"Meat Plow" wrote in message
news
On Tue, 24 May 2011 12:04:48 +0100, Arfa Daily wrote:

"N_Cook" wrote in message
...
Amp used for the first time, in 2 years of regular mains use, with a
generator. Works fine with no problems. Coincidence ?, next gig back to
usual mains supply, at power up, blows the mains fuse. The GZ34 is
failed both sides, 0 percent output . Inspecting the fuse it has failed
at an end ,
not the central (T) section and otherwise complete wire shows no sag or
discolouration. So possibly mechanical failure of fuse. If fast
make/break intermittant action of the fuse wire at an end , would that
knock out an RR
valve? What in general happens in the failure of RRs ? I've only ever
seen 75 percent , same as new, or 0 percent "goodness" at prescribed
current settings of the Avo valve tester.



I've had a number of GZ34s fail short circuit, or suffer from serious
flashover, and knock out fuses over the years, but I've always put this
down to saggy filaments or whatever, where the valves are mounted
horizontally, or upside down.

Arfa

What do you think about subbing the 5AR4 with a 5U4?




Never tried it, but looking at the specs, they look rather different from
one another, see -

http://www.r-type.org/exhib/aaa0997.htm

and

http://www.r-type.org/exhib/aaa0504.htm

The 5U4 appears to be able to handle more current, but at a lower max plate
voltage. Also, the heater requires substantially more current. Might be an
issue for the transformer supplying it ?

Arfa