Project impossible? bringing a magnet-box back from the dead?

[Electronic M]

Originally Posted by Yamamaya42

Been thinking about this for a while now, and this is most likely what I will do, the 24AHP4 works fairly OK, after it has been on a few min, but could do with a slight boost, very slight.
The specs say it can work off of DC as well as AC, right now, its hooked to the 6.3v windings with all the other tubes.
I'm going to make a rectifier / regulator circuit using a LM317 and bridge rectifier, due to the AC-> DC conversion and filtration, I should be getting more than 6.3v DC out of the bridge, how much, no way to know till I build it, then I just set the LM317 to what ever final boosted output level I want.

A few observations. If you are going to source a raw tuner and separate knobs for it then you want a tuner that uses removable interchangeable channel strips, but NOT a wafer switch style tuner. Different knobs for different tuners number the knob and key the shaft different from tuner to tuner. Interchangeable channel strips allow you to change where each channel is relative to knob rotation so you can swap strips and make the channels match the knob.

LM317s IIRC can have a minimum regulation drop 1.35V...so for example if your rectifier outputs 7V you can only get 0-5.65V out of it and have regulation.

You could use a voltage doubler rectification circuit to get around 12V and circumvent that min voltage drop of the LM317.

[Yamamaya42]

Originally Posted by Electronic M

A few observations. If you are going to source a raw tuner and separate knobs for it then you want a tuner that uses removable interchangeable channel strips, but NOT a wafer switch style tuner. Different knobs for different tuners number the knob and key the shaft different from tuner to tuner. Interchangeable channel strips allow you to change where each channel is relative to knob rotation so you can swap strips and make the channels match the knob.

LM317s IIRC can have a minimum regulation drop 1.35V...so for example if your rectifier outputs 7V you can only get 0-5.65V out of it and have regulation.

You could use a voltage doubler rectification circuit to get around 12V and circumvent that min voltage drop of the LM317.

Both the tuners on eBay are the strip type, so if I do get one, that is most likely what I will do.

problem is always with a voltage doubler is stable current with unknown current loads , granted, the regulator could stabilize it.

i played with it some more on a variac , I found that bringing up the input voltage from 120(ish) to 129 raised the heater voltage to 7.1 volts and made a VERY noticeable improvement on the screen.

so i did a bit of digging and found a 12 volt 3 amp DC power brick.
so I will take that, a LM317T,a 5W 8.7V Zener Diode as a crowbar, and a 1 amp mini fuse.
and set it to 7 volts or so, I should never reach the 8.7 threshold, so the Zener Diode should never clamp and blow the fuse,