Ouch. You need the mica for electrical insulation - the (extremely thin layer of) grease is there for thermal conductivity. A thick layer of grease might electrically insulate, but it will most certainly thermally insulate, and that's not good.
Hopefully you haven't zapped your fets.
I have some Mica TO-247's that I can gift you to go with that grease, it would get there next week I think, if you don't need extra stuff from Mouser. PM if interested.
You may still be able to get TO-220 micas at Rat Shack, which can be used if you're fairly careful to position them properly, they're a bit too small for TO247s, but they will work....
Dallas is a large enough market you ought to be able to fine a genuine electronics parts store that would probably have them.
Roscoe
Dallas is a large enough market you ought to be able to fine a genuine electronics parts store that would probably have them.
Roscoe
Thanks guys! I was able to salvage enough pieces of the silicon pad strips that were in the OM-150. I accidentally ordered 1/8 watt 750 ohm resistors, so I also grabbed some 680 ohm (I think) resistors from Radio Shack for R22, thinking that it might not matter too much because P2 could be able to make up the difference.
However, I am not able get the bias high enough. Should R22 make a difference there? Do I just need to lower R9?
Sounds great, though. Perhaps a little more harmonics than I am used to. Looking forward to the caps breaking in. 😛 And building another one. But, I am building my active crossover first, which will have plenty of voltage gain for the F4s.
However, I am not able get the bias high enough. Should R22 make a difference there? Do I just need to lower R9?
Sounds great, though. Perhaps a little more harmonics than I am used to. Looking forward to the caps breaking in. 😛 And building another one. But, I am building my active crossover first, which will have plenty of voltage gain for the F4s.
With R9 at 5K I was able to get the right bias. Is it normal for the voltage across the .47 ohm resistors to vary by as much as 10mV?
Luvdunhill, perhaps the wood is acting as a sounding board.
Luvdunhill, perhaps the wood is acting as a sounding board.
Perhaps your right, once I get things more secure I'll report back. After the kids opened their presents, I'm listening to one of mine. Peter Takács playing the Beethoven Piano Sonatas. Man, it sounds amazing! Tons of dynamics. My first recording on Cambria, definitely one to look at in the future.
Can the schematic of the PSU of F4 be found anywhere else, link seems to be down
Thank you 🙂
I started disassembling my non-working Counterpoint amp and found four 25 mF caps that are the size of soup cans. If I want to use them, do I need them in parallel with some 8 mF caps? Is there any chance that 25 mF is close enough to work?
The life time of these big devices depends on the temperature. (drying) 20.000 hrs is not uncommon, but even then . .
See as an example of the life times: these specs, scroll down to the end
Measure the capacitance first!
See as an example of the life times: these specs, scroll down to the end
Measure the capacitance first!
That's interesting, thanks. However, the amp was in an attic in Texas for nearly ten years, so I didn't bother with them.
Thanks for the offer. That was very generous. I got it sorted out though. I wish the best to you and yours in this new year.
Night and day.
I mentioned that my first impression of the amp was that it added more harmonics than I was used to. Perhaps I spoke too soon. At first it reminded me of an older steel core audio transformer, where the harmonic distortion increased significantly as the frequency lowered. This was pretty much gone after ten hours. After breaking it in further, its probably cleaner than what I am used to.
I mentioned that my first impression of the amp was that it added more harmonics than I was used to. Perhaps I spoke too soon. At first it reminded me of an older steel core audio transformer, where the harmonic distortion increased significantly as the frequency lowered. This was pretty much gone after ten hours. After breaking it in further, its probably cleaner than what I am used to.
I got some aluminum oxide ceramic thermally conductive insulators for the transistors. They are much thicker than I imagined. I can't figure out if I am supposed to use the silicon grease with them or not, so I didn't apply any.
I will be receiving some more binding posts tomorrow, and I will finish this four channel F4 amp as well. The lower level is all hooked up and biased. The upper deck was biased in the other chassis. This chassis originally had two columns of 4 TO-3 type mosfets on each side. It will now have columns of six, slightly staggered. From feeling the heatsinks with only two channels installed, my instinct says they will be adequate.
I will be receiving some more binding posts tomorrow, and I will finish this four channel F4 amp as well. The lower level is all hooked up and biased. The upper deck was biased in the other chassis. This chassis originally had two columns of 4 TO-3 type mosfets on each side. It will now have columns of six, slightly staggered. From feeling the heatsinks with only two channels installed, my instinct says they will be adequate.
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Mica insulators are propably the best. The thinner the better. You can split them using knife and produce 2 or 3 out of one. Thermal silicon or grease is for getting rid of air between surfaces, so you should apply a little amount on any surface to increase heat flow.