fet dont get dead or fry'ed all by themselves. What caused that to happen? prevent the next fet from the same fate.
-RNM
-RNM
Did it twice myself. It's easy to slip with the screwdriver. One short to the metal case and it's toast. Went to a plastic pack PN4392.
Hi all -- Yes I meant PN4091 or 2, sorry, old guy, lousy memory. And Sync, yes, I meant scope the drain of the FET. If you look at that circuit, the maximum possible resistance for the ground leg of the feedback loop is set by R53, 200 ohms, if the FET is open, and the minimum possible resistance is set by the parallel combination of R53, 200 ohms, and R52, 100 ohms, if the FET is a dead short, which is 67 ohms. A working FET will put the ground leg resistance between these two values. The circuit requires a gain of about 34 or thereabouts for stable operation. So you can see what the FET needs to do. Nominal gain = 34, pillar leg feedback resistnace is nominally around 4k, so the total ground leg R needs to be about 120 ohms, so the FET will be a resistor of about 200 ohms or so....
BTW, did you remove the two diodes at the output of the opamp, CR7 and 8? You must do that too.
When you look at your spectrum plots, it's the ratio between the fundamental level and the largest distortion product that is of initial interest -- the buffer amp didn't clear anything up, the crap just went into the noise floor because the fundamental at the buffer output is so low.
BTW, did you remove the two diodes at the output of the opamp, CR7 and 8? You must do that too.
When you look at your spectrum plots, it's the ratio between the fundamental level and the largest distortion product that is of initial interest -- the buffer amp didn't clear anything up, the crap just went into the noise floor because the fundamental at the buffer output is so low.
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I have some of the original jfets stashed away back home if the others dont work for you.
THx-RNMarsh
THx-RNMarsh
@ RichEEM, Yes, I removed them, CR7, CR8. I left in the
R27, R28, as I didn't think they would matter.
@Richard, Yes, of course the JFET didn't just magicly fry itself.
It's not something I really like to broadcast.... A screw up.
I've been doing a lot of that lately it seems--Growing pains.
For lack of a better term, I fat fingered it. There is not a lot
of space in there now with new caps installed and parts connected
to TP8, the oscillator amp pin 6, etc.
Most of my test leads are big for hi voltage tube stuff along with
all my supply of parts. I mean I'd love to put a teflon cap in there
but at 600V the part is so large it would eclipse a whole section
from one rotary switch to another along with 20 other parts below it.
I'll have to look around for a single molex connector to push down
on the Test points.
HOLY COW - As Harry Carey used to say, we sure do need a lot
of connecors and jacks and test equipment for this stuff. To take
measurements, adjust, evaluate, etc, ya need a lot otherwise a lot
of time is spent setting up and taking down during measurements.
I appreciate the offer Richard, I might have to take you up on that.
When are you headed back from the Land of Smiles?
It's probably pretty nice right now...when are you headed
for the monsoon season?
If I recall correctly, aren't the satellite dishes pointing about straight up
there? Kind of a different site than North America with ours about 25 - 45 degrees (I think).
David what about Y'all in The Land of Canuk's are y'all about 60
or more degrees?
R27, R28, as I didn't think they would matter.
@Richard, Yes, of course the JFET didn't just magicly fry itself.
It's not something I really like to broadcast.... A screw up.
I've been doing a lot of that lately it seems--Growing pains.
For lack of a better term, I fat fingered it. There is not a lot
of space in there now with new caps installed and parts connected
to TP8, the oscillator amp pin 6, etc.
Most of my test leads are big for hi voltage tube stuff along with
all my supply of parts. I mean I'd love to put a teflon cap in there
but at 600V the part is so large it would eclipse a whole section
from one rotary switch to another along with 20 other parts below it.
I'll have to look around for a single molex connector to push down
on the Test points.
HOLY COW - As Harry Carey used to say, we sure do need a lot
of connecors and jacks and test equipment for this stuff. To take
measurements, adjust, evaluate, etc, ya need a lot otherwise a lot
of time is spent setting up and taking down during measurements.
I appreciate the offer Richard, I might have to take you up on that.
When are you headed back from the Land of Smiles?
It's probably pretty nice right now...when are you headed
for the monsoon season?
If I recall correctly, aren't the satellite dishes pointing about straight up
there? Kind of a different site than North America with ours about 25 - 45 degrees (I think).
David what about Y'all in The Land of Canuk's are y'all about 60
or more degrees?
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hi all,
Just à little Message to tell you i am still folowing thuis thread. I guess i got sidetracked for à year..but I still plan on fixing my 339a.
Lost of good info posten heer, thx !
Grtzz,
Thijs
Just à little Message to tell you i am still folowing thuis thread. I guess i got sidetracked for à year..but I still plan on fixing my 339a.
Lost of good info posten heer, thx !
Grtzz,
Thijs
Actually it's been rather warm here. At most -7 deg C. that's 19.4 deg F for the fokes down south.
Can't say I any sympathy for your frost warnings.
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Whadd-a-ya-mean??????
Don't tell me that you'd be wearing your shorts
and a tank top?
Heck just a little bit of frost on the streets and bridges here
causes major traffic problems.
Some of it is lack of experience down here.
AND
The other problem is anti-lock brakes and all the electronic
traction and other "fixes" the automakers implemented.
Even in snow and ice you can control your auto with a bit of skill
and cruising around an empty parking lot.
But, one time to me in utter disbelief I just cruised on through
an intersection applying my anti lock brakes that did no good.
with real brakes I would have built up enough snow under the
wheels to stop, but with anti-locks I just cruise through the
intersection red light at 2 mph like I was doing nothing.
I was just glad no one else was on the road!
I have 7 divided bins of adapters, terminations etc and 4 feet of cables and probes hanging on the wall to do this stuff. And, of course with all of this, two days ago I had to build an adapter from BNC to 3.5 mm jack. You will never have enough and never the right one.
Get a good scope probe. For small stuff the HP probes are the best. Larger stuff you want the normal Tek probes. And for tubes/HV the older Tek probes that are big. Buy them used in good shape. its hard to do as well with the third party new stuff.
Almost anything you need to do short of measuring distortion you can do with a scope. Learn how to use it and how to interpret what you see.
I return for 6 months in about a week (14th) and after a short time/sleep adjustment, I can do something I really enjoy -- electronics.
To prevent shorts with screw drivers.... if you dont use plastic adjustment/alignment tools ....... put tape or heat shrink over the screw driver shaft and only leave the metal tip exposed.
-RNM
To prevent shorts with screw drivers.... if you dont use plastic adjustment/alignment tools ....... put tape or heat shrink over the screw driver shaft and only leave the metal tip exposed.
-RNM
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Jimmy Carter and Habitat is doing Nepal next November, we plan to be there. Probably we will do Turkey as our extra visit rather than SE Asia this time.
Well that happened to me up here a couple of years ago. Only it was snow covered glare ice and I was driving a 550 dualy with an 8 ton lift on the back. Smashed the grill and dented the bumper. You should have seen what the dodge journey looked like. Turned out to be a customer of ours. A bandade lady.
David, that glare ice is that the same as what we call the black ice?
That is ice that you don't see because it looks like the road,
but you get no traction?
Or
That ice you can see that is thick, blinds you when the sun hits it
and when snow covered, it fools you into thinking its regular snow
until you go to stop, but then it's too late, you just slide along?
Demian, yep I have a bunch of good TEK probes and some good Fluke probes. Don't have any of the HP probes. I got a couple of old TEK
2246 scopes and the Fluke Scope meter.
The TEKs are good, but one is starting to go noisy on me and the traces
are sort of blinky for lack of a better word. I got them pretty low cost and
they were barely used. Now stuff is getting expensive...and some of the
ebay guys think they are worth big bucks when they are not.
Searching for stuff used to be good before Google screwed it up with
their context searchs which enable them to place paid for sites better.
That is ice that you don't see because it looks like the road,
but you get no traction?
Or
That ice you can see that is thick, blinds you when the sun hits it
and when snow covered, it fools you into thinking its regular snow
until you go to stop, but then it's too late, you just slide along?
Demian, yep I have a bunch of good TEK probes and some good Fluke probes. Don't have any of the HP probes. I got a couple of old TEK
2246 scopes and the Fluke Scope meter.
The TEKs are good, but one is starting to go noisy on me and the traces
are sort of blinky for lack of a better word. I got them pretty low cost and
they were barely used. Now stuff is getting expensive...and some of the
ebay guys think they are worth big bucks when they are not.
Searching for stuff used to be good before Google screwed it up with
their context searchs which enable them to place paid for sites better.
Some people would call me a hoarder but I find it makes more sense to have spares of what I need rather than get shut down when something goes wrong. i have three 7854's for that reason. Its cheaper to pull another than attempt to fix anything seriously wrong.
That would be great to see.... I am usually in Nepal that time of the year. It's only 2.5 hr flight from condo to Kathmandu. Might see you there?! Dont think one or two houses helps much, though. They need hundreds of thousands of homes. And, electricity that works 24 hours and sewer systems and water to/from the home. More paved roads would help. Jobs. food. Most dont have street names and numbers in the city. So many things that it might seem like a joke to the natives there. They need a school and teachers more. Tell Jimmy to build schools. But, what the heck. I'll pound some nails and cut some boards with you. I'll plan to see you there.
Turkey? .... I'll stay away for awhile... wait and see.
THx-RNMarsh
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DemianTheWhoreder.
I'm glad that Im doing the right thing as far as having spares.
Like tires, you never know when you need one.
Buy Cheap and Often.
This works for either the above or with engines,
It might even work in Thailand too whadadya think Richard?
Just don't go out on a long boat ride before low tide...
...don't ask me how I know.
No Cam 1/2 Price.
I'm glad that Im doing the right thing as far as having spares.
Like tires, you never know when you need one.
Buy Cheap and Often.
This works for either the above or with engines,
It might even work in Thailand too whadadya think Richard?
Just don't go out on a long boat ride before low tide...
...don't ask me how I know.
No Cam 1/2 Price.
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BNC from my HP sound level meter to a TR 3.5 mm into the measurement system. It needed to be shielded as well since the level is very low. I'm measuring the residual noise of active headphones. The levels are in the 0-20 dB SPL range.