Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jrusto on February 14, 2024, 04:59:56 pm
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Hey guy,
I am starting a rebuild with a 65 Princeton Reverb Reissue. Removing the board pots etc. and using a Hoffman Princeton Reverb layout. After looking at the schematic for the reissue, I noticed RT1 and C17 on the reissue schematic and board I removed. I would like to use the existing power transformer but do not know what those 2 components circled in blue do on the mains before the primary winding. I have attached a closeup of the section.
So the real question is can I hook this transformer straight to the main power supply on my rebuild. I cannot find the specs on the Reissue Power Transformer.
Thanks in advance for any information.
Rusty
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RT1 is a thermistor. It's a special resistor whose resistance decreases as it's temperature increases. When you turn power on RT1 has a relatively high resistance which decreases the voltage applied to the PT. As current through RT1 heats it up causing it's resistance to decrease which allows more voltage to reach the PT. The purpose is to provide a "soft" start when you turn the power on. This prevents inrush current. C17 is a special cap that acts like a line filter to reduce noise on the incoming AC mains voltage. Both are good ideas but not necessary. Your amp will work just fine without these two components.
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Thanks for the response. I really didn’t want to buy another transformer.