Starting my 12xxx build

[BAinFL]

I just ordered my iron (Classic Tone) and assorted odds and ends from Valvestrom and should be starting my build as soon as those parts arrive. I'll be using a steel 67/68 chassis from George and got my turret boards from Brian H.

Since this is my first build and I'm a beginner in electronics, I'm going to keep it simple and will only add a Lar/Mar PPI MV once I get it running without any problems. This is a bit of a budget build for me. I'll be using good stuff, but nothing NOS (except maybe some 12AX7s when I'm all done). I've read all the 12xxx build threads, reread the step by step for the 100w Plexi several times and have been covering anything related to my build on this site for the last 2 months. I've even taken the '68 Superlead board layout to Kinko's and had a color copy blown up and laminated =) I think I'm pretty well prepared to take on this project thanks to you all!

My main concern initially in planning my build is that in the pictures, and diagrams I've collected and browsed, I still don't have a clear map of all the various grounding points; particularly for the filter cap board. Comparing to the step by step 100w plexi instructions and trying to match the 12xxx FC board layout has me at a loss.

Can anyone point me to a picture, or other information that would help me better understand a standard grounding scheme for the 12xxx as it relates to the FC board? Am I correct in understanding that apart from the FC board, the remainder of the grounding (assuming a standard grounding scheme) of the amp is consistent with the Metro 100w Plexi instruction guide?

Many thanks in advance!

-Bram

[chrisom]

Use this link as your Bible for quiet grounding:

http://forum.metroamp.com/viewtopic.php ... arryground" onclick="window.open(this.href);return false;

I've had parts & chassis for almost a year now and am just getting to the part you're asking about, because I went back to school last Fall. It's pretty straightforward, and it's supposed to be the quietest (better than the original factory) method.

A word to the wise: Do whatever metalwork and drilling of extra holes needed to facilitate the installation of the ground lugs and tube sockets before anything else, or you will have a mess of metal powder/dust to deal with...

[Strat78]

Good advise Chrisom! I'm on my third build with this grounding scheme and it is really great. I have some good high res jpg's if you need them. vhjunkie is a life saver here! Look forward to seeing your build!

[BAinFL]

Thanks chrisom... much appreciate that tip.

Yes, I've looked at that thread a few times. The pictures are great. I'm just a bit intimidated by too much variation from the guide...afraid I might double ground something if I try managing this scheme within the context of those other instructions.

But if you guys say this is the way to go, I'm all in. I'll glady take informed opinions over my own. Just be prepared for a few extra "does this look right?" posts from me on this topic =)

-Bram

[chrisom]

Strat78, what did Larry mean by

"anywhere between 1 & 2 the preamp filter ground"?

That's the one point that confused me.

Am I supposed to drill and install another ground lug in-between 1 &2 to ground the preamp filter cap to, or did he just mean put it in either place, 1 or 2? It was sort've ambiguous.

What did you do for this part, and how did it turn out?

[vh junkie]

Strat78, what did Larry mean by

"anywhere between 1 & 2 the preamp filter ground"?

That's the one point that confused me.

Am I supposed to drill and install another ground lug in-between 1 &2 to ground the preamp filter cap to, or did he just mean put it in either place, 1 or 2? It was sort've ambiguous.

What did you do for this part, and how did it turn out?

Probably best to put it on #2. The problem is that one cap belongs on #1, and the other belongs on #2. With a dual cap you only have one ground, and you have to do one or the other.

Or

You can do what I did. Use two caps. The left cap goes to #1 (see the lead disappearing through a hole on the board), and the right cap goes to #2.

[BAinFL]

Day 1

Progress: I got the irons, tube sockets and 32uf can mounted.

Issues: The Classic Tone PT (40-18046) and choke fit perfectly. The OT (40-18026) was off by maybe a 1/16" in George's chassis so I had to work the screw a bit through the mounting foot at and angle until it would seat itself flat. Took a bit to get it in, but the end result is that it's sitting flush and I didn't have to drill anything.

Question 1 -OT wiring orientation: (see pics). In the CT OT the common is purple and the 4/8/16 OHM are Orange/Yellow/Green respectively. I hope I got it right that these 4 wires are the ones facing the PT. In addition, I routed the common through the hole closest to the front of the amp and the 4/8/16 OHM through the rear grommet. Is this correct?

OT wires #2: The Metroamp OT diagram showed specific routes for the Brown wire to V6 pin 3, Red wire to V5 pin 3 and White as CT. The Classic Tone schematic only lists their blue/white/red wires as 1.7k OHM. Can anyone sort me out on what goes where for these 3 wires or their equivalent to the Metro C 1998?

Next steps:

Build my amp cradle
Sort out Larry grounding points
More soldering practice then wire heaters andpower board

For anyone following at home the CT PT and OT wiring is as follows:

PT (40-18046):
Common (Black)
120V (Brown) 220V (Blue) 240V (Violet)
HV 350V (Red/RY/Red)
98V Bias (Gray/Gray)
6.3V Heaters (Green/GY/Green)

OT (40-18026):
Common (Violet)
4 Ohm (Orange) 8 Ohm (Yellow) 16 Ohm (Green)
1.7 Ohm (Blue/White/Red)

[BAinFL]

[BAinFL]

A couple hours browsing the search returns and I think I've found that the OT primaries should be

BLUE - V6 Pin 3
RED - V5 Pin 3
WHITE - CT

http://www.classictone.net/40-18026.pdf

[vh junkie]

I suspect you are correct on the OT wiring... as insurance you can connect the red wire to v4 instead of v5... that way the wire will be long enough if you have to swap... if it turns out everything is OK you can shorten the wire and move it to v5 if you like...

[Tone Slinger]

Nightowl had a great build manuel.

[BAinFL]

Day 2-3

Progress: V4-V7 Heater wiring is 100% done

Issues: I'm not 100% happy with my red/black lead dressing. I got 3-4 full turns between each socket and was happy with my mechanial contacts of my solder points I decided to leave it as is. It doesn't look as clean as I would have liked, but since this is my first build, I'm not going to stress over it.

Secondly, I broke a rule of working in short periods and screwed up as a result. 2-3 hours at a time - max. I'm going to follow this from now on. I connected the orange wire on V6/V7 and the Green on V4/V5 to pins 5 instead of pins 4. This was really my first major fubar of the build. I used some copper wire braid to remove the solder, but I cursed myself a bit for making really secure mechanical connections. Going to stick with a half turn and let the solder do the work from here on out. I cooked pin 5 on V5 a bit with the iron when removing the solder. I cleaned it up a bit with a wire brush and hope it should be OK. Connecting the Xicom 5W to that pin was fine...no issues with the solder sticking.

In all, the heater wiring was pretty straightworward, but more stressful than I expected. By the time each socket filled up with connections it was pretty hairy getting things "just right". Kudos to the builders out there who make this section of their amp look so neat and tidy.

Finally, I decided to go with standard grounding. First reason was that my Green/Yellow heater CT wasn't near long enough to reach the far end of the amp. And I really wasn't sure on moving it to position 4, etc... and how that might impact other things. Secondly was that after reading and looking at pictures, I couldn't still fully grasp all of the changes requred, especially as related to the back of my turret boards. Once I've built one with standard grounding I think I'll have a better grasp of what goes where and will be able to more easily incorporate the scheme's variations.

Question - PT heater pins: Is cooking one (and then cleaning it up) something I should worry about? I got most of the carbon char off it and the 5W Xicom seemed to have a clean connection, but I definitely cooked that pin a fair bit in removing the green wire.

Next steps:

Finish V1-V3 wiring

Going to skip ahead towiring the power board and main turret board. I don't have panels yet, so the OT, indicator and speaker jacks will have to wait a bit. The boards should keep me busy for a while.

After that I'll probably start on the Alpha pots. I built a jig for them (saw it in a Tube Amp Garage video) and will build these outside of the amp. Will be a nice relief from the tight spacing of soldering the heaters.

[BAinFL]

[vanhalen5150]

The only thing I can see that may be a problem later is your heater wires. A few places your black wire is running fairly straight with the red turned around it. It may not make a difference but its better to get that stuff corrected if needed. Dont wait until take off to realize you got the wings on upside down. With these 12000's its the little details throughout that add up to a good sound in the end. You may get some excess hum from that, but its hard to say until the end.

It's probably of no consequence, but just be aware of it.

[BAinFL]

The only thing I can see that may be a problem later is your heater wires. A few places your black wire is running fairly straight with the red turned around it. It may not make a difference but its better to get that stuff corrected if needed. Dont wait until take off to realize you got the wings on upside down. With these 12000's its the little details throughout that add up to a good sound in the end. You may get some excess hum from that, but its hard to say until the end.

It's probably of no consequence, but just be aware of it.

Thanks for the tip 5150 Should be easy enough to correct. Unfortunately not much build time available to me this week but I wikk go back and get that tightened up some.