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

Boulevardier · 9th Jul 2019, 9:14 pm

Yes, that schematic is different from the original Mullard one. No wonder we've been getting confused. I haven't really been involved with valves for 40/50 years, so I'll leave it to those with more knowledge to say whether that resistor could be the cause of the hiss - which would of course vanish when you grounded the input at the socket as this would bypass the resistor to ground. From your photo that substituted 2.2 Mohm doesn't look exactly new, so could it also be faulty? I can't think why Stern-Clyne changed its value - unless they had a stash of that value they wanted to get rid of. My next move would be to change it for a new/newer 1 Mohm, and see if there's any improvement. They are fine amplifiers when working properly, considered in my youth to be in a similar class to the Quads, etc of the day (IMHO).

Mike

[EDIT - my post just crossed with Hartley118's, and he's saying much the same.]

9th Jul 2019, 9:14 pm	#116
Boulevardier Octode Join Date: Sep 2017 Location: Bristol, UK. Posts: 1,654	Re: Mullard 5-10 amplifier Yes, that schematic is different from the original Mullard one. No wonder we've been getting confused. I haven't really been involved with valves for 40/50 years, so I'll leave it to those with more knowledge to say whether that resistor could be the cause of the hiss - which would of course vanish when you grounded the input at the socket as this would bypass the resistor to ground. From your photo that substituted 2.2 Mohm doesn't look exactly new, so could it also be faulty? I can't think why Stern-Clyne changed its value - unless they had a stash of that value they wanted to get rid of. My next move would be to change it for a new/newer 1 Mohm, and see if there's any improvement. They are fine amplifiers when working properly, considered in my youth to be in a similar class to the Quads, etc of the day (IMHO). Mike [EDIT - my post just crossed with Hartley118's, and he's saying much the same.] Last edited by Boulevardier; 9th Jul 2019 at 9:26 pm.