Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mresistor on September 18, 2024, 10:02:05 am
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Hi guys. Pardon my ignorance. I have a Hammond 290CZ that is unused. I find that it fits perfectly in a Princeton Reverb chassis so I'm going to use it. It's 300-0-300 @120ma, 6.3vac @4amp.
Since it was made to replace the pt in a Vox AC15C1 it also has a 25vac 250ma non center tapped winding, for powering solid state devices in the amp.
I want to use this 25vac winding to make a bias circuit utilizing a voltage doubler. I've read through Merlins page on bias circuits but this example isn't covered. Anyone got some ideas on how this can be done.
Here's a simple voltage doubler circuit. How can I use this?
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I am aware that I can also just tap a bias circuit off of one HV leg as has been done many times. I thought it would be interesting to use this low v winding.
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Tapping on both the HT branch you can obtain a full wave Bias
K
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Tapping on both the HT branch you can obtain a full wave Bias
K
Yes K I didn't add that it's a full wave circuit but it surely is. Should help with noise and filtering, as if there is any in these simple bias circuits. Reason I think is there isn't any real current flowing in a bias circuit, more a potential for the grids.
I'm wondering how to go about completing the circuit all the way to the control grids.
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I'm wondering how to go about completing the circuit all the way to the control grids.
once you have a DCV PS source, the rest of the circuit should be cut n paste from any of a zillion already tried methods
the only thing gnawing at the back of my brain; each PS diode on the + side has a Vdrop, then you'll be grounding that Vdrop so you have a common, -- reference for bias. DISCLAIMER: (been wood-cutting all day, am herbily relaxing the muscles, so, I might be all wet logically) :icon_biggrin:
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Is it easier to look at like this?
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Hi mresistor
Try this (attached) even worked out some nominal values for you. I have done a few Doublers and Quadruplers (for Calibration Mic Preamps) fed into high stability Voltage regulators BUT you wont need that.
Regards
Mirek
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I've read through Merlins page on bias circuits but this example isn't covered.
I have to leave something for the book :laugh:
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Thanks guys! Very helpful.
Merlin I do have your Preamp Design for tube amps book. :icon_biggrin: Thank you sir.
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Mr Merlin thanks for sharing
About the doubler I like it more (for my brain it's easier to understand) when you draw the doubler like in some images on your books, the FWB design doubler where a pair of diodes are subbed with capacitors :icon_biggrin:
K