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F-4/BA-3 Transistor Kit

Original price $ 59.00 - Original price $ 59.00
Original price
$ 59.00
$ 59.00 - $ 59.00
Current price $ 59.00
in stock, ready to be shipped

Included in this kit are the semiconductors needed to complete an F-4 amplifier or BA-3 output stage, with the exception of the input JFETs. MOSFETs were matched in accordance with standard operating conditions. This is enough transistors for 2 channels (one stereo amplifier).

  • 6 x IRFP 240 (F4 and BA-3)
  • 6 x IRFP 9140 (F4 and BA-3)
  • 2 x TL-431 (BA-3)

The IRFP9140/IRFP240 MOSFETs were matched at the rail voltage and current that the BA-3 and F4 articles suggest, specifically, 22v and .4A, and then grouped by VGS to within .1V.

Please note

  1. The current batch of kits includes  Harris IRFP9140 instead of the International Rectifier version. These have better distortion characteristics and are a sonic upgrade, but it should be noted they are rated for 100V.
  2. Any numbers on the MOSFETs are ID numbers only, and are not related to their measurements nor their matching

Customer Reviews

Based on 12 reviews
Nice Build

F4 is a great sounding amp and a fairly straightforward build. Only issue I had was a slight mismatch in the Mosfets that showed up measuring bias across the 0.47 ohm resistors. No idea how common that is but fixing it required swapping two mosfets. If you have the ability to match test the mosfets before installing I suggest you do that otherwise you may have to desolder and reinstall them to get a better match. Also, strongly recommend using a 7-8K resistor for R9 instead of the 10K that is specified in the BOM. I wasn't able to bias one side high enough with that 10K resistor.

Nikolaos K.
Excellent kit

Excellent kit! My F4 works great! Thank you!

Anders A.
F4 Transistor kit review

Excellent kit, service and delivery . Now working perfect in F4 .

Time Saver

Having the mosfets matched in advance is a times saver and worked out well repairing a F4 channel.

Adrien T.
Speedy delivery and as advertised

What more can I say? Support the site!

Robert G.
Quick and Efficient

Great service! Parts arrived very quickly with everything accounted for. About to start my F4 build! Thanks DIYAudio Store!
Rob G