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Old 22nd October 2013, 04:06 AM   #1391
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Quote:
Originally Posted by jkuetemann View Post
You realize the input transistors only are exposed to a little more than ONE rail, yes? A 120V Vceo device will work at rails higher than this design will stand I'm sure.
Yes, but thanks for pointing it out. I have only used the BC550/560 in this particular circuit so far, and those won't get me there. I have not taken the time to research every possible part, so I am happy to start with parts someone else has already tried.
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Old 22nd October 2013, 04:22 AM   #1392
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Originally Posted by jkuetemann View Post
Hmm, interesting. Fairchild lists KSA992F and KSC1845F as 'Full Production' without any reference to being 'End of Life' that I could find. Both polarities of my parts were F rank and seem to be hanging around at an hFE of 400, simple DMM test.
KSA992PTA Fairchild Semiconductor | Mouser

These are an excellent match @30V @2mA for the KSC1845FTA.
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Old 22nd October 2013, 06:24 AM   #1393
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Originally Posted by woofertester View Post
KSA992PTA Fairchild Semiconductor | Mouser

These are an excellent match @30V @2mA for the KSC1845FTA.
No, the excellent match is KSA992FTA + KSC1845FTA & they are still available.
I have the old version 2SA992+2SC1845 only 2 pair match & I use it in my first PeeCeeBee
Click the image to open in full size.

but I change it back to BC550C-560C because only use +/-35VDC.
So I can use it in higher voltage version latter

Now I'm finish mounting the double die (aka double K1058-J162) at heat sink
still missing some parts to finish.
The building must be slowly to ensure no error

Regards
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Old 22nd October 2013, 08:12 AM   #1394
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Originally Posted by JOHN BALI View Post
No, the excellent match is KSA992FTA + KSC1845FTA & they are still available.
I have the old version 2SA992+2SC1845 only 2 pair match & I use it in my first PeeCeeBee
Click the image to open in full size.

but I change it back to BC550C-560C because only use +/-35VDC.
So I can use it in higher voltage version latter

Now I'm finish mounting the double die (aka double K1058-J162) at heat sink
still missing some parts to finish.
The building must be slowly to ensure no error

Regards
incredible
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Old 22nd October 2013, 04:21 PM   #1395
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Originally Posted by JOHN BALI View Post
No, the excellent match is KSA992FTA + KSC1845FTA & they are still available.
I have the old version 2SA992+2SC1845 only 2 pair match & I use it in my first PeeCeeBee


but I change it back to BC550C-560C because only use +/-35VDC.
So I can use it in higher voltage version latter

Now I'm finish mounting the double die (aka double K1058-J162) at heat sink
still missing some parts to finish.
The building must be slowly to ensure no error

Regards
I tested a batch of KSA992FBU (bulk) and the hfe was 550 to 570 and do not match any of my 1845. I have not tried the KSA992FTA. I will have to order some next time I need some parts from Mouser.

Thanks
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Old 22nd October 2013, 05:44 PM   #1396
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Ok, I sat down this morning to swap out the 18K resistors. Pulled them and then realized I didn't have any 20K. Closest I had were 22K so I tried them in there. Not good. 10R resistors now measure 65mv drop and the the highs sound distorted. I guess I'll pop over to Radio Shack and see if they have any 20K.

I'll report back.
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Old 22nd October 2013, 07:33 PM   #1397
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Hi Terry,
If you have 220k and mount them in parallel to the 22k you will have 20k. if you mount 180k in parallel to the 22k you will have 19k6.
At least you can figure out what value works best for you.
Cheers!
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Old 22nd October 2013, 09:08 PM   #1398
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Or you could build a closer value with a series combination standing up vertically on the board to get closer to the 20K mark (which simulated well at your voltages). If you have to err a little then go slightly under the 20k mark but over 18k. It's a fine line.

Otherwise, put the 18k in and put a small heat sink front and back of the VAS devices if you can to run them cooler. Just try not to rework the boards too much, I'm not sure how well they will stand to repeated desolder / resolder cycles.
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Old 23rd October 2013, 02:43 AM   #1399
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Sorry, I should have reported back sooner. I piggybacked 180K on one board and 220k on the other. After letting it play for a couple hours I am getting 150mv across the 10R on the 220k board and 178mv on the other. Sounds better than it did with just the 22K in there. I'm thinking about making bigger heatsinks for the VAS and go back to the 18K. Seemed like it sounded better with that. It's kind of hard to tell at this point. I am getting listening fatigue. I have been playing the Peeceebee along side the DX Super A that I am finishing. They both sound so good and I have been A/B-ing them all day.
Fun stuff!!!!!!!

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Old 23rd October 2013, 11:52 PM   #1400
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Quote:
Originally Posted by still4given View Post
...I'm thinking about making bigger heatsinks for the VAS and go back to the 18K. Seemed like it sounded better with that. ...
Sounds like a plan.

As a side note, I just checked my own PeeCeeBee boards to make a comparison with yours. Here's what I have:

Supply is +/-31.5V and my build uses 15kΩ resistors.
Cold start 197mV over 10Ω VAS transistor emitter resistors, so 19.7mA VAS current.
Full temperature 224mV over 10Ω VAS transistor emitter resistors, so 22.4mA VAS current.
Subjectively the transistors are pretty warm, but without any discomfort when touched and my contact-less thermometer says the VAS reaches about 45C.

I had a look at the data sheet to see the temperature derating information and I don't think there is a problem with these devices even at your 10C higher temperatures. Go back to the 18K and just enjoy the PeeCeeBee.
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