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 Post subject: BK 707 tube tester meter
PostPosted: Jun Sun 09, 2019 7:37 pm 
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Joined: Mar Sun 20, 2016 11:04 pm
Posts: 220
Location: Mesa, AZ 85206
Hi All

I picked up a B&K 707 tube tester locally, for a very good price.

It was actually in good condition, got it from someone who's father had it in his shop in the 70s.

It came together quite well...with the normal attention to details (cleaning, checking pots, checking resistors, replacing electrolytics, hardwiring the #55 bulbs, building a SS 83), it calibrated quite nicely.

The meter, when one releases the test buttons, swings back below the zero, and sticks there. A very light tap brings it back.

Normally, I would take the meter out and clean it; but, even though it has not yet happened to me, one can do damage to it. I of course don't have a spare.

What is notable is that the meter does not have adjustable travel limits, so I couldn't just tweak a stop.

Is the behavior of the swing back below the zero common with these meters? Any one ever seen a replacement just in case?

Thanks!

Steve


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 Post subject: Re: BK 707 tube tester meter
PostPosted: Jun Sun 09, 2019 9:10 pm 
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Joined: Jan Thu 24, 2019 1:22 pm
Posts: 121
Location: Centennial, Colorado 80122
Steve maybe you could just fabricate a stop mounted to the face plate mounting screw. Bill


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 Post subject: Re: BK 707 tube tester meter
PostPosted: Jun Mon 10, 2019 5:59 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 1578
Location: Dallas, TX
You might add a capacitor across the meter to slow down the swing, if there isn't one there already.
It probably have to be at least 1 uF. Recheck the calibration afterward.

_________________
Tim
It's not the Destination, It's the Journey.


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 Post subject: Re: BK 707 tube tester meter
PostPosted: Jun Tue 11, 2019 2:54 am 
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Joined: Mar Sun 20, 2016 11:04 pm
Posts: 220
Location: Mesa, AZ 85206
Well, sometimes the answer is right in front of you, but you don't see it.

Bob at Tubesound suggested I look for something sticky...

The faceplate serves as the stop fro the needle...a swipe with electrical grade alcohol along the faceplate stop...poof...problem gone!

Don't I wish it was always that easy...thanks for your input!

Steve


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 Post subject: Re: BK 707 tube tester meter
PostPosted: Jun Wed 12, 2019 2:53 pm 
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Joined: Mar Sun 20, 2016 11:04 pm
Posts: 220
Location: Mesa, AZ 85206
Well, spoke too soon.

While it did calibrate, the jet-check section tests weak for all tubes, and a number of tubes I checked after warm up pegged the meter when pushing the shorts button. These tubes do not show shorts on other tubes.

So, I think I will have to start looking for possible shorts in the switches and checking voltages off the wiring diagram.

I would welcome any feedback...Is it just me, or is the 707 schematic harder to link up to the actual push buttons and their contacts?

Steve


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 Post subject: Re: BK 707 tube tester meter
PostPosted: Jun Thu 13, 2019 7:55 pm 
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Joined: Mar Sun 20, 2016 11:04 pm
Posts: 220
Location: Mesa, AZ 85206
Apparently, after moving the 707 it needed re-calibrating...not sure why...it is possible when the balance was set it threw some other parameters off, but I ended up having to re-calibrate the grid emissions, signal voltage, DC bias, and balance.

Now all voltages are correct both at the sockets and in accordance with the schematic.

Good tubes now test as they should.

However, I have noticed what others have noticed: one of my 6J6s in the jet-check pegs the meter when pressing the shorts...the shorts light does not light...When this tube is checked for shorts in one of my other testers it does not show a short. I let it warm up quite a bit, but it remained the same.

Does anyone have a good explanation for this? I know it happens, but I am having trouble visualizing why.

Thanks!

Steve


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