Starting my 12xxx build

[Roe]

hum is a problem in the preamp more than the poweramp (the push-pull poweramp has a humbucking effect)

[vanhalen5150]

I guess I mean noise in general.

[vanhalen5150]

Where did you get that choke? 3H?

[BAinFL]

It's a Classic Tone choke (3H). I wanted to see what a full Classic Tone build sounds like. I really liked a lot of clips I've heard from builders using their hardware (and the price didnt hurt). I figure if anything, I'll try it and if I'm not happy I can always replace the OT and save this one for a 2203 build down the road.

My twists look decent from V1 to V4. It gets a bit messy between V5 and V6. Maybe I'll just rewire that section.

[vanhalen5150]

It's just one of those things that kept me up at night. My first try was terrible. I tore out the whole heater wiring and did it again. Lookng back it wasn't that bad.
You learn lots of stuff later. Go back and tidy things up then as well.

[BAinFL]

I took a short study break last night and wired my power board and cleaned up V5 somewhat.

I have 2 clinicals this week, a paper and two tests (finals) on Tuesday. So no amp building from me for a while =/

I need to get my backplate situation sorted out ASAP. I can see that will be my bottleneck if I don't get it soon. I've been holding off ordering anything trying to get both from a single source. I had half a mind not even bothering with a backplate at all but figured spacing on the socket threads might be an issue. Still scratching my head on what to do about this one...

[BAinFL]

Is there any polarity orientation I should be concerned with on the Xicom resistors on the heaters? I just noticed now that mine are reversed from other pics Ive seen.

[Roe]

Is there any polarity orientation I should be concerned with on the Xicom resistors on the heaters? I just noticed now that mine are reversed from other pics Ive seen.

1 those should be on the screens, not the heaters.
2 resistors don't have polarity

[BAinFL]

Been neglecting thios thread for a while...building in chunks between school assignments, clinicals and tests.

Anyway, I'm coming down the home stretch.

Power board, switches, fuses, input jacks, power cord done.
Main board jumpers, leads and components all complete
Lar-Mar wiring in place to main board and V5/V6

Left to do: Mount main board, connect Lar-Mar connections to dual pot.

2 questions...

1. For the Lar-Mar, I'm routing the shielded connection and blue wire underneath the main board...any problem with this?




Wrea398 mentioned that I should use a 33k bias dropping resistor in place of my 27k because I might have problems biasing . Can anyone explain to a noob the relationship between this resistor and the 47k or 68k (not sure what it's functional name is...the resistor in the Bias section following the 15k) I've seen the 27k used with the 47k (what I had originally) and have seen the 33k used with a 68k, but never a 33k + 47k,,,so I wasn't sure which combination I should use...switch only the 27k to 33k or also swap the 47k to a 68k. I hope that makes sense...sorry for not knowing the proper name for the 47k/68k

Thanks y'all...I feel like I know all you guys and your amps personally. Reading everyones journal and looking at all the great pics has been an unbelievable help to this first timer. With any luck I'm hoping to finish the main board connections tonight or tomorrow and hopefully juice this thing up on Saturday!

[BAinFL]

Finished the build a couple hours ago. Troubleshooting went great until I got high readings on V1-V3. Searched a few topics and checked a few connections...nothing worked so far.

Here's what I have so far (posting only abnormal values...if not listed it matches whats in George's table)

12AX7s INSTALLED
Power Tubes NOT INSTALLED
MAINS = ON
STANDBY = ON

(V4-V7 are perfect values)

V1 P1 466 P3 0 P6 466 P8 0

V2 P1 467 P3 0 P6 471 P7 465 P8 0

V3 P1 467 P3 0 P6 214 P7 11 P8 16


Any ideas what area to focus on. I've got clinicals in 5 hours and need sleep. Hope someone can point me in the right direction for tomorrow.

As always...many thanks!

[BAinFL]

Sorry for not posting pics last night...I was up much later than I should have been.

Hope someone can point me at possible component leads (or section of the board) to check based on my voltages. Giving it all the once over, I didnt catch anything last night. I'm wondering why I saw close to normal range for pin 6 of V3 but everything from V3 Pin 1 on down was double (or higher) than it should have been.

Could a bad 12AX7 cause this? Should I swap them out? Or is this most likely a bad or open connection someplace

Again - many thanks. Hopefully someone sees this over the weekend and can help me sort this out. I have the next 2 days off and I'd love to jam thru this thing already! =)

[wrea398]

Check all of your solder joints again. In one pic some of them look a little short of solder. Some of your readings are ZERO when they should have voltage (like PIN3). You should have a nice clean and fairly shiny blob of solder on top of the turret, wire, connection. I would then check all connections with a continuity tester. Here is what I do as it works for me. You would need to start on total opposite ends of each connection. DO NOT TEST SOLDER TO SOLDER. If you just touch the tester leads to the solder joints on each end of the wire, you could easily see good continuity because you are really only checking the wire itself (solder to solder), but the wire may not be firmly connected to the components on each end. With all power OFF, pull the preamp tubes and put one tester lead into the preamp tube PIN # of your choice (on the tube side of the socket) and put the other lead on the corresponding turret base on the board (below the solder joint where it meets the board). This way you eliminate the possibility of a cold/bad solder joint. I learned the hard way. Since I do this, I have never had a problem with connections.

Also... do the same test between heater wire solder joints. Start at V1 with one lead and V7 with the other. Do red and then do black. If it BEEPS then from V1 to V7 you should have good connections. Check all grounds the same way.

This is all very easy to do and wont take 30 minutes to check all joints.

[BAinFL]

Thanks a ton Wrea!

[wrea398]

No problem...Your wiring and components looks good in the pics as I can see. If all wiring is located where it is suppose to be, I would start looking at components. Resistors do just that...resist current. Check your resistor values. You have way too much current in certain places. Also just something stupid....make sure your meter is in the correct AC or DC position when reading. (I made that mistake a few times in the past too). Some of this stuff sounds dumb but most of the time "IT IS SOMETHING DUMB", lol.

[BAinFL]

Had a cold solder on V3 heater.

Only values off a bit are on V3...everything else is 100% now

my value / (georges guide)

V3 pin 2 14.2 (26)
V3 pin 3 20.4 (42)
V3 pin 7 14.5 (27)
V3 pin 8 20.2 (42)

Gonna keep checking around...