Well, after nearly 12 months of playing relentlessly my 45 SE amplifier, had an unexpected failure in the power supply (passive regulator) which forced me to do maintenance to the amplifier. It was a great opportunity to remove the 6J5 driver and do a quick swap for the greatly respected 7193 (i.e. military version of the 2c22)
45SE Amplifier upgraded with the 7193 drivers
Bias point remains unchanged: 7mA and 260V for maximum swing and minimum distortion. Need to look at my notes, but I remember that I was something around 0.30% at 100Vpp driving the 45 (which is not an easy load for anyone). Driver configuration was not changed, so had the 7193 now loaded with same DN2540 single transistor gyrator and mu-follower output for lower impedance. The valve was biased at about 8V with an LED array.
7193 in action
As a test, played the fantastic Symphony No. 3 from Henryk Gorecki….
Hard to describe in words what I felt when I played first time “Goodbye Pork Pie Hat” from Charles Mingus. Perhaps it was the due to the fact that I play saxophone, but inevitably for me this song is one of the best ones to test the response of any amplifier. Sax duets, solos, a great bass line and varied moods along the way can take the amplifier to their best of their abilities. Being a jazz fan, couldn’t help myself when listening this amplifier for the first time. I used to play an EL34 push-pull, and liked its sound and power – specially for rock. But when it comes to the first watt, this amplifier is breathless. Pure and a warm tone. Playing this song made me understand all the fuzz about single ended amps. But, far from opening the debate about that, I’m sure that a 45/46 in push-pull has its own merits and would probably will one of those amps I’d like to build in the future.
Having a FE167E full-range driver that have a relatively high efficiency (94dB/W), the 45 SE doesn’t sound low. It has its own personality. Brilliant for jazz, it may need a tad of power perhaps when playing some rock and classic stuff.
7193 valve
It took me some time to optimise the driver stage. Started with an SRPP, then a paralleled 6SL7 to an 6J5 loaded with a gyrator in mu-follower achieving less than 0.20% THD at 150 Vpp. A great driver in my opinion. Now need to replace the 6J5 for the lovely 7193.
It looks like a Frankenstein valve, but it’s a lovely thing to me. Many claim that it’s a superior valve compared to the 6SN7/6J5 or even CV1988.
Adding the 7193 will require opening my 45SE and not having music at home for some time so at the moment is not what I have in mind.
Perhaps when I get the 4-65A up and running? It will take some time for that…
