UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Mullard 5-10 amplifier

Sideband · 10th Jun 2019, 10:31 pm

One trick you could try to determine if it's coming from the heater supply is to disconnect the heaters while the amp is operating....arrange a switch or something in the heater supply and operate it briefly...the amp will operate for some seconds before the heaters die away. More than enough time to establish if the hum stops of not. If it does then investigate the actual heater wiring...I think it was originally a centre-tapped supply. You could try running the ECC83 and EF86 heaters from DC but as I said, it shouldn't be necessary.

I built two of these back in the 70's....no problems at all with hum.

10th Jun 2019, 10:31 pm	#5
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Mullard 5-10 amplifier One trick you could try to determine if it's coming from the heater supply is to disconnect the heaters while the amp is operating....arrange a switch or something in the heater supply and operate it briefly...the amp will operate for some seconds before the heaters die away. More than enough time to establish if the hum stops of not. If it does then investigate the actual heater wiring...I think it was originally a centre-tapped supply. You could try running the ECC83 and EF86 heaters from DC but as I said, it shouldn't be necessary. I built two of these back in the 70's....no problems at all with hum. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....