I was not clear enough, only meaning to move the 4007s into the position that the 5T twins would be, and keeping the damper diode. Works the same without extra B+ voltage on the winding.
All good fortune,
Chris
All good fortune,
Chris
The schematic in Post # 114, is a good example of a slow warm-up circuit, but that particular schematic has the following characteristics:
DCV, to a vacuum tube rectifier (to give delayed B+), followed by a 10uF cap to ground, followed by a 270 Ohm 2 Watt Resistor, followed by two 100uF caps to ground.
It seems to me, that 270 Ohms does not make for steady B+ voltage, if the output stage goes from quiescent current, to maximum current with signal.
Most music will be OK, but do not expect B+ to be rock steady when the 32 foot organ pipe is high amplitude; at nearly full scale of the DAC, and the volume control is turned high . . . and the 32 foot pipe note is sustained for 8 measures of music.
Many wonderful circuits have one or more tradeoffs.
Just saying.
DCV, to a vacuum tube rectifier (to give delayed B+), followed by a 10uF cap to ground, followed by a 270 Ohm 2 Watt Resistor, followed by two 100uF caps to ground.
It seems to me, that 270 Ohms does not make for steady B+ voltage, if the output stage goes from quiescent current, to maximum current with signal.
Most music will be OK, but do not expect B+ to be rock steady when the 32 foot organ pipe is high amplitude; at nearly full scale of the DAC, and the volume control is turned high . . . and the 32 foot pipe note is sustained for 8 measures of music.
Many wonderful circuits have one or more tradeoffs.
Just saying.
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No , it is not. I have already posted comments those old data sheets are stale, and should be updated. The 100uf/100uf cap is a dual cap, inside one can. and the choke is a Hammond 157G / 30 Henry - 40 millamp. I've been running this combo inside my amplifiers pushing 5 years now, and no issues...
right you are, those 270 ohms are much much lower in the actual build, like i said there were errors in the circuit shown.
I retired from a company that made industrial RF power supplies; some of our customers specified 80,000 hr MTBF, and some of our mature products did close to 300,000 hours. I'd insist on a small input cap (or MOV) with choke input. One circuit used a 120 amp 3-phase bridge and choke to improve power factor (few hundred mH). Had occasion rectifier failures, cured by adding .047 uF/2KV cap across DC output of bridge. This was a 1200V (maybe 1400V) bridge rectifier, operating on 208VAC, with MOVs and gas tubes upstream providing transient protection.
To meet EU standards, all our products were tested with 2KV impulses line-to-line and 4KV line-to-ground - one design standard was the use of avalanche rated diodes for any direct line connection. A transformer limits the amplitude of impulses, though a few small transformers (bifilar primaries connected n series) couldn't take it and failed that test - and were promptly removed from the approved list.
To meet EU standards, all our products were tested with 2KV impulses line-to-line and 4KV line-to-ground - one design standard was the use of avalanche rated diodes for any direct line connection. A transformer limits the amplitude of impulses, though a few small transformers (bifilar primaries connected n series) couldn't take it and failed that test - and were promptly removed from the approved list.
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"I'd insist on a small input cap (or MOV) with choke input. One circuit used a 120 amp 3-phase bridge and choke to improve power factor (few hundred mH). Had occasion rectifier failures, cured by adding .047 uF/2KV cap across DC output of bridge."
Tom
Interesting, in what position did the small mH choke go, just in series with the big L1 input choke or right after the bridge?
Like this?
Bridge --> .047 HV cap --> small mH (high current) choke --> Big L1 input choke --> C1 filter cap --> ... etc.
or like this?
Bridge --> small mH (high current) choke --> .047 HV cap --> Big L1 input choke --> C1 filter cap --> ... etc.
Tom
Interesting, in what position did the small mH choke go, just in series with the big L1 input choke or right after the bridge?
Like this?
Bridge --> .047 HV cap --> small mH (high current) choke --> Big L1 input choke --> C1 filter cap --> ... etc.
or like this?
Bridge --> small mH (high current) choke --> .047 HV cap --> Big L1 input choke --> C1 filter cap --> ... etc.
3-phase bridge, then .047 cap, 2-300 mH choke, few hundred uF electrolytic caps, designed for 30-35 amps DC (input for a big switching supply). Before adding the cap, we were able to induce diode failure repeatedly with a few hundred AC on-off cycles, pretty much unloaded (< 100 watts).
Capacitor charging current is limited by DC resistances of transformer windings. Choose diodes with enough current capability, and there is no problem. Voltage surge in choke input supply is what kills the diodes, not charging current surge.
This voltage surge can be killed by a reverse diode from the choke's input terminal to gnd.
Best regards!
Best regards!
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The bridge has a surge rating of 1500A for one AC cycle. Much less than that due to choke. Point is that reverse breakdown of 1400V junction occurred with only 230 VAC applied, and a "buffer" cap reduced the transient voltage to below the breakdown voltage. An MOV (~750V) was used in a similar 480V supply. No, a diode across the bridge output wouldn't help, but a zener or Tranzorb across each choke winding could (bifilar choke, in plus and minus leads).
If you spend a few million on a machine that printed $1000 bills (completed silicon wafers full of memory, FPGA, microprocessors), you'd be more than upset if it stopped. Semiconductor manufacturers are very concerned about reliability, typically requiring a failure analysis and mitigaton report for any field failure. This was a simple one to solve.
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"This voltage surge can be killed by a reverse diode from the choke's input terminal to gnd."
I'm breadboarding experiments with SS rectifiers and choke input at this time too. So as simple as this?
I'm breadboarding experiments with SS rectifiers and choke input at this time too. So as simple as this?
Yes, this is exactly what I meant. The diode allows continuous current flow through the choke even during the rectifier's commutation.
Best regards!
Best regards!
Thanks,
Additionally, but not drawn above here might be a pulse rated HV capacitor of maybe .047 - .15 uF just ahead of the diode? Like a WIMA MKP10 3000 VDC? (page 8 on this datasheet).
WIMA MKP10 Pulse Rated Capacitor
Additionally, but not drawn above here might be a pulse rated HV capacitor of maybe .047 - .15 uF just ahead of the diode? Like a WIMA MKP10 3000 VDC? (page 8 on this datasheet).
WIMA MKP10 Pulse Rated Capacitor
Ya, nothing wrong with that. If it's that small, it'll still be "choke input" and it'll just smooth any HF spikes I believe.
3kV is excessive though... 1600V should be ok I think.
Et Voilà! --> https://www.lcsc.com/product-detail...rs-CBB_KNSCHA-MMK473J3CE4AJ208G0_C468290.html
What's the AC voltage of the traffo?
3kV is excessive though... 1600V should be ok I think.
Et Voilà! --> https://www.lcsc.com/product-detail...rs-CBB_KNSCHA-MMK473J3CE4AJ208G0_C468290.html
What's the AC voltage of the traffo?
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Here are my 3 cents:
1. SS rectifiers are superior to tubes. Less power loss, less sag, higher reliability and MTBF. The only advantage of tubes is, when you do not route ground wire properly, and the rectifier outputs charging peaks through the ground causing hum. Higher dynamic resistance of tubes decreases current of charging pulses, so voltage drops on wrongly wired conductors is lower.
2. Slow start is misunderstood. It does not prolong lives of tubes. Only huge tubes with high cathode current density per area need it. The only why it may be beneficial, is inrush current. But the best way to fight it is to add a varistor in series with the primary, that is being shunted by relay contacts. Relay powered from some filter cap after the rectifier. I use relays powered from the filament rectifier. Can be used any rectifier, since voltages on all caps after all rectifiers ramp up together. Instead of varistors in some projects I used wirewound resistors. Anyway they re being shunted by relay when the caps are charged.
The harm from delayed start of B+ is, sudden application of anode (plate) voltage causes higher charging currents of coupling caps, that charge through grids of already conducting tubes.
3. In last projects I use gyrator instead of a choke, using one MOSFET, one cap, and couple of resistors. With higher time constant you can get slow B+ start. Simple, cheap, efficient.
Enjoy! 😉
1. SS rectifiers are superior to tubes. Less power loss, less sag, higher reliability and MTBF. The only advantage of tubes is, when you do not route ground wire properly, and the rectifier outputs charging peaks through the ground causing hum. Higher dynamic resistance of tubes decreases current of charging pulses, so voltage drops on wrongly wired conductors is lower.
2. Slow start is misunderstood. It does not prolong lives of tubes. Only huge tubes with high cathode current density per area need it. The only why it may be beneficial, is inrush current. But the best way to fight it is to add a varistor in series with the primary, that is being shunted by relay contacts. Relay powered from some filter cap after the rectifier. I use relays powered from the filament rectifier. Can be used any rectifier, since voltages on all caps after all rectifiers ramp up together. Instead of varistors in some projects I used wirewound resistors. Anyway they re being shunted by relay when the caps are charged.
The harm from delayed start of B+ is, sudden application of anode (plate) voltage causes higher charging currents of coupling caps, that charge through grids of already conducting tubes.
3. In last projects I use gyrator instead of a choke, using one MOSFET, one cap, and couple of resistors. With higher time constant you can get slow B+ start. Simple, cheap, efficient.
Enjoy! 😉
kodabmx... "What's the AC voltage of the traffo?"
I want to make a general-purpose traditional SS - pi filter - choke input PCB that can do any AC input voltage from 100 to 800 in bridge or half wave. Where you just have to size the component voltage ratings for what you are using. I'll post my PCB layout and schematic to this thread when I'm closer.
Here is my "shall have" list so far.
1) Top side has unbroken ground plane
2) Fused at both ends
3) Pads for either bridge or half wave usage
4) Choke input LCLCLC or LCRCLC or LCLCRC or LCRCRC
5) Places for 8 diodes either axial, TO220 or TO247 pads
6) If bridge you can place either 4 diodes or 8 diodes on the board
7) If half wave you can place either 2 diodes or 4 diodes on the board
8) Small value pulse rated cap follows the diodes
9) All pi filter caps are DC link types (because you can buy high voltages in this type and they dont degrade like electros)
10) I might put some pads for that reverse diode Kay mentioned (optionally)
11) Heater elevation divider pads (this divider also serves as the bleeder so its mandatory)
12) Pads for "quasimoto" snubbers to round out the reflected spike into the transformer (values determined by quasimoto test method)
13) Pads for small film cap bybass of the last filter cap
14) Damper tube can be bypassed with a wire if not wanted, same for if you dont need/want series diodes
15) For half wave usage the ground plane is arranged so that the CT connection has a direct path (very short) to the diode anodes and the negative of the small input pulse cap. This satisfies the good practice of running a piece of wire back to the CT from the start of your pi filter if doing point to point.
16) Minimum spacing to the ground plane anywhere is 2mm
17) Damper filament is brought directly to the tube pins because board will use a panel mount socket over a hole, not a PCB tube socket
18) Narrow but longer board so dedicated power packs can be made in narrow but deeper enclosures.
19) DC link caps have pretty standard pin spacings these days so choosing voltages and uf values lots of options
etc...
I want to make a general-purpose traditional SS - pi filter - choke input PCB that can do any AC input voltage from 100 to 800 in bridge or half wave. Where you just have to size the component voltage ratings for what you are using. I'll post my PCB layout and schematic to this thread when I'm closer.
Here is my "shall have" list so far.
1) Top side has unbroken ground plane
2) Fused at both ends
3) Pads for either bridge or half wave usage
4) Choke input LCLCLC or LCRCLC or LCLCRC or LCRCRC
5) Places for 8 diodes either axial, TO220 or TO247 pads
6) If bridge you can place either 4 diodes or 8 diodes on the board
7) If half wave you can place either 2 diodes or 4 diodes on the board
8) Small value pulse rated cap follows the diodes
9) All pi filter caps are DC link types (because you can buy high voltages in this type and they dont degrade like electros)
10) I might put some pads for that reverse diode Kay mentioned (optionally)
11) Heater elevation divider pads (this divider also serves as the bleeder so its mandatory)
12) Pads for "quasimoto" snubbers to round out the reflected spike into the transformer (values determined by quasimoto test method)
13) Pads for small film cap bybass of the last filter cap
14) Damper tube can be bypassed with a wire if not wanted, same for if you dont need/want series diodes
15) For half wave usage the ground plane is arranged so that the CT connection has a direct path (very short) to the diode anodes and the negative of the small input pulse cap. This satisfies the good practice of running a piece of wire back to the CT from the start of your pi filter if doing point to point.
16) Minimum spacing to the ground plane anywhere is 2mm
17) Damper filament is brought directly to the tube pins because board will use a panel mount socket over a hole, not a PCB tube socket
18) Narrow but longer board so dedicated power packs can be made in narrow but deeper enclosures.
19) DC link caps have pretty standard pin spacings these days so choosing voltages and uf values lots of options
etc...
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They really should be called a voltage half-er, to complement the voltage doubler. Arf!
All good fortune,
Chris
All good fortune,
Chris