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Old 10th April 2012, 12:26 AM   #141
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Quote:
Originally Posted by jacco vermeulen View Post
The J74/K170 are 400mW devices, doesn't mean they're supposed to dissipate the full amount.

Standard practice is 50% Max, read chapter 6 of the Toshiba semiconductor reliability handbook, referenced to in any Toshiba part datasheet.

50% is a bit conservative.
The standard F5 design has J108/K370, 200mW devices.
Vds is a little under 20V, derated Idss is 6mA, makes short of 120mW.
Or ~60% of the 200mW Max Pd.

50% derated J74/K170 handle 200mW, at 10Vds good for 20mA drain current.
High current good : higher Idss, better numbers, e.g. capacitances, lower noise.
High voltage bad : more heat, more gate leakage, etcetera.
Sorry to ask, but is this an answer for the bl vs v question?
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Old 10th April 2012, 10:17 AM   #142
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The answer was that (all) Violets can be used in a cascoded F5, in a standard F5 only the lower Idss V-grades due to the elevated dissipation. (or stick heatsinks on them, shave 'm off, etc.)

Personally, i don't have a problem with Blue JFETs in parallel. If it works in a head-amp, it'll work for power amps. Papa did as well in the concept amps for the top of the line Xs.

Prettiest of course would be J72/K147 V's in the +20mA Idss range.
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Old 10th April 2012, 02:13 PM   #143
arche13 is offline arche13  France
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Hello
I plan to make a F5 turbo V1, on the plan the resistances of triggers mosfet (R13 to R16) are of values 47,5 ohms. In the series Dale RN60 1 / 4W 1 %, I have the choice between two values: 49,9 ohms or 44,2 ohms. Which of both values is the best adapted
Thank you for your help
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Old 12th April 2012, 02:37 AM   #144
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Quote:
Originally Posted by jacco vermeulen View Post
The answer was that (all) Violets can be used in a cascoded F5, in a standard F5 only the lower Idss V-grades due to the elevated dissipation. (or stick heatsinks on them, shave 'm off, etc.)

Personally, i don't have a problem with Blue JFETs in parallel. If it works in a head-amp, it'll work for power amps. Papa did as well in the concept amps for the top of the line Xs.

Prettiest of course would be J72/K147 V's in the +20mA Idss range.
Now I see, thank you Jacco
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Old 5th May 2012, 11:03 PM   #145
lhquam is online now lhquam  United States
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Originally Posted by Bksabath View Post
I have source for FQA19N20 they sell minimum of 1000 pieces so no go for me there
If one has the cash to go for it PM.
FQA19N20C is one different kind of beast with more capacitance and more power then there is the FQA19N20 L even more power and again more capacitance.

I use FQP19N20, which is closer match(current wise) for FQA12P20 but has TO220 pack
Having bought 100 each I can spare a few so Pm
They have been running since last August on MY F5.

I quite like the idea to use the 36 and 28 as you mention I am not shure how they perform and my Knolledge is limited so it will have to be a build and see thing the gain of those 2 is quite interesting so try them and report back.

I have seen post about potential buy of the original pair 19 / 12 will need to search for that

I just made measurements of a F5 amplifier using FQA36P15 and FQA28N15 mosfets. The distortion measurements of the amplifier are disappointedly high, probably due to the high input capacitance. I am seeing about .004% THD at 1 kHz, 1 watt into 8 ohms. Unlike all of my other F5 builds, the P3 adjustment will does not reduce the 2nd harmonic below the 3rd harmonic.

I am still looking for a source for FQA19N20C and FQA12P20 or 2SK1530 and 2SJ201. I need 4 each for a pair of balanced amps. It would be nice to have 4 more each for a future build. If I cannot find any other source, I am willing to try the TO-220 counterparts (FQP19N20 and FQP12P20).
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Old 5th May 2012, 11:13 PM   #146
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Quote:
Originally Posted by lhquam View Post
I am still looking for a source for FQA19N20C and FQA12P20 or 2SK1530 and 2SJ201. I need 4 each for a pair of balanced amps. It would be nice to have 4 more each for a future build. If I cannot find any other source, I am willing to try the TO-220 counterparts (FQP19N20 and FQP12P20).
Send me a PM and we take it from there I got same FQP19N20 to spare.
I am using those with the FQA12P20
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Old 6th May 2012, 10:04 AM   #147
AndrewT is offline AndrewT  Scotland
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Originally Posted by lhquam View Post
............about .004% THD at 1 kHz, 1 watt into 8 ohms. ...............
I would class that as a good value for THD. Even more so if there are no measurable harmonics above the 4th.
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Old 8th May 2012, 02:04 AM   #148
lhquam is online now lhquam  United States
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Originally Posted by Bksabath View Post
Send me a PM and we take it from there I got same FQP19N20 to spare.
I am using those with the FQA12P20
With your method of clamping the devices to the heatsink using a metal bar, how would you deal with devices with of different thickness, such as TO-220 and TO-3P?
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Old 8th May 2012, 05:30 AM   #149
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Quote:
Originally Posted by lhquam View Post
With your method of clamping the devices to the heatsink using a metal bar, how would you deal with devices with of different thickness, such as TO-220 and TO-3P?
That is prety easy as they are in 2 separate parts of board use 2 bars
one for TO220 and one for TO247
There are loads of beter pictures about the heath spreaders and clamping on
MY F5 tread

I got no PM from you.
Pity because I was interested in the distortion mesurament you taken and was going to send you 2 pairs of matched FQP19N20 for the price of the postagge
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File Type: jpg FAIR F5boards 006.jpg (616.3 KB, 654 views)
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Old 8th May 2012, 09:13 PM   #150
lhquam is online now lhquam  United States
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Quote:
Originally Posted by Bksabath View Post
That is prety easy as they are in 2 separate parts of board use 2 bars
one for TO220 and one for TO247
There are loads of beter pictures about the heath spreaders and clamping on
MY F5 tread

I got no PM from you.
Pity because I was interested in the distortion mesurament you taken and was going to send you 2 pairs of matched FQP19N20 for the price of the postagge

The clamping I need to do is 4 devices in a line: TO-3P MOSFET, 2 MP915 Caddock resistors, TO-3P MOSFET. The Caddocks are 2mm thinner than the MOSFETs. I am considering some type of compressible material (plastic foam?) as a shim for the Caddocks.
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