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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

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!

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