The diyAudio Firstwatt F6

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#842
I've bought Asian, Hifi2000 plain (un-drilled) cases, and the Deluxe cases.

IMO, when using the diyAudio store boards with the pre-drilled Deluxe chassis, the savings in time and ease more than outweighs the increase in money spent. It really makes things much, much easier.
 
#843
I agree with 6L6 in that the cases at DiyAudio is the best deal out there. I used the standard 4U for my first build and for roughly $250 you will have a nice looking amplifier you can be proud to show off but with the standard you do have to still drill and tap some holes. All the Asian cases I have seen for sale around the same price have much smaller heatsinks. If you do not mind using a fan in the case it would not be a problem. The deluxe chassis sure look nice when all you have to do as for as a case is install the boards and some small assemble. I built an Aleph 30 with the standard 4U and it does get warm somewhere in the neighborhood of 55 to 60 degrees not excessive. The F6 in the same case runs less than 50 degrees all the time. Aleph's are hot running amps. I play with different amps and just having some good heat sinks when you are switching all the time is a nice option too.

David
 
#844
6L6 said:
4U is totally fine for an F6. It has half the Mosfet of a Aleph J. A F6 built in a 5U would be severe overkill.

The 4U is pretty hot for an Aleph J, but with sufficient ventilation, it's OK.

The 5U seems and feels significantly bigger than the 4U. Much deeper, and it's just tall enough to not fit is some places. This, however, shouldn't be a problem as you really need 4-5 inches open above the amp for good ventilation.

All the diyAudio PCB will fit the hole pattern on either chassis.
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Your build guide for the Aleph J states:


Also, this build will show a 5U 'Big Amp Chassis' from the DIYaudio store. (Because that's what I have on hand.) The Aleph J can be made into the 4U 'Jack of all Chassis', everything will fit and the heatsinks are (just) big enough. All the specifics surrounding the 'premium' chassis (back panel, perforated base, pre-drilled heatsink, etc…) are functionally identical, the differences between the 4U and 5U are mainly just size. Regardless of the chassis you use, this amp does get quite hot, and good ventilation will be required around the entire chassis.
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I swear, at some point the store even recommended the 4U "Jack of all chassis" as well. Based on that and your build guide, I bought one. Now I'm reading that it will get too hot and the 5U is recommended. I really don't have the money for another chassis and now I can't use the one I have. Great.
 
#846
dodog said:
Your build guide for the Aleph J states:




I swear, at some point the store even recommended the 4U "Jack of all chassis" as well. Based on that and your build guide, I bought one. Now I'm reading that it will get too hot and the 5U is recommended. I really don't have the money for another chassis and now I can't use the one I have. Great.
Click to expand...

just use what you already have and do not worry

bias it to 55C in summer (Papa's palm rule or temp. probe , whatever)

if you feel for more juice , just make proper Babysitter , which will allow full blast
 
#849
I'm going with 4U for both AlephJ and F-6. I'm sure they will be fine. I am also going to build baby sitters, so 4U is fine for my uses. The only reason I have 5U now is it was intended for Turbo F-5.

100 bucks difference in 4U deluxe and standard 4U....that's not even minimum wage for as long as it took me, maybe no where near close, and all that mess, sore hands, metallic splinters etc. Well worth it to just putting it together, no measure, drill or tapping. Call me lazy, but I prefer building the next 2 like that!

Of course I had to drill couple of holes, ground screw, better feet I bought.:h_ache:

Russellc
 
#851
Thanks everyone for the reassurance. I reread my post and want to apologize to Jim. It reads like I'm blaming him when I was just trying to vent my frustrations. Jim's a really nice guy and I meant no disrespect.

ZM (or Russell), what the hell is a babysitter? Also, regarding biasing temperature. How does one do that? IR thermometer?
 
#858
Zener and their resistors

Hi,

I was thinking about the zener diodes and I wondered if R7/R8 at 10K might be too high
for Z1, Z2=9.1V and so I did a test.

I basically wired up the R7, Z1 and P1 elements of the schematics on Page 1,
replaceing Z1 with a 9.1V zener, and P1 by a 4.75K resistor. (These are the two zeners I tried:

BZX79-C9V1,133 NXP Semiconductors | 568-7958-1-ND | DigiKey (NXP 500mW)
BZX85C9V1-TAP Vishay Semiconductor Diodes Division | BZX85C9V1-TAP-ND | DigiKey (Vishay 1.3W)
)

I hooked this up to a simple LM317 regulated supply and I measured both the supply
voltage and the voltage across Z1.


For supply voltages up to 27V, what I found is that the measured voltage across Z1 is just what you get from
the voltage divider formed by the 10K and 4.75K resistors. Since a chunk of the current
through R7 has gone to the 4.75K resistor, it seems there is not enough left through Z1 for it
to be biased properly. (Things seem to start stabilizing around 28V; unfortunately the transformer
I have hooked up to the LM317 doesn't allow me to go higher.)

Replacing R7 by 5K and the voltage across Z1 stays around the zener voltage once the
supply voltage goes above ~19V.


Would this contribute to the bias drifting with varying AC rail voltages that some
members have observed?

Anyway, I think I'll be using 5K for R7 and R8. 🙂

Cheers,
Dennis
 
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#859
Dennis Hui said:
Replacing R7 by 5K and the voltage across Z1 stays around the zener voltage
once the supply voltage goes above ~19V.Would this contribute to the bias drifting
with varying AC rail voltages that some members have observed?
Click to expand...

Yes, I mentioned this in post #17 here. Always keep the Zener current,
in the worst case operating conditions, over 5% of the maximum Zener
current (P rated / V zener), and preferably more. The Zener's knee is soft
and it will have worse regulation at lower currents than at higher currents.
The best operating point is at around 40% of the maximum current.
 
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#860
I am building a new F6 with IRFP240s (the earlier one was a semisouth based). I realize that I don't have 18 ohms resistors and cannot get easily in the market. I do have 22 ohms, 1% dales. Can they be used instead of 18 ohms in the circuit?

Thanks in advance.

Cheers
 
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