F5Turbo Illustrated Build Guide

Hi all,

I'm in the process of building v3 monoblock version and need a substitute for R17-R24 (1 ohm 3w). The v3 BOM suggests using 71-RW79U1R00F, which is currently out of stock.

I have enough of 667-ERX-3SJ1R0 or 71-RW69V1R0, but I wanted to confirm prior to stuffing whether either would work and if one was preferred over the other.

Thanks in advance!


2009-07-21 1:36 pm
Can someone please confirm a couple things?
1. if you drop the diodes, and assuming 4 transistor pairs, the max current is about 44-46A? And with the diodes the current output can theoretically reach 70A?
2. Do the cascode tip transistors need to be matched?
3. Do the diodes need to be matched?
Thank you and Happy New Year!!!


2009-07-21 1:36 pm
Thanks Zenmod. Lol. Reading papa’s F5 turbo article, I gathered that the only reason for diodes was ability to pass higher current. Was just trying to see how much “penalty” there is for omitting them. Nelson specifically mentions two output pairs without diodes can pass circa 22A and with about 44A. I was extrapolating for 4 output pairs, but maybe It doesn’t work that way. Seems most folks feel higher bias ability outweighs any concession in current.


2009-07-21 1:36 pm
Thank you. You helped me to decide. One last question Please. I purchased two F4 mosfet kits a while ago which are still sitting in bags. I want to build F5tv3 monoblocks but have only one F5tv3 mosfet kit (Good for only one monoblock channel). Diyaudiostore is currently sold out. Can I cannibalize 4 pair of mosfets from the F4 kit and use for one of my F5v3 monoblocks channnels? I ask because the diyaudiostore mentions that f4 semiconductors were matched at operating levels (22v) suitable for F4, whereas my f5 turbos will be at 45v rails. Any issues? Want to keep monoblocks as close to identical as possible. of Course, the diodes are being disregarded, so just the irfp240/9240 in question. Thx


Paid Member
2013-01-30 4:15 pm
Elkhart Lake, WI
Reading papa’s F5 turbo article,
Go back to the website with the F5 turbo article and scroll down to 1993, "Matching Devices". A battery and a resistor a DVM and jumper wires and you can do it yourself to see what you have. 6L6 told me you power and test for 20 seconds, and do your best to test each one for the same amount of time. I spent a hour or so and tested every MOSFET I had in stock, not hard to do at all.
C1 and C2 are in the schematic. Depending on which version you are building (if you use more than one of each N and P type board as an example) you would only populate C1 and C2 on one of the boards; thus the 'sub x' designation.

tl;dir - One set of N and P - Populate C1 and C2
More than one set of N and P - Only populate C1 and C2 on one N and one P board.

Hope I explained that well enough. :D

Edited for (hopefully) better clarity.
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@algg - I was rethinking and relooking at this... I could be completely wrong. It's best to wait until someone more knowledgeable with the V3 boards (board version not F5Tv3) chimes in.

In the build guide, I see that 6L6 has populated C1 and C2 on the FE boards and (what would be potentially) C1x and C2x equivalents on the output boards for one iteration with the blue Panasonic resistors. He did not populate (what could be the equivalent to) C1x or C2x on the output boards for another iteration with the white resistors.

I don't have access to boards at the moment, but from the pictures on the store site, I cannot see where the traces for the positive side of C1x and the negative side of C2x connect on either the front or back of the board. I can see the traces, but I'm away from a good monitor, and I don't want to assume again.

tl;dr - I should not have answered until I was sure. Apologies.


Paid Member
2010-10-22 6:43 pm
Denver, Colorado
Yes, always stuff C3 and C4.

Yes, use only one cap per mosfet bank… I.E., of you daisy-chain multiple boards to hold 3 or 4 Mosfets per side (N, P) you only need one cap, or two per channel.

As always, refer to the F5v3 schematic in Nelson’s guide, the PCBs follow this schematic.
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Hi Jim,

Humble apologies if I've entangled this too much.

I believe what @algg was asking was whether to:

Populate C1 and C2 on the FE board. Seems clear, the answer is yes, and I understand and agree.


Populate C1x and C2x on the N and P boards in various build scenarios.

I could not tell from board pics on my current display if C1x and C2x were in parallel with C1 and C2 respectively (obviously when wired to the FE boards) or how to properly convey when those specific spots should be stuffed.

All are related to the V3 version of the boards. What I am unsure is whether a F5Tv1, F5Tv2, or and F5Tv3 is being built and how to advise accordingly. Your answer will also benefit my understanding since I don't have a board to trace.