HMV 1376 humming - UK Vintage Radio Repair and Restoration Discussion Forum

mancunian69 · 7th Apr 2016, 8:56 am

I have replaced the psu caps and a few resistors in the power supply on my set but it still hums.
Any ideas what it could be?
Cheers

ms660 · 7th Apr 2016, 9:30 am

You need to be more specific, Eg: Is the hum the same level at all volume control settings or does the hum level vary with the volume control setting, Is the hum loud, not so loud etc.

Lawrence.

Herald1360 · 7th Apr 2016, 9:33 am

The dead mouse behind the rectifier?

Is the hum coming from the speaker or elsewhere- transformer etc?

Does hum level vary with volume setting?

Does it stop if output valve grid shorted to chassis?

Does poking at wiring around detector, volume control and AF amp have any effect on it?

Nuvistor · 7th Apr 2016, 10:40 am

Has post #2, how loud, most of these sets had a small amount of background hum, not noticeable when listening at normal volume levels.
Frank

mancunian69 · 7th Apr 2016, 1:29 pm

The hum is constant level coming from the speaker.
I tried another rectifier valve and it still hums.

The sound quality is crystal clear though.

julie_m · 7th Apr 2016, 1:40 pm

Try tacking a suitably-voltage-rated capacitor of a few μF from G2 of the output valve to chassis. Ripple at this point can manifest as hum in the speaker which does not vary with the volume control.

Tim · 8th Apr 2016, 1:26 pm

Try grounding the case of the volume control to chassis. This can sometimes help.

7th Apr 2016, 8:56 am	#1
mancunian69 Pentode Join Date: Apr 2013 Location: Manchester, UK. Posts: 177	HMV 1376 humming I have replaced the psu caps and a few resistors in the power supply on my set but it still hums. Any ideas what it could be? Cheers

7th Apr 2016, 9:33 am	#3
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: HMV 1376 humming The dead mouse behind the rectifier? Is the hum coming from the speaker or elsewhere- transformer etc? Does hum level vary with volume setting? Does it stop if output valve grid shorted to chassis? Does poking at wiring around detector, volume control and AF amp have any effect on it? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

7th Apr 2016, 10:40 am	#4
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: HMV 1376 humming Has post #2, how loud, most of these sets had a small amount of background hum, not noticeable when listening at normal volume levels. Frank

7th Apr 2016, 1:29 pm	#5
mancunian69 Pentode Join Date: Apr 2013 Location: Manchester, UK. Posts: 177	Re: HMV 1376 humming The hum is constant level coming from the speaker. I tried another rectifier valve and it still hums. The sound quality is crystal clear though.

7th Apr 2016, 1:40 pm	#6
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: HMV 1376 humming Try tacking a suitably-voltage-rated capacitor of a few μF from G2 of the output valve to chassis. Ripple at this point can manifest as hum in the speaker which does not vary with the volume control. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

7th Apr 2016, 9:30 am	#2
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: HMV 1376 humming You need to be more specific, Eg: Is the hum the same level at all volume control settings or does the hum level vary with the volume control setting, Is the hum loud, not so loud etc. Lawrence.

8th Apr 2016, 1:26 pm	#7
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: HMV 1376 humming Try grounding the case of the volume control to chassis. This can sometimes help. __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."