Chequered Projects

So here's the first video demo of my first amp build.  I set it to nice crunchy pre-amp distortion setting, and the guitar is straight into the amp and straight into the speaker cab. The guitar is a Takamine GX-200 with the stock pickups (dimarzio's I believe), the cab used is a 212 Weber (Sig12  + Sig12a).  The video is from my Oneplus One, and the audio is from my Zoom H2N, with auto-gain/compression/limiter all disabled.  The H2N is positioned off axis and 4 feet away from the cabinet, with the gain control set just a hair below 1.

Some comments:

This thing is LOUD!  Like REALLY LOUD! (All caps for emphasis),

This thing gets into full blow clipping really early, and the MV is not super useful (considering implementing Ken Fischer's MV-1),

There's a strange phasey effect when I put everything on eleven, I plan to:

Increase the Rk load from 56K on the Cathode follower to 100K (ala Bassman), and reduce the CF gain stages Rk bias to 820r (ala Bassman).  Depending on the results of this, I may try:

reducing the gain of the Parallel Triode input section.

All in all I am extremely pleased with my first amp build.  It responds quite similarly to my AC30CC2 (shown but not used in the above video).  Which I guess shouldn't be too surprising.

The above clip I had the 120r Sage resistor installed between the GZ34 rectifier and the first 33uF eCap.  I have since removed this.

I will post demo's and updates after I've gotten it just the way I like it :)

Cheers,

Here is the output Spectrum Analyzer output my amp with nothing plugged in with the gain on zero, medium and high with nothing plugged into the input. Taken with Advanced Spectum Analyzer Pro android app on my oneplus one.

Zero Gain

Half Gain

Full Gain

And see below for my scope test:

I'm starting to get why there's a premium charged for hand-wired amps. 

I made my current limiter (300W light bulb) for safer testing.

And also spent 4 hours wiring....as you can see not a whole lot of physical progress, but am continuity checking nodes as i go to be sure to be sure...which is a good thing because i found a short from my b+ node straight to ground.  That would have sucked to have found out about later under power...

I scoped out the 6v windings to determine the correct phase on the pt. Then i wired them in series for 12v.  Makes the pre amp wiring nice and neat, but kind of gets messy with the pa tubes because they needed to be wired in series across the 12V. 

Ive also wired up the 5v cct, and pigtailed the pt as the leads were pretty short from the donor amp.  See photo below :)

All in all good weekend progress.

Im still not entirely happy with the power rail section of the board...the HT terminals are hauntingly close to the aluminum stand offs.  I will be working on that and finishing up ac wiring (mains fuse to power switch to primary coil on the pt).

I have finally gotten around to mounting some board components while the Mrs sorts out lettering and a logo for the chassis. 

Here is the power rail (the resistors are a little sloppy due to my not completely thinking through the layout). I will probably remove them and heat shrink the leads before the first power up.

In any case,  here are some photos of the power rail and phase inverter components, mounted and soldered in.

Happy Easter!

So everything is all dry now and its looking pretty good.  I think the fire truck red is starting to grow on me.  The trannys really pop out against the white chassis!

Now to try my hand at some lettering.

Tonight's progress includes a final wet sand of the chassis, as well as sanding and applying the first coat of paint on the iron's.  

The transformers and choke turned out a little brighter red than I would have liked, but caliper paint is slim pickings around these parts so I took the darkest red I could find.  

Here's the white primer coat of my chassis.  I sanded with 220 grit then wetsanded with 600 then gave it a rubdown in a spray nine and water solution.  The paint I used is an automotive wheel paint spray can.  Hoping it will hold up!

So the chassis is in and dad and his colleague did a bang up job!   .050 aluminum CNC machined the top :-).

I've been drilling and tapping all afternoon so I figured I'd put some purple knobs on to cover the holes for a photo op! 

Thanks for the custom chassis dad!  Best birthday present ever!