My X10 has begun

[selloutrr]

can you test with continuity or tone that everything is wired correctly through the circuit. nothing is shorting or bridged under the board that we can't see. all solder points are good. all grounds are secure.

[surfsup]

The metal backing of the NTE is laying on the chassis I believe. There was a thin piece of plastic with it but I thought it would prevent heat transfer, so I didn't use it. The NTE leads don't touch anything though.

[selloutrr]

do you get the correct voltage out of the PT?
did you figure out if the PT's CT is grounded?

Edit: which LED doesn't light up?

why is the toggle switch by the input jack not wired to anything?

did you get your input wiring figured out?

[Gee]

The metal backing of the NTE is laying on the chassis I believe. There was a thin piece of plastic with it but I thought it would prevent heat transfer, so I didn't use it. The NTE leads don't touch anything though.

That's a problem. It needs to be electrically insulated with that thin shaped spacer, from the chassis. It might be fried.

[surfsup]

Yea I see that now in CAPS in the VVR instructions damnit! How the hell did I miss that when I have been so anal-retentive about the design of this amp?

do you get the correct voltage out of the PT?
did you figure out if the PT's CT is grounded?
Edit: which LED doesn't light up?
why is the toggle switch by the input jack not wired to anything?
did you get your input wiring figured out?

PT out was 333? before the 1k 5W Rs with only the main on
462V after the diodes (333*1.4=462)

333 is a bit high, since the 1k 5Ws are burned I will up the R value and Wattage if they can fit between the turrets

PT CT is grounded in my amp and the schematic, I am wondering if that is correct myself.

The LED on the panel didn't light up.

Its the bright switch, didn't add the two pF caps yet (doesn't affect anything really except tone). Since I have the pullpot, I thought maybe its not necessary yet.

Yea I probed the input and output jacks and I *think* they are switching like most others, so they are correct (I think).

[pamaz67]

Hi surf.
I would try to set everything up taking out the VVR for the moment.
The isolation of the VVR mosfet is mandatory for having it working properly.
The Mos is gone.
So take the vvr our and start again the power up procedure.

[Gaz]

The B+ will drop to 300 when loaded - says so on the Edcor site. Not sure why the resistors burned up. How may volts were you trying to drop there? Perhaps they just over-dissipated, or else it seems like there's a B+ short to ground. Pazmaz is right when he says you should get it going without the VVR first.

[surfsup]

Maybe I'll take the VVR out. Gaz, here's my math for the rail, 63V drop for each resistor. I do calc 3.9W for the 1k 5Ws but aren't they only "on" half the time? Mouser: 588-45F1K0E (same as the Xits build)

[img:450:172]http://chicagocadcam.com/ChrisHahn/xen10/voltages.jpg[/img]

[Ian444]

If the VVR needs insulating from the chassis, and it sounds like it does, then if it is NOT insulated it will probably short the B+ to ground, which would cause the 1K resistors to smoke up. Lets see, 330V for example shorted to ground through 2 x 1K resistors = 0.165A. Power through both resistors = 330 x 0.165 = 54W. As suggested earlier, disconnect the VVR, or replace the mosfet and insulate it, and have another go. No need to doubt the rating of those 1K resistors, the first problem needs to be fixed and then you can move forward. Makes one realize that fuses can't protect against everything I guess.

[pamaz67]

333Volt is not so terrible, at least not to the point that everything is transformed in smoke.........
rememner that an Ac30 design is always far to be defined conservative compared to the EL84 dissipations limits
So, don't bother on that value for now.
Turn it on without the vvr.
And you'll immediately understand whether the amp is working or not.
Don't change the 1k 5W resistors by now
Paolo

[surfsup]

pamaz, I ordered four 1k 5w ohmites, same as before, just now from Mouser along with all the resistors and caps for a Rocket. Should be here early next week.

I also ordered a 3.3k and 5.0k to swap for the 1k 3W I have in there now to supply the PI. This gives me several options to try:

1k - 325V at PI
3.3k - 315V
5k - 305V

I ordered a spare mosfet but will see if I can test the one I have now to see if it works before I chuck it. I read on many sites for mosfets if they look fine they probably are. If they fail, they usually burn up. Since mine looks fine it might still be good. Don't worry, I'll swap a new one in this build.

[pamaz67]

surf, the external appearence tells you nothing at all.........
It's a good occasion to learn how to test a mosfet with a tester!

[surfsup]

Keeping this simple regarding the 1k 5W wattage rating. taking 12W as max dissipation and 330 volts on the plate:

12w/330v = 36mA draw
screen = 10mA
3x12ax7 = 5mA

This is 51mA

0.051 * 0.051 * 1000ohms = 2.6W so the 5W being double should be okay. I assume it is if Xits used them but just want to understand this. At 90% dissipation, its even less.

[rhinson]

Keeping this simple regarding the 1k 5W wattage rating. taking 12W as max dissipation and 330 volts on the plate:

12w/330v = 36mA draw
screen = 10mA
3x12ax7 = 5mA

This is 51mA

0.051 * 0.051 * 1000ohms = 2.6W so the 5W being double should be okay. I assume it is if Xits used them but just want to understand this. At 90% dissipation, its even less.

the coating on those type of resistors do smoke sometimes when they first get used and heat up pretty good---i've seen it before. btw on all power resistors like this you should float them up in the air and not keep them down right on the board---the wattage ratings are "free air" ratings, meaning they need air flow all around. also if you look at the xits board pics, the ones in the amp look kinda toasty as well rh

[FunkyE9th]

Keeping this simple regarding the 1k 5W wattage rating. taking 12W as max dissipation and 330 volts on the plate:

12w/330v = 36mA draw
screen = 10mA
3x12ax7 = 5mA

This is 51mA

0.051 * 0.051 * 1000ohms = 2.6W so the 5W being double should be okay. I assume it is if Xits used them but just want to understand this. At 90% dissipation, its even less.

Below are plot simulations of a very simple full wave rectified power supply...
It's a 300-0-300 PT, with 1K resistor before the rectifier diodes. It only has 1 Filter cap (47uF) driving a 12K Ohm load to keep it simple.
It's very similar to a Duncan PS simulation.
This simulation ignores the PT's DC resistance.

The 1st plot shows the voltage charging to about 327V and you can see the ripple on the supply.

The 2nd plot shows you the current (red) through the 1K resistor and the 12K (green) load. You'll see that the 1K resistor is pulsing at 97mA max! The 12K load (simulating your tubes) is seeing a steady 27mA. I am not saying your tubes will only draw 27mA. All I'm saying is what the tube draws is not the same as what the 1K resistor is seeing. So I don't think you should decide on the power rating of the 1K resitor based on how much the tube is dissipating. Also tube current is going to go up at full power (i.e. when the signal is applied on class AB) which will also make the current through 1K resistor go up. What you calculated is current at static conditions. What happens when you apply a signal...the current will go up and the plate voltage will swing low and then current goes down and plate voltage goes up.

Another thing interesting with the current plot... the 1st few pulses are even higher. This happens when you 1st turn on the amp and the cap is not charged. The cap looks like a short. If you ever wondered why tube rectifiers specs tell you to limit the size of your 1st filter cap, that is why. The bigger the cap the bigger the pulse. Then once you hit steady state the pulses get smaller. If you look at a 5Y3 spec it gives you current limits for Transient and Steady State conditions.

There is more info on Merlin's site where he talks about power rating of the limiting resistor http://www.freewebs.com/valvewizard/fullwave.html

I am really wondering what those 1K's are for. It's too big for current limiting purposes or for simulating sag. So maybe it's for dropping the voltage because of the high HT. If it's there for dropping, there are better ways to drop it especially since you are using a VVR.