12XXX Build 05/2010

[vanhalen5150]

So your on HI volt with the switch pushed down towards the bench with the amp inverted? Check you meter scale and get the bias to -35mvdc on pins 1 & 8.

Correct.

[vh junkie]

I meant swap the highest tube! Well actually the highest negative tube!

[vanhalen5150]

That's good for now... significant difference, but not a game stopper. Power down and move the lowest tube to the other side of the quad... does the low voltage follow the tube?

Ok, yup....... it followed the tube with a V4 V7 swap.

[vh junkie]

OK, now switch the amp to LO mode, and adjust the pot on the switch to -43mvdc on the highest tube... this assumes that your plate voltage drops to around 400vdc...

[vanhalen5150]

OK, now switch the amp to LO mode, and adjust the pot on the switch to -43mvdc on the highest tube... this assumes that your plate voltage drops to around 400vdc...

Done, -42.9mvdc

[vh junkie]

You're ready to play! Monitor the voltages on all the tube biases as you play, they will increase dramatically as you bang on it, but should come back to rest. Gotta watch for red plating, watch the tubes, usually a weird MWAAHHH comes out the amp! Not a good time to do an overnite burn-in! If it is gonna redplate should do it within a half hour of playing with it dimed.

I still don't know the answer to the best way to breakin the caps... if your only gonna do LO V mode then just stay there, otherwise I don't no the best way to go.

Don't start modding till you have played at least 100 hours on it!

[vanhalen5150]

Ok, Ill just stick it in the head box and plug in. Time for a beer.......

Thanks alot guys. Thats much aprreciated.

[vh junkie]

Geez! I'm not sure mine has ever been in a head box! You really wanna keep it on the bench to monitor the bias voltages... as it breaks in the tubes may begin to change their character!

[vanhalen5150]

Ok, plugged in, on standby a little hum. Low and High power....quiet as a mouse!

Only problem is its already at room volume with the volumes on 0.

[vh junkie]

If your playing straight into a speaker it will be loud from the get go!

I had problems with original JJ EL34Ls that came with the amp and got lotsa redplating... the tubes will change their character over the first hundred hours... got some tubes from TT that seemed to work great for a while then one started to go off the reservation... went to winged Cs... but finally got back to JJ EL34s(not Ls)...

Give it some time and watch for red plating, monitor biases!

[vanhalen5150]

When I dime the tone controls gets a little more hiss, but not much. When I turn the presence, gets a dull scratchy sound but stops when pot stops.

[vanhalen5150]

What specifically do I watch for in regards to red plating?. Just the bias shifting and staying there?

[vh junkie]

Watch the tubes and listen for the MWWAAHH! Never had time to look at the bias when this happens... just turn off!

As long as your getting a nice crunchy sound should be good... real test will come when your dimed, hopefully reamped then watch for redplating.

In other words, the bias might shift without the redplating. You will probably get better tone if the tubes are not identically biased, but you need to watch all of them to see where they want to go

[vanhalen5150]

Not sure what MWAAAAH sounds like but I havent heard anything alarming yet. Why would it be noisier on standby?

I had it on 3 and the volume is huge......killer. Ill slave it on 10 later tonight after playing a bit and leaving it on for a few hours.

[vh junkie]

Why would it be noisier on standby?

No clue on that one... on standby (switch in the middle?) only thing happening should be tube heaters...

Geez! I hope I can be one of the godfathers! Lemme know when I can smoke a Cuban!