Calcinator Box

When I quite suceeded with Yahamaha MkII (not only myself, but also other people are generally quite satisfied with the sound and power of the little beast), there soon came the idea to realize the same concept with cheapest possible components - I took an old speaker box, used a cheap speaker form TubeTown and soldered scraped components. The only "new" component in the original design was KEMO module. I have included computer PSU as a primary power source and then used homedesigned DC/DC converter to get needed HV for tube preamp circuit. First design included also "Banana booster circuit" - so conceptually speaking I have cloned the Yahamaha. But there was buzzing, bumps and generally low quality sound. I discovered that:
- computer PSU has too "dirty" DC output for audio use (at least it seemed so)
- my HV DC/DC converter fails to produce steady quality power output (it could be a "scrapped" diode I used or the device is genarelly unsuitable for such use - originally it was intended as a high voltage power source for capacitor filling, eg. for electroshockers and airsoft guns) - it heated very much ... I must build another piece and try it in another piece of Alembic, to see what it is about
- there could be a mistake in preamp circuit - but it was extremely hard to troubleshoot, as I have used two back to back pcbs. So instead I have desoldered useful components and used another preamp Alembic board I have already made for another project
At the time I was quite ready to totally scrap the project and was quite doubtful if I will make another electronic project again - it seemed as waste of time.
************
Second try was with the new Alembic plate, put into the chassis of the computer psu, trafo from halogen lighting (used already in Yahamaha Mk1), PSU on the basis of my tiny regulator PCB and for  HV PSU I gave another try to the forementioned unit. Speaker and Kemo module stayed the same.
I made the tone stack from the other schematic, it seemed it will make the tone commands more responsive.
Result: very low output, a lot of noise, random "hiccups" of the system.
Decision: HV DC needs replacement - if anything, I will use ready made eBay module.
I was on the verge of never touching wires again.
******
Third try came when I needed to order a special trafo, for a friend's effect PSU I was repairing. So I ordered a trafo with a HV secondary. I used rectifyer I have experimentaly made on the stripeboard some time ago. With all the modules connected now consistent sound, but very low volume. What now? Still no real incentive to work on the thing - I don't need it myself, and nobody else said he needs something similar.
******
In the middle time I thought what if the different design of the TS is guilty for such a crappy output - I even thought about mixing up the output and input. So the step before me was to disasemble the preamp. (For the other projects: work on only one plane and not so many pcbs. Don't be stingy about the place. Try the sistem before assembling.) I've removed the preamp and started inspecting it. Gain pot wafer was cracked - but that can't be a reason for the problems. Then I looked at the main board (where the tube socket is). I almost concluded everything was right - and then find it! Oh, cremated snail tail, I have mounted the output decoupling cap on the cathode! (it should be on the plate). I've soldered the new cap in the correct position and assembled the amp. Still quite a lot of mains hum (I have made a perfect star ground, what is the problem? With the master pot lower the hum becomes louder.) But the amp was screaming like a stabbed wild boar, just like it should. Yeah, victory!
I have learned previously on the Yahamaha that the Alembic works better (more of a normal gain) with the AU instead of AX tube, so I have replaced AX with 5814, some USA made. Now I can normally use the master pot ...
++++++
THE VERDICT:
All in all, great distorted sound, superb clean sound (but not with two channels, requires some pot fiddling to change), quite noisy and hum with lower volume. Decent amp.
The insides are messy and probably dangerous. Modules fixed on all the inside planes are a bad idea. Make a central chassis and stick to it. Don't scrimp on the room.
The poweramp has 16V input, so it is capable of providing 40W on 4 ohm speaker. I should try it probably sometime on a bigger cab to see the full power of it - it could be impressive.

SPECS:
- Based on Alembic bass preamp design (Fender preamp), single channel only, 5814 tube
- powerstage Kemo module
- two separate rectifiers, HV and LV
- DC tube heater
- combo design
- low cost design (later just partly)

the box

the box - again

the controls: upper row alembic controls, lower row input jack and master pot, lower power button

preamp tone stack

preamp main board

the messy insides (from the top): speaker output jack, preamp in black PC PSU chassis, poweramp module on the cooler, trafo, both rectifiers