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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 14th Nov 2023, 12:50 pm   #1
M0FYA Andy
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Join Date: May 2007
Location: Preston, Lancashire, UK.
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Default 6250 ohm relay in H2S circuit

I have asked if anyone has a PO3000 relay with a 6250 ohm coil in the 'Parts Wanted' section, but no luck, which doesn't surprise me as this is quite an obscure resistance.
The relay is Relay D in the bottom right-hand corner of the attached circuit. It is part of a timer to delay switching the HT on until the LT supply has been on for 30 to 40 seconds.

Why was 6250 ohms specified, particularly as Relay A in this circuit is 6000 ohms, much more readily available?

The resistors in the anode circuit of V305 are 10% at best, so can the resistance of the relay coil be critical? Changing to 6000 or 6500 ohms would be within 5% of 6250 ohms.

My own suspicion is that the team developing H2S comprised mainly scientists and physicists as opposed to engineers, so if the calculations said 6250 ohms then that was specified.

What do others think? Can I substitute a 6000 or 6500 ohm relay coil?

Many thanks,

Andy
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Old 14th Nov 2023, 1:32 pm   #2
60136 Alcazar
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Default Re: 6250 ohm relay in H2S circuit

Would 6000 ohm relay in series with a 250-ish ohm resistor be a viable alternative to keep V305 load as per design?
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Old 14th Nov 2023, 6:12 pm   #3
M0FYA Andy
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Default Re: 6250 ohm relay in H2S circuit

Why add 250 ohms when it would be swamped by R320/R321/R322 and well within their 10% tolerance?

Andy
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