B&K 500 Tube Tester - Page 1
Forum section: electronics / repair

author: Johnny10
author_rank: Frequent Contributor
timestamp: May 22, 2016, 03:31:58 pm
content: 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.

author: Johnny10
author_rank: Frequent Contributor
timestamp: May 22, 2016, 03:39:59 pm
content: More

author: Johnny10
author_rank: Frequent Contributor
timestamp: May 22, 2016, 04:03:29 pm
content: More

author: kgorga
author_rank: Newbie
timestamp: June 15, 2016, 04:45:54 pm
content: The manual I have for the BK 500 with an 83 has:High BIAS -13V Pin 7Medium BIAS -7.5V Pin 6Low BIAS -2.5V Pin 5SCREEN 155V Pin 9PLATE 200V Pin 10DIODE PLATE 205V AC Pin 12 I think this should be labeled RECT PLATERECT PLATE 12V AC Pin 11 I think this should be labeled DIODE PLATEHigh SIGNAL Pin 4 1V ACAlso there is a posting on diyaudio forums on calibration

author: JoeO
author_rank: Frequent Contributor
timestamp: June 15, 2016, 04:52:06 pm
content: Quote from: kgorga on June 15, 2016, 04:45:54 pmWelcome to the forum.

author: Johnny10
author_rank: Frequent Contributor
timestamp: June 16, 2016, 12:53:23 pm
content: 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.