as a few wires have been tagged, new speaker wires fitted and mounting screws have been turned, so it may be a replacement. I can find no make or model on the back, so would Portadyne have commissioned the unit, and bought in the Garrard deck? It is a cheaply made box, which needs a few veneer repairs. I wanted to make sure that all was working with the deck before I made a start on the outside. Once I know it’s all working, then I will strip it out and give the exterior some attention. Probably not the best way to approach the project, but if I know it’s all working well, then it will seem more worthwhile to finish well.

17th Jan 2019, 1:07 pm	#23
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: Portadyne RC75, So it looks like it's definitely an original stereo Ronette 105 cartridge - not sure where the 2.3 number came from then. It's going to be entirely up to you whether you play your stereo records with it, as although it's designed to reproduce stereo, it's a very old design with rather poor compliance which can be seen in the construction of the stylus cantilever. These are exactly the same as the stereo version of the old BSR TC8, the TC8S, which is another example of a stereo reproducing cartridge which uses non-compliant mono engineering in its design. So it's up to you, but as you say, certainly good enough for Barry Manilow (poor old Barry) and you'll only be reproducing half of him due to only one channel of the cartridge being connected! To find the model of your gram, you're going to have to go through all the listed Portadyne radiograms in either the list in the link 'up top', or go through all the ones listed on the Radio Museum website and see if you recognise it from the pictures. You've got the actual item in front of you, so you can check the valve line up against the description. Portadyne, like most manufacturers, would not have made there own record decks, they were always brought in from specialist manufacturers such as Garrard etc. I'm now reasonably sure that the deck in your gram is not the original one, but a later modification. Looking at the radio/amplifier chassis shown in your picture and the type of valves, I would date the main unit as late 1940s, whereas the Garrard RC75 dates from the early to mid 1950s. When you remove the deck for service (if you do remove it), look closely at the woodwork of the motorboard that it's mounted on and see if there's evidence of some additional and non-original cutting on the left hand side where the speed change mechanism would pass through. Motorboard woodwork nearly always has to be hacked about in this position when one of these Garrard decks are used as a replacement, particularly for replacing an original Garrard single speed 78 rpm deck. There's at least two methods of fixing these decks - one is where the four mounts sit in spring wells with nuts which need removing from underneath. The other method is the same, but there are no nuts underneath. Sometimes the whole lot will just lift out if the holes have been made oversized in the wood by a DIY operator in the past, or the bolts are just unscrewed from on top and the unit then lifted out, leaving the spring mounts in place as in the first method - close examination will soon tell you the method required.

17th Jan 2019, 1:12 pm	#24
daveobuchanan Pentode Join Date: Jul 2012 Location: Cambridge, Cambridgeshire, UK. Posts: 136	Re: Portadyne RC75, I had one of those when I was a kid, ( I had a lot of radiograms when I was a kid). The deck had been swapped out for one of those bronze BSR auto changers, I can see why now. Nice one, hope it works well for you.

17th Jan 2019, 5:29 pm	#25
Ukulant Retired Dormant Member Join Date: Dec 2018 Location: Diss, Norfolk, UK. Posts: 9	Re: Portadyne RC75, Thank you, I hope I can enjoy my record collection through it very soon. I have learnt so much from this forum, in such a short space of time! And yes, Techman was right about the inverted cone springs that this deck sits on, just lifts out, and I see that there are other mounting holes that were used for a different deck. I am not removing just now as need to study a bit more first, and clear an area in my cave! I have seen a similar designed cabinet front from 1947, so it all seems to fit now, pity I can’t add Am/Fm to the unit!