HMV 1122, 1126 etc osc probs - UK Vintage Radio Repair and Restoration Discussion Forum

gavinhall · 22nd Dec 2009, 2:09 pm

Recapped this one, new w77 fitted, ht steady at 170ish. However, osc stops working on lw when tuning higher than home service. Doesn't work at all on mw although there is a healthy crackle/buzz which gets louder at I tune up the dial. sw is silent. Could someone hlep me understand why the oscillator should stop at certain frequencies. When it's warm the lw band is improved a bit.

Thanks
Gavin

jjl · 22nd Dec 2009, 3:29 pm

Sounds a bit obvious, but if you've replaced the W77 IF amp, have you also replaced the X78 or what have you frequency changer? The active part of the local oscillator is formed by the triode in the frequency changer valve.
Other than that, local oscillators can be stopped by waveband switching problems, resistors going high in value, leaky or open capacitors, coils affected by corrosion or damp or dirty / shorting vanes in the oscillator part of the tuning capacitor.

John

dr peppers · 23rd Dec 2009, 9:29 am

I've had trouble with junk stuck inbetween the vanes of the tuning cap, might be worth a clean.
Also if you havent, then try switch cleaner in the valve bases. Sounds like something is quenching the oscillator, try measuring some of the resistors around the frequency changer for correct value, and check the oscillator coil primary for continuity, the osc triode section get its anode supply through it (though from your measurement thats ok), also have a look at the oscillator coil tuning ferrite slug if it has one, to see if its disintegrated with age.
You could also try putting the old valve back in, maybe you've a duffer.
I have a similar radio, one of my favorites, its never given trouble, the previous owner had it from new and said its never broken.

22nd Dec 2009, 2:09 pm	#1
gavinhall Retired Dormant Member Join Date: Sep 2007 Location: Maidstone, Kent, UK. Posts: 109	HMV 1122, 1126 etc osc probs Recapped this one, new w77 fitted, ht steady at 170ish. However, osc stops working on lw when tuning higher than home service. Doesn't work at all on mw although there is a healthy crackle/buzz which gets louder at I tune up the dial. sw is silent. Could someone hlep me understand why the oscillator should stop at certain frequencies. When it's warm the lw band is improved a bit. Thanks Gavin

22nd Dec 2009, 3:29 pm	#2
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: HMV 1122, 1126 etc osc probs Sounds a bit obvious, but if you've replaced the W77 IF amp, have you also replaced the X78 or what have you frequency changer? The active part of the local oscillator is formed by the triode in the frequency changer valve. Other than that, local oscillators can be stopped by waveband switching problems, resistors going high in value, leaky or open capacitors, coils affected by corrosion or damp or dirty / shorting vanes in the oscillator part of the tuning capacitor. John

23rd Dec 2009, 9:29 am	#3
dr peppers Retired Dormant Member Join Date: Nov 2009 Location: Lancashire, UK. Posts: 67	Re: HMV 1122, 1126 etc osc probs I've had trouble with junk stuck inbetween the vanes of the tuning cap, might be worth a clean. Also if you havent, then try switch cleaner in the valve bases. Sounds like something is quenching the oscillator, try measuring some of the resistors around the frequency changer for correct value, and check the oscillator coil primary for continuity, the osc triode section get its anode supply through it (though from your measurement thats ok), also have a look at the oscillator coil tuning ferrite slug if it has one, to see if its disintegrated with age. You could also try putting the old valve back in, maybe you've a duffer. I have a similar radio, one of my favorites, its never given trouble, the previous owner had it from new and said its never broken. Last edited by dr peppers; 23rd Dec 2009 at 9:37 am.