replace a 5651 tube with a zener?

[jarthel]

according to the Sylvania 5651 datasheet, the operating voltage is 92V. Does that mean I can replace the tube with a 92V zener?

The circuit I'm thinking of is in RDH chap33 figure 33.14 which is this one: http://img240.imageshack.us/my.php?i...ure33147hl.gif

ps. Do I really need R1 in this circuit? Also is there a way to compute for Vout so I can replace R9 pot with a constant resistance?

Thanks for the help

[tubetvr]

Hi,

You can change the 5651 to zener if you connect a good capacitor in parallell to remove the zener noise, but you will get less stability as a zener of this voltage has high temperature coefficient and high zener resistance and the zener knee is not that sharp.

You need R1 if you want to load the pass tube to max current when you want to make sure that each triode section carry the same current.

Regards Hans

[jarthel]

Originally posted by tubetvr
Hi,

You can change the 5651 to zener if you connect a good capacitor in parallell to remove the zener noise, but you will get less stability as a zener of this voltage has high temperature coefficient and high zener resistance and the zener knee is not that sharp.

You need R1 if you want to load the pass tube to max current when you want to make sure that each triode section carry the same current.

Regards Hans

Am I right in saying that a 92V zener is the the right replacement? I will be using multiple zener instead of just 1.

since it's very difficult to find a 160ohm 10W potentiometer these days, can you suggest a standard value?

thank you for the assistance.

[kevinkr]

The 5651 has much better initial tolerance and long term temperature stability than any garden variety zener, I went the other direction from Zeners to 5651 and other similar gas tube regulators/references and have been pleased with the results. (The 5651 is a reference.) The 5651 is commonly available on eBay for as little as a couple of bucks. Mullard made a beefed up equivalent, part number escapes me at the moment.

You can safely replace the 160 ohm pot with a pair of 100 ohm 10W resistors, one to each plate. I have designed and built a number of very similar regulators over the years and have not had any problems. The pot is "gilding the lily" so to speak and is overkill unless you are running very close to the tube's current and/or dissipation limits.

The pot or replacement resistors are there primarily to force reasonable current sharing between the two sections, it's not that critical unless you are running them right at their dissipation limit or need significantly more current in which case use a 6336A/B/C instead.

[cogsncogs]

Am I right in saying that a 92V zener is the the right replacement?

Min Typ Max
82--87--92V

Yuup! Anywhere from 82-92V will be fine. That's what R9 is for!

Wayne

[jarthel]

can I use a 1/2W pot for R9? thanks again

[jarthel]

using this circuit, can I get 150V? it was never mention in the RDH chap33.

I only assumed I can because of R9 and the description (output voltage control).

thanks again