I have gotten as far as I can go before making two important decisions:
1) What to use for Q2?
2) What to use for Q5?
My options for Q2 are, use nothing, 2SJ109 V grade, 2 x 2SJ74 with IDSS in the 10mA range or purchase 2SJ74 with IDSS in the 7 to 8mA range.
My Options for Q5 are use a matched pair of Semisouth SJEP120R100 that I got from the EUVL group buy or unmatched SJEP120R100 that I got from another source.
For Q1 I am using 2 x 2SJ74 from the EUVL group buy and for Q6 I am using a matched pair of Semisouth SJEP120R100 that I got from the EUVL group buy.
Decisions, decisions.
1) What to use for Q2?
2) What to use for Q5?
My options for Q2 are, use nothing, 2SJ109 V grade, 2 x 2SJ74 with IDSS in the 10mA range or purchase 2SJ74 with IDSS in the 7 to 8mA range.
My Options for Q5 are use a matched pair of Semisouth SJEP120R100 that I got from the EUVL group buy or unmatched SJEP120R100 that I got from another source.
For Q1 I am using 2 x 2SJ74 from the EUVL group buy and for Q6 I am using a matched pair of Semisouth SJEP120R100 that I got from the EUVL group buy.
Decisions, decisions.
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I'd go with the 10mA 2SJ74s in Q2.
I don't think you gain anything from matching Q5, so might as well plunk down the unmatched ones.
I don't think you gain anything from matching Q5, so might as well plunk down the unmatched ones.
I am getting ready to solder the Semisouths and the resistors.
Just remembered I never did any adjustment to the pot.
Couldnt find any recommendations.
Kind of fearful of smoke from a prior experience
Just remembered I never did any adjustment to the pot.
Couldnt find any recommendations.
Kind of fearful of smoke from a prior experience
The 500R pot?
I haven't built this so I'm just guessing here. I would leave it at midpoint
(250R), which should give you a Vgs around 1.2V and less than 2A current.
Adjust the pot to null the dc offset.
I haven't built this so I'm just guessing here. I would leave it at midpoint
(250R), which should give you a Vgs around 1.2V and less than 2A current.
Adjust the pot to null the dc offset.
Thanks Dennis, appreciated.
Cool pics Jeff, life sure seems to go into ultra fast mode when you have kids.
I had an opportunity to go fishing with my son yesterday morning.
He just turned 30, I could not help to wonder how that happened so fast.
Great memories though, I remembered when he found the Klenex box and how amazed he was that, as you pull them out, another one appeared.
Laughed my *** off and it was worth every penny after picking the mess up and throwing it away.
Cool pics Jeff, life sure seems to go into ultra fast mode when you have kids.
I had an opportunity to go fishing with my son yesterday morning.
He just turned 30, I could not help to wonder how that happened so fast.
Great memories though, I remembered when he found the Klenex box and how amazed he was that, as you pull them out, another one appeared.
Laughed my *** off and it was worth every penny after picking the mess up and throwing it away.
The full picture is even better:
That was a *long* time ago, though. A more recent pic (with the other daughter as well):
Beautiful family Jeff!
Any idea about the dimensions of the T aluminium plate bracket and also the exact transformer rating for the J2 amplifier?
Thanks
Thanks
Looking good, flamethrower!
Manniraj, the plate is 14" x at least 1"; holes are 1/2" back from front on 2" centres.
Manniraj, the plate is 14" x at least 1"; holes are 1/2" back from front on 2" centres.
Manniraj, photos from an early 6moons review show a 300VA 2x18VAC Plitron transformer,
so that should serve as a guidance.
so that should serve as a guidance.
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This placement looks fine to me. I might suggest, however, that using "hot glue" to affix something very heavy in a "hot chassis" might be somewhat problematic in practice...
Put a nut on top of that bolt and you'll be in good shape 😉
Put a nut on top of that bolt and you'll be in good shape 😉
In the original FW they are indeed mounted with a layer of silicone. I recently replaced the transformer of my F1J with a bigger one, removing the old one was tricky.
If anyone's interested, more pics here: https://www.diyaudio.com/forums/pass-labs/169509-firstwatt-f1j-3.html#post6231631
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I could see some nichicon 22000uf 25v electrolytic cap in series with the positive and negative terminals of bridge rectifiers. What is the purpose of this cap.
Thanks
Thanks
The F1J does not have a bipolar supply like many other FW amps, so each channel has its own secondary winding and its own bridge rectifier and filter caps. The caps across the rectifiers' outputs are additional smoothing caps. The idea is to have a cap as close to the rectifiers as possible.