Project impossible? bringing a magnet-box back from the dead? - Page 3 - Videokarma.org TV - Video

Yamamaya42 · #31 07-16-2021, 10:02 AM

The failing 18 ohm resistor has been changed, ( reads 61 out of circuit ), replaced main bias filters, not to dredge up this whole reform / replace debacle, but this does sort of add fuel to it.
At this point, I have had power on for over 2 hours, most of it bringing it slowly up.

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

C1, C2a, C3a have been replaced, when tested ( after being isolated), C2a & C3a seemed to check OK, although a bit high, I have no way to do a full power leak test, however.
BUT... I could get no reading at all on C1, it was very dead.

I now have a matching set of 150uf in the voltage doubler circuit.

USPS says that the NOS HOT will be here today, I will see if I can get stable HV now.

Yamamaya42 · #32 07-16-2021, 09:50 PM

YES! YES!

https://i.imgur.com/B8hgItl.jpg

We have liftoff!

Yamamaya42 · #33 07-16-2021, 11:37 PM

Its alive!!! It's alive!!!

https://i.imgur.com/pLjN5Nj.jpg

https://i.imgur.com/g2ndhPl.jpg

Yamamaya42 · #34 07-17-2021, 12:23 PM

Now have a full raster, this is a major step forward, but the audio output tube 6GC5 did NOT come today like USPS said it would, so I can't bring up the IF/video without it yet, cause as mentioned, it is the source of the 120v for the video circuits.

I have rigged up temp controls for horz / vert hold, and they seem to work, but I still need to rig up a contrast control, for w/o it the cathode of video output is just left hanging and thus inert.

Yamamaya42 · #35 07-19-2021, 08:37 PM

first images of video..

NOTE,,
I have no brightness control yet, and I have not got IF input to work yet, this is video input direct.
and I'm seeing the same issues that I saw with 8yp4 that I saw on the Arvin, it just NOT seem to work well with cathode input, but loves G1 input.

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

https://i.imgur.com/DNijuP1.jpg
I dread having to rig up something to hold the 24ahp4 tube, or the 21aup4a out of my SC again

Yamamaya42 · #36 07-20-2021, 09:26 AM

Does anyone have experience with the 8YP4 Test CRT? And may have any idea why it seemed to work so well with my FADA 895 ( rca 630ts clone ) 12LP4 G1 video input, but work poorly with the arvin model 5204cm chassis 21EP4B and now this magnavox one using a 24ahp4 both with cathode video input, are the voltages just too far out of range for the 8YP4 to work well, is a 20+ sized just too much for it? I'm not sure why it is not liking it, it IS hooked up right.

Yamamaya42 · #37 07-20-2021, 07:43 PM

First video using the native CRT. it IS a bit weak, but it's pretty damn good for a weak tube.
came up to this level after 90 sec or so.

https://youtu.be/KmF9YlAy-U8

electronjohn · #38 07-21-2021, 08:58 AM

Impressive!

old_tv_nut · #39 07-21-2021, 10:27 AM

Video response and focus look great - see all those chroma dots!

Yamamaya42 · #40 07-21-2021, 11:09 AM

It seems that the 24AHP4 is not as bad as I thought, ( or what the BK 490B told me it was,)
The unstable brightness issue seems to be due to me not having the correct control for brightness yet, calls for a 200k pot, tied to 120v and gnd, with the center post going to CRT G1, using what I had on hand used a 500k trimpot.
Obviously now, not a good idea, because I noticed that it's overheating and causing an unstable picture, too small to take to load, so until I can get the right parts for it, I intend to replace it with 2 ½ watt 100k resistors, with the CRT G1 hooked to the center, this should give a decent pic, otherwise I would have to adjust the values.

As for sound, that too is a bit tricky, since I have not gotten IF up yet, it did not seem to work with the tuner subber, direct input at the audio output where the volume control USED TO BE, gave too weak of a output, (point 32) , I have found the output of the detector, which used to go to the tone control, (point 31 ), these can be linked to enable sound at full blast.

https://i.imgur.com/22toG2w.jpg

From what I have read, the 6DT6A is very close to the 6BN6 which was used in my Arvin, which had a AUX/phono input hooked to the detector at G3 (point 30) via a resistor and bypass cap, gonna try to see if something like that will work here as well.

Yamamaya42 · #41 07-21-2021, 10:12 PM

now with sound!
https://youtu.be/KxRb9aPu8Cs
will look a bit better once I can set contrast and brightness correctly!

Yamamaya42 · #42 07-22-2021, 09:24 PM

I just ordered a handful of pots, to try and recreate the controls for this thing, MOST are all of the same type, except for the brightness cont, which I got a one of a bigger power rating, cause it has 120bias to gnd across it, i don't want any burn outs, all the rest have minor voltage on them.

I could not find a 600 ohm for contrast, using a 500, don't think it will matter that much.

this TV did not have a tone control, don't see the need to add one, even though I could.

Yamamaya42 · #43 07-24-2021, 02:18 PM

control assy made

https://i.imgur.com/SDqrxZ3.jpg
https://i.imgur.com/7O46OW1.jpg
https://i.imgur.com/qGPQzDA.jpg

it all works!

Yamamaya42 · #44 08-02-2021, 08:14 AM

Progress update...

Over the weekend, I did manage to get something tuned in through the IF section using a Castle TV Tuner Subber, however there was a noticeable 60hz noise in the video, so strong that it was interfering vert lock, I'm not sure if this was a grounding issue or due to bad caps in the subber, I did only pay $9 for it after all, I could try to stick batteries in the thing and not have it on AC, and see if the noise is gone, but the point was to see if the front end worked and it seems it does somewhat.

Now the choice is, find an alien tube VHS tuner someplace, hook it up make it work, or stick with A/V input...

Yamamaya42 · #45 08-03-2021, 02:33 PM

I'm still trying to decide what to do with this thing, point #1, 24AHP4 is weak but not dead, and still gives a decent picture, surprisingly, but there is no telling how long it will last, with limited use, could be months or even longer, a year or more, no way to know.
Once I have the chassis all patched, I intend to build SOME KIND of wood cabinet to fit all it in even knowing the tube may fail some day, even if it does, ETF has several compatible 23 inch tubes that I can fall back on in the event the 24AHP4 does croak.

I already have a rough idea what the final project will look like, which comes to the other thing that I'm on the fence about, tuner or no tuner, since I have already established that IF is working, RF input is an option, however, the tuners to be found on eBay are just tuners only, where as they can probably be made to work, and adjusted to ACG and all that, they come with no knobs/ dials/ channel indicators, all that would have to be found, granted, once tuned, they will almost never be set again, or almost never, but finding the right ones that fit/ work and are aesthetically pleasing will be tricky, vs just going with direct A/V input.