April already. So the amp is finally fixed, i bought 5 NOS 829Bs from the US and they arrived the other week. I also replaced the two 10R resistors that burned out . After biasing, the amp works again. Some observations..
1. Mains hum - not affected by the volume pot so i guess being picked up from the pre amp stage - i have diodes and resistors so i will try rasing ground to eliminate ground loops - where do i put the circuit? I think there was a photo in a previous post..
2. I now have 11 829b/GU/FU29 type valves - of these..
2 are gassed and glow purplr
1 was shorted internally and took out the 2 beefy 20R resistors
1 is duff and i see no cathode glow
1 I cannot bias - i go to the end of the pot and i am still at 80mv - 30 mV off the 50 mv i am looking for
1 has an immense amount of hum when i plug it in - i know hum doesn't come from valves, but something funny is going on there
So i have 5 good valves - 2 that came with the amp, and 3 form the 5 i have purchased recently. I guess this is par for the course on 60 year old valves..?
SO just the hum now which i am hoping is ground loop and the ground lift circuit will sort that.
ALSO - how do i add another input - the amp has 2, ideally i need 3... is it just an different selector switch and RCA sockets, or do i need to do something more cunning..?
1. Mains hum - not affected by the volume pot so i guess being picked up from the pre amp stage - i have diodes and resistors so i will try rasing ground to eliminate ground loops - where do i put the circuit? I think there was a photo in a previous post..
2. I now have 11 829b/GU/FU29 type valves - of these..
2 are gassed and glow purplr
1 was shorted internally and took out the 2 beefy 20R resistors
1 is duff and i see no cathode glow
1 I cannot bias - i go to the end of the pot and i am still at 80mv - 30 mV off the 50 mv i am looking for
1 has an immense amount of hum when i plug it in - i know hum doesn't come from valves, but something funny is going on there
So i have 5 good valves - 2 that came with the amp, and 3 form the 5 i have purchased recently. I guess this is par for the course on 60 year old valves..?
SO just the hum now which i am hoping is ground loop and the ground lift circuit will sort that.
ALSO - how do i add another input - the amp has 2, ideally i need 3... is it just an different selector switch and RCA sockets, or do i need to do something more cunning..?