The diyAudio Firstwatt F6

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#562
The rating of the IRFP240 is 200Volts and we have a Zener at 9.1volts controlling the gate so why would 31 Volts be an issue? According to the Data sheet the Vgs is -+ 20 Volts.
It might generate a bit more heat but with the 5U case this should not be an issue? I'm just trying to avoid spending more money since I have this transformer available. (call me cheap)
 
#563
Keep in mind the input jfets may or may not survive rail voltages that high. I would not do it myself without circuit changes. Also, power rating of those little guys is 0.4 Watts, so use ohms law to know for sure what your dissipation is going to be... if you want a good reliable amplifier. It's smart to run things a bit more conservative rather than close to the limit. And those IRFP240's, voltage rating is not the issue. Again use ohm's law to figure out your power dissipation in each device. Looks like about 50 Watts per device or so and that's working them pretty hard. Might be OK, can the 5U maintain the sinks at 50C at that dissipation? I don't know.
 
#564
Thanks william2001 I should have made it a bit clearer but I'm not running the JFETS as the input to this output stage but another buffer instead and they have their own supply rail.
You're correct I had forgotten ohms law if I'm biasing the output devices with anything above 1.6 AMPS then indeed they will be dissipating 50 watts at a supply of 31 volts.

But again if I go back to the data sheet they are able to dissipate 150 Watts but are derated 1.2 W/C above 25C so theoretically I could run them at 90 Watts given the size of the 5U heatsinks.

I still have some components left to purchase before I start the build but will post when the project commences. Thanks for your concern.🙂
 
#565
6L6 said:
Thanks! That's pretty amazing results, considering I matched them myself and wasn't trying for results that close. (There just isn't the quantity available to make super tight pairs.) And anyway, they don't need to be all that tight for these amps, 10% is more than good enough.
Click to expand...

Jim, I very much appreciate your effort in making these matched parts
available. Great job!

Dennis
 
#569
Fired up my F6 using store boards and the matched Fets. This was an easy amplifier to build with so little parts. No pops on start up or down and almost dead quite with 104 db speakers. I have not done a lot of listening yet, maybe an hour but the sound is very, very good. There appears to be a little more detail and it seems to be a little more cleaner than the SE Ba3 I just built. I am pleasantly surprised with the sound of a PP amp with feedback, degeneration, and transformer. Single ended with no feedback is supposed to sound better in theory anyway. I think the soundstage is a little better also but I need some more hours to really give any kind of review. I am indebted to Mr Nelson Pass for making this diy amp possible.

David
 
#570
6L6 said:
Likely not until the PCB+transformer sets have a) got to the store, and b) sold enough to merit another PCB order.
Click to expand...

6L6,

Please, please can you pray to Jason in the Store for us, mortals!

Been waiting on the Matched Grade B JFETS, F5T Boards, F6 Boards and Jensen Transformers. Never could get the store's notifications to work until just now. Been watching and waiting and see it's come and gone. 🙁 Will order piecemeal if I have to but alas still not fast enough.

Pray for us so he knows to get a goodly stock so all will be blessed by Papa...

... And eagerly awaiting your Illustrated Build Guide for the F6 as F5 T bits are so hard to come by I've put all my efforts towards the F6, for now.

Thanks,
P { margin-bottom: 0.08in; } Holzarbeiter
 
#571
You could pray to Jason, I suppose... but the Jfets, Transformers, and PCB are all in my basement...

The PCB+Transformer is the next project. I need to find proper packaging for them. There is a company here in Denver that produces/stocks about a million different box shapes and sizes, I'm sure they'll have one. Hopefully I can get that done tomorrow, and box some up and get them to the store. Even If I get that all done tomorrow (and I won't) it's late next week at the very, very earliest.

I'll be sure to send some more Jfet in that shipment.

As for F6 guide, have you seen post 500? http://www.diyaudio.com/forums/pass-labs/258613-diyaudio-firstwatt-f6-10.html#post4341419
 
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#572
I am one of the cheap Diy'ers. I already had a 500VA 18 volt non shielded transformer and did not want to buy another transformer so I took a Maxwell house coffee can and cut the bottom off, made some cutouts for the wires and placed it over my transformer. Almost a perfect fit. I cannot detect any interference between power transformer and audio transformers. Some tubing over the cuts will make the can safe.

David
 
#577
6L6 said:
You could pray to Jason, I suppose... but the Jfets, Transformers, and PCB are all in my basement...

The PCB+Transformer is the next project. I need to find proper packaging for them. There is a company here in Denver that produces/stocks about a million different box shapes and sizes, I'm sure they'll have one. Hopefully I can get that done tomorrow, and box some up and get them to the store. Even If I get that all done tomorrow (and I won't) it's late next week at the very, very earliest.

I'll be sure to send some more Jfet in that shipment.

As for F6 guide, have you seen post 500? http://www.diyaudio.com/forums/pass-labs/258613-diyaudio-firstwatt-f6-10.html#post4341419
Click to expand...


6L6,

I will pray to you, bless you, and Jason!

I have been moving so no, I have not seen post 500, need to get caught up and is the reason the F6 is better as it's simpler and will, if I can get the bits ordered while in transit, finished.

Colorado is on the way if you could somehow manage to leave enough parts that you 'may not find packaging for'. I could swing up and take care of them for you!!! 🙂

Again thanks for all that you are doing and I'm hoping notifications will give a heads up as it seems to be working now.

Best,
Holzarbeiter
 
#579
F6PCB.jpg

There should be stock in the store within the month.
 
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