Philips 22RH541 Motion Feedback Speakers - UK Vintage Radio Repair and Restoration Discussion Forum

TonyDuell · 16th Mar 2024, 5:26 pm

Having restored the 22AH985 music centre I needed a pair of speakers for it. It has an output socket for the Motion Feedback (MFB) units and as I had a pair of those sitting in the corner of the workshop I decided to use them.

All the electronics is fixed to the rear panel. I removed this by undoing the 6 screws, swinging it open, unplugging the 8 pin connector and lifting the panel off the hinges.

The 8 pin connector carries 2 wires each for the 2 voice coils, the MFB transducer and the power-on LED. First test was to check the 2 voice coils were not open-circuit. They were fine.

Next I fitted a dummy load (47 ohm resistor) from the speaker side of the output coupling capacitor to ground. Plugged the electronics into the mains and operated the relay by hand. Checked :

Supply rail (fine)
Midpoint voltage of the output stage (about half the supply -- good)
DC across the dummy load (zero -- so the coupling capacitor wasn't leaking)

Measured the quiescent current in the output stage as mentioned in the manual. A little high, but not ridiculous. Tweakng the preset got it right.

Applied an input from a signal generator. This caused the relay to operate electrically (as it should) and I checked there was an amplified version across the dummy load.

OK, remove the dummy load and plug the 8 pin connector into the cabinet socket to connect the speakers. Feed in a low frequency signal (120 Hz). My 'scope showed there was a signal from the MFB preamplifier stage which vanished when I cranked the frequency up to a few kHz. At that frequency, the tweeter is the only speaker in operation, and the MFB signal comes from the woofer. So all looks good.

Put the screws back in, carry them to the living room and connect them to the music centre.

Silence.

OK, time to work logically. The music centre amplifier is a bit unusual. There is a low-power push-pull stage that feed the headphone socket. If there are no headphones plugged in, it also feeds the MFB socket and the input of the main amplifier (for passive speakers).

I knew everything was good as far as the headphone socket. So I took the casing off the music centre and checked the wiring for continuity. The signal did indeed get to the MFB socket. But no further. The DIN lead I was trying to use was not conventionally-wired (screen on pin 4

).

Make a replacement lead and it's fine.

And those little speakers sound very impressive.

Sideband · 16th Mar 2024, 8:20 pm

Those MFB's are stunning. First time I heard those back in the 70's playing the 1812 overture (what else)? Besides it was the only test record the demonstrater had at the time...the whole system was made up of pre-production samples. The cannons were really impressive but I wanted to hear what cathedral pipe organs sounded like so came to work (at Philips) the next day armed with Bach's Toccata and Fugue in D Minor and Widor's Symphony No.5 (a real floor shaker)! I was suitably impressed by the sound of those little speakers particularly with Widor.

Unfortunately I never aspired to any of the MFB's and had to make do with my Leak Sandwhich 600's which did sterling service until the mid 1980's.

Radio Wrangler · 16th Mar 2024, 10:17 pm

That's good.

I heard pairs of two sizes of them in Woods Music Shop on the high street in Huddersfield. About 200 yards from the 4-manual Willis in the town hall - which does a very good Widor 5! I can't remember what they were using as demo material. Try Widor's quiet movement from this 4th symphony 'andante cantabile' it's subtle, wistful and generally gorgeously French.

There's an old saying that you should never meet your heroes, but sometimes it's good. Very good!

David

TonyDuell · 17th Mar 2024, 9:50 am

By coincidence Bach's Toccata and Fugue in D minor was one of the first things I listened to on said speakers. Organ music is a very good test of bass response.

The 22RH541s are the smallest MFB speakers. Bookshelf sized. But they sound a lot 'larger'.

That Philips music centre with said speakers sounds a lot better than most music centres I can tell you. I am very glad I bought it.

Sergeauckland · 17th Mar 2024, 1:19 pm

I had a pair of those when I worked for Philips. We were clearing out an old store-room when moving offices and there was a pair there, together with several brand-new 14" portable colour TVs. None of these items were on any inventory so one TV and the 'speakers found their way home with me.

They were great, had them in a second system for years, then gave them away to an friend who's need was greater than mine.

S.

16th Mar 2024, 5:26 pm	#1
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,228	Philips 22RH541 Motion Feedback Speakers Having restored the 22AH985 music centre I needed a pair of speakers for it. It has an output socket for the Motion Feedback (MFB) units and as I had a pair of those sitting in the corner of the workshop I decided to use them. All the electronics is fixed to the rear panel. I removed this by undoing the 6 screws, swinging it open, unplugging the 8 pin connector and lifting the panel off the hinges. The 8 pin connector carries 2 wires each for the 2 voice coils, the MFB transducer and the power-on LED. First test was to check the 2 voice coils were not open-circuit. They were fine. Next I fitted a dummy load (47 ohm resistor) from the speaker side of the output coupling capacitor to ground. Plugged the electronics into the mains and operated the relay by hand. Checked : Supply rail (fine) Midpoint voltage of the output stage (about half the supply -- good) DC across the dummy load (zero -- so the coupling capacitor wasn't leaking) Measured the quiescent current in the output stage as mentioned in the manual. A little high, but not ridiculous. Tweakng the preset got it right. Applied an input from a signal generator. This caused the relay to operate electrically (as it should) and I checked there was an amplified version across the dummy load. OK, remove the dummy load and plug the 8 pin connector into the cabinet socket to connect the speakers. Feed in a low frequency signal (120 Hz). My 'scope showed there was a signal from the MFB preamplifier stage which vanished when I cranked the frequency up to a few kHz. At that frequency, the tweeter is the only speaker in operation, and the MFB signal comes from the woofer. So all looks good. Put the screws back in, carry them to the living room and connect them to the music centre. Silence. OK, time to work logically. The music centre amplifier is a bit unusual. There is a low-power push-pull stage that feed the headphone socket. If there are no headphones plugged in, it also feeds the MFB socket and the input of the main amplifier (for passive speakers). I knew everything was good as far as the headphone socket. So I took the casing off the music centre and checked the wiring for continuity. The signal did indeed get to the MFB socket. But no further. The DIN lead I was trying to use was not conventionally-wired (screen on pin 4). Make a replacement lead and it's fine. And those little speakers sound very impressive.

16th Mar 2024, 8:20 pm	#2
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,582	Re: Philips 22RH541 Motion Feedback Speakers Those MFB's are stunning. First time I heard those back in the 70's playing the 1812 overture (what else)? Besides it was the only test record the demonstrater had at the time...the whole system was made up of pre-production samples. The cannons were really impressive but I wanted to hear what cathedral pipe organs sounded like so came to work (at Philips) the next day armed with Bach's Toccata and Fugue in D Minor and Widor's Symphony No.5 (a real floor shaker)! I was suitably impressed by the sound of those little speakers particularly with Widor. Unfortunately I never aspired to any of the MFB's and had to make do with my Leak Sandwhich 600's which did sterling service until the mid 1980's. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

16th Mar 2024, 10:17 pm	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,917	Re: Philips 22RH541 Motion Feedback Speakers That's good. I heard pairs of two sizes of them in Woods Music Shop on the high street in Huddersfield. About 200 yards from the 4-manual Willis in the town hall - which does a very good Widor 5! I can't remember what they were using as demo material. Try Widor's quiet movement from this 4th symphony 'andante cantabile' it's subtle, wistful and generally gorgeously French. There's an old saying that you should never meet your heroes, but sometimes it's good. Very good! David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

17th Mar 2024, 9:50 am	#4
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,228	Re: Philips 22RH541 Motion Feedback Speakers By coincidence Bach's Toccata and Fugue in D minor was one of the first things I listened to on said speakers. Organ music is a very good test of bass response. The 22RH541s are the smallest MFB speakers. Bookshelf sized. But they sound a lot 'larger'. That Philips music centre with said speakers sounds a lot better than most music centres I can tell you. I am very glad I bought it.

17th Mar 2024, 1:19 pm	#5
Sergeauckland Pentode Join Date: Apr 2023 Location: Bury St Edmunds, Suffolk, UK. Posts: 174	Re: Philips 22RH541 Motion Feedback Speakers I had a pair of those when I worked for Philips. We were clearing out an old store-room when moving offices and there was a pair there, together with several brand-new 14" portable colour TVs. None of these items were on any inventory so one TV and the 'speakers found their way home with me. They were great, had them in a second system for years, then gave them away to an friend who's need was greater than mine. S.