Intermittent rumbling noise from HMV radiogram amplifier - UK Vintage Radio Repair and Restoration Discussion Forum

laceholes · 23rd Feb 2018, 9:38 pm

A vintage HMV radiogram kept making a very low frequency rumble when switched to gramophone, even when the turntable was stationary. I suspected a electrolytic cap and changed one or two of them, with no effect. It eventually turned out to be the 4 layer yaxley switch was slowly burning away through the action of the HT voltage. I only found it by chance one evening when the light was off, when I saw this blue sparking and investigated it. I didn't want to strip all the wires off the four bank switch so I scraped the carbon off the offending switch and made good any important damage with Araldite. After that all was well.

RojDW48 · 24th Feb 2018, 1:07 am

Hello and welcome to the forum. That reads like a very useful fire hazard warning! It would be helpful to know which model HMV RG that was!

laceholes · 26th Feb 2018, 1:25 pm

Sorry but I don't know which HMV model it was. The case had been modified a bit and the pickup replaced by a more modern one. I later took out and used the amplifier etc for a few years until the speaker rotted around the edges where the cardboard folds. I even spread rubberised glue over the rotting and the speaker continued working!

Nickthedentist · 26th Feb 2018, 8:36 pm

Hello and welcome from me too.

This is quite a common phenomenon, which seems to be known as "HT tracking".

e.g. https://www.vintage-radio.net/forum/...ad.php?t=89602

23rd Feb 2018, 9:38 pm	#1
laceholes Retired Dormant Member Join Date: Feb 2018 Location: Ely, Cambridgeshire, UK. Posts: 4	Intermittent rumbling noise from HMV radiogram amplifier A vintage HMV radiogram kept making a very low frequency rumble when switched to gramophone, even when the turntable was stationary. I suspected a electrolytic cap and changed one or two of them, with no effect. It eventually turned out to be the 4 layer yaxley switch was slowly burning away through the action of the HT voltage. I only found it by chance one evening when the light was off, when I saw this blue sparking and investigated it. I didn't want to strip all the wires off the four bank switch so I scraped the carbon off the offending switch and made good any important damage with Araldite. After that all was well.

24th Feb 2018, 1:07 am	#2
RojDW48 Nonode Join Date: Jun 2014 Location: Bristol, UK. Posts: 2,074	Re: Intermittent rumbling noise from HMV radiogram amplifier Hello and welcome to the forum. That reads like a very useful fire hazard warning! It would be helpful to know which model HMV RG that was! __________________ '....don't go mistaking Paradise for that home across the road!' (Bob Dylan)

26th Feb 2018, 1:25 pm	#3
laceholes Retired Dormant Member Join Date: Feb 2018 Location: Ely, Cambridgeshire, UK. Posts: 4	Re: Intermittent rumbling noise from HMV radiogram amplifier Sorry but I don't know which HMV model it was. The case had been modified a bit and the pickup replaced by a more modern one. I later took out and used the amplifier etc for a few years until the speaker rotted around the edges where the cardboard folds. I even spread rubberised glue over the rotting and the speaker continued working!

26th Feb 2018, 8:36 pm	#4
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,846	Re: Intermittent rumbling noise from HMV radiogram amplifier Hello and welcome from me too. This is quite a common phenomenon, which seems to be known as "HT tracking". e.g. https://www.vintage-radio.net/forum/...ad.php?t=89602