Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mini612 on August 30, 2023, 02:06:52 pm

Title: Help with Power Transformer voltages?
Post by: mini612 on August 30, 2023, 02:06:52 pm

To Admin ***I hope I'm in the right thread, if not, please move this or cancel it and I can post it in the right place***

I bought a box of misc old radio parts a few years back and this past weekend I dug through it to look for a PT for my new project.  Unfortunately, there was only one PT in the whole box!  It's physically smaller than the other PTs I have.  The PT has two black leads for primary, and secondary consist of two Red leads (no CT) and two Greens.  I decided to test it to at least know the values of the leads and the result is; Red leads = 172vac., and Green = 6.5vac.  I decided to to see if I could raise up the voltage a bit by using a full bridge rectifier with four 1n4007, and I got 156vdc.  I was a bit disappointed.  Without knowing any additional details of this PT, can someone tell me why I got 156vdc instead of something a little higher?

Thanks

Title: Re: Help with Power Transformer voltages?
Post by: sluckey on August 30, 2023, 02:29:12 pm

Put a filter cap across the bridge and the unloaded voltage will increase to 240VDC.

Title: Re: Help with Power Transformer voltages?
Post by: mini612 on August 30, 2023, 02:45:52 pm

Quote from: sluckey on August 30, 2023, 02:29:12 pm

Put a filter cap across the bridge and the unloaded voltage will increase to 240VDC.

OH YES!  Got it.  Thank you.