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.


..... Phil