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How to use solid state rectification the best way
How to use solid state rectification the best way
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Old 26th July 2021, 07:59 AM   #51
MikyK is offline MikyK  Czech Republic
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Originally Posted by sarcastic1 View Post
Don't believe any of that.
The old Bogen MO200 uses ordinary Si rectifiers (yes from 1963-68), once the design is well sorted, Gillespie showed they sound excellent.
I have a pair and they are just gorgeous.

All those old MO/MX amps use the same design of PSU with voltage doubler also AND a steel chassis (!), apparently all wrong according to modern folk tales.
(You can improve on the screen grid supplies with a choke in the 310V to reduce ripple).

In my own amp design I use ordinary bridge rectifiers with both a Choke input filter for the main HT, and a miniature TV damper diode to give it gentle warm up.
The screen supply is regulated via a proper triode and cold cathode VR device (300V) from a 2nd Toroid power transformer winding, so peak currents on the main HT rail doesn't show up in the main AF amp/driver supply.

Everyone has remarked on how truly wonderful, and how astonishingly powerful the (PPP Pentode) amp is for its size (2 x 50W per channel) with very low IMD and THD.
Ultra clean, no compression, high power and low noise all in one hit with an amp weighing just 13kg.
Your amp is pushpull pentode. Pushpull amps are MUCH more tolerable to any noise and hum in power supply because of their balanced topology. Single ended tube amp will not do that. The simpler your amp and whole audio chain is, the bigger differenge between the components will be.
What about to take big ferrite beads and slide them over wire that goes to the main 5-10H choke?
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Old 26th July 2021, 09:47 AM   #52
Chris Hornbeck is offline Chris Hornbeck  United States
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Repeating Merlin B's post #44 "Use fast diodes and put an RC snubbing network across the transformer secondary. Easy." There is no Special Sauce here.


All good fortune,
Chris
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Old 26th July 2021, 04:29 PM   #53
sarcastic1 is offline sarcastic1  Russian Federation
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Quote:
Originally Posted by MikyK View Post
Your amp is pushpull pentode.
Pushpull amps are MUCH more tolerable to any noise and hum in power supply because of their balanced topology.
A fully balanced pushpull amp (No phase invertor) is TWO single ended amps back to back. Pentodes have the lowest IMD, and full balanced amps (balanced XLR input) can be very simple designs, even DC coupled.

The Bogen amps weren't pentodes they were specialised semi-frame grid beam tetrodes.
Beam tetrodes have much higher IMD characteristics than pentodes, especially the xL6, xCA7, KTxx crowd.
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Old 26th July 2021, 06:12 PM   #54
Zung is offline Zung  Switzerland
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Quote:
Originally Posted by Merlinb View Post
Use fast diodes and put an RC snubbing network across the transformer secondary. Easy.
Yes.
After that, there're still a bit of refinement:
  • For a dollar more, Schottky diodes eliminate switching transients
    Click the image to open in full size.
  • Then the RC snubber can be tuned to eliminate ringing from the transformer - This requires a LRC meter to measure the inductances and capacitances of the transformer
    How to use solid state rectification the best way-xformer-snub-jpg
Attached Images
File Type: jpg Xformer-Snub.jpg (546.1 KB, 122 views)
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Old 26th July 2021, 07:54 PM   #55
50AE is online now 50AE  Bulgaria
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How to use solid state rectification the best way
Quote:
Originally Posted by MikyK View Post
Your amp is pushpull pentode. Pushpull amps are MUCH more tolerable to any noise and hum in power supply because of their balanced topology. Single ended tube amp will not do that. The simpler your amp and whole audio chain is, the bigger differenge between the components will be.
What about to take big ferrite beads and slide them over wire that goes to the main 5-10H choke?
If you're searching for a warm tone with SS rectification, try germanium diodes. Some Russian HV ones are still available. I'm using these in my bias circuits.

Otherwise, I'd go with analog_sa, synchronous rectification has it all, but it's still too low voltage.

Third option - schottky's.

Fourth option - take a mellow sounding wire (soft copper) and solder it to the lead outs of the SS rectifier. You can add mass on the rectifier. If you wish, PM me for more info.
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Old 26th July 2021, 11:43 PM   #56
trobbins is offline trobbins  Australia
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Zung, why would you obtain measured parasitic components and then use a simulation to determine an RC snubber across a secondary HT winding without also doing an in-situ measurement as per the quasimodo style ring test ?

Showing a scope screen without any description on what is being shown and what the test setup involved is imho just a waste of space.

No diode solution 'eliminates switching transients'. The issue is more about how a diode solution softens the forward current step transition when current reaches zero, and whether there is any aspect of reverse current recovery that may also occur.

Last edited by trobbins; 26th July 2021 at 11:45 PM.
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Old 27th July 2021, 12:40 AM   #57
bondini is offline bondini  Australia
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How to use solid state rectification the best way
Default Mark Johnson on diodes in Linear Audio Vol 10

Mark has generously shared Quasimodo with us (takes the guesswork out of snubbing, Zung) as well as a survey of transformer ringing to find the best (actually least-worst) diode available for a very affordable 3Euro (here: All articles | Linear Audio - thanks, Jan). Here's the Abstract to persuade you to part with your money:
Power transformer secondary ringing was measured with 48 different semiconductor diodes; ringing amplitude was 10-20X lower with the best diodes than the worst. They all rang, including Schottkeys and HEXFREDs. A 1R + 2C snubber directly across the secondary completely eliminated ringing in every case.
(My emphasis).
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Old 27th July 2021, 12:59 AM   #58
TonyTecson is offline TonyTecson  Philippines
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rectifiers distort secondary currents as a result of rectification.....
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Old 27th July 2021, 01:25 AM   #59
trobbins is offline trobbins  Australia
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Somewhat like the quasimodo test setup, the diode test setup in that Linear Audio article forces a very high peak current through the DUT, which is likely not what people will experience in their power supplies, but which does accentuate the transient disturbance at diode turn-off and so makes observations more distinct to then characterise.
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Old 27th July 2021, 04:04 AM   #60
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by TonyTecson View Post
rectifiers distort secondary currents as a result of rectification.....
Thats true but only as far as the smoothing cap then its smooth after that.
Given there are sharp charging impulses every 100Hz anyway it isnt a problem.
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