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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 12th Oct 2019, 8:43 pm   #21
M0FYA Andy
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Default Re: Solartron SRS153 information

Looking at your circuit, given the two 12E1's are in parallel, does it make sense that the two control-grid resistors are wildly different?

Amdy
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Old 12th Oct 2019, 9:24 pm   #22
m0cemdave
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Default Re: Solartron SRS153 information

They are both 1k on mine (SR153.2). Classic grid stoppers, I think.

The original solder joints should all have a dab of lacquer or paint from the manufacturer's QC inspection - any that don't have probably been re-made during servicing or modification.
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Old 12th Oct 2019, 10:50 pm   #23
ahankinson
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Default Re: Solartron SRS153 information

That was my question too, Andy, but I just checked and they both have a brown coating on the pins so as m0cemdave suggests, it came from the factory like this. Certainly in the newer schematics they're both the same value, but those have different valves.
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Old 12th Oct 2019, 11:24 pm   #24
m0cemdave
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Default Re: Solartron SRS153 information

I would be very surprised if two grid stoppers were intended to be different values. Are they wired to the same point on the tag board?
If you haven't done so already, it is worth measuring them to see if the paint has changed colour due to running hot.
I'd suspect a Friday afternoon job at the factory, but having said that I don't think the different values will affect operation (assuming no grid current).

Last edited by m0cemdave; 12th Oct 2019 at 11:30 pm.
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Old 12th Oct 2019, 11:56 pm   #25
ahankinson
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Default Re: Solartron SRS153 information

I've attached a close-up with some annotations. They are connected to separate terminals, but with a connection between them (the red line). The valve base numbers are shown for orientation, since they're in different ways. The brown lacquer can clearly be seen on both terminals.

I wonder if the tech installing them had a problem distinguishing orange from brown? I believe certain types of colour blindness can have that effect.

It's good that this shouldn't be a problem, but if I wanted to 'fix' it, am I right thinking that R8 would be closer to the desired value?
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