12XXX Build 05/2010

[Omn]

Remember the purple NFB-wire... It "needs air" - will pick up noise if it is close to anything.

[Omn]

And for the fluxing voltage; I had to get me an other multimeter. The old one was all over the place. So; it could be the meter...

[vh junkie]

Probably best to get the tubes out until we iron out the voltage issues.

With dual voltage switch off (middle), power on:
Only the heater voltage should be measured on AC settings:
Should be 6.3vac between the red and black heater wires on the preamp sockets.

Now switch your meter to DC testing. Turn the amp on the high voltage setting.
Let's take some measurements on the tub side of the board:
1) Where the two inline 10k res meet the blue wire
2) Each side of the 10k that is hanging off the side of the board.

[vanhalen5150]

Thanks for the help fella's, much appreciated.

I'm going to take out the tubes and check them in another amp. Got a new tester. I'm confused about the 3 way switch positions. Miiddle is off, up is 120, down is 95?

Girlfriend wants me to take her out for lunch, what is she thinking? Doesn't she understand, I've got important stuff underway here! WTF........

[Roe]

Voltages may be a little high without the load from the tubes. How are the other voltages? Look at the chart with the 100 w instructions. Are the fuses FastBLO (like what George would give you?)? ARe they holding up?

Important to remember that some voltages are DC and some are AC in the chart but it is not really clear. Let us know what you have on the pins.

Yup, just going get a new tester. Wierd because V1 pin 1 shows no voltage, but unplug and bleed from V1,pin 1 it shows 154v and then disapates to 0.

Hmmm....

reflow on v1 and v2

[vh junkie]

I'm confused about the 3 way switch positions. Miiddle is off, up is 120, down is 95?

Depends how you have it wired. Need a better pic of it. For now just put it whichever position gives higher voltages on the places I asked about.

Gotta keep the tubes out til we go through the voltages else put tubes and/or OT at risk. Don't forget if the tubes are in you need a speaker hooked up.

[vh junkie]

Girlfriend wants me to take her out for lunch

If you fellas up North celebrate Mother's Day, it gonna be hard to find space anywhere!

[vanhalen5150]

Girlfriend wants me to take her out for lunch

If you fellas up North celebrate Mother's Day, it gonna be hard to find space anywhere!

Yeah we do. Bad timing. Ill check this all out this afternoon. I have it on a 16 ohm 300 watt resistor.I have a chart Ill fill out and post so you guys can have a look. I only had it on and off for a toal of maybe about 10 minutes yesterday and shut it off when the voltages were no making sense.

Anything to do with "cap forming"?

[vh junkie]

I was hoping the voltage looking weird was maybe because you were measuring on AC instead of DC. Bad battery in a digital meter will also make it read crazy. I have that read 20v to high when the battery gets low.

Voltage chart is a good idea.

Cap forming will not significantly affect the voltage. I thought these newer caps were pre-formed anyway. Does bring up an interesting question:
If they do need further forming or breakin, what is the best way to do it with the dual voltage option?

You need to get the amp working with the higher voltage first so you can get the bias dialed in on with the pot on the PTP board ( about -35vdc @ 500 plate v), then you leave that pot alone, switch to low voltage, and adjust the pot on the back of the switch until you get the right bias for the low setting (about -43vdc @ 400 plate v).

[Strat78]

Thanks for the help fella's, much appreciated.

I'm going to take out the tubes and check them in another amp. Got a new tester. I'm confused about the 3 way switch positions. Miiddle is off, up is 120, down is 95?

Girlfriend wants me to take her out for lunch, what is she thinking? Doesn't she understand, I've got important stuff underway here! WTF........

The girlfriend has no power until you hand her a ring. Up against a 12XXXX she is at a great disadvantage at this point. Better iron out these relationship details now, because they will make or break things down the road (and will cost you a hell of a lot more than what a real 1968 amp would go for).
I should get my kit by the middle of this week (and the divorce papers if the wife finds out), totally sick with anticipation (for the kit that is)!

[vanhalen5150]

V1 Pin 1 is measuring 380.
V2 pin1 is 280
V3 P1 is 480.

Your right I was measuring AC. I'll leave my mistakes for those that follow.

[vanhalen5150]

Ok, new multimeter. Set bias pot halfway. This is what I got.

Following the Nightowl instructions, middle is standby, up to "Standby" Logo is high power, down to "On" logo is low power.

[Omn]

Looks good to me.

[vh junkie]

That all looks good to me!

Not sure about the bias voltage... what does it read on pin 8 of the Power Tubes?

[vh junkie]

Whoops you already said what it was! Adjust it to the lowest (closest to zero) negative voltage with the bias pot, then power down and install the tubes.

Power up and adjust the pin 8 voltage up to to -35mv.

EDIT: Do this with the volume pots all the way down