cheap component testers from China (10-20 bucks) are clever investment nowadays
WOW! Thanks to all for the quick responses. I did get a few of those "mega" testers off of eBay. I even paid for the Amazon book re: how to use it... I suppose I should put it together, learn how to use it, and fire it up.
So glad I asked...
The topic of matching seems to be covered quite a bit particularly for the JFETs. However, I have only found a little bit of information on the MOSFETs.
I found a few mentions of it, but in this article linked, it seems relatively straight forward.
http://www.firstwatt.com/pdf/art_matching.pdf
First a few questions please.
1) Is it critical to match these at 22V - 0.4A? I see that the ones in the store are matched at those parameters. Can I achieve a good match at a lower voltage and/or current? I'd prefer to not need to put each of these on a heatsink. However, if it is critical or even advisable, I can can make it happen.
2) If I have a laboratory DC supply to set at 22V that I can current limit to 0.4A and a DMM, that should be all the tools required, correct? If I can set the current limit to 0.4A, do I need any resistors in series with the drain?
Edited to add - Thank you Dennis. It looks like we were posting on top of each other.
Edited again - I also found this. PassDiy Last section covers things very well.
So, my main questions are regarding the resistors and proper operating parameters.
With thanks as always!
I found a few mentions of it, but in this article linked, it seems relatively straight forward.
http://www.firstwatt.com/pdf/art_matching.pdf
First a few questions please.
1) Is it critical to match these at 22V - 0.4A? I see that the ones in the store are matched at those parameters. Can I achieve a good match at a lower voltage and/or current? I'd prefer to not need to put each of these on a heatsink. However, if it is critical or even advisable, I can can make it happen.
2) If I have a laboratory DC supply to set at 22V that I can current limit to 0.4A and a DMM, that should be all the tools required, correct? If I can set the current limit to 0.4A, do I need any resistors in series with the drain?
Edited to add - Thank you Dennis. It looks like we were posting on top of each other.
Edited again - I also found this. PassDiy Last section covers things very well.
So, my main questions are regarding the resistors and proper operating parameters.
With thanks as always!
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I match mine at 23V w/ a 50ohm resistor. That's about 0.38A, which is pretty close to the store parameters. I don't bother with heat-sinks; you're only going to be running it for 10 seconds or so.
I would think using your PSUs current limit would be equivalent to the resistor -- but I've never tried it.
I would think using your PSUs current limit would be equivalent to the resistor -- but I've never tried it.
Thank you very much, Jeff.
I have been fearlessly DIYing for the last little bit trying not to release any magic smoke. I used two 3W 100 Ohm resistors in parallel per one of Papa's articles where he was using 15V @ ~170mA for the output MOSFETs. The resistors still get very hot.
FWIW - Without the resistors, the lab supply won't get nearly up nearly to voltage and runs into the current limit. I'm not sure I fully grasp why yet, but I'll get around to understanding.
re: 10 seconds. I can't seem to get one to stabilize that fast. They seem to continually drop. Do you simply take the value at 10s even if it's not stable, or do you find that they stabilize before then in your set up?
I'll keep plugging.
Edit - I continue to learn. The store ones are matched to within 0.1V. I was waiting for them to stabilize to almost the millivolt level. Live and learn.
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Yes, exactly; you're not waiting for the last word in stable, just for the rate of change to slow down a bit.
A resistor is going to feel really hot at 50ºC. The de-rating curve for most metal foils ends between 150ºC and 200ºC; ceramic substrate wire-wounds often go up to 275ºC. "Hot" for resistors is relative.
A resistor is going to feel really hot at 50ºC. The de-rating curve for most metal foils ends between 150ºC and 200ºC; ceramic substrate wire-wounds often go up to 275ºC. "Hot" for resistors is relative.
Great advice gentlemen. Truly appreciated.
I think I need a more sophisticated jig and/or to use some heatsinks if I'm going to use voltages / current that high. I let them all stay at the same room temp and tried not to handle them differently.
They all read 4.2xxV immediately. By 10 sec, they are at 4.1xxV (or rounded to it). By 20 sec, they are all at 4.0xxV. Then the decline slows down.
For fun, I let one get to what I'd only describe as really, stupid, fargin' hot. It had to be 65+ C on the device. It took a minute+ or so, but it got down to 3.7xxV.
I went by the advice of others and get a "tube", so I can do the F4 and F5 also (I got the 9240s too).
Is it to be expected that the first 8 I measured are all good to go and matched that tightly? If so...
I think I need a more sophisticated jig and/or to use some heatsinks if I'm going to use voltages / current that high. I let them all stay at the same room temp and tried not to handle them differently.
They all read 4.2xxV immediately. By 10 sec, they are at 4.1xxV (or rounded to it). By 20 sec, they are all at 4.0xxV. Then the decline slows down.
For fun, I let one get to what I'd only describe as really, stupid, fargin' hot. It had to be 65+ C on the device. It took a minute+ or so, but it got down to 3.7xxV.
I went by the advice of others and get a "tube", so I can do the F4 and F5 also (I got the 9240s too).
Is it to be expected that the first 8 I measured are all good to go and matched that tightly? If so...
Well, I thought this was to be a post of resounding triumph. Not quite.
Everything went smoothly with the board installation etc. I've powered up both channels and done the initial checks. I can't get the amps to bias past 289mV. The pots are "to the click".
I saw earlier in the threat that could be attributed to forgetting to put in the R27 jumper, but I put that in. I suppose the good (or bad) news is that it is on both channels. I set them to 68k per the guide prior to powering up.
The good news is DC offset nulls like a champ.
I've re-read the thread and my notes. Pics of the boards are in post #3762.
Any help is appreciated.
With thanks!
Everything went smoothly with the board installation etc. I've powered up both channels and done the initial checks. I can't get the amps to bias past 289mV. The pots are "to the click".
I saw earlier in the threat that could be attributed to forgetting to put in the R27 jumper, but I put that in. I suppose the good (or bad) news is that it is on both channels. I set them to 68k per the guide prior to powering up.
The good news is DC offset nulls like a champ.
I've re-read the thread and my notes. Pics of the boards are in post #3762.
Any help is appreciated.
With thanks!
Over a whole tube my Harris IRFP240s varied between 3.64 and 4.15:
3.64
3.70
3.71
3.72
3.73
3.74
3.75
3.76
3.77
3.78
3.78
3.78
3.82
3.85
3.85
3.87
3.88
3.97
3.97
4.01
4.05
4.06
4.07
4.09
4.10
4.11
4.12
4.12
4.15
But you could have picked 8 out of there that all measured the same to a tenth of a volt.
Cheers,
Jeff.
3.64
3.70
3.71
3.72
3.73
3.74
3.75
3.76
3.77
3.78
3.78
3.78
3.82
3.85
3.85
3.87
3.88
3.97
3.97
4.01
4.05
4.06
4.07
4.09
4.10
4.11
4.12
4.12
4.15
But you could have picked 8 out of there that all measured the same to a tenth of a volt.
Cheers,
Jeff.
OK - Well, I'm never afraid to admit I goofed. Particularly if my goof may help prevent someone else from doing the same thing.
Always! Check your DMM, and don't start building at 3am b/c you're excited to hear your new amp.
I had my DMM set to mA instead of MV... DOH! Jim clearly explained how to do it properly in the build guide (and kindly caught my error again).
What an awesome group. It's got the lid on cooking...
Always! Check your DMM, and don't start building at 3am b/c you're excited to hear your new amp.
I had my DMM set to mA instead of MV... DOH! Jim clearly explained how to do it properly in the build guide (and kindly caught my error again).
What an awesome group. It's got the lid on cooking...
We have beautiful music! Set properly to 0.40xV on both sides with <1mV of DC offset. I goof up literally the last thing in the build.... DOH!
Jeff, the rite of passage will need to wait until I'm a bit more daring, a bit more foolish... or both.
Once again, thanks to Nelson Pass for his generosity providing these fabulous designs for us to learn, try to build, and most importantly sing and dance with when successfully built.
A special thanks to Jim @6L6 for his build guides and the continuous support. Last, but certainly not least, thanks to the entire community. There were those that overtly helped me out on the thread and many more that don't know how much they've helped by posting their issues and questions. All the Q&A allows me to learn before potentially crossing the same bridge. This an incredibly generous group.
2nd First Watt...
Jeff, the rite of passage will need to wait until I'm a bit more daring, a bit more foolish... or both.
Once again, thanks to Nelson Pass for his generosity providing these fabulous designs for us to learn, try to build, and most importantly sing and dance with when successfully built.
A special thanks to Jim @6L6 for his build guides and the continuous support. Last, but certainly not least, thanks to the entire community. There were those that overtly helped me out on the thread and many more that don't know how much they've helped by posting their issues and questions. All the Q&A allows me to learn before potentially crossing the same bridge. This an incredibly generous group.
2nd First Watt...
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generosity of this group is all in your head
they're just bunch of Greedy Boyz and Dodosssesss
Especially, the Mighty Zen Mod
A hearty thanks to you as well!
Hey...congratulations!
So...which will be your third?
Cheers,
Dennis
This one
Fourth is F4, Fifth is F5. I couldn't help it...Attachments
Especially, the Mighty Zen Mod
A hearty thanks to you as well!
naah
no need to thank me , after all
my intentions are always just to mock and ridicule
