B&K 500 Tube Tester

[Johnny10]

Just started to restore a B&K 500 Tube Tester I purchased a few years ago.
After turning the unit on all the tubes tested with shorts.
Meter moved to downward to the left on GM test.

So I decided to try and find info on repair and calibration.
The schematic was available and a lot of conflicting information on Bias and voltage settings.

I opened unit and found all original capacitors, selenium rectifiers, original resistors.
So I started by replacing electrolytic smoothing capacitors. Then changed selenium rectifiers for 1n diodes.

And then I started taking some measurements.
This B&K unit has a RCA 83 rectifier tube which I have provided an image of waveform.
I do notice that the waveform jumps around a bit between 183 and 178Vdc RMS volts.
The anode DC is not smoothed.

The screen voltage is steady 155Vdc with smoothing caps and has 1.7 volts ripple.

An extra image of the negative bias to the grid.

Tested a 12au7, 6189W tube with both the B&K and my uTracer and at the same voltages I am within 5% of the uTracer measurements on GM.
Utracer shows 4850GM compared to the B&K showing 5000GM.

I will add some more images later today.

My questions are does anyone use a B&K 500 that they have tested voltages?
Or do you have calibration data?
There are 4 voltages I am most interested in: Low Bias, Medium Bias, High Bias and High signal.

[Johnny10]

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[Johnny10]

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[kgorga]

The manual I have for the BK 500 with an 83 has:

High BIAS -13V Pin 7
Medium BIAS -7.5V Pin 6
Low BIAS -2.5V Pin 5
SCREEN 155V Pin 9
PLATE 200V Pin 10
DIODE PLATE 205V AC Pin 12 I think this should be labeled RECT PLATE
RECT PLATE 12V AC Pin 11  I think this should be labeled DIODE PLATE
High SIGNAL Pin 4 1V AC

Also there is a posting on diyaudio forums on calibration

[JoeO]

The manual I have for the BK 500 with an 83 has:

High BIAS -13V Pin 7
Medium BIAS -7.5V Pin 6
Low BIAS -2.5V Pin 5
SCREEN 155V Pin 9
PLATE 200V Pin 10
DIODE PLATE 205V AC Pin 12 I think this should be labeled RECT PLATE
RECT PLATE 12V AC Pin 11  I think this should be labeled DIODE PLATE
High SIGNAL Pin 4 1V AC

Also there is a posting on diyaudio forums on calibration

Welcome to the forum.

[Johnny10]

Thank you kgorga for your reply.
I have seen the DIY video and also watched tomtektest videos.

My reason for asking for actual voltages was the confusion by all the video  listers on the actual voltage measured.
Seems they all had different marking on the schematics.
The questionable voltage was the High Bias which is at the top of the divider circuit.
I have seen 18V, 15V, 13V.

Also using VTVM vs DMM for these measurements? There is a difference .
My unit is from 1959 I believe techs used VTVMs ?



I am going to pull this baby back out and do some further measurements.
Also purchasing a VTVM.
My unit is working quite well compared to my uTracer Tube tester I believe a cal using information gathered from individual tubes comparisons will be the best answer.

Also, I realize these units are not meant to be Laboratory grade.

Just having a heck of a good time restoring and using these old units.