Bush AC31 instability. - UK Vintage Radio Repair and Restoration Discussion Forum

chaz007 · 7th Sep 2012, 8:02 pm

My dad acquired this little Bush and it's internally very good condition and doesn't seem to be messed wIth, I've replaced the waxies and the electrolytic smoothing caps. It powers up fine and works but after a minute it gets instability and if tuned off a station will whistle and motorboat if left on longer

gram works fine though. Seems to start playing up when it gets warm. I'm pretty new to this so any ideas?

chroma04 · 7th Sep 2012, 10:26 pm

Hi,

I own an example of this radio which also had the same issue after replacement of all the usual suspects, giving instability (whistling) when tuned either side of a station. In my case, replacement of the EBF80 (I.F. amplifier, AM detector, AGC) completely cured the problem.

Inspection of the faulty valve revealed 'silvering' of the glass envelope. May be worth a shot if you have one to hand, although this valve is not found in most 'standard' superhet receivers.

Best Regards,

Adrian.

chaz007 · 6th Oct 2012, 6:27 pm

Update.

I decided to give replacement of the EBF80 a go, got a new old stock replacement from eBay and it's working perfectly now! Thanks for the suggestion

.

chroma04 · 6th Oct 2012, 11:49 pm

Well done! Glad to hear it lives again!

7th Sep 2012, 8:02 pm	#1
chaz007 Triode Join Date: Jul 2009 Location: Salisbury, Wiltshire, UK. Posts: 44	Bush AC31 instability. My dad acquired this little Bush and it's internally very good condition and doesn't seem to be messed wIth, I've replaced the waxies and the electrolytic smoothing caps. It powers up fine and works but after a minute it gets instability and if tuned off a station will whistle and motorboat if left on longer gram works fine though. Seems to start playing up when it gets warm. I'm pretty new to this so any ideas?

7th Sep 2012, 10:26 pm	#2
chroma04 Pentode Join Date: Jul 2008 Location: Doncaster, South Yorkshire, UK. Posts: 116	Re: Bush AC31 instability. Hi, I own an example of this radio which also had the same issue after replacement of all the usual suspects, giving instability (whistling) when tuned either side of a station. In my case, replacement of the EBF80 (I.F. amplifier, AM detector, AGC) completely cured the problem. Inspection of the faulty valve revealed 'silvering' of the glass envelope. May be worth a shot if you have one to hand, although this valve is not found in most 'standard' superhet receivers. Best Regards, Adrian. __________________ Chroma 04

6th Oct 2012, 6:27 pm	#3
chaz007 Triode Join Date: Jul 2009 Location: Salisbury, Wiltshire, UK. Posts: 44	Re: Bush AC31 instability. Update. I decided to give replacement of the EBF80 a go, got a new old stock replacement from eBay and it's working perfectly now! Thanks for the suggestion .

6th Oct 2012, 11:49 pm	#4
chroma04 Pentode Join Date: Jul 2008 Location: Doncaster, South Yorkshire, UK. Posts: 116	Re: Bush AC31 instability. Well done! Glad to hear it lives again! __________________ Chroma 04