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ThSpeakerDude88 4th August 2007 04:11 AM

B&K 700 problems?
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 4th August 2007 09:40 AM

Calibration & schematic here (B&K 700 = 707)
more manuals here:

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

Arne K

finwbu 4th August 2007 10:52 AM

2 Attachment(s)
my change on a BK707

finwbu 4th August 2007 10:53 AM

2 Attachment(s)
B&K 707

finwbu 4th August 2007 10:55 AM

2 Attachment(s)
from B&k 707 manual , same lke 700

Cobra2 4th August 2007 11:33 AM

2 Attachment(s)
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.. :cool: )

Arne K

ThSpeakerDude88 6th August 2007 12:47 AM

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

Cobra2 6th August 2007 05:05 AM

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 14th January 2008 08:32 PM

Kallibrering av B&K 700
Hei Arne.
Jeg har nettopp kj°pt en B&K 700 og trenger info om hvordan jeg kan kalibrere denne.

Cal Weldon 14th January 2008 08:34 PM

Please use English on these forums. If you wish you may post using both English and your native language but please ensure the English version is accurate.

Thank you.

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