Share:
Notifications
Clear all

Portogram Mark Eleven record player

 
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

I thought I'd tell of my experiences with one of these; it's a portable record player, notable for having a Goldring GL72 fitted to it - it also features external loudspeaker outputs and a microphone input too.

It might be worth explaining a bit about Portogram first. Their main market for a long time has been providing playback equipment, some with variable speed, primarily to teachers of dance classes. As a result, Portogram are still in business: this is their 75th anniversary. So the GL72 with its fully-variable speed turntable is ideal for a teacher to start a record off slowly so that the students can get a feel for the steps before speeding the disc up to the correct tempo for the dance. Incidentally, Bert Ambrose used to do this whenever he saw the then Prince of Wales (Edward) in attendance at the club he played in (Embassy, I think) - because he wasn't a very good dancer. Once he got into the swing of things, he slowly sped up to the correct tempo!

The turntable is fitted with a ceramic cartridge - a Sanyo, to my surprise.

As received, the unit was (and mostly is) filthy. So I've cleaned some of it up with my preferred detergent, and it is slowly improving. However, plugging it in and switching on gave me complete silence! Not even a hum from the loudspeaker. I tried operating the internal loudspeaker cut switch (it really is intended for use with external speakers) to no avail. There's also a fuse on the front panel, of 1.6A. Ah-ha! That's open circuit. Time to get it to bits.

Having worked out how to dismantle it, I wasn't prepared for what I saw. Too many opportunities to get your fingers on bare mains for one! So some sleeving has been retro-fitted to the mains switch and a boot on the IEC mains inlet.

More on this later...

ReplyQuote
Topic starter Posted : 07/11/2019 9:53 pm
Nuvistor and PYE625 liked
Nuvistor
(@nuvistor)
Famed V-Ratter Registered

Will this have been made in the 1970’s?

ReplyQuote
Posted : 07/11/2019 10:40 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

Now... this player is built up on three PCBs. One carries the main pre-amplifier and tone controls, another carries the microphone pre-amplifier and the final PCB - mounted alongside the power supply - is the power amplifier.

First thing I noticed was that the main electrolytic was venting, so I made a note to replace it as a "just-in-case" measure. Then I looked at the power amplifier board, and wondered why it was connected to a second bridge rectifier bolted between the two output transistors. Having noticed that the bridge only had two terminals connected, it suddenly dawned on me that this was being used as the thermal stabilisation for the output pair! So I took it upon myself to sketch the amplifier out; it's a very simple design of a quasi-complementary Darlington output pair fed from a BC107 driver transistor. With a supply of 39V off-load with the new electrolytic fitted I reckon the amp is good for about 15W RMS.

Portogram power amplifier

But what of the lack of sound, I hear you ask?

Well, there was a double whammy waiting for me here. Remember that open-circuit fuse? It protects the amplifier output; there's no fusing for either AC or DC in the amplifier itself, which I thought a bit nasty. However, I thought I'd also do a multimeter check on the loudspeaker - and that too was open-circuit. Looking at it, no way could it have handled the full output of the amplifier; it also looked as though it didn't really belong there.

Now, with the main electrolytic replaced and also the coupling capacitor replaced, I powered up and took the meter to the power supply - 39V. Then I put the meter on the output coupling cap and got 18V. That will do nicely, I thought. I then connected up a suitable loudspeaker - a big KEF job from the 70s - and switched on. I was rewarded with a few crackly pots, but stroking the stylus made noise!!

I should explain the purpose behind getting this operational, other than "because it didn't work". Several years ago I restored a Columbia Type AK 'Graphophone' for a work colleague, and I also borrowed the box of early Berliner discs that came with it to transcribe to a PC. Me being me, I got the AK done and restored... and then I 'lost' the Berliner discs when I emptied the house for renovation in 2014.

I only found the blessed things a couple of months ago (!!) and they'd been right under my nose in the storage unit! I bought a 78 stylus for the Sanyo pickup (thank you, Musonic!) and I then hoped to use the Portogram to do the transcription - the variable speed will be a great help with Berliner discs as you can almost guarantee many won't be 78 rpm (Columbia stuck to 80 rpm for years until they were absorbed into EMI) and it has a tape output, which could feed my PC's sound card. Also, the absence of any autostop on the Goldring is a blessing as Berliner discs would normally trip a turntable fitted with an automatic stop.

The eagle-eyed amongst you will however have noticed the awful way this unit derives a feed to a tape recorder; a padded-down feed from the loudspeaker. I've decided it's less than ideal so I have ordered bits to make a buffered preamp that intercepts the pickup feed, matches it and then passes it on to the gram's internal amplifier, but also passes the pickup output before volume and tone controls (and the microphone pre-amp) direct to the tape output. The circuit on that will follow shortly, along with photographs. I need to oil the idler wheel bearing, and perhaps the motor too along with the turntable bearing itself. The idler has been cleaned with Rubber Roller Restorer, and the underside of the turntable will be cleaned with isopropyl alcohol next.

Photos will follow, I promise...

ReplyQuote
Topic starter Posted : 07/11/2019 10:57 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

@nuvistor

Not far off, Frank - to my surprise the amplifier unit has a test date of January 1980 on it; a date where I'd have thought the Lenco GL72 was well past its sell-by date. I am minded to drop Portogram a line and see if they have any service information on it.

ReplyQuote
Topic starter Posted : 07/11/2019 11:00 pm
PYE625
(@pye625)
Famed V-Ratter Registered

I agree, the "tape out" as it stands is pretty crude. Almost an after-thought. I suppose the only advantage is that you could modify the tone controls to "improve" a poor record for a tape recording. All well and good until you forget you are recording, then go and alter the volume control !

ReplyQuote
Posted : 07/11/2019 11:05 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

Funnily enough Andrew, a friend of mine made exactly the same comment - it seemed to be an after-thought and yes, adjusting the volume would be a disaster for any recording.

For those who fancy a quick read - portogramltd.co.uk

ReplyQuote
Topic starter Posted : 07/11/2019 11:09 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered

Reading about your Berliner discs brought back memories of a conversion to a Dansette type record player I did for a customer who had bought a number of Pathe 90rpm, hill and dale recordings.

If the player is still around, unlikely after some 40 odd years, it will cause some head scratching.

ReplyQuote
Posted : 11/11/2019 9:52 am
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

@nuvistor

Wouldn't that involve wiring a stereo cartridge in anti-phase, Frank? Never mind sleeving the motor to get 90 rpm!!

ReplyQuote
Topic starter Posted : 11/11/2019 8:20 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posted by: @cathovisor

@nuvistor

Wouldn't that involve wiring a stereo cartridge in anti-phase, Frank? Never mind sleeving the motor to get 90 rpm!!

Yes, exactly that and removing the auto feature to allow manual playing. The records played from the centre outwards.

The man was a really good customer, spent a lot of money over the years at the shop, it was his record player and wanted to have it converted if possible. I enjoyed sorting it out, something different to have a go at.

Now with Audacity he could have recorded them onto a computer at 45rpm and used the software to sort it out.

ReplyQuote
Posted : 11/11/2019 8:54 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

Well, time for an update on the Portogram!

First, the o/c loudspeaker. It turns out a DAC90A loudspeaker is a perfect fit, but as I was down at Mike Barker's the other day (delivering stuff for the RWB auction) I found a nice ELAC unit that also fitted perfectly. To avoid a repeat of the fate that befell its predecessor, I added a 33 Ohm 3W resistor in series with it to limit the power.

Having lost the components I bought for the pickup buffer, I had to buy them all again... and finally, today I had a chance to sit down with a soldering iron and some Veroboard. I simplified things somewhat from the original design to become a pair of unity-gain buffers in series, and the input simply became a 2M2 resistor in series with the decoupled half-rail supply. Having found a suitable point to pick off some power, and then paying careful attention to the audio wiring to avoid any potential earth loops I applied power, followed by a finger on what would be the pickup terminals.

Bzzzzzz! Otherwise... completely silent background. This is what we want.

I then refitted the deck, made a best guess at the tracking weight and then found a random, easily accessible 78 - in this case, a German Polydor disc with a German rendition of Memories Are Made Of This. I soon discovered that the Sanyo cartridge is somewhat lacking in top (even when played via the outboard KEF), so a BSR SC12H kindly donated by a friend will most likely replace it but for now, the lack of top is unlikely to be a problem with the discs it is going to be transcribing soon.

Photos to follow; including the completely tasteless method of enclosing the pickup buffer...

ReplyQuote
Topic starter Posted : 04/12/2019 9:17 pm
PYE625 and Nuvistor liked
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

Yesterday the Portogram was finally put to the use I intended, which was transcribing twenty-seven Berliner discs to my PC. It didn't go entirely to plan though; I had to make a slight modification to the output of the buffer amp as it was overloading the input of the sound card. Although there's a mixer in the sound card, it seemingly works after the A-D (which seems counter-intuitive to me) so I padded the output down by 10dB. That was much better, and so a few hours were spent recording, re-recording and topping/tailing the recordings, then resampling them to 44.1kHz for a couple of CDs.

Some of the discs are so bad they were solely included for completeness, but some are remarkably good considering their age and how they were made.

So, apart from photos of the setup, a replacement, better turntable mat has been ordered (ex - Dual CS505/3) and further work is to follow. I may investigate a different pickup buffer - one that's stereo with a proper summing amplifier to feed the internal amplifier.

ReplyQuote
Topic starter Posted : 11/12/2019 11:04 am
Nuvistor liked