In service!

OK:

There's the working guts.

The start-up process went well - no smoke, no blown fuses. I biased a matched pair of newer J/J EL84s on the cool side, checked voltages again, and plugged it into my single 12 cabinet. It made sounds, but didn't quite sound right, and I trace the problem to a shorted cathode on the second tube. I neglected to trim the lead of the resistor connected to directly to V2 pin 8 after soldering it on, and it was touching the chassis. 

Once I corrected that everything started to feel and sound like I imagined it should: clean and bright, responsive and loud, with no discernable hiss or hum until very very loud. Really nice crisp sound with the Telecaster. The line out and built-in dummy load features work nicely, as do the bright and normal channels and their blending circuit. I mistakenly reversed the wiring of the channel switch so that the "up" side of the toggle is connected to the bottom gain pot and and vice versa (see pic below) - it will be a pain to fix, so I might just leave as is. 

It will take me a while to get used to the interactive tone controls. For example, the range and effect of the "mid" knob depends somewhat on the position of the "bass" and "treble" knobs, and likewise for all of them. 

The overdrive sounded was, well, just not very good - sort of weak and scratchy - and I remembered that I had introduced a voltage divider coming out of the OD gain pot to bleed off some signal prior to the tone stack driver, because the simulation and calculations showed that the signal would be way too much for the next stage. That was just wrong. I un-did the voltage divider and it sounds much better now - hotter and juicier as one would guess, but it doesn't overwhelm the next stage like I imagined it would. I'm not sure I like the overdrive sound though - it creates its distortion by saturating the following triode, producing a hard-clipped, squared off signal. This is intentional, and some players like that sound - I will have to play around with it to see whether there is something in there for me. If not, there are strategies for softening and smoothing this kind of distortion that I can try, but any modifications to that part of the circuit will also affect the clean sound, so I may have to do some experimenting. On the other hand, these amps are known to be very good at accepting pedals, so perhaps this amp is good starting point for experimenting with pedal distortion effects.

Looking forward to lots more playing through it to understand it better. Tomorrow I'll try playing the MC5 through it.

 

Planning

 It's been clear from the start that planning is crucial to a successful build, probably regardless of how you measure success, but especially for me since I'm so easily frustrated and flustered by mistakes. This amp seems particularly unforgiving of poor planning compared to the first two amps. I've done a lot of planning and prep for this one, but I think there have been at least a dozen times I have started to do something semi permanent - drill a hole, solder a connection, spec-tighten a nut - and paused to think one last time about the next few steps to come, and realized I should NOT do the thing I was about to do. The Hiwatt layouts from the early days are certainly different than the two I've built (based on Hoffman Amps' layouts strategy) and most others I've seen, and I'm guessing the two separate circuit boards, the front to rear combined with right to left circuit flow, and the limited two-row main circuit board requiring lots of underboard jumpers and connections, all contribute to the practical complexities of this build. However, for each time I caught myself before making an error, I've probably made two others that could have been avoided with a bit of forethought. 

Hopefully I'm improving... mainly, I suppose, for the sake of exercising my problem solving and planning skills generally, as it's hard to see building another amp anytime soon... probably the last amp for a while... just don't need another one... nope.

Recent progress

Populated main board and soldered all finished connections, leaving those points connected to off-board components unsoldered: 

Completed the impedance selector, speaker out, line out bits:

Input jack, channel selector, channel gain pots, overdrive push-pull selector pot:

Tone, master volume and presence pots pre-wired and installed:

Now I'll do as much testing as I can just to make sure there's circuit continuity at least, and to make sure all the pots work in the right direction, and that all solder joints are good. Then I'll install the main board and complete all connections.