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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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12th Oct 2019, 8:43 pm | #21 |
Nonode
Join Date: May 2007
Location: Preston, Lancashire, UK.
Posts: 2,510
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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 |
12th Oct 2019, 9:24 pm | #22 |
Octode
Join Date: Feb 2009
Location: Bletchley, Buckinghamshire, UK.
Posts: 1,205
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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. |
12th Oct 2019, 10:50 pm | #23 |
Triode
Join Date: Sep 2016
Location: Banbury, Oxon, UK.
Posts: 33
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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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12th Oct 2019, 11:24 pm | #24 |
Octode
Join Date: Feb 2009
Location: Bletchley, Buckinghamshire, UK.
Posts: 1,205
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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. |
12th Oct 2019, 11:56 pm | #25 |
Triode
Join Date: Sep 2016
Location: Banbury, Oxon, UK.
Posts: 33
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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? |