"Phil Allison" wrote in message
...

"Gareth Magennis"
"Phil Allison"

**Hi to the amp techs,

there is something odd about the HEATERS in current production EH
branded valves.

If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between
pins 4 and 5.

Check any other brand and the reading is 10 to 14 ohms.

The EH ones still draw 160mA at 12.6 volts like the others.

Similar but smaller differences exist with EL34EHs and 6V6EHs too.

That Bugera I posted about a few days back would NOT have developed
the nasty AC fuse blowing fault it did if EH brand 12AX7s were fitted -
as the start up heater current would be 3 times less.


I have quite a few Svetlana "Circle C" ECC83 here with 37 ohm heaters.
All others read the lower resistance range.
Except I have 2 Marshall branded ECC83, one reads high, one low, the
higher looking identical to the Circle C.

The 3 EH ECC83 I have all read high and look nothing like the Circle C.


** I have a few Sovtek branded 7025s with small, silver anodes - pulled
from an amp.

Heaters all read 32 ohms.

Despite a long search this morning, no pic of one quite the same is on the
net.

Seems incredible that Russians have found a new ( and suitable ) high
conductance heater wire to use in the last few years that is cheaper than
tungsten.



.... Phil




Oops, my error, the ones I have are Winged C Svetlana, not Circle C.


Here is one of them:

http://imageshack.us/photo/my-images/545/mpcx.jpg/



Gareth.