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Gas rectifier vs vacuum rectifier
Gas rectifier vs vacuum rectifier
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Old 23rd January 2016, 04:18 AM   #1
Pentium100 is offline Pentium100  Lithuania
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Default Gas rectifier vs vacuum rectifier

I want to build a powerful (80W or maybe more) tube amplifier and do not want to use semiconductors in it (just because). Since vacuum rectifiers have high internal resistance, the power supply can sag when I turn up the volume. How about using inert gas (not mercury) filled rectifiers like GG1-2/5, which is rated for 2A current and 16V drop? Is there any downside to using gas filled rectifiers as opposed to vacuum ones?

I have built one low power SE amp and have almost completed another, they both use vacuum rectifiers (5C3S - 5U4G). However, SE uses the same average current whether at idle or at full output, so the rectifier resistance doesn't matter, where a PP class AB amp uses more current when playing louder.
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Old 23rd January 2016, 05:27 AM   #2
Eli Duttman is offline Eli Duttman  United States
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Use low forward drop damper diodes and avoid all sorts of unpleasant issues. The 6CJ3 has huge current handling capability.
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Old 23rd January 2016, 08:20 AM   #3
hpeter is offline hpeter  Slovakia
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Quote:
Originally Posted by Pentium100 View Post
I want to build a powerful (80W or maybe more) tube amplifier and do not want to use semiconductors in it (just because). Since vacuum rectifiers have high internal resistance, the power supply can sag when I turn up the volume. How about using inert gas (not mercury) filled rectifiers like GG1-2/5, which is rated for 2A current and 16V drop? Is there any downside to using gas filled rectifiers as opposed to vacuum ones?

I have built one low power SE amp and have almost completed another, they both use vacuum rectifiers (5C3S - 5U4G). However, SE uses the same average current whether at idle or at full output, so the rectifier resistance doesn't matter, where a PP class AB amp uses more current when playing louder.
CHoke input is a must
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Old 23rd January 2016, 12:32 PM   #4
Miles Prower is offline Miles Prower  United States
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Quote:
Originally Posted by Pentium100 View Post
I want to build a powerful (80W or maybe more) tube amplifier and do not want to use semiconductors in it (just because). Since vacuum rectifiers have high internal resistance, the power supply can sag when I turn up the volume. How about using inert gas (not mercury) filled rectifiers like GG1-2/5, which is rated for 2A current and 16V drop? Is there any downside to using gas filled rectifiers as opposed to vacuum ones?
There are a couple of disadvantages: since the operation depends on a glow discharge, that means negative resistance that can lead to high frequency oscillations that could require plate stoppers. The other big disadvantage is gas clean-up, same as for a neon sign.. As the gas pressure drops, the cathode fall increases, eventually overheating and ruining the cathode. This type is specced for 500 hours.

Quote:
I have built one low power SE amp and have almost completed another, they both use vacuum rectifiers (5C3S - 5U4G). However, SE uses the same average current whether at idle or at full output, so the rectifier resistance doesn't matter, where a PP class AB amp uses more current when playing louder.
I think you're overestimating the problem. Audio amplification isn't like "brick on the key" modes like FM or CRT deflection where you're doing max power continuously while transmitting followed by intervals of listening when the power finals are cutoff. In that case, a PS whose voltage soars when the load drops is very bad.

As for "same average current", that applies to SE and PP regardless of class of operation. The DC plate current meter will stay rock solid when a Class C RF amp is being operated correctly, even if it's plate modulated to produce AM. Indeed, a bouncing DC meter needle means overmodulation and "splatter", or it could be due to a bad impedance mismatch that's causing a higher than normal SWR. The only thing that differs is the magnitude of that average current: from SE and PP and Class A, B, C, D (seldom used in hollow state audio) E or F (never used with hollow state audio)

Audio stays at some low average value with peaks, so sag isn't that much of a problem. Guitar amps often use undersized power supplies and the finals are driven well into clipping, and for that, sag is desirable since this makes for compression and "sustain". You want to keep reproduction amps out of clipping except for the occasional peak that clips the finals. If you avoid blocking distortion, you simply won't hear the occasional clip.
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Old 23rd January 2016, 12:52 PM   #5
TonyTecson is offline TonyTecson  Philippines
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Gas rectifier vs vacuum rectifier
my favorite damper tube: http://www.shinjo.info/frank/sheets/127/6/6CD3.pdf
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Old 23rd January 2016, 02:10 PM   #6
analog_sa is offline analog_sa  Europe
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Gas rectifier vs vacuum rectifier
My favourite rectifiers are two: 83 and 866. Willing to put up with their peculiarities as nothing else matches the sound.
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Old 23rd January 2016, 03:05 PM   #7
JMFahey is offline JMFahey  Argentina
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What sound?
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Old 23rd January 2016, 06:05 PM   #8
Palustris is offline Palustris  United States
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You have received the answer: damper diodes, choke input filter, and low resistance chokes. I would add Wima DC Link MKP 4 capacitors: no electrolytics!
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Old 23rd January 2016, 10:46 PM   #9
Pentium100 is offline Pentium100  Lithuania
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Thank you for the answers. I was thinking about using 6S33S in PP or using paralleled other tubes (that do not require 1kV plate supply), but then it means high current. I have a couple of 5C8S tubes that are rated for 420mA DC but was worried about the sag and started looking for alternatives, came across mercury rectifiers, but did not like the fact that they are full of mercury.

It turns out that the sag does not happen as much as I thought.

I used choke input filter for the amp I already built and will use one for the amp I am currently building - lower peak current means I can get a bit more current out of the rectifier, well, at least according to the datasheet.

If I need more current than that, then I guess using rectifiers in parallel is still better than the gas discharge tube...
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Old 24th January 2016, 09:42 AM   #10
hpeter is offline hpeter  Slovakia
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Quote:
Originally Posted by Palustris View Post
and low resistance chokes.
rather the opposite
Quote:
Originally Posted by Palustris View Post
I would add Wima DC Link MKP 4 capacitors: no electrolytics!
Did good change to my system, more details
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