• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Supreme 45 tube amp

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Merry X'mas and Happy New Year to DIYers.

I just finished off building a stereo amp with 6SN7 driving the 45 tube for my friend. The design is based on the Sun Audio's 2A3 circuitry. Some modifications were made:-

Double choke C-L-C-L-C filtering for B+. Separated RC filtering for the 1st and 2nd 6SN7 drivers. All power supply capacitor for B+ are Blackgate WKZ's. The cathode bypass for 45 is Blackgate 100uF non-polarized one, and for 6SN7 is Blackgate 100uF FK.

I used the Hammond 302AX power transformer because it has all the secondary voltages for this stereo amp - 300V-0V-300V HT, 5V (rectifier filament), 6.3V (6SN7 filament), and two 2.5V (for the two 45 tubes).

The amp employs Lundahl Amorphous LL1620AM 30mA SE OPT. This OPT is customs made for running 30mA bias current for the 45 tube.

After burn in for couple hours, I had it delivered to my friend. He hooked it to his system and started singing songs. We listened to it for several hours, we were so excited with the sound from this amp. It has very fine, smooth details in all frequency ranges - bass, mids, and treble. It also very wide and deep sound stage.

This is the best tube amp that I ever built during the past few years. I really missed it. I feel sad when I left it to my friend... Good bye baby.


Joined 2004
Paid Member
Gluca said:
Hey! You must be cheating!? None here loves 45s (LOL)! It seems that 45 cannot dissapoint anyone. Where is that cabinet from?

I remember my first 45 amp - I still have it, and I was coming from the world of big PP amplifiers - my expectations were rather low, and it literally blew them out of the water. There isn't a much better choice IMO when all you need is a couple of watts.. :D

Congrats on a great job by the way!
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