Sooo. a Hallicrafters 815 followed me home...
 

Argh... the sickness... it's getting worse :P
(Since I've last been around here I sadly had to sell my Fleetwood console TV; it was simply too large and bulky to take with me :tears: ... I guess this is an attempt to fill the hole in my heart? :D)

This followed me home for a song and a taxi ride (because there was no way I was gonna carry that to and from relevant public transit) No power cord, which means nobody's plugged it in to try it out. Cabinet is pretty beat up, but inside looks to be in pretty good shape and had an easy life. All the tubes are there, no melted flyback or scorch marks on the underside of the chassis, and no critters have made it a home. Minor chassis corrosion, and I don't see any signs of large-scale butchery on the circuitry.

Step 1... Get some service info. Any leads? Looks to be a Hallicrafters 815-A5. Quick google points to a SAMs and not much else, but I will admit it was cursory and not in depth yet.

Initial pictures - note the revision stamps on the tube chart where they've opted to make the whole set a 6v one...

http://vintagepc.forceanature.com/site/hctv/hc.jpeg
http://vintagepc.forceanature.com/si...m_IMG_0009.JPG
http://vintagepc.forceanature.com/si...m_IMG_0010.JPG
http://vintagepc.forceanature.com/si...m_IMG_0011.JPG

looks like the set I had, i sold it a couple years ago to someone from Chicago. i got it for free about 1989 at an estate sale.

Looks like the service info is either Riders 7-1 or Sams 124-6. Anyone have a scan or will I have to cough up some cash? :)

I looked up your set in Sam's 124-6. The Sams schematic shows a 16GP4 round crt. What's in your set? There seem to be a few production changes too.

Did some more checking, the Riders' 7-1 schematic shows a 16RP4 crt for the 815. Looks like Sams tried to cover eight chassis in one schematic. Some had an AM radio in a console version.

Thanks for checking, mine's got a 16RP4

Probably a common chassis, there's provision for a phono input in this even though it's a tabletop doghouse (including populated and labeled front switch, not just a "hidden" thing that got left in)

I'm unable to make you a digital copy from my Rider's disk, copy protected for some reason.

Darn, appreciate you trying. Seems my local library has in-house Sams and Riders (hopefully the right volumes). If no luck here I can go take a look and spend some time on a photocopier if they have the right ones.

Is the Sams also a no-go? Even if not identical I'm curious whether it has additional info not in the Riders.

Here's the SAMS available for purchase:

https://www.samswebsite.com/en/photo...index/id/66461

Given the above info that it might not be for the right set/revision, I'm sure as heck not dropping $15 on a SAMS.

Library did not pan out, only had SAMS up till volume 91, Riders was supposedly there but not on the shelf. They're gonna go hunting for it.

Looks like the flyback's been replaced. Cap lead to the HV rectifier was disconnected and some anti-arcing bodgery inside the HV cage. Probably arcing because there's a bad pointy solder joint on the clamp.

Lead is too short to reconnect, so perhaps the doorknob cap has also been replaced. Interesting, since the CRT also has a coating. Didn't think doorknobs + dags were common together but it could be because there are several revisions of this chassis, and the earlier ones were roundies.

Still getting my thoughts organized, replacing the caps I have on hand and figuring out what I need to order. I've obtained a SAMS and the Beitman's schematic, and hopefully will have the Riders soon too. More pictures coming this weekend!

Doorknobs and Dags. Sounds like something outa Edgar Allen Poe. :D:tongue:

...When suddenly there came a zapping, of corona gently snapping, snapping within my HV cage door...

A'right, some progress. Spent the day familiarizing myself with the set and figuring out what capacitors I'll need to order.

Started by taking a look at the focus control... it made nasty crunching noises when turned, and on opening, my suspicions were confirmed - it's burned up, as is common with some designs.

http://vintagepc.forceanature.com/si...m_IMG_0015.JPG

How likely am I to find an exact replacement? This is a dual-control with brightness. Rear control is 50K 1/2 watt, focus part (front) is 2500 ohms, 2 watt. Clarostat 25B889. Can always mount focus somewhere else on the rear of the chassis, but would be nice to retain it by the front knob where labelled.


There are also two sand resistors... as is the case with most, the leads are corroded and this one (while it still measured OK) fell apart when I looked at it funny. I didn't have the required value for the other one on hand, I'll have to order it.
http://vintagepc.forceanature.com/si...m_IMG_0017.JPG


Whoever replaced the flyback did some bodgery, and there was a half-baked attempt at squelching some arcs with electrical tape on the inside of the HV cage... Likely because the rectifier cap lead had a terrible solder joint with pointy stray wires everywhere. After unsoldering, there was enough folded/bunched up wire to make it long enough to reach again.... Nice clean and smooth joint now, and also added some heatshrink for good measure since the insulation on the lead was too short.
http://vintagepc.forceanature.com/si...m_IMG_0019.JPG
No, I didn't solder while it was connected to the rectifier... You can see the allen key I clamped to the chassis to hold the HV lead ring while soldering.

More flyback bodgery. Looks like somebody miscalculated wire length; those aren't original wires, so I'll clean that up at some point.
http://vintagepc.forceanature.com/si...m_IMG_0020.JPG

Another interesting thing... these piggy-backed fuses:
http://vintagepc.forceanature.com/si...m_IMG_0021.JPG
I could see this if a homeowner was too lazy to unsolder a fuse and just put a new good one in parallel... but both of these fuses measure good. Any idea why this might have been done?

Another interesting thing is that the doorknob cap under the rectifier isn't really connected to anything... it's bolted to the corona guard ring/mount for the HV rectifier, but that is isolated and just floats. Huh?

I'll also have to take a look at the flyback mounting... the transformer is kinda squished in in an odd position and the replacer bent the cage when replacing it to make it fit. Looks like it might be possible to neaten up if I reorganize the inside of the HV cage a little bit...
http://vintagepc.forceanature.com/si...m_IMG_0022.JPG
http://vintagepc.forceanature.com/si...m_IMG_0024.JPG

Maybe the previous person only had fuse values half as large as called for.:lmao:

That's something I considered, but they're both the correct 1/4 amp value. I guess it's a free spare for me then... that said this is a replacement flyback, so perhaps it was part of the service kit to put it in as it draws more current.

Spent the day checking various things. The important bits like transformers seem OK, though the flyback does have a high resistance on the primary... schematic says ~180 ohms, but it's reading about 460.

Most of the controls were pretty crusty. Apart from the already found busted focus, they came good with disassembly and some deoxit.

Also spent some time panel-beating the front brass decoration. It was pretty beat up and bent. Managed to get it quite decent again... only downside is the little metal spring that is supposed to hold it closed was bent and broke when I tried to bend it back. We'll see whether there's enough tension in the hinge to keep it closed or if I'll have to figure out something else.

Also got my cap list together, will be ordering that shortly. Looking forward to first power-up once that's done!

I've been helping a noob work on a Hallicrafters 602 floor model, not unlike yours. After a complete recapping, we have a very dim but full raster. The 12RP4 is pretty weak though.

I think yours may be a bit newer but the 602 uses 12AU7 tubes in many places including as the video amp. cranking up the contrast control causes this video amp to red-plate, because it alters the cathode bias resistance which seems archaic considering most video amp circuits only vary the resistance in series with capacitance in the cathode circuit, leaving bias unchanged. Very strange circuit, may have to change it for it to work right.

Once you replace the paper and electrolytic caps throughout your set, you'll have some real clues to what it still needs.

I've finished nearly all of the recapping, only a 4 section can left. I stopped because I can't make sense of what I'm seeing vs the schematic:

What is *supposed* to be happening is a 190v line from the LV rectifier feeds one of the sections (40 mfd), which then bridges thru a 10W resistor, to another 40mfd section, for a ~120v DC line.

The bits after the 750/10W resistor all make sense. What doesn't is that the first 40mfd section (the 190v line) is bridged to the 40mfd section that resides in the audio circuit just off the output transformer. That's already a WTF, since that section sees 260v and the bridged section is only rated for 250. (the section for that area is a 450v one)

... I wonder if that's what made the focus control burn up in the first place?

... and should it be corrected? I've found only a few minor differences between my schematic and the set otherwise (39k vs 47k resistors in some spots, and swapped component order in one spot) otherwise.

Pin 8 of the secondary B+ (150V) supply rectifier only connects to the junction of C135c and R164. R164 the 750 ohm 10w resistor is connected between C135c and C135d, which forms a standard PI filter. C135c and C135d are the 40-40mfd 250 volt sections. They share the the same ground with C135a a 20mfd 25vdc and C135b the 40mfd 450vdc sections. The focus control may have cooked if C135b had shorted. The primary B+ (260V) is filtered at the audio output transformer. The 260v supply voltage comes from the primary rectifier a 5U4.

Yes, that's what I gathered it should have been. Looks like the person that replaced the focus control shunt resistor made a pretty severe mistake, as its lead is the one that appears to bridge the two sections.

Well well... I think we found the reason that bridge existed. Just went for first powerup with only the 6AX5 installed... no HV. 390VAC into the tube, filament is lit, no output.

This also explains the double-ganged fuse on the primary B+... naturally it's going to draw more current if it's got more stuff on it.

Don't have any spares on hand... I was planning on getting some spare tubes for this set next time there's a local swap meet. Guess it's on the shelf 'till then.

Why would I spend the better part of $10 on a single tube + shipping when I can wait a few weeks and probably get most of my tubes for $1 or $2 each?

That said, I am being a little silly... I have a parts box full of things and I just realized i can almost certainly find some 1N4007s and a resistor to make a temporary replacement....

At the risk of sounding cliché...

WELL THERE'S YOUR PROBLEM:

http://www.videokarma.org/attachment...4&d=1496627688

:yikes::yikes:

Pretty sure 6AX5s do NOT have inbuilt cathode fuses! Yowza! (Yes, it's melted, not just snapped)

First signs are promising... I pulled the horizontal oscillator and tried a power-up with the 5U4 and my improvised diode rectifier. (Ended up adding a switch to it as well as a resistor since the DC voltage is too high for the caps until the tubes warm up, but too low if I have the correct resistor value to keep it in range... so I just give them a bit to heat up and then switch the AC to the diodes.

First time I heard a rather ugly crackling noise and killed the power... fortunately it was just the speaker and nothing emitting magic smoke.

Anyway... I was rewarded with audio from the speaker!

Everything seemed fine with both B+ voltages up, so I plugged in the oscillator and powered it up again. Heard the HV come up, and was treated to a pretty light show in the rectifier.

http://www.videokarma.org/attachment...1&d=1496710981
I'm going to go ahead and guess my rectifier is just a teeny bit gassy... but I'd say that probably means my flyback is good and producing plenty of HV. Awesome!

Did you try another HV rectifier, to see if the blue glow goes away ? That's really bright.

Don't have one at the moment, I'm tube-poor. I'll be picking up a full compliment of spares in a week or two.

Future TV variac advice: DO NOT pull the H oscillator tube(!), pull the H output tube instead (if series string pull the top cap or better yet clip only the heater leads in with clip leads).

If the output gets no signal from the osc, then the output will red-plate when that happens for more than ~10 seconds you will ruin the (often pricey) output tube, or weaken it greatly, and if you run it longer you put other sometimes unobtainium parts like the flyback at risk of destruction.

My bad, though the output tube is right up top and I always watch for those kinds of things when doing a powerup if the set is not known working.

I could have sworn I saw a comment somewhere in the service literature about pulling the H. oscillator for one reason or another (which is why I did it) but can't for the life of me find it again by skimming the pages.

Did not see any signs of it red-plating, and it was indeed only for a few seconds.

Found an ebay seller with a large variety of NOS tubes and a free shipping promo for over 20 items. I stocked up and got everything I need for about a dollar each except a spare 5u4 and some 6sn7s.

Looked closer at my 1B3, getter is completely gone, so it's totally gone to air. No obvious cracks.

Electronic M - In retrospect, I'm intrigued by your comment... One would think sets would be designed so that typical failure of any arbitrary tube would result in minimal or no damage. What is it about the circuit design that makes the HO tube red-plate if there is no oscillator? Are there other parts of the circuit that are similarly affected if another single tube fails?

Granted, in a typical case I would assume tubes wear out rather than failing abruptly and a weak oscillator would get replaced before it reached that state, but I can imagine it certainly wouldn't be uncommon for a tube to sometimes go poof from thermal stresses or filament burnout.

Quick update before dinner. Got my tubes today, popped in a new 1B3 and a real 6AX5.

WE HAVE RASTER!

Baby steps...

No video signal yet, but given some of the things I have had to do so far that's not surprising. Ion trap magnet probably needs adjusting, as do all the controls (I had to disassemble and work many of them to clean them, so they are likely all out of whack).

To be continued...

There were a couple of chassis I'm aware of (IIRC the CTC-2 was one) with fail safes, but most neglected them. In most output stage designs the output tube is biased by DC, but in the case of TV Horizontal outputs the grid is normally biased by grid-cathode rectification of the horizontal osc drive waveform....No waveform no bias...Or more accurately the grid in absence of the waveform pulling it negative instead drifts positive in lieu of it's bias source and ceases to limit the cathode current. The cathode current skyrockets well beyond it's design ratings, the emissive cathode material rapidly burns off, the plate and grids get more energy than they are designed to handle and sometimes melt, and the fly is subjected to DC current well in excess of it's ratings and begins to heat...Sometimes until burning open.

It ain't pretty seeing a Horizontal output destroy it's self...Well maybe it is, but it ceases to be once you know what your seeing. :D

Fascinating, it's the pre-silicon equivalent of SCR latch-up *grin*

Good news, we have video! Problem was "dumb user". Sometimes my cable box gets in a state where it will output sound but no video (while off). So when I powered the set and got audio, I foolishly assumed the box was on. Actually turning on the cable box got me a picture. It's watchably bright with the controls low, so it looks like the picture tube is in pretty good shape.

http://www.videokarma.org/attachment...1&d=1497060850

Spent some time poking and prodding. Had to adjust the horizontal drive waveform, probably because there was a cap right across the relevant coil that got swapped (all the ones that came out of the set were well out of spec).

A couple of issues observed that I will need to dig into. Some input here would be helpful, but if not I will start from square one since I have three different service guides with all the voltages and waveforms.

1. Looks like bad HV regulation, or low HV. Turning up the contrast or brightness controls makes the picture bloom and lose focus. It fades if you go further, and comes back if you turn it down. The focus control is also at the extreme end of its rotation.
I surmise this may have something to do with the non-connected doorknob cap?

2. Possibly related, picture takes an appreciable amount of time to come up, and does so very slowly. (A good 1-2 minutes. My previous tube set would have a picture not long after you heard the HV come up)

3. Observed that the width coil does not seem to have an effect when adjusted. I'll check if it's gone open.

4. I was setting up the horizontal oscillator per P 18 of the SAMs. There were times where I got to a point that something would go funny when adjusting the front horizontal hold. I'd hear a 'thup-thup-thup' noise both from the speaker and somewhere in the set, and the horizontal drive waveform flickers on the scope screen.
Something arcing somewhere? Didn't see anything immediately obvious.

Last thing... remember that rectifier's melted cathode connection? I just had a closer look at it. Check this out - there isn't much left of the cathode either:
http://www.videokarma.org/attachment...1&d=1497060850

Dayum, looks like this set basically had a complete meltdown in its past, must take some serious business to get that kind of sustained arcing in a rectifier. But it's all right now, it's been brought back from the dead! :)

I know, it's been awhile since this thread started, but, may I see the set as it's playing now? Seriously, those focus rectifiers look as if they need seriously being replaced..... Thanks. Interesting thread. Thanks.
Bill Cahill

Just remembered that I once had a halicrafters model 822.
The set was beyond with a dud tube, and, an arcing flyback.
I gave up.
Bill Cahill

Not sure I follow, Bill. The photo in my last post is of it currently playing after replacing the 6AX5 and the 1B3. Did you want a video, or a photo of some specific thing?

I think I'm on the trail of the HV problem... Looks like the 1B3 socket may be dirty or bad; I noticed that turning up the brightness slowly the picture just fades out; turning it up quickly I heard a snap from the rectifier area. Didn't see anything visible, but will disassemble the area and look closer/clean it.

Edit: Further update - Just finished cleaning the socket, also found the 3.3 ohm resistor was nearly 7 ohms. After replacing it and reassembly, things are looking better. No more fade-out when the controls are turned up, but the picture is still very jittery and I still hear corona hiss coming from somewhere in the HV area.

Is that old doorknob still in the circuit? If it is, it may be intermittently shorting, causing all kinds of strange effects.

No, it was actually out of circuit. It still measures the proper value, and had a decent charge on it when I went to discharge the CRT... got two separate snaps, one from the picture tube anode, and one from the corona ring attached to the 'knob.

I put it back in to see if it would help any. Picture is maybe a little stabler, but still jittery and shifts left and right a bit. There's also no more discharge from the HV lead to the corona ring on warm-up, since it's now at the same potential.
Also replaced the HV lead, the old one was pretty crusty and the rubber parts were cracked. I had a spare more modern one I scavenged from an old monitor some years ago. Glad I never threw it out.

The jitter seems to get worse/better as I adjust the contrast control. Control is good though, I verified that it changes smoothly on a meter as I operate it.

Width coil is not open, but I haven't tried it since fixing the first HV issue.

I've tried looking around the HV area in the dark and nothing obvious is visible, but I'm also not able to see some parts well with the set on its side. I'll try again tomorrow - I feel comfortable wiring in the NOS dual pot for focus and brightness now that I know the replacement focus control isn't going to instantly burn up. That will let me flip the set rightside up again and take a better look around. There's still some electrical tape handiwork around the flyback that I haven't replaced yet, also worth investigating.


Maybe relevant but I also hear three or four "thup" noises as the HV comes up. Identical to what I heard when I was messing with the hold adjustments. I wonder if it's just the vertical hold trying to lock in.

Doesn't bode well... I still hear the hiss and subtle "warble" that accompanies the flicker in the HV whine if I run the set without the HV rectifier top cap connected... so no HV to the tube or filament winding.

Does that mean what I think it means... that the flyback probably needs replacing because it's got an internal problem?