I fired up my new build and voltages seemed to be ok until I got to the PI.
Here's what I got on V3
1-337v
2-1v
3--5.5v
6-341v
7-1v
8-5.5v
I did a quick measurement and when they looked really high I shut it down and changed the tube. We'll needless to say that didn't help. There didn't seem to be any sound either... not hum or hiss. I've checked my wiring and can't find anythntg, what should I look for?
You plate voltage is quite a bit high. Did you measure B+3 before the tubes? B+3 should be in the 290 to 300V range, but that's dropped down by the plate resistors to about 200V on the plates.
Conversely, the other measurements are quite low.
I'd take a couple of shots around the PI and the power cap that feeds it and post here.
For some reason the plate resistors are only dropping 5v not the 100v that they should. The 82k I got was actually 8.2k so that is now 100k, not that it really matters.
I checked the presence pot and resistor and that seems fine. FWIW all my voltages are just a little over (5v-10v) what the voltage chart shows.
The resistors measure correct so why don't they drop the voltage?
I'll try to find some batteries for my camera and get some pics so I can get some fresh eyes on it.
Plate resistors won't drop voltage unless the cathode connection is correct. Hence the advice from jjman to check the cathode and tail resistors (and the presence pot connections).
tubelovin wrote: For some reason the plate resistors are only dropping 5v not the 100v that they should. . .
FWIW all my voltages are just a little over (5v-10v) what the voltage chart shows.
First concern is as the others have stated, the PI. Kinda wondering about the B+3, If it's 342V, that's definitely high, and something to look at, after the PI. Once you get more current flowing in the PI, that should come down.
Well I think all my grounds on the PI are good. I used the typical ground buss on the pots and star ground for the filter caps just like the layout. I even went ahead and reflowed a bunch of joints but that wasn't it.
I don't have the diode string on my power tubes, would that have any effect? I was under the impression that it was only a safety device.
Here's a shot of the PI and caps, do you guys see anyhting obvious? Earlier, I disconected the presence pot and put in a jumper from the tail to ground... nothing.
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What's with the 460K bias resistor? shouldn't that be a 820R with a 10K tail
<edit> actually I think it's worse than that. It's a 460K. Can't push much current through that.
Last edited by skyboltone on Mon Jan 19, 2009 9:13 pm, edited 1 time in total.
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
It actually looks violet, which would make it 470k. I thought it was 470 Ohms (not 820), but in either case, that resistor is waaaaay to high.
<edit> What is the value of the resistor directly attached to the bias pot? It's supposed to be 47k, but there is no green.. If you changed it to bias up with your current setup, might need to revisit that after fixing the PI resistor.
Last edited by gearhead on Mon Jan 19, 2009 9:19 pm, edited 1 time in total.
gearhead wrote:It actually looks violet, which would make it 470k. I thought it was 470 Ohms (not 820), but in either case, that resistor is waaaaay to high.
Yeah, I don't build many of those so I'm not sure what's it's supposed to be. It ain't that though.
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Yep, right under my nose. Thanks for pointing out my newbie mistake . I even measured it with my meter and still didn't notice.
I would have probably stared at this thing for another day until I rebuilt and noticed. Thanks to your eyes and experience, I definately learned a few things on this build.
Now my only problem is that now all my neighbors are home and this thing is freakin loud!!! Airbrake here I come
. I even measured it with my meter and still didn't notice. 
