B&K 700 problems?

[ThSpeakerDude88]

I have a B&K 700 that I got from a neighbor who used to be a TV repairman. I have tested a bunch of tubes on it, but I have started to notice that a lot of un-used new tubes that I have (JJ's and sovteks) are testing bad or minimal.

For example: a new un-used JJ 12AT7 tests 60/80
A new un-used JJ 12ax7 tests 20/22
A new un-used Sovtek 12ax7 tests 18/19


For the books, some 1964 sylvania 12ax7A's both tested a matched 30/30 per tube.

Also , some EL84's have been testing a bit low too. I am wondering if the unit is out of calibration? I am using the correct sensativity/socket/heater settings.

This unit has two tubes in it, an 83 rectifier and I don't remember the other one...

Any help would be greatly appreciated.

[Cobra2]

Calibration & schematic here (B&K 700 = 707)
http://tone-lizard.com/B%26K_tube_te...nformation.htm
more manuals here: http://bama.sbc.edu/b&k.htm

The 83 tube can easily be replaced with a ss/diode rectifier.

Arne K

[WALTER BURKHARD]

my change on a BK707

[WALTER BURKHARD]

B&K 707

[WALTER BURKHARD]

from B&k 707 manual , same lke 700

[Cobra2]

I have used this for SS-replacement (attached).
I think the lower drawing is a better replacement, as the "83" is supposed to have some voltage-drop...
I used 2 x 1,3W zener in paralell (having plenty of the 9,1V.. )

Arne K

[ThSpeakerDude88]

would any of these things cause any problems though? Do some tubes really come reading THAT low?

[Cobra2]

And what does the chart tell? " Good if it reads 22 or more "
It does not need to be off calibration by much, to get your result...

Arne K

[skaffern]

Hei Arne.
Jeg har nettopp kjøpt en B&K 700 og trenger info om hvordan jeg kan kalibrere denne.

[Cal Weldon]

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