[sdiy] Calling Harry or some of you knowing old hardware..

[Bob Weigel]

Yup you were right.  The schematic was weird...the way they drew the 
tube etc.  I should have noticed there is no other bias. lol.  That 
metal part going around it clipping on to the porcelain ....tha'ts all a 
battery clip.  THe batter is shaped like a narrow flying saucer.  
Fascinating.  Never seen that one.  So I just wired it like a Fender 
Bassman old design that uses the same tubes...but the freaking thing is 
still humming like crazy.  It's coming from after the tube but before 
the volume.  So it's either on the preamp power supply (where I put a 
huge 100uF 350V cap...) or the 470K is enough antenna isolation to put 
that kind of signal on the location.  I'll test it tomorrow.   Thanks 
again! -Bob


On 8/31/2012 5:12 AM, Paul Perry wrote:
> Could indeed be a battery, providing grid bias.
> But it won't be a battery NOW of course, just a resistor!
>
> best, paul perry melbourne australia
>
> ----- Original Message ----- From: "Bob Weigel" <sounddoctorin at imt.net>
> To: "synthdiy" <synth-diy at dropmix.xs4all.nl>
> Sent: Friday, August 31, 2012 7:39 PM
> Subject: [sdiy] Calling Harry or some of you knowing old hardware..
>
>
>> I was working on an old Knight unit...probably the first DJ unit.  lol.
>> Turntable on a metal box that uses 6SJ7 preamp tubes that get quite
>> noisy when I turn volume up.  I eliminated the power supply cap by
>> putting in a huge one which did help some but not much.  Very quiet now
>> past the volume controls..very simple circuit there.  Except... these
>> strange parts on the input.  A series thing that is a.... battery
>> or..capacitor with uneven length plates on the schematic.  With B.C.
>> written by it.  One on each input and both are doing the same. If I
>> short one side of the device away from the grid, little difference. If I
>> short the side on the control grid then it totally eliminates the hum 
>> noise.
>>
>> Now...these things...have like a wire going into a porcelain 'tube' on
>> both ends.  And a piece those fit into that looks like a funnel shaped
>> washer with some rubber insert on one side... and there is a wire
>> crimped around the porcelain on both sides so it's just a U shape
>> basically with the open ends of the U crimped around both porcelain
>> pieces if you can picture that.
>>
>> What were those supposed to be?  Anyone?  Never seen a part quite 
>> like that.
>>
>> -- 
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Check out sounddoctorin.com for songs, a studio tour, help
repairing old synthesizers and parts or thought provoking
articles that could help make your eternity!