How to build the F5

6L6

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Adjusting both is how you get your DC offset to go to zero -- and that is hugely important in this amp.

The trick is to get things to .2v bias or thereabout and zero the offset.

Then increase the bias to .4, and zero the offset - you will notice that one ill effect the other, so it's always two steps forward and one step back - that's normal.

go to .5, zero the offset, and then set .6, and zero the offset again.

Also you need to have the thermistors on the amp PCB touching the plastic body of the power mosfet, that way they can track the temperature properly.
 
Ok, I got a couple minutes to work on the amp last night.

My broken channel seems to be in worse shape than last time. I no longer measure any voltage across r12. With the pots fully open I measure .015 Volts across r11. I also noted that with 30 minutes of warm up, the heat sink was still very cool, whereas the 'functioning' channel biased to .36 was slightly warm.
 

6L6

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Joined 2010
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Don't worry about the F5v3 boards.

With the amp powered off, measure resistances from pin to pin on the Jfets and Mosfets. (Pin 1 to pin 2, pin 2 - 3, pin 1 - 3, etc...) Compare to the good channel. Report any gross variances.

Another thought - di you have the proper device properly inserted in the limiter circuit? (ZTX transistor?)
 
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JIm's (6L6's...) comment above is right on the mark. I just posted this on another F-5 thread, but it applies to your case, as well:

If you know you still have one GOOD channel, and suspect you have successfully repaired the bad channel--I'd take some "comparison" resistance checks WITHOUT APPLYING power as your first remediation step. You already have your two most available tools for troubleshooting--a good channel, and a DMM. Check resistances. If you have repaired the board, such comparison checks can give you a good indication of other bad parts, to include resistors, pots, capacitors, semis, and the occasional PCB short or open.

(In your case, it sounds as though you have one known good channel, and one known bad channel.... The advice is still the same--take comparative measurements, and let us know what you find.... In some cases, it might be worthwhile to unsolder a component (same one, on BOTH boards) to take measurements to isolate the bad actors. Yes, throubleshooting is NOT for the faint of heart.... :) )
 
After quite a bit of time off to get ready for my first children arriving next week (twins!) I found some time for measurements. Everything seems to line up pretty well. I am more stuck than ever.

Q1a SG 99.7K Q1b SG 99.7K
SD 41.1 SD 42.1
GD 99.9K GD 99.8K

Q2a SG 99.8K Q2b SG 99.7K
SD 41.1 SD 38.4
GD 99.9k GD 99.9k

Q3a GD 117 Q3b GD 118.3

Q4a GD 117 Q4b GD 121

Q5a BE 129.5 Q5b GD 129

Q6a BE 129 Q6b GD 128.5

What's my next step guys? Cheers!
 
I would suggest these capacitors from mouser - Panasonic TSHA, 35v,

18,000uf - ECO-S1VA183EA Panasonic Electronic Components | Mouser

15,000uf - ECO-S1VA153EA Panasonic Electronic Components | Mouser

10,000uf - ECO-S1VA103CA Panasonic Electronic Components | Mouser

Which one you use is dependent on the final PSU configuration, I.E., how many capacitors you plan on using.

If you are going to use the chipamp.com PSU board, with one transformer and PSU board per channel, you may use smaller caps.

But, this is DIY, and complete and utter overkill on the PSU is de rigueur... :D :D :D

These caps are not available anymore. Could someone please point me to another suitable 15000uf cap from Mouser? Thanks in advance!