OK. I was thinking to a cascoded DN2540 but having just two of them I looked for an alternative (FET) to link right below. Don't mind if I don't get the same performance, also a happy medium between the cascoded and the single one is welcome.
I don't like DN2540 as upper transistor, burnt a lot, now using IXTP 01N100D with great success.
As lower transistor:
2SK170/LSK170
2SK3557
CPH3910
N.B.
Always Idss of lower transistor must have more mA than device target
IXT gate stopper use CC like Arcol, 100R are perfect and not expensive
Be sure the Grade of lower transistor to ensure you can get your CCS target
As lower transistor:
2SK170/LSK170
2SK3557
CPH3910
N.B.
Always Idss of lower transistor must have more mA than device target
IXT gate stopper use CC like Arcol, 100R are perfect and not expensive
Be sure the Grade of lower transistor to ensure you can get your CCS target
Last edited:
Bela paralleled 4R7 to 2R2 of right channel, time to listen.
If I don'like the sound, I will order 10R Mundorf M-Resist 20W & I will change the power tx for the LL1683 to have 250V in place of the Bartolucci 125VAC to get the typical bias 140-150V 9V 6mA or don't worth the work because the sound don't will increase the SQ, what's your opinion?
If I don'like the sound, I will order 10R Mundorf M-Resist 20W & I will change the power tx for the LL1683 to have 250V in place of the Bartolucci 125VAC to get the typical bias 140-150V 9V 6mA or don't worth the work because the sound don't will increase the SQ, what's your opinion?
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No I don't but I will do later, that's a good way to see if the gain is more or less the same in both tubes, thanks.
What's the role of R1 (33R) series with the LED?
U= 33*0.01 only 330mV, it can be omitted, if you choose another (higher saturating voltage at 10mA) LED.
Each (AC unblocked) series resistance increase the dynamic impedance of cathode complex, so should be avoided if possible.
E180F is happy with 2V bias, so -old type- red or green LED is perfect for this purpose.
Bela subjectively both channels seems to have the same gain.
Do you believe the general bias used by you and others 140-150V 9V 6mA will increase the sound quality?
Do you believe the general bias used by you and others 140-150V 9V 6mA will increase the sound quality?
Changing power tx also give the possibility to use regulated HV, also more filtering possible at PSU.
The #26 linearity almost the same in 4-6mA, 100-150V range .... if you use good working CCS and clean bias.
Are you sure, you tested CCS with different B+ voltages as I suggested in #46 post?
If CCS not working perfectly (for example setting it to 6mA the real CCS loaded tube MUST to work at 6mA -if bias does not disable it-), the loadline of the tube isn't horizontal, so anything can happen.
The good linearity is necessary condition, but does not guarantee "sound quality".
If the preamp sounds bad, something other problem could perform: HF oscillation, bias disturbance, overloading, PSU oscillation etc. etc.
The detailed measurement with signal generator and oscilloscope is mandatory.
Sounds good, but missed SSHV2 like in other projects.
CCS is solid as a rock with bench PSU at 20, 25 & 30VDC.
CCS is solid as a rock with bench PSU at 20, 25 & 30VDC.
Euro21, you are right but the red led I'm using is an old tipe (square shape) with a Vd of about 1.65V at normal conditions. If you consider 10mA on the cathode to reach 2V the resistor is needed, based on the op. point of the loadline (V=165-170V). Am I wrong?
Thanks for you suggestion Merlin, the only thing is to see if IXTP 01N100D is easily available here (Italy). About the rest, I agree about the restriction of the Idss on the 2nd fet (transistor).
I mean "old": real old. I have 40 years old 5mm diameter LEDs. 🙂
At 10mA the red ones forward voltage average is 1.89V, the green has 2V.
The red has slightly lower dynamic resistance (dV/dI) than green (below 10mA).
I usually use LED bias only for CCS or "gyrator" loaded tube.
BTW the "new" Kingbright L-7104 series LED are also good ... if you use it with constant current.
Yes, they are about forty years old... as a recovery from old appliances with a square led vu-meter. Among the various LEDs tested they seem to me the most linear (even if I have made approximate measurements).
I've already spotted Knightbright's you mentioned on the bay, if they are not only sold from the UK due to customs I might give them a try.
Just out of curiosity, can you maybe post the gyrator/CCS circuit you used? 🙏
I've already spotted Knightbright's you mentioned on the bay, if they are not only sold from the UK due to customs I might give them a try.
Just out of curiosity, can you maybe post the gyrator/CCS circuit you used? 🙏
The cascode CCS (Dn2540, IXTP 1kV depletion MOSFETs) schematic as you post in #62.
The gyrator schematic is in #28 post there:
https://www.diyaudio.com/community/...hybrid-mu-follower.384775/page-2#post-7377521
The gyrator schematic is in #28 post there:
https://www.diyaudio.com/community/...hybrid-mu-follower.384775/page-2#post-7377521
Farnel or TME sells this within EU.
https://hu.farnell.com/search?st=l-7104&gs=true
https://www.tme.eu/hu/en/katalog/th...esc&search=kingbright L-7104&s_field=accuracy