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Old 21st Apr 2013, 5:06 pm   #1
Mike Phelan
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Default Quad FM3 tuner.

This was Acousticalís first FM tuner using semiconductors and as all their equipment, mechanical and electronic design is top-class.

This one must have been lying in a loft or outhouse as the paintwork was chipped, the acrylic scale had scratches on it and the tuning knob was reluctant to move.
Closer examination showed that it must have had a bit of a bash as the frame was bent causing the knob to rub the front panel and the station marker rail didnít move.
The rear plastic panel had most of its pegs to attach it broken but they were all still attached to the frame. A good coating of nicotine on it, as well.

To get the tuning knob off, thereís a 4BA grub-screw. As usual, even with a long soak, heat and all the rest, wouldnít budge so I removed the spindle and knob complete and drilled out the screw using a drill just smaller than the tapping size. Cleaned up the thread with a tap and made a new grub screw.

Repainted the case, front panel and knob.

I removed all four pulleys to clean and lubricate them, and while they were all off, straightened the front of the frame. Fortunately, the two PCBs werenít cracked.

The "mute" preset on the rear was broken, but Keith (sTV) came to the rescue and dropped one off tor me - Thanks, Keith.

Now itís testing time:

Of course, the last thing to do would be to apply mains for very long without doing a few tests.
The FM3 uses a -14v and +14v supply rails, and they read -20v and +8v (!) The two PCBs are (a) front end and (b) power supply, stereo decoder and tuning light system.

Hooked up an aerial and an audio lead connected to my faithful Taylor 22 Fault Finder. Nothing; not even a panel light.
A quick check showed that one of the earth rails on (a) that wasnít earthed; a 5mm link between the panels had an almost invisible DJ.
Thatís better; two 14v rails now and some audio out.

Still no panel light Ė the bulb didnít like 20 volts applied to it. One of the tuning lights now worked.

These operate from a long-tailed pair (see pic). TR7 base is zero when the signal is tuned in and therefore both lights are illuminated as the two Darlington pairs turn on fully. As this would also occur if there was no signal, TR8 turns both lights off when D1 receives no output from the CA3089 IF / detector chip.

The four lights (panel, stereo and tuning) use LES 14v bulbs with curious holders consisting of a spring.
This is one of the few poor designs; the spring connects to one tag for the bulb supply, by just using pressure from the rivetted centre contact. The slightest amount of tarnish and it doesnít work.

I took forsook originality and replaced both bulbs with LEDs and a 1K series resistor (see pic). They are just the right size to go through the plastic bush that the bulb fitted.

The setting for the 19 KHz pilot tone was off; adjusted it using a frequency counterand we now have an output on both channels, but still no stereo light.
There was a supply to the bulb and the bulb itself was fine, so no guesses as to the reason!
Another yellow LED and 1K resistor, and everything now works.

Even looks better.
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Old 21st Apr 2013, 5:07 pm   #2
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Default Re: Quad FM3 tuner.

And ...
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Old 21st Apr 2013, 6:38 pm   #3
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Default Re: Quad FM3 tuner.

That looks a very tidy job. I especially like the yellow LEDs to mimic the colour temperature of the glowing tuning bulbs.

TR4 TR5 D1 look a bit odd. It seems that without a signal they reduce the long tail bias current, so the collector loads go high and the emitter followers make both bulbs bright.

Less light for more signal does seem counter intuitive.

David
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Old 22nd Apr 2013, 6:56 am   #4
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Default Re: Quad FM3 tuner.

Thank you.
Some good solutions in your write-up!

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Old 22nd Apr 2013, 8:41 am   #5
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Default Re: Quad FM3 tuner.

Quote:
Originally Posted by Radio Wrangler View Post
TR4 TR5 D1 look a bit odd. It seems that without a signal they reduce the long tail bias current, so the collector loads go high and the emitter followers make both bulbs bright.

Less light for more signal does seem counter intuitive.

David
Interesting point, David. It certainly gives no light for no signal, and I think that in those circumstances, TR8 is turned on fully, thus the long-tailed pair are also on, and their collectors are nearly grounded.
I might open the unit up and measure all these voltages and check the polarity of D1 isn't an error in the maker's diagram, just for interest!
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Old 23rd Apr 2013, 9:01 am   #6
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Default Re: Quad FM3 tuner.

Certainly, when I've used an FM3 the light balance for centring the signal on the discriminator worked very well, but situated high, close to Holme Moss, Emley and Moorside edge, signal strength was never less than huge. So I've never used one on weak signals.

(I spotted the mention of Mirfield in the newspaper.... Auntie Milly lived on Fenton street for almost 40 years... there was a well-reputed radio/tv shop at the end of the street.... Herbert Senior ?)

David
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Old 23rd Apr 2013, 4:09 pm   #7
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Default Re: Quad FM3 tuner.

A low light null is easier to spot than a bright one.
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Old 24th Apr 2013, 10:39 am   #8
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Default Re: Quad FM3 tuner.

Mike,

Did Quad use a dreaded Rifa capacitor/ snubber across the mains?
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Old 24th Apr 2013, 12:49 pm   #9
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Default Re: Quad FM3 tuner.

Quote:
Originally Posted by SteveCG View Post
Mike,

Did Quad use a dreaded Rifa capacitor/ snubber across the mains?
They certainly did in the 33 preamp and mine's well blown up as is the one I'm fixing for a friend at the moment

Cheers,
Steve.
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Old 24th Apr 2013, 5:19 pm   #10
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Default Re: Quad FM3 tuner.

The FM3 doesn't have a cap across the mains at all, Steve.
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Old 26th Apr 2013, 4:00 pm   #11
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Default Re: Quad FM3 tuner.

Thank you Mike, however it seems from 'fettler Steve' that the 33 preamp does - do we know about the 303?
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Old 27th Apr 2013, 12:22 am   #12
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Default Re: Quad FM3 tuner.

Quote:
Originally Posted by SteveCG View Post
Thank you Mike, however it seems from 'fettler Steve' that the 33 preamp does - do we know about the 303?
Yes we do!
The 303 has no cap across the mains - like the FM3, why would it need one? The cap (snubber) on the 33 is there to suppress switch arcs and noise, since the 33 is the component which supplies switched mains feeds to the 303 and FM3, then it's all that's required.
I seem to recall that the 303 has a ceramic cap across the AC side of the rectifier, presumably to reduce rectifier noise??

Cheers,
Steve

PS I forgot to say.... Mike, that's a lovely restoration of the FM3 there, well done. I love that tuner.and another one saved from oblivion!
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Last edited by fetteler; 27th Apr 2013 at 12:27 am. Reason: sense and PS
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Old 27th Apr 2013, 11:13 am   #13
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Default Re: Quad FM3 tuner.

Thank you 'fettler Steve' for the 303 info. Now I know that if I come across an FM3, 33, 303 combination then it is only the 33 that needs to be given a snubber change before it blows and takes the switch contacts with it.
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Old 27th Apr 2013, 4:29 pm   #14
Mike Phelan
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Default Re: Quad FM3 tuner.

Thanks, (fetteler) Steve.

I think we'll switch this one off as it's heading Quadwards in general, and there will soon* be another Quad resto without these new-fangled three-legged beasts and rectangular black things with even more legs.

*soon in Mike terms = 2013 - 2015.

Watch this space!
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