Loud things come in small boxes

[swarfrat]

Transformers & stuff came today. I think I have all the electrical parts I need, but my chassis is blank (no holes), and I have a bunch of layout and stuff to work out.

Ironically enough the idea of power scaling was what led me to consider EL-34's instead of the original plan for 15w 2204 on EL-84's. Then I decided to quit monkeying around with my 'based on' designs and just build a 2204 clone in a smallbox head. I dropped the power scaling for now. Still got schemes rolling around in there, but it'll be retrofitted later. I don't know WHY on earth I insisted on getting the Marshall style Impedance and Voltage $elector$ - I think it was because that's what the Ceriatone rear faceplate (the ONLY smallbox 50w faceplate I know of) is cut for. None of the rest of is it is from Ceriatone, and with their shipping cost I'll probably make the rear faceplate. (Anybody want the selectors? PM me before I cut holes in the box.) 

I bought a turret board for a 2204 style amp from Watts about 2 years ago. Faceplate and chassis box last winter. Yeah it's looking like the Warmoth is going to be in good company.  I'll do the cabinetry/tolex/piping/hardware once the amp is done (IOW probably next summer).  Just now noticed that the Ceriatone faceplate goes to 11.

Thanks fdesalvo for the inspiration to kickstart this thing going again. My first homebuilt amp is nearly 'vintage' now, it was time for another.

 

[swarfrat]

Still gotta find my  hole saws to finish the cans and power tube sockets. IEC power plug is fused, B+ and heater fuses will be internal. I left space for the mains selector but am not planning to use it for mains selection. If I come up with a logical use for it (like power scaling) then I may use it for that.

 

[swarfrat]

Found the holesaws, decided to go with a hamertone paint - aluminum is so soft - and once it gets scratched - it's a ton of work to get em out.  Riveted what I could, but I had to use machine screws on the 9 pin sockets as the nose of my rivet gun was too big. I'm planning to paint the tube shields flat black (mostly for looks, but ostensibly to radiate heat better

Screwed up my pot order, most of my existing stock appears to be too big to fit 1/4" splined pots, half of what Tayda sent was thru hole instead of solder lug. Also like  a dummy I painted, not remembering I got four more holes to drill to mount the turret board.

The front panel is going to be covered up (front panel is in earlier photos)

 

[Cagey]

Coming right along and looking good! Only 3,915 more details and it'll be ready to rock!

 

[swarfrat]

Yeah, at this rate my 2204 clone should be done ... Right about the time the baby gets here.
:guitarplayer2:  :binkybaby:  :sad:  :dontknow: :dontknow:

I may have to redo the chassis. Its a bit thin for the transformers. I'm going to see if I can rig up spacers so the chassis doesn't have to take the weight, but I have some circuitry planned for that area.

 

[Jumble Jumble]

Don't worry, babies like loud rock music. Well, mine does. Didn't get a choice I guess.

 

[swarfrat]

My nephew tells me I'll need the headroom to be heard over the baby anyway.

We saw Petra in concert Sunday night. (I've waited almost 30 years for that concert - my favorite lineup/material. I was too young to see that version of the band when I was a kid.)  The baby *loved* the drum solo.  Ruh roh......What's worse than a kid banging on toy drums? A kid with the discipline to practice learning to play the drums, doing quarter note drills with a metronome for hours on end. 

 

[bagman67]

Don't worry, babies like loud rock music. Well, mine does. Didn't get a choice I guess.

My boy's favorite is Ray Charles.  You should see him bouncing around listening to "I Got A Woman."

 

[swarfrat]

Got my holes drilled in my turret board, and its mounting holes in the chassis today.

Heresey! The Arduino is a standin. What will be in the space somewhere over the transformer is some sort of ATMega328P doing startup sequencing, bias/balancing and monitoring. There's a couple other tricks going into this one - heaters will be elevated by 40v or so, and most of RG Keen's Immortal mods (fuses, MOV's, and clamps out the wazoo). Power transformer has a 1/16" rubber sheet for mechanical isolation.  The audio portion is going to start out bone stock 2204 though.

First time using rivets. Can't say I'm a huge fan, have to re-anchor the cap can that lives inside, couldn't get em onto the preamp sockets, so they're bolted.  What's really frustrating at this point is that except for my transformer fuses, I have everything I need to get it making noise this weekend, but I still have hours and hours of work left.  (And that's BEFORE we get to cabinetry and tolex. Ughh!)

Also tried fabbing a 1U rack box to house my 13 pin breakout stuff that I finally wired up (Ricky Graham's Septar that is, I still have more grandiose plans for my own filter/breakout box - something I can filter and then spit out a HPF'd 13 pin feed into my Yamaha G-50). But the Septar will let me get to MIDI conversion in software at least.

And try as hard as I can, I still cannot for the life of me get used to looking at a head being REVERSED. Input should be on the left, power on the right! I actually had a moment of horror tonight when I was bolting my transformers on, and saw the power/standby holes (actually no standby, but a mute in my plans - the sequencing is going to take care of softstart) - for a moment I had 'input jacks' in my head, and was thinking for about a second or two that I had just done all this work, and mounted the power transformer directly over the input jacks.  :tard:

I'd planned a plexi back panel too, but the paint is such a good match, I may just use waterslide decals directly.

 

[Cagey]

What do you mean by "startup sequencing"? Also, what do you mean the heaters will be elevated by 40V?

Those Arduino boards are interesting little widgets. I'd like to think up an excuse to use one for something. Always loved playing with microprocessor prototyping boards. Did a lot of work about 100 years ago with Motorola microcontrollers. Steelcase Furniture still has a security system in place for their materials storage crib that I designed using one of those things and some little key-shaped EEPROMs...

 

[swarfrat]

Elevating heaters is for two reasons. First is to reduce the heater-cathode voltage on the cathode follower. The second is that by elevating the heaters positive to the cathode,  you can remove any hum coupled through the heaters without going to DC heaters.

By startup sequencing, the plan is something like:
Power on - heater inrush limited to half power for 5 seconds
Heater full power for 30 seconds
B+ enabled - FET, the gate slowed down so B+ ramps in over 1/4 second. Slow, but not so slow that I need to worry about dissipation beyond instantaneous rating.
Read the bias trim pot, micro biases the two tubes individually to balance.
Once cathode current stabilizes, unmute the power amp.

Once running, the micro just monitors B+ voltages and cathode current for faults, and the bias trim pot for changes. My bias scheme is actually fixed cathode bias, so I lose 40-60V off B+ but I'm ok with that.

My circuit design is done, but layout takes me forever, so I plan to wire it up stock initially except for individually fused HT windings and fusing the heater winding. Actually the arduino could basically be used as is, everything else is switching and dividers, and that stuff needs to live somewhere.

 

[swarfrat]

The rest of my pots & fuse holders came in from Tayda. I've already managed to beat the paint job up getting stuff on and off.  Once I have everything ready to go, I'll hit it with another coat and let it cure for a day or so.

I just love the look of the Marshall knobs, and it makes me want to jump ahead to cabinetry. But that would be even more maddening to have a sweet looking white half stack sitting there that can't make noise. Sadly, there isn't really as much to look at between now and finished.

 

[Cagey]

I just love the look of the Marshall knobs, and it makes me want to jump ahead to cabinetry. But that would be even more maddening to have a sweet looking white half stack sitting there that can't make noise. Sadly, there isn't really as much to look at between now and finished.

I know exactly what you mean. I'm a big fan of the Marshall knobs, too. I'm also a big fan of making obvious progress at the expense of real progress (I used to like Visual Basic for that very reason - any programmers will know what I mean).

But, sometimes you have to shoot the engineer and get on with production, so... GET TO IT! <grin>