Hello,
for a capacitance multiplier which powers a audio tube preamp phono section, can someone please advise for a high gain TO 220 Darlington Transistor to be implemented in this circuit? It should provide high noise supression and excellent sound. Thank you.
View attachment 109449
Thank you. Noise suppression of a cap. Multipler depends on the current gain of the Darlington pair and the value of the external resistor. A protecting Diode is integrated into the IC als well. So how about 2N6045 doing the Job? The circuit needs 300VDC and 26mA.It should provide a higher effective capacitance. Noise suppression will depend on the rest of the associated circuitry. It doesn't provide excellent (or any other quality of) sound.
The 2N6045 is a 100V device. I wouldn't use it in a 300V circuit.Thank you. Noise suppression of a cap. Multipler depends on the current gain of the Darlington pair and the value of the external resistor. A protecting Diode is integrated into the IC als well. So how about 2N6045 doing the Job? The circuit needs 300VDC and 26mA.
I don't recall all the details but back in the 70s when my computers and test bench were all assembled from heath kits, my computer monitor went dark. There was a flyback switching PS for the crt supply that used a hard to source darlington. Heathkit could not promise a replacement part for several weeks. I was unwilling to go that long without my computer. So I jury rigged a DIY darlington from two adequate voltage bipolar transistors. It worked well enough to get my terminal up and working again.Hi Walter
A high voltage Darlington is uncommon. Use a 400 volt (min) NPN power as a pass through and a smaller 400 volt (min) NPN to make a HIGH VOLTAGE DARLINGTON. Add a diode across the pass device as upon the TURNOFF the reverse voltage will kill this regulator circuit. The 300 volt supply also needs a bleeder to ground.
You need more DATA to design the circuit to insure that the circuit will not FAIL to work in the long term.
Duke
Hello,
for a capacitance multiplier which powers a audio tube preamp phono section, can someone please advise for a high gain TO 220 Darlington Transistor to be implemented in this circuit? It should provide high noise supression and excellent sound. Thank you.
View attachment 109449
A Darlington is "easily" achieved with two individual transistors. No reason to seek a Unicorn Darlington in a single package.
And regardless of chosen parts, all capacitance multipliers have what I consider as a fatal design fault. Any overcurrent fault on the output, the pass transistor usually fails with a collector to emitter short circuit.
Wow....I'll try that in my next valve design...as if I do that any more. lolIRF730 or IRF830. These are Mosfets.
In this case I recommend:
T1 = IRF830
R1 = 6M8
R2 = 1k (this is a gatestopper in series with with the gate)
R3 = 100R (this is a protection resistor in series with source/emitter before Vout)
ZD1 = 1N5245B (or similar - Gate protection diode from Vout [anode] to Gate [cathode])
C1 = 100nF/450V Film (e.g Wima MKP2)
C2 = 100uF/450V Film or Electrolytic (this capacitor is attached between Vout & GND)
View attachment 109510
This circuit will produce around 280V DC from a 300V input. The Turn on time of Vout will be around 7 seconds to 70% of full HT.
Output current will start limiting around 100mA. It is not a foldback limiter, so with 300V in and a permanent short, 30W get dissipated in the Mosfet. This simple protection circuit is not intended to reliably provide indefinite time short circuit protection, but to rather ensure a slipped probe does not release black smoke and capacitive loads are unlikely to kill the Mosfet.
100Hz ripple rejection is ~ 70dB with the values shown.
Increasing C1 increases the 100Hz ripple rejection proportionally, but turn on time is increased. It is possible to use an additional trick to speed up turn on if desired, I consider the HT hold-off/slow-turn on quite desirable.
Thor
Wow....I'll try that in my next valve design...as if I do that any more. lol
I'm dense I guess the series resistor on the output is all that keeps the transistor from blowing up with a rando short?
Hmmmm...a RCRCRC filter would do the same?
I have done a few passively smoothed HT supplies that take several minutes to ramp up , I dont mind that at all because a tube and its asscociated components can take 30 minutes or more to reach full opperating temp the slower the rise of the HT the better .
For the same reason I hate tube amps without a standby , some have tried to argue it makes no difference , I say it does . You also find some who instead of using the standby as it should be used , to allow your heaters pre-warm ,just flick both power and standby on at the same moment ,
Its similar to the engine in a car , you wouldnt start up on an cold morning and tear straight off down the autobahn at 155 , would ya?
Many thanks For your suggest, Thor.
What I search For is to understand what TO 220 Power Transistor or Darlington would fit the one external resistor circuit shown in my first Post. This circuit is used by Shindo Labo of Japan in their Tube amps and it Sounds Superb.
It doesnt need minutes to Ramp Up and seem to Filter voltage quite well. It has one 27k resistor employed. No extra diodes, No Second Transistor being used.
Very simple and elegant solution. Beside BUX85G, is there a better part available For the Job?
Darlington has internal Diode employed and Higher gain means better filtering, so I thought it could be that Kind of active Part. But Darlington is hard to find with high gain and high voltage.
The internal protection diode will only protect against reverse voltage but not against shorting the output.What about IRF830 when applied in this circuit? It has an internal protection Diode already implemented. So why Not Do it this way, please? Resistor value can be changed.