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Old 21st February 2010, 12:45 PM   #11
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Quote:
As far as diodes, will need something >1200 V. PSUDII is showing just under 1100V PIV.
That's real easy. Use series wired pairs of UF5408s or even UF4007s. Snub each pair with a 10 nF. part of the highest WVDC you can get/afford. Even though a cap., by itself, is an imperfect snubbing setup, it's quite adequate. The "hash" filter keeps switching crud out of the B+ rail and there are no filament windings on this power trafo core.
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Old 21st February 2010, 01:09 PM   #12
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Default PSU Revised

Latest PSU attched. I'll check the UF5408s, I put the snubber caps in as it is a good design practice.

Schotky's for the other locations.

boywonder, I am interested in the delay setup.



FYI, Bias ripple now at 0.043mV
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File Type: pdf Visio-Opus5_0 Power Supply_v2.pdf (42.7 KB, 210 views)
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Last edited by SGregory; 21st February 2010 at 01:12 PM. Reason: added ripple value
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Old 21st February 2010, 01:17 PM   #13
smbrown is offline smbrown  United States
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I see you have modeled this for 135ma, but in the other 5-20 thread we were talking about 75 per KT88. What are you planning to use?
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Old 21st February 2010, 01:53 PM   #14
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I am running a little hotter b+. 75mA pushed the kt88 too close to max plate power. It is a simple tweek at this point to change however, the transformer will be speced at a little higher current and then some current will be sunk to bring the supply in line. That will give me flexibility to run it at different bias points. (NOTE: I just realized I didn't take into account the current to be sunk from the FET Followers)

I have NO experience with PP designs. So I am absolutley ALL ears on he best way to set it up. I choose the higher voltage since I am not placing a limit on b+ to fit electrolytics. The higher B+, does give a little more room to set up the ltp. (not much though).

I attached what I was thinking
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File Type: pdf Visio-Opus5_0 Power Supply_v3.pdf (43.1 KB, 140 views)
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Last edited by SGregory; 21st February 2010 at 02:06 PM. Reason: added updated psu
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Old 21st February 2010, 03:13 PM   #15
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Originally Posted by SGregory View Post
Latest PSU attched. I'll check the UF5408s, I put the snubber caps in as it is a good design practice.

Schotky's for the other locations.

boywonder, I am interested in the delay setup.



FYI, Bias ripple now at 0.043mV

Scott,

Have you given thought to selection regarding C117, which bypasses the gargantuan 'lytics? Something that "lays the lumber" to ESR and ESL is in order. With that in mind, I suggest a 630 WVDC/40 μF. Axon MPP bypassed, in turn, by a 600 WVDC/1.0 μF. PPMFX MutiCap. Respectively, Michael Percy's prices for those parts are $15.95 and $11.50. Obviously, shopping around is appropriate.
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Old 21st February 2010, 04:35 PM   #16
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I was going to use a GE Motor Run there as well. I have a quite a few laying around from a purchase a while back from a surplus house.

I was going to put a poly film on top of that. maybe a ppmfx.

Let me make this statement to those following along. You don't need the monster caps in this thing. I just happen to have 4 x 3500uF 450VDC caps staring at me from an industrial DC Drive. And Yes I store them with ground straps. There is enough energy in these things to REQUIRE an "ARC FLASH" study and to make a enclosure to contain it. Because of my line of work I am used to these requirements.
(Although steel mills don't use audio tube amps ;-) ).

If enough interest, I would be happy to model a more "reasonable" Power Supply.
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Old 21st February 2010, 05:05 PM   #17
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I was going to use a GE Motor Run there as well. I have a quite a few laying around from a purchase a while back from a surplus house.

I was going to put a poly film on top of that. maybe a ppmfx.

Let me make this statement to those following along. You don't need the monster caps in this thing. I just happen to have 4 x 3500uF 450VDC caps staring at me from an industrial DC Drive. And Yes I store them with ground straps. There is enough energy in these things to REQUIRE an "ARC FLASH" study and to make a enclosure to contain it. Because of my line of work I am used to these requirements.
(Although steel mills don't use audio tube amps ;-) ).

If enough interest, I would be happy to model a more "reasonable" Power Supply.

GE motor runs are FINE! So, the monster 'lytics are for an industrial DC drive. That suggests good heat tolerance and a long service life. No problems in this PSU with current reserves for transients. When you measure the finished product, I expect 3+ dB. of dynamic headroom will be available.
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Old 21st February 2010, 05:14 PM   #18
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Looking at the HT diodes, I would like to stay with a 1200V part.
Two come to mind
1) IXYS DSEP30-12A-ND (I think Tubelab had problems with the new IXYS)
2) Fairchild RHRP8120. 1200V

Also what would be a good ferrite bead? The list is endless and I am not sure how to spec it.

As a final note I am omitting the 5V supply and meter and going with test points. Easier to implement and elminates issue of getting noise back into HT and bias supplies.


The moster caps are BHC Ultra Long Life. It is a PERFECT Example of Dumpster Dive. The drive was actually good with minimal usage. It was being tossed cause we switched to AC Freq drive in that application. I also pulled a perfect heat sink from it to which will be used in this project.
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Last edited by SGregory; 21st February 2010 at 05:17 PM.
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Old 21st February 2010, 05:47 PM   #19
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Looking at the HT diodes, I would like to stay with a 1200V part.
Two come to mind
1) IXYS DSEP30-12A-ND (I think Tubelab had problems with the new IXYS)
2) Fairchild RHRP8120. 1200V
Stacked and snubbed UFnnnn pairs are low cost and work well. In 1200 PIV parts, DigiKey stock # C2D05120A-ND rules the roost. It's a Silicon carbide (SiC) Schottky made by Cree, inherently quiet, and no snubber cap. is needed. Search the archives for "cockeyed bridge". It's a technique for using a combination of fast PN and Schottky parts, which emphasizes the cost and noise performance of the 2 technologies.

Quote:
Also what would be a good ferrite bead?
A part that's chamfered, to prevent nicking wire insulation, is appropriate. The central hole should be large enough in diameter to permit at least 1 turn of wire around the bead's body.

Quote:
As a final note I am omitting the 5V supply and meter and going with test points. Easier to implement and elminates issue of getting noise back into HT and bias supplies.
Good move.
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Old 21st February 2010, 07:03 PM   #20
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Latest PS schematic. Decided on SiC Schottky. Left snubber caps in for now, I don't think it would hurt. I also updated wattage rating of components to give higher margin of safety.

I agree UFnnnn will work stacked and would be a good fit. For right now easier to think about 1 piece. For $6 diff in price per block it is worth it. I will re-read cockeyed bridge.

Getting close to my goal of having parts list complete to make orders tonight.

I would like to get a little more feedback on trafo's and experience at my indicated operating points before I order them however.
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File Type: pdf Visio-Opus5_0 Power Supply_v4.pdf (42.4 KB, 169 views)
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