"Phil Allison" wrote in message
...

**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.



... Phil




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.


Its possible my Circle C are fake - I bought 100 of them cheap from a
reputable supplier some years ago, and on testing a lot were too microphonic
for high gain use.
I probably ended up with 60 good ones, 25 marginal ones, and 15 downright
unuseable.
The have tall, bright silver Anodes.



Cheers,


Gareth.