View Full Version : Sooo. a Hallicrafters 815 followed me home...

05-21-2017, 02:47 PM
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...

05-21-2017, 04:17 PM
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.

05-21-2017, 05:52 PM
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? :)

05-21-2017, 08:07 PM
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.

05-21-2017, 08:24 PM
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.

05-21-2017, 08:40 PM
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)

05-21-2017, 08:50 PM
I'm unable to make you a digital copy from my Rider's disk, copy protected for some reason.

05-21-2017, 09:01 PM
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.

05-22-2017, 08:23 AM
Here's the SAMS available for purchase:

05-22-2017, 05:45 PM
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.

05-25-2017, 08:26 PM
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!

05-25-2017, 11:53 PM
Doorknobs and Dags. Sounds like something outa Edgar Allen Poe. :D:tongue:

05-26-2017, 06:25 AM
...When suddenly there came a zapping, of corona gently snapping, snapping within my HV cage door...

05-27-2017, 04:31 PM
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.

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.

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.
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.

Another interesting thing... these piggy-backed fuses:
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...

05-28-2017, 12:42 PM
Maybe the previous person only had fuse values half as large as called for.:lmao:

05-28-2017, 04:04 PM
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!

06-02-2017, 12:41 PM
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.

06-03-2017, 08:35 PM
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.

06-04-2017, 12:29 AM
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.

06-04-2017, 07:45 AM
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.

06-04-2017, 04:19 PM
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.

06-04-2017, 06:26 PM I

06-04-2017, 06:34 PM
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....

06-04-2017, 08:56 PM
At the risk of sounding cliché...



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

06-05-2017, 08:08 PM
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.
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!

06-05-2017, 08:31 PM
Did you try another HV rectifier, to see if the blue glow goes away ? That's really bright.

06-05-2017, 08:50 PM
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.

Electronic M
06-05-2017, 09:28 PM
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.

06-06-2017, 06:54 AM
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.

06-06-2017, 06:58 PM
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.

06-09-2017, 06:06 PM
Quick update before dinner. Got my tubes today, popped in a new 1B3 and a real 6AX5.


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...

Electronic M
06-09-2017, 08:32 PM
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?

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

06-09-2017, 09:25 PM
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.

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:

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! :)

Bill Cahill
06-09-2017, 09:38 PM
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

Bill Cahill
06-09-2017, 10:39 PM
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

06-10-2017, 08:42 AM
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?

06-10-2017, 12:47 PM
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.

06-10-2017, 06:48 PM
Is that old doorknob still in the circuit? If it is, it may be intermittently shorting, causing all kinds of strange effects.

06-10-2017, 08:20 PM
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.

06-11-2017, 02:08 PM
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?

Bill Cahill
06-12-2017, 12:14 AM
Your problem may also be failing hv wiring. A good thing to do...
First, with tv turned off, look at high voltage donut coil. Does it have any pin prick holes in it? Try running the set with hv cage open, in a dark room.. Do you see any corona areas?

The earlier comment I made was just a note on the one I had. It's interesting that yours is an 815, and, mine was an 822.
Mine was very ugly. It used a 16gp4. It had a big rectangular metal mask.
Bill Cahill

06-12-2017, 07:02 AM
I think there's some more at play. I did suspect the filament wire on the 1B3 as that has to carry the HV too. Didn't see any obvious damage but I relocated further from the chassis to see if it would help. I'll retry the dark test tonight now that I have a better view of the area (I completely removed the HV cage)

I also found some interesting behaviour with the horizontal area while swapping around some tubes. That led me to dig deeper and find some more resistors that are way out of tolerance. I'll be replacing those first since it's low-hanging fruit.

Bill Cahill
06-13-2017, 03:09 AM

The old interest is coming back........
Bill Cahill

06-14-2017, 05:38 PM
Of course it stopped doing it when I tried to continue locating the source of the HV leak. Nothing obviously visible in the dark, but I did keep thinking I'd occasionally see faint blue-purple auras here and there before they'd go away. The orange glow from adjacent tubes reflecting off surfaces doesn't help. Will continue trying.

Side question, anyone have a picture of a stock flyback for any of the Hallicrafters 800 series? Best I have is the B&W drawing in the Sams, and it's not very detailed. Google is no help.

06-14-2017, 08:31 PM
Progress! Was still doing it after I replaced all the wonky resistors. Much scrutiny later, I still didn't see anything, but could still hear the HV hiss. It stabilizes and gets better as the set warms up but still has occasional bouts.

Figured I'd try to make the problem a little more visible.
Cobbled together a chicken-stick with a grounded lead and a multi-megohm several-watt resistor (so I don't draw a giant arc, just enough to make leakage visible), passed it all around the filament wire. Nothing, that's all good.

Started nearing the outer edge of the flyback donut (well away from the lead coming out). A-HA! started getting some glow going, some spots I even get ticklers. Looks like the HV insulation on the flyback has broken down some and isn't quite up to the task anymore. Added a few turns of electrical tape to see if it helped my theory. This time the image came up and stabilized MUCH faster than before. Still funny, but better, so there's something to that line of thought. It probably stabilizes after a bit once the air around the flyback has built up a charge.

I'll probably need to recoat this flyback. I know there are tubes of silicone specifically for this purpose as I've seen Bob A use it in his videos, but I'm looking for something cheaper and more single-serve... Is Corona Dope the suitable thing for this?

I'm thinking I'll have to carefully remove the old wax and give it some hefty coats - if it's breaking down then just smearing a coating over top of it isn't going to help much.


06-17-2017, 11:32 AM
This explains a lot... I made a string of resistors to measure the HV and by my calculations it's only outputting about 3.5KV. (Measured 80 VDC across the 1 meg resistor in a 50meg chain).

Flyback is almost definitely hosed then, despite not looking too bad. Makes sense given the higher resistance readings I got when I first tried to verify the windings.

Picture tube must be in pretty damn good shape if I can get a watchable picture at that low a potential.

Bill Cahill
06-18-2017, 12:56 AM
:no:Personally, I wouldn't have hosed it down. Here, there are more chances of water left in the windings.

06-18-2017, 06:43 AM
:no:Personally, I wouldn't have hosed it down. Here, there are more chances of water left in the windings.

Huh? I never did that...

06-18-2017, 11:50 AM
Huh? I never did that...
He's yankin' yer chain.:D "Hosed" = fubar, irrepairably shafted etc.

06-18-2017, 12:57 PM
Clearly that went over my head... Looking back I see I used that phrase.
Flyback is almost definitely hosed then

Very punny :D

Bill Cahill
06-19-2017, 10:48 AM
That's what made me think that. Sorry. Thanks..........
Bill Cahill

Electronic M
06-19-2017, 11:25 AM
:no:Personally, I wouldn't have hosed it down. Here, there are more chances of water left in the windings.

I've cleaned plenty of sets with the garden hose. It don't hurt anything, but I don't apply power for at least 3 days so it can evaporate.

06-25-2017, 02:09 PM
Good news, looks like my original fly is repairable. It rings out fine, so not shorted internally - just suffers from wax breakdown and arcing. I've got some corona dope now, I'll attempt to remove the old wax and give it a few good coats of dope.

Bill Cahill
06-25-2017, 07:59 PM
Be very careful. The windings are very delicate, and,Eacj Turn in it looks like ne wire, but, it's several wires are wrapped into little strains.

Bill Cahill
06-25-2017, 08:06 PM
Be very careful. Each winding of the insulated wire is several very tiny wires wrapped into It is done that way so they could weave them in, and, out so they could produce more high voltage.
Bill Cahill

Bill Cahill
06-25-2017, 08:10 PM
if it isn't already damaged the corona dope should be a big help...

Bill Cahill
06-25-2017, 08:16 PM
if it isn't already damaged the corona dope should be a big help... Sorry.. The latest page it gives me is page 4.

06-25-2017, 08:22 PM
Thanks for the warning. I did flake some wax off carefully to see how it went. I think it's probably safer to attempt to melt it off.

06-29-2017, 08:24 PM
The wax came off very easily (looked like very little wax for the size of the donut), and I found a possible culprit... there was a break in the HV winding about 1/2" from the anode lead. A bit discolored too; looks like that's where it might have been arcing.

There was also a fair amount of bubbling when the wax was melting. The other part of my problem may have been moisture ingress into the coil/wax. With the amount/time of heat given to get most wax off, it should be all dried out now.

Repaired the break, was a little tedious but not too bad. I never thought I'd be soldering something where the surface tension of the solder was going to be a problem ;)

I've also given it a first coat of corona dope, will give it another tomorrow, and we'll see how it looks.

Things are promising!

07-01-2017, 04:46 PM
Back to the cleaning a chassis with water. Back in the mid 1960s, our organization bought a new Tektronix 'scope (one of those models with 42 vacuum tubes). Part of the purchase price included a class by Tektronix. The instructor started the class talking about cleaning the innards periodically with water. I don't think we ever cleaned it that way. Of course, I don't think the 'scope had a flyback made out of unobtainium.

07-02-2017, 06:13 PM
Certainly you can wash out electronics with distilled water without harm... and it works better at air than removing dust and other debris. If you don't let it dry, or if you use water with minerals, that's when you get issues. Would I hose out my scope? No. Would I rinse a particularly nasty PCB given the right facilities and a supply of DI water/IPA? Sure.

Some interesting developments. I've re-coated the flyback with a total of three coats of dope and bake-cured it. Reinstalled it with new wires.

Powered up the set to verify all was well; after a few minutes, the image goes all jittery, dims, I hear a *plink* and I lose HV entirely. No 15KHz whine from the HV area either. Strange.

Pull the output tube, re-verified my wiring, and start measuring. Both 200V and 300V B+ are fine. Horizontal drive waveform on the HOT is fine, so no issues with the oscillator.


Plug the tube back in, start set again. Hear the HV come up, get a picture. After about 30 seconds, picture jitters, blooms and fades, and the HV shuts down again with another *plink* noise.

One thing I take away from this is my HV woes may not have been flyback related, but rather wonkiness on the part of the horizontal drive... but I sure feel a lot better knowing the fly is likely good to go for much longer now that it's rid of the wax and coated with a better material.

Now I'll need to study the output stage in detail and figure out what's going funny. Likely going to be tricky as my scope and probes are only rated for 600V input so I can't go probing willy-nilly.

Anyone have any knee-jerk reactions as to the cause? You might save me a few hours. :)

07-03-2017, 09:16 PM
Progress. Having found no funny components in the area, I realized I don't need direct contact to observe the HV waveforms. Hooked a small loop of wire around the HOT plate lead and to my probe... ta-da, there is the flyback pulse for easy viewing, and at a safe input level for the scope.

It occurred to me the symptoms above are very similar to the issue I had with a dud HOT I bought; it would work on startup but fail shortly after. Did some tube swapping and now have some slightly burnt fingers (Laboratory lesson #1: Hot glassware and cold glassware look identical until you pick them up. Then the hot glass is broken on the floor) and observations to show for it.

Here's what I saw:
1. Known "dud (?)" 6AV5: Oscillator comes up, along with HV pulse. There's some chitter on startup that I get in all tube combos. Seems to be caused by the HOT waveform getting out of sync with the Horizontal drive...?
Once the picture comes up, the height of the HOT pulse wavers a bit, and then it all dies (H. Oscillator shuts down too). Killed power.

2. Original 6AV5: HV, oscillator come up. Also chitters a few times as they sync up. HV pulse wavers quite a bit in sync with all the picture funny business I've been trying to troubleshoot. Sure enough, *plink* and the HV pulse disappears. H. Osc. stays running this time.

3. New 6AV5: Comes up as expected, pulses stablilize. Doesn't go out, but still funny business with the picture flickering and pulse jumping around. Shut it off and I notice the spot stays on the screen a LOT longer now. Maybe picture is a bit brighter and more in focus too, so I almost certainly had a weak HOT.

4. Swapped the damper. Lo and behold, my wavery HV issues seem to be gone. Nary a flicker after a minute or two whereas before it would have been acting funny already. The arc from discharging the HV (5meg resistor so it's a bleed-off, not a bang) also seems much stronger now.

Looks like we can chalk it up to a flaky damper diode as well. I'll swap my original 6AV5 back in to see if it's still funny, perhaps it was the damper all along.

Weird I didn't see this previously when I swapped some tubes, but at the same time, not surprising if it was convoluted with some flyback issues and a dirty rectifier socket.

I'm questioning if that 6AV5 I thought was a dud really is... the HV pulses on it were quite strong compared to the other two tubes. Calling it a night for now, but will do some more swapping tomorrow to find out once and for all.

One final observation is I'm now hearing a soft ticking coming from somewhere. Best I can pinpoint by ear is either the HV anode lead or yoke, the former being far more likely. I'll give it a good cleaning tomorrow, could just be some crud causing the odd arc

07-04-2017, 03:39 PM
Observed something interesting. The chittering I hear on startup is the horizontal oscillator flipping out for a few moments. This is with the horizontal output tube removed, so the fly is not involved. (Still does it with the HOT installed, you just hear it more)
Anyone seen this before? Doesn't seem to matter if it's a hot start or a cold start, it always does this.

I scoped the waveform. The second trace is just on the B+ for reference so I can see when it comes up.

07-04-2017, 09:01 PM
By pausing the video I see what seems like a series of three near normal cycles and then a short one. Also it seems like the signal is riding on a slower sawtooth, maybe there is a circuit with that longer time constant. It would be interesting to see what the sync pulses are doing during this time.

07-04-2017, 10:09 PM
Interesting thought. I'm in the process of following the pulses back up the chain, so I'll keep an eye out. Maybe there's a leaky mica cap somewhere. I was looking at the sync pulses earlier, but they were a little non-sensical; I suspect I need to trigger off the vertical instead of the horizontal for them to make sense otherwise I see what I think are artifacts of the blanking period in between. Might be tricky with just a 2 channel scope but if I can get the EXT trigger to work it should be doable.

Should comment that this video was with the oscillator free-running (no video input) but if there is an input it still behaves the same. I'd be less surprised if it did this only with input as it could be explained by the sync circuits pulling the oscillator into phase.

07-05-2017, 02:09 PM
Oh, OK, no video input. I thought that maybe the sync pulses were screwy during start up and effecting the oscillator.

07-08-2017, 03:36 PM
No appreciable progress on the funny behaviour, I think it is simply how the 6SN7 warms up. It's definitely not caused by the sync pulses and is siightly different if I swap around the 6sn7s in the set.

I also disassembled the yoke to investigate the ticking I was hearing... quite possible it was arcing to the dag as the varnish on the windings is cracked and crumbly. Gave it a coat of corona dope and letting it dry now.

Also changed the 560 ohm resistors in the vertical section, they were way off at over 700 ohms each.

There's a 1.2k in the horizontal section that someone seems to have swapped for what's supposed to be a 1K. Dunno if that affects the width much, so I'm debating whether to change it back or not.

Bill Cahill
07-09-2017, 01:22 PM
Especially in those circuits You want to stay as close to specs as possible. If your oscillator is way off it will overload the circuit from the wrong pulse, and, picture can shrink.

Is there a large tapped resistor in, or, near the high voltage? If so If that resistor opens, it will raise havoc. That resistor is a bypass for the damper tube.

07-09-2017, 04:34 PM
No, don't see any resistors like that. Replaced the 1.2k in the yoke with the correct 1k, as well as another 15k that someone had swapped in a 12k for.

Still no luck though; width coil is doing nothing and the picture is still too wide.

Something's still funny with the horizontal as well; it's got a tendency to wig out and drift as things warm up... even with a new damper and output tube. Strange...

AHA! progress! I was trying to get horizontal in sync and accidentally whapped the chassis with my screwdriver. Whaddya know, it makes the horizontal drive go funny, and come back again if I hit it again. Guess there was something to the old stereotype of whacking the side of the TV to get it to sync! *grin*

At least now I know I am on the hunt for a funny/bad connection.

Bill Cahill
07-09-2017, 07:36 PM
I thought you said picture was t00 short??
00000000000000000000000000 Are you getting blooming when you turn up the brightness?
Is picture also out of focus.??

07-09-2017, 09:35 PM
No, focus is fine, height is fine. Maybe a little bit of bloom but it is typical for what I recall.

Main issue is funny business in the horizontal section; it's going out of whack and drifting a lot. Possibly related symptom is that the width control does not do anything. Picture is too wide.

I did also see there's a strange vertical behaviour on startup; huge divots in the top right and bottom left of the raster that gradaully stretch out to normal as the system heats up.

Flyback and power tubes also seem to get pretty warm, don't think that's normal but probably also related to my horizontal issues. HOT isn't red-plating or anything. I'm out of ideas, I'll get a video tomorrow and upload it, perhaps actually seeing the symptoms means someone can point me where to start looking.

I did check the system (300V B+ supplying sweep circuits) B+ current, it's is running around 125mA or so, not excessive. Probably reasonable given the max plate current of the 6AV5 is 110mA and there's a few other things on that B+ line.

Electronic M
07-10-2017, 09:18 AM
Were those different value resistors obviously changed after the set was made or are you assuming they were changed after the sets was made based on them not matching the schematic?.....If the latter you may be making a mistake.

I've beat this drum before, and I probably will again: Electronics of that era usually under went several production changes between new chassis designs, Schematics of the day often only show one revision and do not tell you if what is in your set was a change for the good or an old flawed design....Add to that schematic sources are known to contain typos (Sam's is especially infamous). Use the schematic as a crude guide/overview and take it with a grain of salt, but never as the Bible for your set.
Unless the solder joints, brand/vintage of part, installation methods clearly show it was replaced after leaving the factory it is usually best to assume a production change and leave it as is. At this point questioning production changes is a valid part of troubleshooting, but note the effects of changes, and note how it was so that if you need to go back to factory configuration, you can.

If the sides of the raster curve in and that curve rolls vertically at a rate of ~11 seconds with respect to vertically synced signal on screen then you have 60Hz hum leaking into your deflection stages....Which could be caused by B+ filtering/supply issues, grounding problems, Heater to Anything shorts in tubes, among other things.

If you have a variac and the set will maintain a raster when turned down to achieve slight H under scan then you can use that to check the sides of the raster for pull in after warmup.
If you have a large amount of hum leakage in the deflection stages (power supply hum will be worse) it can cause odd symptoms like disturbing oscillators during warmup like you describe.

07-10-2017, 05:23 PM
Sorry, I wasn't clear on those divots, they are irregularities in the vertical deflection, not the horizontal. If I can catch it on video or camera I'll post a picture tonight. Does not look like 60hz hum, the horizontal drive waveform is clean once B+ is up but before the tube warms up as far as I can tell.

Re: parts changes - I'm going off reasonable suspicion it's not right. The 560s I swapped were not "wrong parts" those were marked correctly but just way off value, as is common for old carbon-comp ones in a hot environment.

The 1.2K I swapped out in the yoke was also definitely not factory, had the same crusty electrical tape bodge-job as the work done elsewhere in the set.

The 15K was of a different type of resistor than the majority in the set. Most of the carbon comps were smooth glossy brown bodies, this one (and a few other ones that had drifted) had a very different body texture to them; pretty beat-up and pitted surfaces too like they had been floating in somebody's junk drawer for a while).

I hear you on not taking the schematic as bible, but for this set it is certainly something I need to give a little more credit than normal when working in areas that are not behaving properly. The last "tech" that worked on it couldn't be bothered to replace the bad 6AX5 rectifier and instead bodged the separate B+ systems together, probably making a bunch of these changes to correct for the voltage differences (including the doubled-up fuse hackery for the higher current draw)

07-10-2017, 06:14 PM
Here's the vertical "divot" issue. You can see it top right and just a hair on the bottom left. Yes, the yoke is slightly tilted but I have not been able to get a stable pattern up to fix it yet.

Also here's the video of the sync issue. Sorry for the potatovision, apparently stabilization does not like unstable CRT traces.

The tapping you hear is me hitting the side of the chassis with a screwdriver handle. Sounds like I'm hitting it pretty hard, but it's probably about the same amount of force I'd use to crack an egg, for lack of a better comparison.

The odd thing here is if I flip the chassis on its side, it's better. It just won't work properly if I have it sitting right-side up.

07-10-2017, 07:35 PM
If I am looking at the right thing, those divots look more like some sort of beam shadow in those corners. I wonder if the ion trap or the like is aligned wrong.

07-10-2017, 07:47 PM
That's what I initially thought too, but if you look closely the raster scan lines actually follow that curve instead of fading out like they would for bad centering or misaligned ion trap. Slightly visible here at full resolution, but not great, the trace lines always seem to come out overexposed on my camera.

07-10-2017, 08:20 PM
Did you follow the horizontal frequency and drive adjustment procedure from your schematic? From your video it looks as though the horizontal lock-in and drive are not set correctly, even though your double peak sine wave looks good. It also seems is if there is a loose connection when you tap the screwdriver. A faulty tube could also be the culprit.

07-10-2017, 08:36 PM
Yes, I'm trying to follow those steps but it is not locking at all. I was able to do it fine with the set on its side, so I do know how it's supposed to go.

All signs point to a loose connection but I have not been able to locate it; everything I ohm out seems OK.

Perhaps it is not a completely loose connection but a high-impedance one instead; that would explain why I can't find anything checking resistance but it acts up without fail at 15 kHz... that's gonna be tricky to find.

Am I right in thinking that it's the horizontal waveform coil that creates that double-hump shape? If so, perhaps that's the place to start looking, you can see it goes away leaving only the horizontal drive sawtooth sometimes when tapping.... perhaps that coil is going open circuit.

07-10-2017, 08:46 PM
A loose or bad mica cap at the horizontal coil could cause the saw tooth wave form. Did you oil/ lube the drive pot? Checking with a meter doesn't always verify a good pot.

07-10-2017, 08:54 PM
Yes, I got all the controls early on with deoxit and verified they turn and change resistance smoothly. Good point on the mica caps. I know they usually don't go bad but it is possible.

Thanks for the suggestions, will dig some more tomorrow and report back.

Electronic M
07-11-2017, 09:00 AM
A loose or bad mica cap at the horizontal coil could cause the saw tooth wave form. Did you oil/ lube the drive pot? Checking with a meter doesn't always verify a good pot.

Another pot related issue it could be is tin whiskers. Cleaners and lube often won't clear tin whiskers.

07-11-2017, 10:01 AM
That divot thing is weird, I think it has something to do with the crt geometry, they probably will go away when you get other things straightened out.
I kind of suspect the horizontal coil also. Maybe you can localize the problem by using a small wooden dowel and tapping various components. Could be tube socket, capacitor, pot, etc. Is it still shock sensitive when you swap tubes?

07-11-2017, 11:13 AM
That divot thing is weird, I think it has something to do with the crt geometry, they probably will go away when you get other things straightened out.
I kind of suspect the horizontal coil also. Maybe you can localize the problem by using a small wooden dowel and tapping various components. Could be tube socket, capacitor, pot, etc. Is it still shock sensitive when you swap tubes?

I think the divot is a "charge bubble", which was sometimes seen on un-aluminized CRTs during warmup or other times when the HV is not stable.

Agree.... tap everything in the horiz circuit.


07-11-2017, 05:58 PM
Success! Swapped the horizontal oscillator for the one in the vertical sync circuit, and my horizontal problems went away. (Well, the width coil still doesn't do much, but the major ones are gone)... and now my vertical is sensitive to vibrations. This is one of the original three, I'm guessing it must have been the one not being used as an oscillator. Certainly a red herring chase... it was so damned sensitive it would change frequency/drift if I blew on it... or tapped literally anything. Yeesh.

Apparently that one 6SN7 is just very microphonic. Why are replacements so damned expensive? (*glares at audio crowd*)

Still no idea what's making it the horizontal chitter on startup though (like the first video I posted). I guess if it's not likely to hurt anything it's not a big deal, just curious.

07-11-2017, 07:19 PM
Great news! That tube must be more than microphonic if turning the chassis on its side effected it. Must be something really loose inside!
"Charge bubble" is a new one on me. I guess I learned something new today.

07-26-2017, 08:26 PM
After acquiring some more 6SN7s and eliminating the vibration-sensitive one, the funny business is back. I swapped out the horizontal oscillator for the four ones I have now, and I'm still seeing funny business like weak HV, blooming, etc... and I doubt that all of my 6SN7s are that bad. I'm left scratching my head because the symptoms aren't consistent with changes I make - e.g. swap the damper, picture is suddenly dim and blooms. Swap it back, it doesn't go back to the way it was before.

Having had suspect HOTs and dampers already, I need to pick some expert brains... What kind of symptoms can one expect for weak:
-> H. Oscillator
-> Damper
-> H. Output
Specifically, are there differences that can help me ID the culprit(s) without a tester, or are those symptoms all over the place?