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In Reply to: RE: Alternatives posted by Triode_Kingdom on September 14, 2016 at 08:18:41
At some point I will probably try one of these low DCR chokes, using a ST-70 as a test-bed. I'll be honest and say that I'm confused regarding a lower H making an improvement, since the overwhelming opinion over the years seems to be that Dynaco's 1.5 H, 200mA C-354 choke is undervalued for that power supply.
"Buy Chinese. Bury freedom." I appreciate you taking the time to remind me of that, and offering an alternative.
Follow Ups:
"...opinion over the years seems to be that Dynaco's 1.5 H, 200mA C-354 choke is undervalued for that power supply."The output tubes draw 200ma. so that's a problem.
As for the Henry value, 1.5Hy is better than no inductance. They could have just used a resistor. 1.5Hy is better than that.
When we use a choke as an input choke, to get the full effect of a input choke (each diode, in turn, stays on for it's entire half cycle and therefore the charging current remain low without current spikes) we need to calculate and use at least the critical inductance value.
The definition of critical inductance is the inductance value that will cause the diodes to each, in turn, stay on for the entire half cycle.
That value is calculated by, critical inductance (in Hy) = ((current in amps / voltage) + the DCR of the choke) / 1000
But in a pi filter (CLC, like the Dyna uses) things are different.
"The component value for the inductor can be estimated as an inductance that resonates the smoothing capacitor(s) at or below one tenth of the minimum AC frequency in the power supplied to the filter (100 Hz from a full-wave rectifier in a region where the power supply is 50Hz). Thus if reservoir and smoothing capacitors of 2200 microfarads are used, a suitable minimum value for the inductor would be that which resonates 2200 microfarads (μF) to 10 Hz, i.e. 115 mH. A larger value is preferable provided the inductor can carry the required supply current."
I would think (but I haven't bothered to figure it out) that the 1.5Hy does meet the minimum. More would be better.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/16/16
Thanks for the feedback, Trè.
As for the Henry value, 1.5Hy is better than no inductance. They could have just used a resistor. 1.5Hy is better than that
Not necessarily..It depends on a lot of other factors such as filtering before and after the choke.
The HF87 that I love so much lately is powering my family room system which are Newform Research 645s..I put the typical McShane power supply in with the 820uf doublers and dual 100s downstream..This particular amp has Hexfreds in doubler and I may change over to Schotkys.I did take out the 50 ohm 10 watt resistor that ties the doubler stack to the reservoir caps.
I used a 1.5hy,50 ohm 250ma in its place and it sounded very good and I used the amp on and off for six years when I tested EL34s/6CA7s and KT77s for evaluation.
Two months ago I took out the 1.5hy choke and put in a .5hy,300ma choke that was 30 ohms.Every aspect of this amplifier changed for the better and it's like you are listening to another amp just from going to that low mu,low DCR choke. I've been streaming JAZZRADIO.com direct out of my I-PAD and I even took the DAC off..The accuracy and harmonic structure of the percussion and piano section is like none I've heard except on the big ML CLXs driven by the Citation 2s.I have never cared much for EL34s but in the HF87 with the McShane upgrades and that added choke,I've been listening non stop with unbelievable enjoyment. I wish you could hear this amp.I run the Gen reissue KT77s most of the time but this amp is a sonic marvel and I know that low DCR choke is responsible because it's the only thing I changed from the 1.5hy.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
A little late to the discussion, but, when you put in a lower value choke with lower resistance you could also change the output voltage of the power supply, especially if you're going from an inductance that is above the critical value to one that is below. If that is the case, and I'm speculating here, the voltage could change enough to alter the operating point of the circuit and that might be what you're hearing. At least worth checking out.
Thanks Mike.
What I'd be curious to know is if the power supply in your HF87 measures worse, but sounds better with the lower inductance choke.
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