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Alternative output transistors for the Baby AKSA 55
Alternative output transistors for the Baby AKSA 55
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Old 11th September 2013, 05:10 PM   #1
cs is offline cs  United Kingdom
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Default Alternative output transistors for the Baby AKSA 55

Has anyone had any experience of using different output devices to the 2SC5200/2SA1943 in the Baby AKSA 55 circuit ?

Although the Toshiba parts are readily available in the UK, mounting kits for the TO-264 packages are like hen's teeth, so I would like to use some TO-247 (TO3P) packaged transistors instead. The Sanken 2SC3519/2SA1386 for example, have similar specs apart from the Vce rating:
Vce = 160V
Ic = 15A
hfe = 50 (min)
ft = 50MHz
They also have a very flat hfe vs Ic curve, like the Toshiba devices.

Even more radical, would integrated Darlingtons be suitable, such as the Sanken 2SD2390/2SB1560 ?
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Old 11th September 2013, 05:42 PM   #2
jaycee is offline jaycee  United Kingdom
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You could also look at the Onsemi devices like the MJW3281/MJW1302 which are in TO247 packages.

I wouldn't try Darlingtons in a circuit not designed for them.

An alternative is to buy a sheet of thermal pad material which you could cut to size, or some Kapton tape. You may also find that pads for TO-3P type transistors (as long as they are square) will cover the metal part of a TO-264 just fine, as long as you take a bit of care with alignment.
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Old 11th September 2013, 06:00 PM   #3
Ian Finch is offline Ian Finch  Australia
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Toshiba supplied "same die" TO3P versions in the 2SC5198/A1941 pair. They are obsolete but you may find some around. These would be your best guarantee of performance, as long as heat transfer is really good, so as to avoid running at higher case temps.

Fairchild still supply FJA4213/4313 which are fairly close and were a second source.
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Old 12th September 2013, 04:12 AM   #4
farjon is offline farjon  Brazil
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I have used some Sanken MT-200 types and BD drivers, with good results.

Based on Hugh Dean's AKSA 55

Based on Hugh Dean's AKSA 55
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Old 12th September 2013, 09:55 AM   #5
cs is offline cs  United Kingdom
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Thanks for the useful tips.

Farjon, what mounting kits did you use for the MT-200 transistors ? Would two TO-247 pads back-to-back work ?
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Old 12th September 2013, 04:09 PM   #6
Ian Finch is offline Ian Finch  Australia
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Go to the UK Ebay site of Yoyo Electric Co. (UK Seller)
They offer 6 x mica MT-200 pads for UKP 1.95 - Not a bad deal considering the absurd prices asked for such inexpensive bits at the Farnell/RS outlets. I'm yet to see, let alone locate silpads of these, so why not use the best - mica.

Don't fiddle with mounting on 2 pads as you'll never be sure of insulation quality. Use the right one or close enough when trimmed from oversized pads or sheet. Don't forget insulating bushes with exposed metal tabs like TO220, TOP3, TO218.
Try this link, most Ebay links now time out. http://www.ebay.co.uk/sch/i.html?_nk...ING+Mica+MT200
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Last edited by Ian Finch; 12th September 2013 at 04:39 PM.
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Old 12th September 2013, 04:43 PM   #7
Ian Finch is offline Ian Finch  Australia
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Sorry, ignore link, its dead the moment I posted and the darned edit limit ran out again!
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Old 12th September 2013, 08:14 PM   #8
farjon is offline farjon  Brazil
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Quote:
Originally Posted by cs View Post
Thanks for the useful tips.

Farjon, what mounting kits did you use for the MT-200 transistors ? Would two TO-247 pads back-to-back work ?
Exactly. You have to cut to fit. I prefer cut only one of them, in order to put the gap between the two pads out of the center. The gap must be as small as possible.

After mounting, test continuity between colector terminal and heatsink.

Last edited by farjon; 12th September 2013 at 08:21 PM.
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Old 13th September 2013, 01:17 AM   #9
ontoaba is offline ontoaba  Indonesia
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You could use many type of replacements, even TIP2955/3055 with lower rail, just choose the better sounding one.
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Old 13th September 2013, 08:24 AM   #10
JOHN BALI is offline JOHN BALI  Indonesia
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How about Sanken's 2SA1294-2SC3263.
Maybe a good candidate for replace the Toshiba,
NJW0302/0281 also TO3P

John
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