That "fuf fuf fuf pop" noise....

[johnmarshmanagain]

Hi All,
This noise with the valve sets will be familiar to all, but I've never looked into it.
It's a posh-looking HMV radiogram, playing through the PU input,and I've removed the "radio" section valves. I'm thinking capacitor, of course, but does the team have any more specific suggestions ?
With thanks John

[cathoderay57]

It's motorboating. If it is still doing it with just the audio amplifier operating then it is either a bad HT smoothing capacitor (this usually manifests as hum rather than motorboating) or a decoupling capacitor on the HT feed to a pre-amp triode valve. You need to tell us what the model number is to make any more informed judgement. Cheers, Jerry

[johnmarshmanagain]

Many thanks Jerry, it's a HMV 1628 as it 'appens, but I'll download a trader and trace that decoupler you've mentioned. Cheers John