new express power up problem/question

[pinkmarkos]

hey guys- i fixed the jumpers on the 9k1 resistors (must have been the problem)- but now i am moving down the line of problems
my B+ voltages are better now, but still not quite correct...
B+1- 413v, B+2- 407v, B+3 328v, B+4 311v, B+5 294v
my v1 voltages are still way out- v1a plate 112(210) V1a cathode 4.9(1.9)
v1b plate 290(182) v1b cathode 4.6 (1.6) so i am now stumped. my v4 and v5 voltages are still pretty close, but v1, v2, and v3 are still way off. any ideas?
BTW- heatshrink on r18 and 19 is a good idea and i will do it, clearance now about a mm

[paulster]

When you say V1a do you mean the first gain stage (actually on pins 6-8) or pins 1-3? If you swap the figures for the two V1 triodes around then you're pretty close, but that might just be coincidence.

Now that you've got your B+ dropper resistor jumpers sorted out, just make sure that the B+ lines under the amp board are correctly connected as well, so measure the B+ voltage at the top of the respective plate resistors as well for V1, V2 and V3.

[pinkmarkos]

when i say v1a, i am referring to the voltage chart in the build guide which has v1a as pins 1-4 and v1b as 6-9 with 4 and 5 jumpered. i also traced all the B+ voltage through the underboard jumpers and all is well. i have a couple of new suspects- no voltage drop across r3, and i'm getting a really loud pop at the soldered joint of r9 and the jumper to pin 1 on v2 when i check the voltage. so i will work my way down the line looking for problems. thanks again and i am still open for more suggestions- MP

[Structo]

Using a light bulb current limiter is a good way to power up an amp the first time if you don't have a variac.
It will give you a visual display if there is heavy current draw or a short circuit possible saving expensive parts like transformers and tubes.
I used a 60 watt bulb in mine.
It will throw the voltages off a bit but it is a good way to form the caps and show any serious wiring faults.

[IMG:800:618]http://i23.photobucket.com/albums/b392/ ... iter-1.jpg[/img]

[pinkmarkos]

thanks again for this info- the build guide has this info but i must have wired it incorrectly because I got some fireworks. these instructions are more explicit so i believe i will try this again. this being my first build and really first experience delving into electronic circuitry in any form, stuff you guys take for granted is new to me. my learning curve is very steep. i appreciate the patience of the forum members because i believe we all share the same goals- great music=great guitar+great tone. right? thanks again

[Structo]

For Gods sake be careful!!!!

A nasty shock can hurt like hell!

A shock across your chest can kill.

That's why you never want both hands inside the amp.

[pinkmarkos]

no- i didn't mean the amp itself! i meant the light bulb limiter. i have been draining the HV from the caps with a bleeder resister before every time i put my hands in the chassis just like the build guide says. i understand exactly what a high voltage conducted through cardiac muscle can do, i work in an ICU as a nurse. i wasn't clear before what i was referring to.

[Structo]

Ok, you convinced me

Then you know it takes less than 300 ma to stop your heart or get it going again.

Even experienced builders can make a wiring error.
But they usually won't cop to it!

So your voltages still aren't where they should be, check out your resistor values, make sure you have the right ones in the right place.
Sometimes those darn color codes can be a biatch.

Knew a guy that was color blind, he had to measure everyone and label it or he couldn't tell what it was.

Check your grounds, look for missing grounds, bad solder joints, etc.

It's funny I was helping a guy with a 18 watt build and he had looked it over 100 times. He finally sent me a picture of it and I saw right away that one of the wires on the board (actually it was an under board wire) was connected to the wrong place.

I'm not bragging, it just was apparent when I looked at it.
So coming at it with a different perspective or walking away from it for a day or two can sometimes be the best thing to do. Because then you come back fresh and will see things you missed.

Good luck on it. I'm sure you'll get it right.

[Structo]

Not sure if you have it but I have found this little program indispensable for understanding tubes.
It's the Duncan Tube Data Sheet Locator.
It will show you the pin-outs of any tube, the ratings and links to data sheets.

For example if you don't know that a 12ax7 is a dual triode and that it contains two tubes in one or that pins 1 & 6 are the plates (anodes) and that 3 & 8 are the cathodes, 9 - 4 & 5 the heater pins.

It really helped me.

http://www.duncanamps.com/tdslpe/

[Ron Worley]

Yikes, I really never thought about it... that guys new to amps would be following my words in the build guide that closely....

I sure wish more experts would look it over so that I'm not giving out bogus advice based on my own ignorance....

I really need to do a revision on the guide, but this working for a living seems to get in the way...

[Structo]

If you aren't getting voltage on R3, do you have the underboard wire going from the junction of R3 and R6 to the B+5 turret which then goes to the + side of C20?

That should be one wire, that is uninterrupted to the turret for B+5.

Same on the R9 resistor, that underboard wire should go to the B+4 turret then to the + side of C19.

[pinkmarkos]

yes i agree this working for a living does get in the way .
i will take the advice about giving it a rest for a day or so, then return to troubleshooting. i am a newb but i do understand how tubes work conceptually. i have copies of the data sheets for the tubes i use.
answering the B+ question, yes I have traced all the B+ underboard wires and they all appear to be good. i will just have to keep tracing backwards until i find the error. thanks again for the suggestions- MP

[fishy]

Looks like your making good progress.
The B5 issue appears very much as previously pointed out. I've traced a bunch of signals before and said they were fine only to be proved wrong at a later date when I look again. A fresh start makes sense after a break from it.

Keep this up and you should be in business very soon.

[pinkmarkos]

hey guys- i found my main voltage issue- i had forgotten to ground the jumper going from C1/R2 to the volume pot. when i fixed that, all my voltages fell into line. they are just now about 10 volts above where they should be to v1, v2 and v3 . however- my new issue is that my volume level is way quieter than it should be. with everything at 12 o'clock, it is quieter than my other amp at 1 watt. it also sounds like i have some hum and oscillating as well. so i know i still have to rule out tubes, set power tube bias correctly, and go through the rest of the troubleshooting steps, but i feel like i am making progress. thanks again for the help will keep you posted

[paulster]

It sounds like you're making good progress.

One thing you can do is to print out another copy of the layout and then go through it wire by wire, component by component, and cross them out on the layout one at a time once you've verified the placement in your actual amp.

Doing it like this forces you to switch off from glancing at the amp and thinking it looks okay, to undertaking a methodical check-list approach which can help to identify anything wrong.

In your particular case I'd be checking the tonestack wiring and ensuring that all resistor values on the amp board are correct as one of the first things I did.