Simplistic Mosfet HV Shunt Regs - Page 279 - diyAudio
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Old 23rd February 2012, 12:46 AM   #2781
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Changinf 840 as we speak. Got new tube and went to retest and kids had switched probes and i didnt notice. Nice pop and now replacing entire sensing circuit.
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Old 23rd February 2012, 01:07 AM   #2782
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Upper bjt measuring 9mV lower bjt 1.6V. Irf840 is 3.5V. I fi place probe to measure Vgs of irf 840, output voltagr begins to rise. Seems upper bjt may b eproblem.
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Old 23rd February 2012, 01:09 AM   #2783
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Quote:
Originally Posted by Salas View Post
All well then. What type is it? SSHV1? Post some picture with your (SRPP?) phono.
Yes it is SSHV1.I will try to get some decent pictures in the morning if you are still interested after seeing that mess but this is a work in progress so no nice enclosure here and since I like to use only 20-30cm armtube wire to phono input there are space limitations(the sound is on the oposite side ,beautiful).
The phono is Eric Barbour 6s17k-v circuit.I only changed output tube with 6n6p-i led biased so no electrolyte in chain from PSU to phono.RIAA uses Soviet teflon caps that are opened from their metal enclosure and unwounded on desired value and the windings are then wrapped with cotton thread from outside to desired value (if you need 39,6 nF unwind the cap on around 39 nF and with wraping you ad the rest of 0,6 nF).
This way the cap sound much better because the windings of original cap are pretty loose inside.
After few years of using SSHV1 I finally found time to replace sand diodes with hybrid vacuum rectifier.I started with 6x4 then ez80 and ez81.The sound was wonderful in mid frequencies but else was missing somehow and after thinking of the problem I tried ey88 which is 220mA damper diode and the whole spectrum is here including mids but not so euphonic like with EZ types.I suppose that magic is distortion of 90 mA tube (60mA consumed by SSHV) which work near it's current limits.
The tubes in supply are completely quiet (black sound stage) and almost no hum compared to sand diodes on max volume.
Maybe this is of topic but just wanted to encourage someone who wonders himself about result regarding tubed PSU.It is worth the effort ,especially in the phono circuit.My researches resulted that weak rectifiers leads to romantic presentation and tough are more like solid state regarding dynamics but still pleasant ,in fact the best of both.If you have heavy heat-sink you can fine adjust the type of the sound from romantic to more honest by loading the tube rectifier more or less with regulator CCS settings ,one among great features of Salas regulator.With EZ types you are stacked with romance only if you need higher regulator ratings.
Can somebody suggest other rectifier tubes and describe it's sound with various loading but only indirectly heated ,since I don't have 5V windings.I also use py83 which sound more on flat side when is lightly loaded but it's extremely detailed.That is the nice side of the tubes ,they are mud flexible ,the different sound for each day
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Old 23rd February 2012, 02:12 AM   #2784
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Quote:
Originally Posted by buzzforb View Post
Changinf 840 as we speak. Got new tube and went to retest and kids had switched probes and i didnt notice. Nice pop and now replacing entire sensing circuit.
KIDS around open HV rig ???? LOCK them out.

Quote:
Originally Posted by buzzforb View Post
Upper bjt measuring 9mV lower bjt 1.6V. Irf840 is 3.5V. I fi place probe to measure Vgs of irf 840, output voltagr begins to rise. Seems upper bjt may b eproblem.
That upper one is responsible to bias the fet also, it can be the problem.
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Old 23rd February 2012, 02:12 AM   #2785
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As far as i can figure, the problem ha sto be with the voltage refernce for the bjt 's. They are not controlling the shun tproperly and it is shorting all the current away. When i measure Vgs, i steal some current from the gate, lowering the Vgs and along with it, the curren tthe fet will pass. This reduces shunt current and the rails begin to climb. The bjt's begin to balance better. I dont full yunderstand the control mechanism though. Is it the jfet.? The led is working fine or at least test good.
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Old 23rd February 2012, 02:15 AM   #2786
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Is there enough Vbe on both BJTs by now, changed the upper one? Is the CCS current ~20mA more than the actual load so there is enough for inner consumption? LED working means jfet working.
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Old 23rd February 2012, 02:15 AM   #2787
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No kids. Left out the dmm on the table. Replaced the bjt and no change. Other sid eworks flawlessly. If led is not lighting up, doesn this mean that the jfet is not functioning? Ccs is set to 45mA. Checking both side swith same tube and other works fine.
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Old 23rd February 2012, 02:17 AM   #2788
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LED working means jfet working.
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Old 23rd February 2012, 02:20 AM   #2789
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Could the Vref protection zener had become a short?
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Old 23rd February 2012, 02:24 AM   #2790
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Ill try another. Led not working unless i measure 840 vgs. Then it begins to glow. Is my thinking correct that this is a direct result of the dmm stealing some of the gate voltage and lowering shunt current. I will change zener.
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