Guess what?  My amplifier works.  Sort of.

There are some problems.  My brilliant idea to use quick connectors to connect all the tubes and pots to the main board turned out to be a not-so-brilliant idea.  It certainly made assembly cleaner, but the connectors are not very reliable.  I’ll be replacing them all with proper permanent soldered connections next.  Still, the new layout is a good one (using perf board instead of point-to-point wiring was a GREAT decision), and the inside is actually quite clean and, I daresay, rather pretty.  I’ll post pictures on Thursday.

Also, I need more gain after the tone stack.  I used a unity-gain phase inverter before the power tubes.  This, coupled with the large attenuation factor in the Baxandall/James tone stack preceding the inverter, means that I can’t get the full possible volume out of my power amp, even if I drive the tone stack buffer into saturation with the preamp.  I plan to fix this by using a single anode-follower to drive the tone stack (instead of a direct-coupled two-stage cathode follower), and use the extra triode stage to form a long-tail pair phase inverter, which itself has substantial gain.  This should allow me to get the full volume from the amp.

But the sound.  The SOUND – it is pretty breathtaking (when it works right).  Very high gain, but very tight and clear.  I can play full chords at full overdrive levels and they still ring out pretty clear.  Couple that with a healthy dose of sag from the series resistor in my power supply, and I’ve got myself a tight little high-gain rhythm guitar amp.

There are a few other issues- something is wrong with the grounding on my input jack, my power tubes are biased a little hot, I’ve decided to redo my power supply to use the full B+ available from my transformer.  There are a lot of little fiddly things to fix here.  And it should be a blast!  Man, I feel like Rachel right now.

 

Alright, enough amp stuff for now.  I’ll see you on Thursday.