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Some oscilloscope pictures

Started by Sylvia Else August 22, 2021
<https://www.dropbox.com/s/rddddzpkwqo44sc/TransformerWiring.jpg?dl=0>

Shows how the power transformer is directly wired to two separate 
boards. Not sure how, or why, they'd want to do that.

<https://www.dropbox.com/s/nlzx6f0w5deomb1/SolderThroughHere.jpg?dl=0>

Shows the hole through which the transistor has to be soldered. Note the 
two resistors in plastic tubing that have one end soldered to this 
board, and the other end soldered to a board at the back of the tube. 
Also a wire directly soldered to the board that also goes there.

<https://www.dropbox.com/s/degb7topima7yle/TransistorLeads.jpg?dl=0>

Shows the formed leads for the transistors. Fortunately, I now have a 3D 
printer and have been able to make a template for bending the leads. Not 
sure whether the white stand-offs have any useful thermal properties. 
They have to withstand about 170 volts.

Another oddity is the two leads covered in yellow insulation. They are 
only connected at one end, and are marked on the schematic as "wired 
capacitors" across the resistors that lead to the tube X axis plates. No 
doubt they do produce some capacitance, but I can't imagine it's much. 
Anyone know what the purpose would be?

Sylvia.

On Mon, 23 Aug 2021 12:30:08 +1000, Sylvia Else <sylvia@email.invalid>
wrote:

><https://www.dropbox.com/s/rddddzpkwqo44sc/TransformerWiring.jpg?dl=0> > >Shows how the power transformer is directly wired to two separate >boards. Not sure how, or why, they'd want to do that. > ><https://www.dropbox.com/s/nlzx6f0w5deomb1/SolderThroughHere.jpg?dl=0> > >Shows the hole through which the transistor has to be soldered. Note the >two resistors in plastic tubing that have one end soldered to this >board, and the other end soldered to a board at the back of the tube. >Also a wire directly soldered to the board that also goes there. > ><https://www.dropbox.com/s/degb7topima7yle/TransistorLeads.jpg?dl=0> > >Shows the formed leads for the transistors. Fortunately, I now have a 3D >printer and have been able to make a template for bending the leads. Not >sure whether the white stand-offs have any useful thermal properties. >They have to withstand about 170 volts. > >Another oddity is the two leads covered in yellow insulation. They are >only connected at one end, and are marked on the schematic as "wired >capacitors" across the resistors that lead to the tube X axis plates. No >doubt they do produce some capacitance, but I can't imagine it's much. >Anyone know what the purpose would be? > >Sylvia.
Poor planning ?
Sylvia Else wrote:
==============

> > Another oddity is the two leads covered in yellow insulation. They are > only connected at one end, and are marked on the schematic as "wired > capacitors" across the resistors that lead to the tube X axis plates.
** Not what the shem shows. There are two 111k resistors ( for each X plate) in parallel plus the "trick capacitor" in a feedback path to the base of a BF119. Likely purpose is frequency compensation for a bit of L in the Rs. Sometimes you see two plastic coated wires gently twisted for the same job. ...... Phil
On 23-Aug-21 12:52 pm, Phil Allison wrote:
> Sylvia Else wrote: > ============== > >> >> Another oddity is the two leads covered in yellow insulation. They are >> only connected at one end, and are marked on the schematic as "wired >> capacitors" across the resistors that lead to the tube X axis plates. > > ** Not what the shem shows.
No, not sure why I misread that. t.>
> There are two 111k resistors ( for each X plate) in parallel plus the "trick capacitor" in a feedback path to the base of a BF119. > Likely purpose is frequency compensation for a bit of L in the Rs. > Sometimes you see two plastic coated wires gently twisted for the same job. > > ...... Phil >
Sylvia.
On Mon, 23 Aug 2021 12:30:08 +1000, Sylvia Else <sylvia@email.invalid>
wrote:

><https://www.dropbox.com/s/rddddzpkwqo44sc/TransformerWiring.jpg?dl=0> > >Shows how the power transformer is directly wired to two separate >boards. Not sure how, or why, they'd want to do that. > ><https://www.dropbox.com/s/nlzx6f0w5deomb1/SolderThroughHere.jpg?dl=0> > >Shows the hole through which the transistor has to be soldered. Note the >two resistors in plastic tubing that have one end soldered to this >board, and the other end soldered to a board at the back of the tube. >Also a wire directly soldered to the board that also goes there. > ><https://www.dropbox.com/s/degb7topima7yle/TransistorLeads.jpg?dl=0> > >Shows the formed leads for the transistors. Fortunately, I now have a 3D >printer and have been able to make a template for bending the leads. Not >sure whether the white stand-offs have any useful thermal properties. >They have to withstand about 170 volts. > >Another oddity is the two leads covered in yellow insulation. They are >only connected at one end, and are marked on the schematic as "wired >capacitors" across the resistors that lead to the tube X axis plates. No >doubt they do produce some capacitance, but I can't imagine it's much. >Anyone know what the purpose would be? > >Sylvia.
It's a gimmick capacitor, a twisted pair variable cap. I showed one of my young engineers how to do that last week. We didn't yet have the code to drive a digital variable capacitor, so she couldn't tune an oscillator to within phaselock range, so that was a temporary fix to let us test her FPGA phaselock code. -- Father Brown's figure remained quite dark and still; but in that instant he had lost his head. His head was always most valuable when he had lost it.
 On a sunny day (Mon, 23 Aug 2021 12:30:08 +1000) it happened Sylvia Else
<sylvia@email.invalid> wrote in <iogfhiFmhdsU1@mid.individual.net>:

><https://www.dropbox.com/s/rddddzpkwqo44sc/TransformerWiring.jpg?dl=0> > >Shows how the power transformer is directly wired to two separate >boards. Not sure how, or why, they'd want to do that. > ><https://www.dropbox.com/s/nlzx6f0w5deomb1/SolderThroughHere.jpg?dl=0>
Thin wires mains side? Kept away from sensitive electronics on other board?
>Shows the hole through which the transistor has to be soldered. Note the >two resistors in plastic tubing that have one end soldered to this >board, and the other end soldered to a board at the back of the tube. >Also a wire directly soldered to the board that also goes there. > ><https://www.dropbox.com/s/degb7topima7yle/TransistorLeads.jpg?dl=0> > >Shows the formed leads for the transistors. Fortunately, I now have a 3D >printer and have been able to make a template for bending the leads. Not >sure whether the white stand-offs have any useful thermal properties. >They have to withstand about 170 volts. > >Another oddity is the two leads covered in yellow insulation. They are >only connected at one end, and are marked on the schematic as "wired >capacitors" across the resistors that lead to the tube X axis plates. No >doubt they do produce some capacitance, but I can't imagine it's much. >Anyone know what the purpose would be?
When I worked for Tek we calibrated the V amp to the CRT by bending the wires to the CRT, that changed C and the frequency response needed to be within some limit. This insulated wire, if bended, does the same Maybe the is also some inductor in there?
On 23/08/21 03:30, Sylvia Else wrote:
> Another oddity is the two leads covered in yellow insulation. They are only > connected at one end, and are marked on the schematic as "wired capacitors" > across the resistors that lead to the tube X axis plates. No doubt they do > produce some capacitance, but I can't imagine it's much. Anyone know what the > purpose would be?
It is a gimmick capacitor, often made with a couple of wires twisted together to make a ~1pF fiddlable capacitor. Quite a lot of old Tektronix equipment relied on parasitic stray capacitance and inductance of circuit tracks. They had the decency to include the caps on the schematics, and to indicate they couldn't be seen on the boards.
On 23-Aug-21 4:38 pm, Jan Panteltje wrote:
> On a sunny day (Mon, 23 Aug 2021 12:30:08 +1000) it happened Sylvia Else > <sylvia@email.invalid> wrote in <iogfhiFmhdsU1@mid.individual.net>: > >> <https://www.dropbox.com/s/rddddzpkwqo44sc/TransformerWiring.jpg?dl=0> >> >> Shows how the power transformer is directly wired to two separate >> boards. Not sure how, or why, they'd want to do that. >> >> <https://www.dropbox.com/s/nlzx6f0w5deomb1/SolderThroughHere.jpg?dl=0> > > Thin wires mains side? Kept away from sensitive electronics on other board? >
It's not the positioning I'm questioning, but the mode of attachment. There are plenty of wire-to-board connectors available, and that would surely have made assembly easier. It would certainly have made repair easier, though they probably didn't care about that. The transistor I have to replace is at the edge of the board, and can be desoldered and resoldered, albeit with some fiddling. If I had to replace something closer to the middle of the board [*], I'd have to unsolder all the soldered wires, and somehow hope to be able to reconnect them later - perhaps by installing the wire-to-board connectors the thing should have had in the first place. [*] Of course, one bodge is cut the defective component off its leads, and solder the new component to them, hoping that they don't become unsoldered from the board. Sylvia.
On a sunny day (Mon, 23 Aug 2021 17:04:41 +1000) it happened Sylvia Else
<sylvia@email.invalid> wrote in <iogvkbFpd32U1@mid.individual.net>:

>On 23-Aug-21 4:38 pm, Jan Panteltje wrote: >> On a sunny day (Mon, 23 Aug 2021 12:30:08 +1000) it happened Sylvia Else >> <sylvia@email.invalid> wrote in <iogfhiFmhdsU1@mid.individual.net>: >> >>> <https://www.dropbox.com/s/rddddzpkwqo44sc/TransformerWiring.jpg?dl=0> >>> >>> Shows how the power transformer is directly wired to two separate >>> boards. Not sure how, or why, they'd want to do that. >>> >>> <https://www.dropbox.com/s/nlzx6f0w5deomb1/SolderThroughHere.jpg?dl=0> >> >> Thin wires mains side? Kept away from sensitive electronics on other board? >> > >It's not the positioning I'm questioning, but the mode of attachment. >There are plenty of wire-to-board connectors available, and that would >surely have made assembly easier. > >It would certainly have made repair easier, though they probably didn't >care about that. The transistor I have to replace is at the edge of the >board, and can be desoldered and resoldered, albeit with some fiddling. > >If I had to replace something closer to the middle of the board [*], I'd >have to unsolder all the soldered wires, and somehow hope to be able to >reconnect them later - perhaps by installing the wire-to-board >connectors the thing should have had in the first place. > >[*] Of course, one bodge is cut the defective component off its leads, >and solder the new component to them, hoping that they don't become >unsoldered from the board. > >Sylvia.
Yes, but that may degrade the soldering on the board side.. Not easy to service this thing, same for my old Trio scope, although that is a bit better accessible. Sometimes it helps before taking apart such a wire labyrinth to take a few pictures so you at least get the colors of the wires right... Cameras are a great help. OTOH the less connectors the less problems :-)
 Sylvia Else wrote:

=================
> > [*] Of course, one bodge is cut the defective component off its leads, > and solder the new component to them, hoping that they don't become > unsoldered from the board. >
** What I would do. Recently had to replace a pair of 5 leg, dual transistors in an old Sansui home amp ( AU5900 ) Saved about 2 hours time and a lot of grief by snipping off the device itself off leaving 5 x 1cm leads behind. ..... Phil