GM751 Philips Philicorda - UK Vintage Radio Repair and Restoration Discussion Forum

pwynpwyn · 17th May 2023, 9:41 am

This is my first time posting so I hope I am posting in the correct place. I just bought a Philips Philicorda organ - GM751. It's a beauty and the vibrato and spring reverb sounds wonderful. Unfortunately the two lower Es don't work and the others along the keyboard are very faint. I tried different combinations using the selectors but no luck. Is this just a matter of some dust needing to be blown off, a spray of DeOxit somewhere or something else?

I'm a musician not a vintage repair geek and so I am really hoping this is an easy fix. I am also looking for a second leg/stand for it as it was sold with only one. So wondering if there is a place that I could have one made.
Thanks in advance for suggestions!

Lucien Nunes · 18th May 2023, 3:28 pm

Hi and welcome to the forum. I think there might be a couple of versions of this organ but the one I have in mind uses valve oscillators, neon dividers and solid-state audio amplification.

Each letter name of note is derived from a single oscillator. If any notes of that pitch class are working at all, then the oscillator is running. AFAIK the output of the oscillator itself is not used as a voicing tone, it is immediately divided so that all the tones fed to the keying circuits, including the top octave, are derived from neon dividers. Each divider lowers the pitch by one octave, so if there is a problem with a divider it will typically affect all octaves below it.

It sounds like the E oscillator is working but one divider is not. Given that each key can draw on between three and five pitches according to the footages in use, it is possible for some keys to sound weak because one or more of the pitches is missing, while others don't work at all because none of the octaves are present.

To diagnose this you are probably going to need some electronic troubleshooting techniques. One one hand it might turn out to be as simple as slightly tweaking the divider trimmer capacitor, or it might be that you have to replace a neon (they do fail) or something. If you want to dig in, we can probably help you, although it is many years since I had my fingers in a neon divider organ. I probably have a manual in Dutch or German. Do you have a multimeter and / or any experience using it?

jamesperrett · 18th May 2023, 10:37 pm

Lucien's description sounds very much like the one that I had years ago. I seem to remember that I had a few problems with key contacts on mine. I also remember seeing some of the neon dividers flickering and some notes making strange noises at times although they often worked in the end if you gave it enough time.

The stand consists of two metal end brackets with a wooden shelf connecting them.

McMurdo · 19th May 2023, 12:10 pm

The key contacts on the Philicordas are not the best in my experience, they use the gold-plated springy wire technique and they are easily bent or displaced if the organ has been gigged roughly. They also seem to accumulate all sorts of detritus underneath them.
I would agree with lucien however regarding any problem with all or most of the same note across the board. Have a look at the diagram and see what is shared.
The last one I did with this fault (GM752 I think) had the later plug-in boards and it was simply dirty edge connectors...yours I think is all hand-wired.
In the first instance I would carefully inspect the wiring loom for broken wiring as Philips loomed it up quite tightly and it can stress the joints. Remove and replace the valves - one by one and testing in between - just in case you have a dirty base/pins.

These old organs are not for the faint hearted.

17th May 2023, 9:41 am	#1
pwynpwyn Diode Join Date: May 2023 Location: Cusop, Herefordshire, UK. Posts: 1	GM751 Philips Philicorda This is my first time posting so I hope I am posting in the correct place. I just bought a Philips Philicorda organ - GM751. It's a beauty and the vibrato and spring reverb sounds wonderful. Unfortunately the two lower Es don't work and the others along the keyboard are very faint. I tried different combinations using the selectors but no luck. Is this just a matter of some dust needing to be blown off, a spray of DeOxit somewhere or something else? I'm a musician not a vintage repair geek and so I am really hoping this is an easy fix. I am also looking for a second leg/stand for it as it was sold with only one. So wondering if there is a place that I could have one made. Thanks in advance for suggestions!

18th May 2023, 3:28 pm	#2
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: GM751 Philips Philicorda Hi and welcome to the forum. I think there might be a couple of versions of this organ but the one I have in mind uses valve oscillators, neon dividers and solid-state audio amplification. Each letter name of note is derived from a single oscillator. If any notes of that pitch class are working at all, then the oscillator is running. AFAIK the output of the oscillator itself is not used as a voicing tone, it is immediately divided so that all the tones fed to the keying circuits, including the top octave, are derived from neon dividers. Each divider lowers the pitch by one octave, so if there is a problem with a divider it will typically affect all octaves below it. It sounds like the E oscillator is working but one divider is not. Given that each key can draw on between three and five pitches according to the footages in use, it is possible for some keys to sound weak because one or more of the pitches is missing, while others don't work at all because none of the octaves are present. To diagnose this you are probably going to need some electronic troubleshooting techniques. One one hand it might turn out to be as simple as slightly tweaking the divider trimmer capacitor, or it might be that you have to replace a neon (they do fail) or something. If you want to dig in, we can probably help you, although it is many years since I had my fingers in a neon divider organ. I probably have a manual in Dutch or German. Do you have a multimeter and / or any experience using it?

18th May 2023, 10:37 pm	#3
jamesperrett Octode Join Date: May 2007 Location: Liss, Hampshire, UK. Posts: 1,873	Re: GM751 Philips Philicorda Lucien's description sounds very much like the one that I had years ago. I seem to remember that I had a few problems with key contacts on mine. I also remember seeing some of the neon dividers flickering and some notes making strange noises at times although they often worked in the end if you gave it enough time. The stand consists of two metal end brackets with a wooden shelf connecting them.

19th May 2023, 12:10 pm	#4
McMurdo Dekatron Join Date: Jun 2009 Location: Staffordshire Moorlands, UK. Posts: 5,271	Re: GM751 Philips Philicorda The key contacts on the Philicordas are not the best in my experience, they use the gold-plated springy wire technique and they are easily bent or displaced if the organ has been gigged roughly. They also seem to accumulate all sorts of detritus underneath them. I would agree with lucien however regarding any problem with all or most of the same note across the board. Have a look at the diagram and see what is shared. The last one I did with this fault (GM752 I think) had the later plug-in boards and it was simply dirty edge connectors...yours I think is all hand-wired. In the first instance I would carefully inspect the wiring loom for broken wiring as Philips loomed it up quite tightly and it can stress the joints. Remove and replace the valves - one by one and testing in between - just in case you have a dirty base/pins. These old organs are not for the faint hearted. __________________ Kevin