My Yeti-clone build

[M Fowler]

Yup you better make a new board or flip that one over.

[drew]

The problem is that the chassis was drilled a mirror image of how it should have been.

[M Fowler]

Yeah I've done that and then had to make a reverse board. Kind of like wanting to make a tubes down chassis but end up making a tubes up instead.

Shit happens but you should have stopped long before wiring it.

[Meat&Beer]

Yep, I also did this! But thankfully I noticed before installing turrets in the boards. Flipped the boards over, installed them on the other side, and read my layout drawing backwards to build it! That was a long time ago, and that amp is going to be 100% rebuilt starting with a blank chassis.

Don't feel bad Mr Wright, we all fudge things up. I took my major screw up and looked at it this way; I can now take this opportunity to make an amplifier the likes of many drool-worthy super neat and clean ones like a lot of 'em around here. The thought is really encouraging to me, anyway. You'll get it, man!

[morcey2]

I built a 7591 Plexi that was going in a combo, but with the controls going the same direction as my others with the input on the left followed by the volumes, tone, and presence moving toward the right. So I needed to use a mirror image of the layout, basically put the turrets on the other side of the board.

I got it drilled, mounted and staked the turrets. Then I realized that I had done the turrets on the wrong side of the board. I drilled out all of the turrets and installed new ones on the other side of the board. Only after I got the board populated did I realize that my initial attempt was correct. I had compared it to the non-mirrored layout. I mounted it in the amp upside-down on 1.75" nylon posts. I call it the hanging turret-boards of babylon. It works great, but I don't want to have to modify it in any way. Eventually I'll make a new more correcter board for the combo and swap this one into a head. When I get home, I'll post a couple of pictures. I did put the bias trimpot on the backside of the board.

It's ugly, but it works.

Matt

[MrHaroldA]

I call it the hanging turret-boards of babylon.

I'm giving my Yeti build a cleaning and visual inspection now. I don't have the 'era' witching in yet, but I'm too worried there's a mistake here and there, so I'm gonna test it before the final wiring goes in.

I use these guides for the measurement and testing instructions: http://www.metroamp.com/downloads/50_WA ... CTIONS.pdf

[MrHaroldA]

I'm giving my Yeti build a cleaning and visual inspection now.

Done! Next up: voltage measurements without any tubes installed.

[MrHaroldA]

Page 26: Testing part 1:
A. Done!
B. Wall outlet: 225V~
C. Heaters: 3.5V~ That seemed a little to high, so I switched from the 220V~ to the 240V~ tap, and it went down to 3.2V~, which should be ideal. Keeping it at that tap for now.
D. -27V= to -40.4V= on both V4 and V5, not such a big range (Metroamp: -20 to -50) but should be sufficient
E. 444V=, way above the 350V= mentioned in the Metroamp manual, but that's due to the Drake PT from my 1987x.

Votage chart:

Code: Select all

    1   2   3   4   5   6   7   8   9
V1 135     1.4 3.2 3.2 232     2.2
V2 182     1.1         320 182 184
V3 203      40         211      40
V4         447 446 -27 446
V5         447 446 -27 446

This is before installing the EL34 power tubes.

I did found one mistake in my build: since I re-used my 1987 power amp, the B+ droppers are out of spec ...

[statorvane]

Your voltages will drop some when you install your tubes.

Good luck and hope this helps.

[MrHaroldA]

Your voltages will drop some when you install your tubes.

Good luck and hope this helps.

All voltages look just fine to me, so up to the next step ...

Shall I install the power tubes, or check for oscillation with my scope first?

[statorvane]

Before you install your power tubes I'd run the bias voltage as negative (-40.4 volts), or as cold as possible first to reduce the possibility of red-plating on your first power up. Then you can reduce the bias voltage to get close to optimum.

Using a simple bias calculator http://www.webervst.com/tubes1/calcbias.htm I get -39.1 volts (39.1 ma) for a plate voltage of 447 volts for EL34s in class AB. Good place to start.

Hope this helps.

[statorvane]

Oops, never mind, You've got it set right at -27. That should be around 50% idle dissipation. Sorry for the bum steer.

[Mr Wright]

I'm going to leave mine alone for a bit. I intended to jump in over my head with this build and I succeeded in doing so.

I may attempt an easier build in the mean time. (There is a meeting tomorrow to decide how much of a raise my coworkers and I will all get, so I need a reward of some sort right?)

I will attempt to rework the yeti-mess when my basement is warm enough to work in again and I regain the patience to work on it.

[cbass]

Hey Harold not trying to tell you what to do but I think the polite thing would be to start a new thread about your amp .I'd like to know all about it it looks good.

[M Fowler]

Mr. Wright you can salvage this amp when your ready just requires removing the board, remove the components, drill out the turrets and re-install new turrets on opposite side.

Or make a new board.