Quad FM1 tuner - UK Vintage Radio Repair and Restoration Discussion Forum

jlaldridge · 20th Jul 2017, 1:05 pm

hi, I am trying to get some life out of my Quad FM1 valve tuner with stereo decoder. I have changed a couple of really ropey looking capacitors in it, and now I can get some very quiet and distorted stations out of it. But this is accompanied by a very loud buzz, not dissimilar to 50Hz mains interference, but at a much lower frequency. I plan to carry on changing capacitors, but wondered whether anyone had any other useful checks I could do, or suggestions. perhaps I am on the wrong track completely.
Thank you in advance, James.

Beobloke · 20th Jul 2017, 1:15 pm

Randomly changing things is not the way to go and you could cause more harm than good - I know of one chap who changed the capacitors in hs Technics SP10 MK2 turntable "as a precaution" and it didn't work properly afterwards!

Take it to someone who can fault-find it properly and also re-align it for best performance. The results will be worth it.

nutteronthebus · 20th Jul 2017, 1:20 pm

Hi this is the users and cct for the FM1

Dave

SteveCG · 20th Jul 2017, 3:41 pm

For what it is worth: I tried an FM1 quite a few years ago - and found that it just kept drifting in Frequency even after it had warmed up. I puzzled over this for some time and gave up. Essentially it made the tuner unuseable. However since then - and thanks in a large part to this forum - I discovered the real extent to which even post-war paper and some other capacitor types can cause problems due to electrical leakage. This leakage often increases with increasing component temperature, hence they are a possible cause of the frequency drift problem.

I mention this, as looking back with hind-sight I can see that getting that FM1 working as Quad (Acoustical) intended could have been a non-trivial exercise.

20th Jul 2017, 1:05 pm	#1
jlaldridge Retired Dormant Member Join Date: Oct 2010 Location: Northampton, East Midlands, UK. Posts: 16	Quad FM1 tuner hi, I am trying to get some life out of my Quad FM1 valve tuner with stereo decoder. I have changed a couple of really ropey looking capacitors in it, and now I can get some very quiet and distorted stations out of it. But this is accompanied by a very loud buzz, not dissimilar to 50Hz mains interference, but at a much lower frequency. I plan to carry on changing capacitors, but wondered whether anyone had any other useful checks I could do, or suggestions. perhaps I am on the wrong track completely. Thank you in advance, James.

20th Jul 2017, 1:15 pm	#2
Beobloke Heptode Join Date: Oct 2007 Location: Southampton, Hampshire, UK. Posts: 821	Re: quad fm1 tuner Randomly changing things is not the way to go and you could cause more harm than good - I know of one chap who changed the capacitors in hs Technics SP10 MK2 turntable "as a precaution" and it didn't work properly afterwards! Take it to someone who can fault-find it properly and also re-align it for best performance. The results will be worth it.

20th Jul 2017, 3:41 pm	#4
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Quad FM1 tuner For what it is worth: I tried an FM1 quite a few years ago - and found that it just kept drifting in Frequency even after it had warmed up. I puzzled over this for some time and gave up. Essentially it made the tuner unuseable. However since then - and thanks in a large part to this forum - I discovered the real extent to which even post-war paper and some other capacitor types can cause problems due to electrical leakage. This leakage often increases with increasing component temperature, hence they are a possible cause of the frequency drift problem. I mention this, as looking back with hind-sight I can see that getting that FM1 working as Quad (Acoustical) intended could have been a non-trivial exercise.