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In a 2-stage 2A3 amplifier (6C45P-2A3) which should be the values of ripple in the B+ supply of the first and second stage ?
Follow Ups:
you should be absolutely certain that the first stage is VERY well
filtered, even below 20Hz. Hammond makes a small 60-henry, 8mA
chome which sells for about $10 each U.S. If you feed each 1st stage
with one of these, along with a minimum of 100uf filter capacitance
(prefferably 200uf or so), then you may totally transform the sound
of your amp. Seriously --it makes a HUGE difference, and most SETs,
(even otherwise good commercially made SETs) somehow seem to
over-look LF stability/ feedback issues.Try it, and you will thank me.
Good luck!
Thomas,
... the first stage (that is also the dirver stage for the 2A3) works with 14 mA (so 8 mA should be too little) ... and my intention was to utilize a LCLC filter ... possibly with low DCR.I have read (in the tube DIY section) that low DCR power supply sounds better than standard filters.
So, I'd like to experiment low DCR chocke and low-uF Capacitor in the power supply ... but I cannot find any specific schematic with this implementation.Antonio
P.S.
Thomas ... why when i run the PSUD with the values reported in 300B section of this schematic (http://home.att.net/~chimeraone/axiom300bschematic.html) I obtain different Voltages (> 500 vs 385)?
It depends on the power supply rejection of each stage's design. If you power the filament from AC, you can expect about 3mV peak to peak hum (1mV rms) at 120Hz on the 8 ohm tap from the heater. Assuming a 20:1 transformer (3200 ohm primary impedance) That would be 60mV peak to peak (20mV rms) at the plate. You would want to match that with the high voltage supply, at a minimum:1) 2A3 with series feed output transformer: the transformer impedance (3200 ohms) makes a voltage divider with the 2A3 plate resistance (800 ohms) so that 80% of the power supply ripple appears across the transformer. So the power supply needs less than 75mV pk-pk (25mV rms) ripple.
2) Parallel feed with the smallest practical choke, 10 henries: The choke impedance is 7500 ohms at 120Hz, and forms a voltage divider with the tube (800 ohms) in parallel with the load (3200 ohms). Maximum ripple would be 750mV pk-pk (250mV rms)
3) Parallel feed with a serious, high-inductance plate choke of 40 henries: Choke impedance - and power supply rejection - is four times higher, so you can get away with 3v pk-pk (1v rms) ripple.
A similar analysis holds for the driver stage, except the driver plate ripple is amplified by the 2A3. An amplification factor of 4 is close enough for estimating purposes.
Of course there are finer details if you want to get fancy, e.g. phasing the power supply ripple to cancel some of the filament ripple. This analysis just gives a general ballpark idea of where you want to be. Hope that helps!
If I have well understand ... with our 6C45P direct coupled to 2A3 (*) I'd obtain (with the simulation on PSU-Designer) a < 75 mv p-p ripple in the B+ supply of the power stage
and about 20 mv p-p in the driver stage.
Is it correct ?Paul,many thanks for your lesson and your competence.
Antonio
* The schematic (of the 300B version) is reported here http://www.diyaudio.com/forums/showthread.php?s=&threadid=73513&perpage=10&highlight=&pagenumber=2
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