CV2493 in an old Tek h

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CV2493 in an old Tek h

Postby Martin » Sun Sep 16, 2012 2:13 am

hello friends,

I am restoring an old Tek 585A scope.
The tubes in the distributed amplifier section are "collected" from the pre owner, "to make it working". So there is a colored mix of ECC88, E88CC, 6DJ8, PCC88 (this is a 7v TV... ), some are good, some are tired, some are short before the end...

So I am planig to plug the complete stage with new old stock tubes, "CV2493" made by mullard, uk. I have a bulk pack of them, enough to refill the Tek.

This tubes are selected by the manufacturing for low noise.

My question:
Are they burned in by the manufacturer bec. they are selected, or will my calibration run away after some hours bec. they are fresh ? Then I have to make it self, calibrating a Tek is a very lot of work and I do not like to do that two times.

greetings
Martin

Tek 585A Ser. No 0015 he is one of the first made in Heerenveen, NL
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Postby Geek » Sun Sep 16, 2012 4:04 am

Hi Martin,

Always burn them in yourself to be safe.

I've had several perfectly good NOS tubes of the 6DJ8 variety that show weak grids and need a 24H "boiling" on the tester at 10mA to clear junk from them and they are just fine :))

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Postby Shannon Parks » Sun Sep 16, 2012 5:38 am

I think your BEC tubes will be fine. I would let the unit burn-in for an initial 4-6 hours one day, and then come back and calibrate the next day after a 1 hour warm up.

The modern Electro Harmonix 6922 tubes are true 6DJ8/6922 tubes (filament current, biasing, Gm, Mu, Rp, etc.), and are lower noise, as measured on my Boonton 1120, than any old stock tubes I have. Of the old stock, Amperex are the tops. I do have some Amperex made for HP (most likely OEM tubes for their test gear), that seem to be extremely well-matched triode halves.

Shannon
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