My first tube color set
 

Set was a basketcase and is long gone.

Kewl ! All-tube, or hybrid ? Looks to be in pretty decent cosmetic shape... Might have been one of the "Last-Gasp" tube sets...

It's a 7-tube hybrid. I had never heard of the K-series chassis, no idea what their reputation is. The finish on top is marked up a bit, no big deal. It's far better than the Hitachi I got earlier this year, that's for sure. However, just like the Hitachi, the UHF tuner is partially frozen. Ah well.

Cool find! Tube set are pretty rare around here, better snap them when they show up!

Yeah, especially if they weren't made by RCA. There was a late-60s RCA in the local listings a while back that went pretty fast.

By the way, I checked the date code on what is likely the original CRT as it's Admiral-labeled; it says 7052, so it's pretty safe to say that this set is a 1971 model.

Well, considering that it's an "instant play" set, I decided to plug it in and just wait for a while. Of the four tubes in the front row, the middle two were showing no signs of life. Please bear with me, the only tube whose function I know is the horizontal output tube. Upon applying full power I get the usual "no signal" audio, but there is no sign of snow on the screen and in a few seconds, pop goes the breaker.

I posted chassis pics to my Flickr account.

Do the filaments in the CRT light up? On my iPhone one of the small tubes look to have a white getter (gone to air) but it is hard to tell. I like the layout inside this tv - looks like a worthy project.

Yessah they do. On a side note, I don't know about Admirals, but I see that the D16 Sylvanias roast the area of the PCB under the horizontal output tube quite badly. That area on this chassis is spotless. An indicator of low hours perhaps? Most of the dust in this is light gray. I've got to get a paintbrush to clean up the chassis a bit.

Well well well, look at this 6BV11. The dust was obscuring the getter. Thanks for picking that out. That's one problem down anyway. It's an original Admiral tube.

Yeah that guy has had it, the horizontal output tube looks a little tired too. The TV looks clean and nice though, it would be a pleasure to work on that one.

Brightened up the Admiral pics a bit.

-Steve D.

Wow its not every day you see a set fail from a tube going to air.

It has a very different look from my 67' USA Admiral.

No idea if that's what caused the breaker to pop.

Naturally I can't find a Sams for this chassis. There is a service manual that covers the K20 though, I'll have it soon enough.
I decided to re-shoot them as I had been using the wrong camera settings. Thanks though.

If that's the horizontal oscillator it would explain the no picture condition - I could be wrong about that though. No horizontal oscillator would red plate then horizontal output and pop the breaker.

It's the color demodulator actually. Perhaps the other tube that isn't lighting is the horizontal oscillator.

Good call. The horz osc is the 6JW8. BUT the horz hold coil is
delicate & they would get smashed in. Usually you can fix them
but we stocked them. windings are apx 15 ohms & 85 ohms.
May also have got pushed out of PCB. Thats it for easy stuff.
These Admirals were OK to work on, didnt like the older ones.

73 Zeno:smoke:

I just had the tubes out for a quick clean-up and chassis pic re-shoot, no 6JW8 in sight. The tube complement is as follows:

6KD6 horizontal output
6MJ8 (not lighting)
6BV11 (gassed out)
12HG7
6LU8
6LX8
6CG3
6KV6A regulator
3DF3 rectifier
6AQ5A (hiding behind power supply filter cans)

New chassis pics. I had to switch off full auto to make the camera flash and not blur the pictures, but I got rid of the custom white balance settings used for a pic I took long ago.

https://www.flickr.com/photos/spacec...57638419636316

https://www.flickr.com/photos/spacec...57638419636316

https://www.flickr.com/photos/spacec...57638419636316

This shows at least 2 Sams 1281 I have & another I dont.
Compliment I have

6KD6 hoz out
6LU8 vert osc / out
12HG7 video out
6MJ8 r-y, b-y, g-y amps
6BV11 demodulator
6CG3 damper
3DF3 HV rect in cage
6KV6 HV regulator behind cage
6JW8 horz osc. May be a production change or a sub. It is near the coil.

73 Zeno:smoke:

It appears that the 6JW8 and the 6LX8 differ *only* in heater current requirements:
http://www.radiomuseum.org/tubes/tube_6lx8.html
Should make no difference in a set with 6.3 volts supplied to the tubes from a power transformer.

Nice job of fixing the pictures!

jr

Am I right in guessing that bad HV rectifier/regulator tubes will not cause CRT damage like bad safety caps in SS sets? That reminds me, I saw white caps under the chassis but I have no idea if they're safety caps.

No. Decapitation of the CRT from its neck due to excessive HV was unheard of in tube sets. It occured only in SS sets with the 4-legged "safety" caps.
When the cap failed, it allowed the HV to soar to 50 KV or higher, which exceeded the dialectric strength of the glass. Bleed-through resulted in thermal stress in the glass which sheared off the neck slick as a whistle.
Tube sets could only make 30 - 35 KV when the regulator failed, which wasn't enuff to hurt the glass.

In reading the tube complement of your set, I was hoping to see a HV regulator tube listed. Are you sure there isn't one lurking back there somewhere? If not, the set uses the nefarious feedback regulation setup which was very problematic. Hoping yours is an exception to the rule.

Not to worry. I dont remember much destroying a CRT in
a tube job. Only thing that may is arcing at the anode that etches
into the glass & cant to my knowledge be fixed. Seen that once.
Maybe a burning yoke could do it to.
White caps are always suspect & AFTER you know you got a good CRT
may be best to change them.
IMHO at this point the best thing is to get the HV up & see how
good the CRT is with minimal investment. Quick lesson

The hoz osc drives the horz out.
The hoz out runs "class C" so is turned off most the time.
If the horz osc is running OK there should be a large negative
voltage on the hoz out G-1 ( -75 VDC) on pins 5 & 9.

If the negative voltage is not there the tube is on all the time
& it will soon glow red & even melt but the breaker sees the
heavy current & pops. Thats the short story but things after
the H out can load it down & cause the same thing. Often
when you get it going the H out is weak or bad, usually width is
in but you can judge the CRT at that point.
6KD6's are used in home brew HAM amps so they bring a
premium price. Maybe if you need one a kindly soul on the list can
help, it was a very common tube..........

73 Zeno:smoke:

There probably is considering the tube lineup posted by zeno, but I haven't been in there far enough to check it out. I've only had the back off and the immediately visible tubes out so far.

By the way, I have an extra 25V pulled from a real basketcase that hopefully will work without too much trouble should the original prove weak.

I do not think so...the final "dense hybrid' color sets--with under 10 tubes--often did not use any regulator tube at all. Our beloved 4 tube Zeniths are a good example. Nothing much more than a VDR or 2 to control the voltage applied to a feedback ckt from the flyback--tied in the grid ckt. of the H-out tube. I suspect this is quite similar. By 71--NO set used a shunt reg. I think--and not nearly all used a pulse reg (such as the 6KV6 or 6HS5). By that time--mfg's were finding it easier to eliminate them--just using a vdr or 2 as the reg.element.

STILL my favorite--is the old reliable 6BK4 shunt reg. tube--as used in my 1969 or so Sylvania D-12 set--I think it has 9 or 10 tubes or so. FULL SS audio and IF. One is a shunt reg, one is an HV rect. Later sets that used triplers eliminated both of those tubes--such as the D-16 set.

d 12?very,very good sets.those and the d 16 chassis sets were awesome.love to have a few of those now

After digging a little further, I'm pleased to report that this set uses a 6KV6A regulator and a 3DF3 rectifier. I doubt that the regulator's "A" suffix means much at all.

By the way, is it safe to power up with missing tubes? The 6BV11 is toast of course, and I'm hoping that I can check for those negative voltages with the hoz out removed.

I updated my tube complement list in post 16.

Well, I finally got to test the CRT. Low emission on all three guns, the red gun being especially bad. Also, it's had a lot more use than I first thought; I discovered a lot more black dust, so instant play is not totally to blame for the CRT's condition. I know just about all delta-gun CRTs are electrically the same, but which ones will sub directly for a 25VABP22?

I finally noticed a switch next to where the power cord goes in. No indication as to what it does, it's simply marked "on/off". It can only be accessed by removing the rear panel. I'm hoping it disables instant play.

I discovered a cracked resistor, R545 near the horizontal output tube.

My sam's sub manual lists:25VADP22, 25VAJP22, 25VALP22, 25VAMP22, 25VBMP22, 25VCGP22, 25VCKP22, 25VDAP22, 25VDEP22, 25VDXP22 as subs.

This manual likes to cross 3 letter tubes to 3 and 4 letter tubes, but to only cross 4 letters to 4 letters. If you have a spare 3 letter type I can try to cross it forward to a 4 letter type and see if that crosses back to a 25VABP22.

Thanks for the info. Unfortunately the only good spare I have is a 19" inline.

BTW are you aware of the phenomenon of CRTs being asleep? In a nutshell if a good tube is not used for a few years gas inside the tube gathers on the cathode and forms a coating which blocks emission. The coating can be boiled off if you run the tube heaters at 1.4X their rated voltage for about 10 minutes give or take. Any weak tube that I don't know the full history of gets the 'cooking' treatment before I write it off...And most bounce back well.

I have heard of it but didn't know anything about it. I did hit all guns with auto-restore more than once but it didn't bring satisfactory results.

Another thing that I had never seen before in a tube that was still under vacuum: the phosphor coating looked, for the lack of a better word, uneven around the middle of the screen. I cleaned it, no difference.

Let the tube sit on about 7.5 volts filamant for at least 10-15 minutes. See if that helps. if not--go to 8.5 volts for a minute or two. If that does NOT improve things...then you may indeed have a tube that is beyond saving. I would NOT go much beyond 9 volts...if it does not improve at that level--there is no use in risking an y higher.

It's toast, but at least this set is otherwise complete. I would have had to pull the CRT to have the cabinet refinished anyway. It's arguably the finest piece of furniture I have ever owned.

It's a very nice looking set that looks to have been well taken care of by the previous owner.

Hi Gary, thanks for your comments.

The finish was in worse shape than the pictures show, especially on top, and it's more filthy inside than I originally realized. However, it's one of my favorite sets and will eventually be restored back to its former glory. The plus side is that it's complete other than the CRT and the wood is solid. Actually, it's my only set with a real wood cabinet.