Frank's JEL 300Bdx Rebuild
Based on JEL 300Bdx
8 wpc, Pure Class A, SE DHT
2x 76's, 2x 6SN7's, 2x 300B's,
and 1x 5U4
Built for Frank Hangenbuch
Completed on 6/9/10
amp looked like this when it was first built (see here), then after shipped around at least a half dozen times due to change in ownership the amp looked like a beat up pinata (as
seen in the pictures below). It also apparently went through some modifications in the power supply to further hum reduction,
but when Frank, the last owner of the amp, got the amp it had a dead channel plus an excessive hum on the working channel.
Frank initially asked me if I could get the amp fixed, but I suggested to him that it be would better if the amp was rebuilt
on a new chassis. Fast forward a few weeks, Frank now has amp that not only looks better but is hum-free. Notice that I added
a large 10H choke followed by a small 5H choke in the power supply as called for in JEL's schematic.
Viola! Resurrected amp! At this point, I still had one of the
channel intermittently going dead on me. I say "intermittently" because when I wiggle the 300B tube on the dead
channel, the sound went off and on. Don't worry, I have very insentive fingers (from building too many amps) so I don't get
burned from touching hot tubes that easily unless it was 845's It turns out that the 300B socket was the cuprit. I swap
them out with new ceramic ones and the problem went away.