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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: 'regenerated' E88C ? posted by Pär on September 26, 2000 at 04:26:38:
Many small signal 'heater' triode valves can be reactivated after having lost cathode emission - most of the time being caused by 'cathode poisoning' (the build-up of a resistive layer on the cathode surface impairing emission).I have been using a AVO VCM-163 mutual conductance valve tester for the 'regeneration process' - learned from an 'old salt' radio/TV repairman in about 1980...
The process works on the VCM-163 as follows:
Test the valve with standard settings for Uh, Uba, -Ug for Ia and Gm. If the heater is glowing, tube is gas-free, and Ia and Gm are way too low (near zero), proceed with the following steps:
* Get the maximum ratings for the tube from the data sheet.
* Increase Uh by 10 %.
* Set -Ug to -Ugmax.
* Set Ua to Ua0max.
* Watch meter readings for Ia and Gm.
* Decrease -Ug cautiously, until Ia and Gm pick up.
* Wait until Ia reaches about 2*Iamax or the anode shows a red glow.
* Interrupt Ua supply immediately and let the valve cool down.
* Measure Ia and Gm at standard settings for Uh, Ua and -Ug.
<<< measuring Gm with hot tube may be misleading or undo success.
* Repeat above procedure until valve reaches appropriate Gm/Ia or fails completely.In case of success the tube gets a new lease of life - sometimes thousands of hours again.
Caveat Emptor: Valves should have a some flashed getter substance left, and good vacuum beforehand, otherwise the procedure will not work. The method does not always succeed - and often does not bring the valve back to full specification. Sometimes the treatment kills the valve off completely - so try at your own risk - I have applied it only to valves which were not useable any more.
With E88C and similar tubes I have recovered about 50 'dead' pull-out tubes successfully - about 90% of the attempts ended with tubes having specifications within their 'lifetime' tolerances. Some failed completely, though. Setting for E88C regeneration were Uh=7V, Ua=350..400V, -Ug0=-50V, Ia peaking at 30..40mA. The anode is heated up to orange glow for a moment... if left glowing for too long, the valve tends to be killed for good (by ourgassing, I think).
Warning: Do all this at your own risk - I am not responsible for the destruction of your valves or your health (;->)...
Regards,
---mb---
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Follow Ups
- Re: 'regenerated' E88C ? - mb-de 07:16:46 09/26/00 (2)
- Re: 'regenerated' E88C ? - Pär 08:01:34 09/26/00 (1)
- Re: 'regenerated' E88C ? - mb-de 08:28:22 09/27/00 (0)
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