High voltage driver for AB2 operation GU81m tubes - Page 29 - diyAudio
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Old 12th September 2012, 12:51 PM   #281
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I tried to think of a resettable mecahnism.


Current limiting resistor is missing however r1 and r2 are part of the voltage divider. When voltage exceeds 4kv the divider will output above 300/350v. The cap to gnd will be charged and trigger the spark gap. It should also generate oscillation which the second cap will transfer to g1 of the thyratron permanently biased to -150v.

Coupling cap should be small and charging cap larger. I hope it makes sense this is my best shot. Thealternative is to use the thyratron in reverse.

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Old 12th September 2012, 12:56 PM   #282
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Old 13th September 2012, 10:33 AM   #283
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They have arrived!

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Huge 1965 proudly made in CCCP

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Old 13th September 2012, 05:22 PM   #284
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G1 must be highly negative to interrupt flow.

G1 is visible as the center section

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Old 13th September 2012, 10:39 PM   #285
djn is offline djn  United States
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That is a really cool looking tube, but in laymans speak, could you tell me what it does?
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Old 14th September 2012, 09:15 AM   #286
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Hi! it is a grid controlled switch or rectifier. In my case i would like to use it as an emergency switch should opt voltage exceed permissible voltage.

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Old 23rd September 2012, 02:54 PM   #287
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The gu81m can take a beating!

Activating getter before final run with new opt. 1800+ main anode voltage and -160v bias.

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Old 23rd September 2012, 02:55 PM   #288
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Don't worry i red plated the gu81 for just 45seconds at a time.

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Old 23rd September 2012, 03:10 PM   #289
nhuwar is offline nhuwar  United States
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Just an fyi, your not supposed to show color with graphite plates. Only tantalum. I don't think the getter is in the plate with those.

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The gu81m can take a beating!

Activating getter before final run with new opt. 1800+ main anode voltage and -160v bias.

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Old 23rd September 2012, 04:25 PM   #290
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Well AFAIK Tantalum displays getter like properties natively and does not require any additional treatmont to perform this task. It can display an inverted process of gas emission when exceeds a specific temperature.

GU81m has a graphite anode and no getter so to speak. I seriously doubt any coating was applied to the thin grid wire. I am almost certain the anode performs this task.

In graphite anode tubes the effect is obtained (AFAIK) by way of coating the exposed surface with a thin layer of zirconium powder which, once heated, displays getter like properties.

I am positive that gu81m has no other means of maintaining hard vacuum except the activation of the anode plate coating.

Also the process I forced the gu81m to undergo was designed to cure the filaments of any occurence of cahode poisoning. Unfortunately the tubes were at times powered with no anode voltage. If the surface of the filaments was poisoned a high enough flow of electrons ought to have cured it.

I am pretty confident the gu81m can take 45secs of red plating and according to some sources this is even advisable for the reasons above.

Getter Materials

However I am not a tube engineer so if any of my statements are erroneous please tell me!
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