On 17/01/2016 3:04 PM, Phil Allison wrote:
Trevor Wilson wrote:



* I have a valve tester (AVO VCM163).


** The VCM163 ( Valve Characteristic Meter) is oddball among valve
testers, uses only AC voltages for ALL supplies - plates, screens and
grids !!

http://www.radiomuseum.org/forum/tub...principle.html

Expensive too, working examples go on Ebay for up to $3000.


* The initial fault (AFAICT) was due to the owner transporting the
foot pedal inside the enclosure. At some time, the foot pedal made
contact with the nipple on one EL84, thus allowing the ingress of
air. Amp was switched on and two other valves failed soon after.


** Valves need a good vacuum in order to work. When air gets in,
valves stop working immediately and a broken nipple lets air in
FAST.

You previously said three 3 valves had let air in ??

BTW most versions of the Classic30 leave the valves fully exposed:

http://profile.ultimate-guitar.com/p...86_image_0.jpg

Later versions have a full, perforated steel cover over all the
valves.

**Two of the other output valves had very small cracks near the pins. I
can only surmise that the owner had been rough in removing the valves
(she admitted to doing so) and cracked the glass.


--
Trevor Wilson
www.rageaudio.com.au

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