Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Randy Lahey on November 29, 2024, 12:15:35 pm
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Forgive me if this has been asked many times in the past - I did a quick search but couldn't find a solution.
I am installing Hoffman's relay switching circuit in an amp and I am only measuring +3vdc and -3vdc on either output of the bridge rectifier which is fed 6.3vAC from a dedicated 6.3v transformer.
I understand I should see 9vdc at the output - why the low voltage? It's obviously not enough to actuate the relay. I have measured and confirmed the correct orientation for all components on the relay switching power supply board.
I should also mention that the 6.3vac filament supply has a virtual centre tap with 150R resistors. I have also not grounded the relay power supply board.
Any suggestions?
Thanks!
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The output is taken BETWEEN the negative and positive terminals of the bridge so that would give you about 6V pulsed DCV. Add a filter cap between the negative and positive terminals to increase the voltage to about 9VDC.
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Lots of relay information in this thread, Relay circuit & layout board & ft. switch;
https://el34world.com/Forum/index.php?topic=14348.0 (https://el34world.com/Forum/index.php?topic=14348.0)
It's found in Archives of favorite topics, 2nd in the list;
https://el34world.com/Forum/index.php?board=11.0 (https://el34world.com/Forum/index.php?board=11.0)
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I should also mention that the 6.3vac filament supply has a virtual centre tap with 150R resistors. I have also not grounded the relay power supply board.
Since this is a dedicated transformer that is not being used for tube heaters, you don't need a center tap. So remove the 150Ω resistors and just connect the bridge negative terminal to chassis ground.
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I highly recommend Doug's little relay power supply board. Small, inexpensive, works great.
Voltage also depends on the voltage regulator you're using, right?
https://hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=Lamps&ORDER_ID=559940839#google_vignette (https://hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=Lamps&ORDER_ID=559940839#google_vignette)
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I highly recommend Doug's little relay power supply board. Small, inexpensive, works great.
Voltage also depends on the voltage regulator you're using, right?
https://hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=Lamps&ORDER_ID=559940839#google_vignette (https://hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=Lamps&ORDER_ID=559940839#google_vignette)
+1! It's also neat, clean & all the bugs have been worked out of it already. Simply feed it the heater supply and it's ready to go!
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This guy asked exactly the same question four years ago. May be helpful to you:
https://ampgarage.com/forum/viewtopic.php?t=33226