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Old 27th March 2013, 12:43 PM   #41
CV6045 is offline CV6045  United Kingdom
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Default 833 amp

Thank you

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Old 27th March 2013, 01:41 PM   #42
Magz is offline Magz  United States
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Regarding the transformers, and shielding from line noise, the 369KX has an electrostatic shield between primary and secondary, and the filament transformers are split bobbin design and thus do not need a shield as they will inherently reject line noise.

The 733A has no shield, but it will be fed from a soft start circuit with integral RFI and DC filters. PCX was blowing these out at 50% off a month or two ago and I picked two up specifically for the 733A both to soften the start-up and filter the line. They're similar to this unit:

NewClassD Soft Start
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Old 27th March 2013, 06:12 PM   #43
hpeter is offline hpeter  Europe
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Quote:
Originally Posted by Magz View Post
That makes sense. I thought about using Xenon rectifiers but decided that SS would be smaller, lighter, and a lot safer.
xenon has (at least c3ja has) ~1200Vmax, xenon is nicer than mercury because you donīt need to wait so long before applying the anode voltage (mercury evaporation) bugger that filament though (2,5V 9A)
edit: you still have to wait, but is shorter than mercury ,AFAIK

Last edited by hpeter; 27th March 2013 at 06:29 PM.
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Old 27th March 2013, 06:20 PM   #44
rmb is offline rmb  United States
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hpeter: How much current is being drawn on the HT leg? Thought of using two 3B28 or 8008XE rectifiers, depending on the current load?
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Old 27th March 2013, 06:36 PM   #45
hpeter is offline hpeter  Europe
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Quote:
Originally Posted by rmb View Post
hpeter: How much current is being drawn on the HT leg? Thought of using two 3B28 or 8008XE rectifiers, depending on the current load?
http://frank.pocnet.net/sheets/049/3/3B28.pdf
http://frank.pocnet.net/sheets/077/8/8008XE.pdf
http://frank.pocnet.net/sheets/049/c/C3JA.pdf

reason why i put thyratron, is because i had this on mind: (far future project)
http://img201.imageshack.us/img201/5...tronsupply.jpg
(schematics has some error)
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Old 27th March 2013, 07:23 PM   #46
Magz is offline Magz  United States
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Quote:
Originally Posted by hpeter View Post
xenon has (at least c3ja has) ~1200Vmax, xenon is nicer than mercury because you donīt need to wait so long before applying the anode voltage (mercury evaporation) bugger that filament though (2,5V 9A)
edit: you still have to wait, but is shorter than mercury ,AFAIK
3B28 has a PIV of 10KV. I would have used it in a bridge setup. Too much space, too much filament voltage to supply, too much HT topcaps!
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Old 28th March 2013, 01:27 AM   #47
Magz is offline Magz  United States
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The filament supply chokes arrived today, along with the two small 12V transformers for the fan supply (if I use a fan). Now just waiting on the one 733A and the custom Monolith OPT and choke.

Time to start exploring layouts and decide on a chassis.
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File Type: jpg 833 filament chokes.jpg (282.8 KB, 1108 views)
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Old 28th March 2013, 01:44 AM   #48
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I tried the 3B28, still have a few around here somewhere. I was hoping for some cool tube glow, but they are so dim that you can't see the glow in a lit room...or anywhere near the 833A.

Breadboard and test everything before thinking about the chassis. With 100 watts of heater power in the 833A hum will be a problem. I HAD to use DC for the filament. I would get audible hum in the speakers with ONLY the filament transformer switched on, NO B+. Moving things around did not help. I needed a big fat bridge some big caps, and a choke wound with something resembling welding cable!

The 833A has so much emission that you will measure negative voltage on the plate from heater power alone. Put a voltmeter between the heater and grid or plate, then light the filament with AC. The plate will go a few volts negative from the electrons hitting it.
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Old 28th March 2013, 02:06 AM   #49
Magz is offline Magz  United States
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Quote:
Originally Posted by tubelab.com View Post
I tried the 3B28, still have a few around here somewhere. I was hoping for some cool tube glow, but they are so dim that you can't see the glow in a lit room...or anywhere near the 833A.

Breadboard and test everything before thinking about the chassis. With 100 watts of heater power in the 833A hum will be a problem. I HAD to use DC for the filament. I would get audible hum in the speakers with ONLY the filament transformer switched on, NO B+. Moving things around did not help. I needed a big fat bridge some big caps, and a choke wound with something resembling welding cable!

The 833A has so much emission that you will measure negative voltage on the plate from heater power alone. Put a voltmeter between the heater and grid or plate, then light the filament with AC. The plate will go a few volts negative from the electrons hitting it.

Yes, definitely DC on the filaments. I'll be using Rod Colemans excellent filament supply boards which use a CCS and Gyrator to control the current and voltage. I have to parallel two per side at 5A each to get to 10A. The chokes in the post above are rated at 2.5mH at 10A, so they should do.

Below is the PSUD simulation for the supply to the Coleman boards. Ripple will be ~40mV going into the boards, and in the uV range at the tube filaments.

I will definitely be breadboarding/testing before assembly, I just want to get an idea of the size of chassis needed - I'd like to keep it around 18"x22"x4.25"deep if I can.
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File Type: jpg 833 Filament PSUD.jpg (168.3 KB, 1088 views)
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Old 28th March 2013, 02:15 AM   #50
iko is offline iko  Canada
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You plan to run two of those regulators in parallel? That will be interesting.
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