Relaxing FNR with a 1949 Admiral 12X12
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- Опубліковано 4 жов 2024
- After working hard on customer sets these past couple years, I needed a little break. So, I pulled out a chassis I'm very familiar with that has been long neglected. The idea is to pair it with the empty bakelite cabinet I picked up a couple months ago. Let's see if we can breathe some life into it.
Also, I experiment with direct video injection. This bypasses the tuner and IF and feeds composite video directly into the video amp.
Phil Nelson's article referenced in video
antiqueradio.o...
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I really like sets of this era, I am sure further tweaking will improve performance to a decent level, would be interesting to test the tubes, no doubt there will be a few weak ones.
Great video Bob! I would terminate the composite video input with a suitable non inductive resistor to ensure voltage levels are correct; also, using this resistor may help dampen any flashover voltage transients within the video output valve that may damage the external video source. As a simple form of DC restoration, maybe think about using a diode to clamp the video input during a negative synch pulse?
Nice Admiral set nice to see a great restoration every video I watch I learn more and more which is so fantastic. Love this channel my Favorite of all. Wish I lived near by to see this in person.
wish I could do what you do. Still learning many thanks Mike
Nice Job ! Phil sure has a great website lots of great info !
All those customer repairs means there is support and preservation underway.
Really good video, Bob!
you could install one of those RCA jacks with the switch in it like VCRs have so when you plug the cable in, it uses the composite off the cable, and when it's unplugged it will pass the internal video through. that way it can be used either way. a similar thing can be done with the audio, too.
hey sounds like a great idea!
I would just use a separate DPDT switch, then you can switch between modes without unplugging everything. A separate switch also lets you insert components needed for direct injection (capacitor, termination resistor, maybe an amplifier) which you don't want for RF reception.
wow Ive seen the 12 x 12 reference when hunting for my 20b1 schematic. Yeah, same passion here getting it working is slightly more fun that being done and just watching it.
Excellent, probably your best FNR.
Yep, doing a resurrection but I like the way you do your videos and get right to the point 👍
Is it though? I mean I just did what I normally do. Recapped it, replaced the tubes etc
Well, sometimes you get lucky and don't have to replace everything to get them going. You did start with a lot of leftover parts so I think it counts. When I was rebuilding sets to sell mostly it was bad tubes and transistors, burned up resistors, stuff like that. Didn't end up replacing a lot of caps.
Time and heat have taken their toll since then. Looks like it's going to throw a nice picture when you get done.
Fascinating....
I think video amplifier IC's are available that have a 75 ohm input impedance. You would need a gain of at least 2 to offset the termination voltage decrease. You could use diode clamps on the output to help protect from a tube short, one to ground (or negative supply) and one to the positive supply for the amp. Those diode would have to have a low capacitance so that they didn't effect the video signal. Any DC restoration would have to be applied to the video output tube circuit, once you pass the video through a capacitor you nullify the effect.
Excellent video, Bob! That set has some really *awesome* bandwidth! Of course, it rolled off the assembly line a few years before the 1954 NTSC color standards that black-and-white sets manufactured later had to accommodate for with reduced bandwidth.
Only if I bypass the tuner and IF. Otherwise it's around 3.5.
@@bandersentv Granted, the tuner and IF *did* degrade the picture, somewhat. The tuner and IF sections of higher-end sets produced at that time would have likely replicated the transmitted video signal with better clarity and fidelity; but injecting the signal at the video outputs even in *those* sets probably would have still produced a crisper image than one from their tuners/IFs, bypassing any RF distortion.
@@chetpomeroy1399 Yes, I'll be restoring an RCA 8TS30 in the near future. It was designed to have full bandwidth. I'm curious to see how good test patterns look
Direct video injection is a more complicated question than it seems. I can understand the purist viewpoint for sure and the direct injection would make more sense if the set was going to be used a lot but I suspect that most of these are not. Having the option for both sounds like the sensible solution. It's a beautiful set too 😊👍 PS: I am about to take the back off a 14" Panasonic (1999) to check the caps. Wish me luck! 😄
Great job getting this done in one night! We always run into stuff that ends up taking longer or not quite coming out as perfect as we hope. Really looks excellent though, and I'm surprised the direct injection worked that well with just one video amp stage. I have done it once on a 19" Zenith porthole a few years ago, it worked well but I guess the color information herringbone effect explains why those patterns were appearing in the picture, despite having great bandwidth and definition. The Zenith did have 2 stages of video amps but perhaps less gain per stage, can't remember the exact tube types. The audio was a bit trickier because the Zenith used only an output tube to drive the speaker, and the previous stage was a gated beam detector (with buzz control). I was able to make that tube a regular audio gain stage by replacing the quad coil with a resistor and feed the combined mono audio to its grid, and it worked well.
To elaborate on why I had to modify the gated beam audio tube to make it an audio only gain stage was because injecting the audio to the volume control yielded insufficient volume, because the volume control feeds the output tube, and that tube by itself did not have enough gain.
Ah yes the sencore pr57.........mine just got here so hoping I can get it to work.
Hello Very Very Very Very Very Very beautiful Admiral TV Brazil 🥰💓✌️
The CRT is half way towards the end of it's life. Wouldn't that be wonderful to find one in new condition.
"golden tubes.... faintly glow"
"Electric faces seem to merge..... Hidden voices mock your words."
composite outputs expect a 75Ω load. Without it (and assuming the grid/bias circuit of the video amp is a much higher impedance), you’re essentially piping in double the 1.14Vpp amplitude. This isn’t necessarily going to damage anything, but it would explain the choppiness of the window-circle pattern and excessive contrast.
(Ergo, slap a 75Ω resistor across the clip leads and you’re good to go)
Yes, video amp has a 1M grid leak bias resistor. Ideally, I'd like to add a video amp with adjustable gain and add DC restoration.
When you're so early you have to watch in 360p 😅
ohhhhh ok when you said speaker was the problem I thought the field coil had opened up, I didnt catch that the speaker was just NOT plugged in. Me Im crazy and would have rewound the field coil!
I have one of those sets and I restored it and it has a good picture but I could use and original focus control and the door is there but the top is cracked.
One way to get a b/w video source with full bandwidth and without color subcarrier is to use the HDMI output of the digital receiver with an HDMI -> S-Video converter, and only use the Y signal from the S-Video connector.
Or the green from component out. I do wonder if it's full bandwidth though.
@@bandersentv Yes, it should work, as long as it's not common with the composite output. Some component output has the green/yellow RCA connector which means that it doubles as a composite connector. If it is a fully separate component output, than it probably has full bandwidth on the green RCA.
@@mrnmrn1 Oh I've done it before in a video. Years ago in the old apartment. I picked up some over the air ATSC to NTC boxes with component output I'll be experimenting with.
Great idea, thanks for the tip, I might have to try this!
Really enjoyed this video!...great idea to show the picture with a direct injection signal!...always wanted to see how the color information would have displayed on an early B&W set capable of 4.5 MHz bandwidth!!! Were many early sets capable of full bandwidth? Have you seen the color dot pattern interference in any of your other set restorations?
Yes and yes. Going way back over 10 years ago I showed it in several similar Admiral sets. Early RCA, Dumont, Zenith, Stromberg, etc had excellent bandwidth. All the high end brands in other words.
In the video you feed the composite video from the generator and set top box into the set without using a 75 Ohm terminating resistor. This is bad practice for two reasons;
First, if you look at circuits of composite video outputs in DVD,VCR,Set top boxes, video distribution amps etc, they almost always have it set up so, that there is a 75 Ohm series resistor going into their video output jack, and once connected this will form a 50/50 voltage divider with the terminating resistor at the receiving end, eliminating ringing and other effects. Ofc adding the 75 ohm termination in that case may reduce signal level by half, but that then should be taken care of by a video amp which would also be the place to employ black level clamping. And secondly attaching the grid of a tube to some VLSI chips found in set top boxes etc is asking for trouble. A simple arc over in the tube putting voltage spikes on the grid, and your set top box is toast because no coupling cap will block sharp voltage transients from feeding back into the source. There is very valid reasoning behind using a transistor video amp before going into the video tube. If not as amplifier, then at least to act as buffer.
All excellent points. I was just following along with the linked article and hadn't considered the issues you brought up. The 6AU6 video amp uses a 1M resistor to ground for bias. I assume I'd want to leave that alone and connect the output of the video amp via a capacitor?
What?! Half of a 12AU7 as vertical output? Even the two sections in parallel feels too weak for the task for me.
Runs pretty darn hot!
@@bandersentv I absolutely believe that! They probably don't last long in that position. I don't know how they came up with that idea...
Are those twin lead wires made that way to minimize capacitance between the two leads?
Gives a consistent impedance of 300 ohms to minimize loss
You are doing a "shango " You should do a " how not to service a tv set"
well that's what these quick-fixes ARE. tv repair meet clickbaitiness.
Or is shango doing me? I think I've been doing videos longer
Quick? About eight hours of recapping and troubleshooting
@@bandersentvactually I believe shango started a year before you.
His oldest video is 14 years ago - mine is 15.