UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

bikerhifinut · 26th Feb 2016, 7:32 pm

a quick one:
I confess to a bit of a lack of understanding on this one.
I have an inkling that the EL34 gridleak resistors on this amp might be a bit too high in value.
I used the values as per the leak TL25+ circuit, these are specified as 680k.
I suspect this was to squeeze as much as possible out and reading various tomes on the leak products seems to suggest HJL ran the valves at or beyond their normal operating limits?
Mullard specify 470k on the 5-20 and i wondered if using this value or maybe even down to 330k would ease the load on the EL34's?
I am not worried about a reasonable reduction in output power as I measured 37W into 8 ohms when I had it on the scope when first built. In fact getting them down to 25-30W might be an advantage in terms of valve life?
Thanks guys.

Andy.

26th Feb 2016, 7:32 pm	#144
bikerhifinut Octode Join Date: Nov 2013 Location: Penrith, Cumbria, UK Posts: 1,993	Re: EL34 power amp project a quick one: I confess to a bit of a lack of understanding on this one. I have an inkling that the EL34 gridleak resistors on this amp might be a bit too high in value. I used the values as per the leak TL25+ circuit, these are specified as 680k. I suspect this was to squeeze as much as possible out and reading various tomes on the leak products seems to suggest HJL ran the valves at or beyond their normal operating limits? Mullard specify 470k on the 5-20 and i wondered if using this value or maybe even down to 330k would ease the load on the EL34's? I am not worried about a reasonable reduction in output power as I measured 37W into 8 ohms when I had it on the scope when first built. In fact getting them down to 25-30W might be an advantage in terms of valve life? Thanks guys. Andy.