Thanks Zen Mod. Do you think I should order new JFETs, or are you satisfied they're okay based on the test results?
JFtets are good, considering your measurement in jig
regarding mosfets matching - now you gonna learn how to do that, and that's much better than being gifted with matched set
question of quantity of your luck with mosfets being put in your working channel - measure voltages across all 4 source resistors and write down (here too)
if said voltages are in 10% bracket, you're lucky bstrd
if said voltages are outa 10% bracket, you're still lucky bstrd, but you're gonna change them , once when you have matched pairs from your order
be happy** ...... DIY audio bug got ya for good .....
**choice is - happy or suicide.......... cocaine addiction is at least shorter.....
regarding mosfets matching - now you gonna learn how to do that, and that's much better than being gifted with matched set
question of quantity of your luck with mosfets being put in your working channel - measure voltages across all 4 source resistors and write down (here too)
if said voltages are in 10% bracket, you're lucky bstrd
if said voltages are outa 10% bracket, you're still lucky bstrd, but you're gonna change them , once when you have matched pairs from your order
be happy** ...... DIY audio bug got ya for good .....
**choice is - happy or suicide.......... cocaine addiction is at least shorter.....
Thanks Zen Mod.
It looks like I'll be changing MOSFETs! At least one pair, unless I should change them both.
Good side reads like this:
R18 - 387mv
R19 - 336mv
R16 - 355mv
R17 - 359mv
All things considered, it seems like I'm kinda lucky 🙂
It looks like I'll be changing MOSFETs! At least one pair, unless I should change them both.
Good side reads like this:
R18 - 387mv
R19 - 336mv
R16 - 355mv
R17 - 359mv
All things considered, it seems like I'm kinda lucky 🙂
I'm gearing up for my misfit matching, and have been trying out measuring the units I pulled from the original stuffing of the broken side. If I'm doing this correctly, the measurements range between ~320mv to ~560mv.
Please validate my test, as the schematic I'm using is a little blurry.
Test:
I cobbled together a 15.1 (as measured) volt source by putting a 9V and 4 rechargeable AA's in series.
Battery positive is connected to a 2.2kR resistor, who's other end is connected to the source and positive lead of the meter.
Battery negative is connected to gate, drain, and the negative lead of the meter.
Please validate my test, as the schematic I'm using is a little blurry.
Test:
I cobbled together a 15.1 (as measured) volt source by putting a 9V and 4 rechargeable AA's in series.
Battery positive is connected to a 2.2kR resistor, who's other end is connected to the source and positive lead of the meter.
Battery negative is connected to gate, drain, and the negative lead of the meter.
ppinto1 - congrats on scoring some MOSFETs and trying the matching. Hopefully they won't be misfits 😀
You are talking about Q5-Q8, correct? The Vgs should be in the 4V range.
A couple things -
1) I don't know enough about batteries to know if they'll provide a steady current / voltage supply for the length of time it will take to match. If you have a laptop supply like ZM suggested, that would be great.
2) I think you got the resistor value from your matching of input devices. You need more current.
I use this article - http://www.firstwatt.com/pdf/art_matching.pdf
and this one
http://www.firstwatt.com/pdf/art_mos_test.pdf
you can skip to the part about measuring Vgs.
Someone should definitely verify... as I said, my mojo has suffered a beating today. I may not have it correct 😀
I use 22V from voltage source (bench supply) => ~18V across R1 accounting for Vgs when I match for FW amps. That's ~0.36A with R1 = 50R.
If you use a 19V supply => ~15V across R1 => R1 = 50ohms = Current ~0A3.
I let them test for 30s +- 1s. I make sure all the devices start at the same room temp. Some people advocate a heatsink / longer time etc. etc. You'll see that the device won't have one precise value. It will change as the device heats up. So, you want to take your reading the same way for each device.
The rest of the setup you described sounds good. Note, check to see if you have some higher rated resistors (0A3*15V=>4.5W) ... Two 3W in parallel should be okay. They will get very toasty and/or go up in smoke if not.
That may be a good start. Someone will be helpful and confirm or correct soon, I'm sure. The good news is that if I've been doing it poorly all along, then you'll have saved yourself from a badly matched set.
You are talking about Q5-Q8, correct? The Vgs should be in the 4V range.
A couple things -
1) I don't know enough about batteries to know if they'll provide a steady current / voltage supply for the length of time it will take to match. If you have a laptop supply like ZM suggested, that would be great.
2) I think you got the resistor value from your matching of input devices. You need more current.
I use this article - http://www.firstwatt.com/pdf/art_matching.pdf
and this one
http://www.firstwatt.com/pdf/art_mos_test.pdf
you can skip to the part about measuring Vgs.
Someone should definitely verify... as I said, my mojo has suffered a beating today. I may not have it correct 😀
I use 22V from voltage source (bench supply) => ~18V across R1 accounting for Vgs when I match for FW amps. That's ~0.36A with R1 = 50R.
If you use a 19V supply => ~15V across R1 => R1 = 50ohms = Current ~0A3.
I let them test for 30s +- 1s. I make sure all the devices start at the same room temp. Some people advocate a heatsink / longer time etc. etc. You'll see that the device won't have one precise value. It will change as the device heats up. So, you want to take your reading the same way for each device.
The rest of the setup you described sounds good. Note, check to see if you have some higher rated resistors (0A3*15V=>4.5W) ... Two 3W in parallel should be okay. They will get very toasty and/or go up in smoke if not.
That may be a good start. Someone will be helpful and confirm or correct soon, I'm sure. The good news is that if I've been doing it poorly all along, then you'll have saved yourself from a badly matched set.
you need to use steady voltage , which is keeping it (voltage ) ...steady in time
point is - your setup must be same for all DUTs, so avoid batteries
you can use them for JFets because current is small, but not with greater current needed for mosfets
as I said - use laptop brick
if scared , put 1-2A fuse in line with rail
point is - your setup must be same for all DUTs, so avoid batteries
you can use them for JFets because current is small, but not with greater current needed for mosfets
as I said - use laptop brick
if scared , put 1-2A fuse in line with rail
Thanks ItsAllInMyHead and ZenMod.
The laptop brick I have is rated at 19.5v output, but I measure it at 14v. Maybe it negotiates final voltage.
I don't mind using rail voltage from the amp's power supply if that's my best bet. I have a few 2.5A fuses around.
Or, how about this:
https://www.amazon.com/Powseed-Univ...niversal+laptop+charger&qid=1588042515&sr=8-8
Thought: 15v @45w should provide the 03A ItsAllInMyHead mentioned.
The laptop brick I have is rated at 19.5v output, but I measure it at 14v. Maybe it negotiates final voltage.
I don't mind using rail voltage from the amp's power supply if that's my best bet. I have a few 2.5A fuses around.
Or, how about this:
https://www.amazon.com/Powseed-Univ...niversal+laptop+charger&qid=1588042515&sr=8-8
Thought: 15v @45w should provide the 03A ItsAllInMyHead mentioned.
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Your link will work.. plenty of power.
Note - It's 0A3 =>0.3 Amps Not 3A. 😀
You can also just adjust the resistor to provide your target current. Those are just examples.
More to the point... IMHO, yes - matching is important. However, you'd very likely get away with pulling 4 from the tube and installing them without worry. They're all from the same lot code if you bought a full tube, and they're very likely to be closely matched enough for this purpose. You're just verifying.
Still, try it - it's fun.
Note - It's 0A3 =>0.3 Amps Not 3A. 😀
You can also just adjust the resistor to provide your target current. Those are just examples.
More to the point... IMHO, yes - matching is important. However, you'd very likely get away with pulling 4 from the tube and installing them without worry. They're all from the same lot code if you bought a full tube, and they're very likely to be closely matched enough for this purpose. You're just verifying.
Still, try it - it's fun.
ItsAllInMyHead: Thanks for helping me with the notation.
I don't have many resistors laying around. I *did* find a pair of 100R 3w. Can I use these in parallel? Will 50R be inappropriate for the 15v PS?
I saw this on Amazon, and I can order it with the laptop PS if you think it's a better idea:
https://www.amazon.com/Valuepro-Pot...ords=potentiometer+watt&qid=1588043876&sr=8-2
I don't have many resistors laying around. I *did* find a pair of 100R 3w. Can I use these in parallel? Will 50R be inappropriate for the 15v PS?
I saw this on Amazon, and I can order it with the laptop PS if you think it's a better idea:
https://www.amazon.com/Valuepro-Pot...ords=potentiometer+watt&qid=1588043876&sr=8-2
Sorry to beat a dead horse here... I had an old PC power supply I completely forgot about. When I measure between the -12 and +12 outputs, I get 23.3V. I took a measurement between -12 and +5 and got 16.4V. I think I have what I need on the PS end.
Same question about the two 100R/3W resistors in parallel, though.
Same question about the two 100R/3W resistors in parallel, though.
Great news on finding some resistors and a PSU. As long as the PSU is rated for 0A5 or better, move on.
If you think you may build a few more amps and have the budget, I find a bench supply invaluable. There are a zillion models all with pros and cons. A nice single channel one in this general range may serve you well.
https://www.amazon.com/3-Digital-Pr...lja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1
I never like to assume anyone's level of knowledge or how comfortable they are with certain things. I also never like to assume whether now is the time for learning a bit or just getting the #$@# working and worrying about learning later. 😀
I just started learning the very, very basics about a year ago with help from people on this forum... So...
Using the examples I gave and the articles I linked along with the voltages you provided for your PSU options, can you figure out:
1) The current through R1 assuming R1 is now 50R using 2, 100R resistors in parallel
2) The power in W through each of R1, and R1a
3) Hypothetically why one of your power supply options may be a bit better for matching with this amp based on what you know about the PSU for the amp.
If that's a PITA, I'll give it a go. No one has chimed in to say my previous analysis was bonkers, so I'll assume for now, it was close enough to correct.
If you think you may build a few more amps and have the budget, I find a bench supply invaluable. There are a zillion models all with pros and cons. A nice single channel one in this general range may serve you well.
https://www.amazon.com/3-Digital-Pr...lja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1
I never like to assume anyone's level of knowledge or how comfortable they are with certain things. I also never like to assume whether now is the time for learning a bit or just getting the #$@# working and worrying about learning later. 😀
I just started learning the very, very basics about a year ago with help from people on this forum... So...
Using the examples I gave and the articles I linked along with the voltages you provided for your PSU options, can you figure out:
1) The current through R1 assuming R1 is now 50R using 2, 100R resistors in parallel
2) The power in W through each of R1, and R1a
3) Hypothetically why one of your power supply options may be a bit better for matching with this amp based on what you know about the PSU for the amp.
If that's a PITA, I'll give it a go. No one has chimed in to say my previous analysis was bonkers, so I'll assume for now, it was close enough to correct.
just be aware of fact that ATX PSU is able to give no more than 1A at -5V output
in 99% of them , that's nothing else than 7905 there
if you keep testing current at no more than, say, 300-350mA , you're good
in 99% of them , that's nothing else than 7905 there
if you keep testing current at no more than, say, 300-350mA , you're good
Thanks for all the tips ZM and IAIMH!
Sorry I'm delayed in getting back. Lots of work today!
Let me see if I can answer those three questions:
1) @23.3V, the current going through R1 would be 0A466. @16.4V, the current through R1 would be 0A328.
2) @23.3V, the power through R1 and R1a would be 5.43w. @16.4V, the power for each would be 2.69w.
3) I don't know how to answer this, and would like some direction. But, if I'm correct with 1 & 2 above, 16.4v is my only option because my 3w resistors aren't going to be able to dissipate enough heat @5.43w.
Feedback? Thanks in advance!
Sorry I'm delayed in getting back. Lots of work today!
Let me see if I can answer those three questions:
1) @23.3V, the current going through R1 would be 0A466. @16.4V, the current through R1 would be 0A328.
2) @23.3V, the power through R1 and R1a would be 5.43w. @16.4V, the power for each would be 2.69w.
3) I don't know how to answer this, and would like some direction. But, if I'm correct with 1 & 2 above, 16.4v is my only option because my 3w resistors aren't going to be able to dissipate enough heat @5.43w.
Feedback? Thanks in advance!
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You were very close... and I'm an amateur... so I based it off the article and some of the readings I took when doing it myself.
1) Don't forget to subtract roughly 4V accounting for Vgs => (23.3 - 4)/50 etc.
2) Got it based on one pretty close - but if you're using 2 resistors in parallel, they share the current - thus recommending to use 2, 3W 100 ohm vs. 1, 50ohm 3W.
3) Some people like to get the voltage closer to the rails used in the amp... me, I dunno....truthfully, I just target a ballpark current and keep it consistent. So, some people may lean to your 22ish volt supply.
Ultimately - follow what ZM says. 😀 😀 😀 That's what I do.
1) Don't forget to subtract roughly 4V accounting for Vgs => (23.3 - 4)/50 etc.
2) Got it based on one pretty close - but if you're using 2 resistors in parallel, they share the current - thus recommending to use 2, 3W 100 ohm vs. 1, 50ohm 3W.
3) Some people like to get the voltage closer to the rails used in the amp... me, I dunno....truthfully, I just target a ballpark current and keep it consistent. So, some people may lean to your 22ish volt supply.
Ultimately - follow what ZM says. 😀 😀 😀 That's what I do.
LOL! Thanks to you both! I'm going to test the MOSFETs I cut out as practice tonight. It looks like my order from Newark will come tomorrow.
Incidentally, I got word from Cable Solutions that they're now able to ship me the input transformers for the F6. My plan was to swap the boards in and out of this current chassis/PS. After having put all the effort in, I think I want this to be a discrete amp now 🙂. Looks like I'm saving up for another chassis and PS kit! I was dissatisfied with the content in the HW kit for the chassis and may start another thread to solicit suggestions.
Incidentally, I got word from Cable Solutions that they're now able to ship me the input transformers for the F6. My plan was to swap the boards in and out of this current chassis/PS. After having put all the effort in, I think I want this to be a discrete amp now 🙂. Looks like I'm saving up for another chassis and PS kit! I was dissatisfied with the content in the HW kit for the chassis and may start another thread to solicit suggestions.
I'll definitely follow your thread re: chassis suggestions. I use the Modushop ones b/c when I got them, I was so new to this and didn't need the complexity of metal work etc. I wanted to follow the build guide to the letter. However, another member has inspired me to possibly try out a chassis build.
I also had trouble getting the F6 transformers for a while. They're the same ones that can be used in ZM's Iron Pre... so, I might <cough> have robbed Peter to pay Paul and stole them from F6 kits I bought until Jensen got back in stock.
I also had trouble getting the F6 transformers for a while. They're the same ones that can be used in ZM's Iron Pre... so, I might <cough> have robbed Peter to pay Paul and stole them from F6 kits I bought until Jensen got back in stock.
See if this works: Jensen Transformers ISO-MAX Products
scroll way down to JT-123-FLPCH Mine came pretty quickly.
Russellc
scroll way down to JT-123-FLPCH Mine came pretty quickly.
Russellc
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I'm not sure if I'm conducting my measurements properly - or if this is the behavior of a blown MOSFET.
I'll try to present a visual of my circuit (gulp):
+ --- {50R}----{Positive Meter Lead and Source}
- ----{Netative Meter Lead, Gate, and Drain}
I turn on the power supply with clips connected for Drain + Gate + Negative Meter Lead.
The meter reading is 16.3V.
I attach a clip, already wired downstream from the resistor and with the Positive Meter Lead, to Source.
The meter reading never changes.
I'll try to present a visual of my circuit (gulp):
+ --- {50R}----{Positive Meter Lead and Source}
- ----{Netative Meter Lead, Gate, and Drain}
I turn on the power supply with clips connected for Drain + Gate + Negative Meter Lead.
The meter reading is 16.3V.
I attach a clip, already wired downstream from the resistor and with the Positive Meter Lead, to Source.
The meter reading never changes.