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

[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.

[Tube TV]

Picture sure looks nice for a set with a weak tube.
Good job bringing it back to life.

[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,

[Yamamaya42]

Brightener circuit done.

https://i.imgur.com/IHTbXYq.jpg

source is a 12 volt 3 amp DC PWS, set to 7.2 ( aprox ) have a hefty 8.5 ZD clamp on the output to protect from overload, and 100mf filtercaps, I don't foresee ever going above 8v with this, and if I do I will just replace the ZD.

https://i.imgur.com/39W7mv1.jpg

I will most likely will try going with a tuner, the input to the video output is 1.5 or so, and composite is 1.1 or so, so the contrast is a WEE bit low for direct video input, but not very much, abut there is also no agc, so the best way would be to try a tuner, i guess.

[Yamamaya42]

https://www.youtube.com/watch?v=pbTrs9OdTFQ

latest video test.

pretty much at the point to build something to put it into now.

[Yamamaya42]

Meanwhile, while I'm working out how and what to build to put the guts of this “Big Mama Magnavox” into, looking around locally I found a mystery Admiral television, looks to be in poor shape, and so far, the only info I have is the pictures of it, no date or MO#.

Anyone seen this Admiral before?

https://i.imgur.com/aqhzyyJ.jpg
https://i.imgur.com/nqWsJAM.jpg

[kvflyer]

Originally Posted by Yamamaya42

Meanwhile, while I'm working out how and what to build to put the guts of this “Big Mama Magnavox” into, looking around locally I found a mystery Admiral television, looks to be in poor shape, and so far, the only info I have is the pictures of it, no date or MO#.

Anyone seen this Admiral before?

https://i.imgur.com/aqhzyyJ.jpg
https://i.imgur.com/nqWsJAM.jpg

I have seen them at our local radio club auction. That is typical early 50s Admiral styling, with the chassis on its side. Very easy to get going usually with plenty of room under the chassis and no crazy parts. Similar to the 26R12 Admiral that I have.

[Tube TV]

The Admiral is a 1952-53 model by the looks of it. Looks pretty nice if it's local and the price is reasonable. I'd want to test the CRT in it first if I was going to spend any significant amount of money for it.

[jr_tech]

A slightly earlier model used a 16” metal cone round tube...

http://www.tvhistory.tv/1950-Admiral-26X56A-16in.jpg

My guess is that the set in question has a first generation rectangular CRT, like a 20CP4 instead of a later, more common 21inch tube. Might be difficult to find a replacement.

jr

[kvflyer]

Originally Posted by jr_tech

A slightly earlier model used a 16” metal cone round tube...

http://www.tvhistory.tv/1950-Admiral-26X56A-16in.jpg

My guess is that the set in question has a first generation rectangular CRT, like a 20CP4 instead of a later, more common 21inch tube. Might be difficult to find a replacement.

jr

Or, it may just be a 17 inch CRT which is from about that era.

[jr_tech]

Originally Posted by kvflyer

Or, it may just be a 17 inch CRT which is from about that era.

A likely possibility! Sams 135-2, which covers a bunch of early 50s Admirals shows both 17” and 20” tubes in use.

http://www.earlytelevision.org/pdf/a...sams_135-2.pdf

A 17BP4 should be easier to find than a 20” jug.

jr

[Yamamaya42]

Unfortunately, someone got it before I could.

Thanks for the info though.

[Yamamaya42]

decided to add a retro mod to my project!

https://www.youtube.com/watch?v=GC8MnvbTrts

[Yamamaya42]

Since I lost the chance to get the zenith television, I have decided to pull this project out of the shed and try to toss it together again.

It does work even though the CRT is weak and lacks contrast, but does get a bit better as it has been on a while.
It uses a 6EB8 for the video output / sync sep, looking on the sub chart, it;s said that a 6JT8 is a drop in compatible replacement, and on an audio site I saw... " Plenty of cheap tubes to choose from in that footprint, though - 6GN8, 6HF8, 6AW8 and more. 6LY8 and 6JT8 have more gain in the pentode section,"

And more gain in the pentode section may be just what this tired old CRT needs to limp along for a few more years of light use!