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Electro Harmonix Valves ??

**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

Reply to
Phil Allison
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"Arfa Daily"

** I thought it was obvious.

The filament wire is not made from tungsten, as in all the others.

** Been there, done that.

12.6 volts at 160 mA = 79 ohms.

Duhhh ..............

** Same valves previously sold a "Sovtek " far as I know.

BTW: Ever see a " Sovtek " amplifier ?

Like the MIG100 or MIG 60.

The couple I've seen were amazing pieces of work - no PCB, laced wiring, ceramic sockets, heavy as hell and full of MIL high parts.

Like something built for the Russian military.

... Phil

Reply to
Phil Allison

"Arfa Daily"

** What are pins 4 and 5 ??
** FFS read my post before you reply with such nonsense !!!!!!!!!!!!!
** What are pins 4 and 5 ??

FFS read my post before you reply with such nonsense.

The resistance goes UP from 32 to 79 ohms when power is applied.

Shakes head, over and over............

.... Phil

Reply to
Phil Allison

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.

Reply to
Gareth Magennis

"Gareth Magennis" >

** 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

Reply to
Phil Allison

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

Here is one of them:

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Gareth.

Reply to
Gareth Magennis

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