#1 Border Patrol SET...hummmmm
Posted: Thu Jan 22, 2015 8:28 pm
I am trying out a BP SE300B that someone built from 90% original parts.
The main difference is in the PSU which is in it's own Hammond case
and has very large mains transformer and main choke. The psu must
weigh around 20 kg.
It came with no audio valves so I have fitted them including a pair of EH300b.
I discovered that one op transformer Rp=127ohms and the other 136 ohms.
I set the bias to 70ma. I found that turning the hum pot has little effect
and there is a fair hum whether or not my (active) pre is connected.
I played some music and despite the hum, if the volume is increased
It sounds very capable and in another league to my Leak 20.
Any comments on the op transformer primary resistance difference and
if it might affect anything? I particularly am looking at a way to sort out the hum.
The amp and psu aren't in standard BP chassis but if I decide to keep it I would like to rebuild particularly the amp into something with a wooden plinth.
The main difference is in the PSU which is in it's own Hammond case
and has very large mains transformer and main choke. The psu must
weigh around 20 kg.
It came with no audio valves so I have fitted them including a pair of EH300b.
I discovered that one op transformer Rp=127ohms and the other 136 ohms.
I set the bias to 70ma. I found that turning the hum pot has little effect
and there is a fair hum whether or not my (active) pre is connected.
I played some music and despite the hum, if the volume is increased
It sounds very capable and in another league to my Leak 20.
Any comments on the op transformer primary resistance difference and
if it might affect anything? I particularly am looking at a way to sort out the hum.
The amp and psu aren't in standard BP chassis but if I decide to keep it I would like to rebuild particularly the amp into something with a wooden plinth.