Current Color TV Project ...

[jshorva65]

I'm currently working on a recap of a Motorola 19CT1 for a customer. The set is in very good condition and has been upgraded to the 21" CRT with the factory-supplied kit as many of this model had been. The 21AXP22 shows excellent emission and balance. The R195 plug-in resistor is open, but I temporarily subbed 8-ohms 20 watts for the 7.5-ohms, unknown-wattage original. Sams only lists a Motorola part number and the resistance, no other specs. Using a 3A fast-acting fuse, a Variac, voltmeter and ammeter, I ramped the set up to about 100V at which I heard audio, high-voltage and vertical sweep come up as I watched the ammeter smoothly rise to about 2.5A. As I brought the Variac up closer to 120V, though, the ammeter reached 3A at about 110V and the fuse opened before I could raise it to 120V and look for a raster. I'd have used a 3A slo-blo, but I need to go pick one up. The 3A fast-acting was the closest I had on hand. Here's a photo with the covers opened/removed.

[jshorva65]

Here's another view of the 19CT1. So far, it looks like it should be a fairly routine recap.

[Kamakiri]

Hey John,

What do you charge for such a service, say, if I wanted you to do up my CTC5?

[Charlie]

John,

I have the factory Motorola book on this set... and many other Motorola color sets. I looked at the 7.5 ohm resistor you mentioned. Motorola did not list the wattage either, but it does say this on the parts list...

Special wire-wound 7.5 ohm. Caution: Use only special fusing resistor as replacement.

[jshorva65]

Tim: Recapping, debugging plus alignment and setup generally runs about $1,500 for a color chassis of that vintage and includes inconspicuous updates to the overload protection (fusing of AC line. all master B+ sources, and horiz. sweep cathode circuit) which were usually only partially addressed at the factory and fresh-stock CE or NOS exact-replacement "can" 'lytics pre-conditioned and tested (subject to availability), standard axial-lead 'lytics cost a little less but I prefer the factory-fresh CE units if I can get the proper ones. A color chassis involves 2-3 weeks' work to get everything just right. I'm currently scheduling bench appointments for July. As a general rule, I can finish work on two B/W sets in the time it takes to get one color chassis up to spec.

Charlie: I'll be fusing the master AC feed to the set at 3.15A slo-blo since Sams specifies normal line current as 3.0A The doubler stacks are 460mA units so each half of the doubler will be fused 500mA slo-blo as well. The +410V "stacked" B+ will be fused at 200mA since the rectifier is a 170mA unit. Additionally, I insert a 315mA fast-acting fuse in the horiz. output cathode circuit to protect the tube and transformer. I typically conceal mini fuses under the chassis.

As a rough estimate, that 7.5-ohm resistor looks like one of those white ceramic Xicon 10-watt units (AES "R-RXXX" series) with the outer square portion removed and only the resistance element and U-shaped potting material remaining. The ceramic exterior probably acts as a heat sink, so the lack of it would probably result in a derating of perhaps 30% from the full 10 watt spec, so roughly the equivalent of a 7 watt resistor. Rather than gamble with my estimate, though, I'd just as soon put a fuse in series with it to hedge my bet.

For fast-acting 250mA fuse applications (B/W TV B+ Boost), I use PicoFuse units which are about the size of 1/4W resistors and I usually use a blank pin on the damper tube socket as a tie point. For the slo-blo fuses, I use 5x20mm pigtail/axial Littelfuse 228-series. Most often, I rivet an AES P-0100H tie point strip beside the AC interlock for the main AC fuse. I'll be ordering some Littlfuse 227-series fast-acting pigtail types this week as they're available in ratings that are suitable for protecting anything from 6X4 rectifier applications in FM tuners (32, 63, 80 and 100mA) all the way up to about 10A for heater circuits. Unused tube socket pins are favorite places for tie points, unless the manufacturer already used all the available ones with the same reasoning and/or unless all available ones are identified by tube specs as having some reason for being left unused. I've got more tube manuals than I ever thought I'd need, but each one has something that none of the others has. I've got the RCA RC15, 17, 23 & 30; GE's "Essential Characteristics"; and a Sylvania 5-ring binder plus a Sylvania CRT booklet. Most of my books and a significant portion of my test gear was bought from a retiring service tech and US Army Signal Corps veteran who closed up his shop in Kent, Ohio in the late 80s when I was a Graduate Student at KSU. IIRC he said he was a radioman during both WWII and the Korean War. Last time I visited his shop at the end of the Spring 88 semester, he had a nicely-restored CTC15 roundie prominently displayed across from the counter. I bought my first Tektronix scope (a Type 531) from "Mr. J." for $20 before upgrading to a 547 a few years later. He also had lots of Bud chassis boxes NOS still in the brown paper wrappers that he was able to sell me at 1960s-era prices and still make a profit. I'd have bought that CTC15 roundie from him if I could have gotten it home. It was the massive TV/Hi-Fi combo version and about 5' from end to end.

Incidentally, my 14-year-old son has recently expressed some interest in vintage gear. I gave him a study assignment of a 1947 radio repair book and he'll be recapping his first AM radio soon after that. He's a guitarist, too, so we're also planning to restore a vintage Fender guitar amp. We picked one up that's been partially recapped. It's in working condition as-is, so most of the work it needs is cosmetic. The Tolex, grille cloth, and knobs are still rough but someone obviously started to fix it up.

[Chad Hauris]

I have found that using a fuse too close to the actual current draw of the set will cause the fuse to heat up and eventually open after a period of a half hour or so. This has happened when I have retrofitted horizontal output circuits and the ac line of old equipment. Using a 250 ma fast acting fuse in the 6JE6 cathode circuit opened after about 1/2 hr even though current was set at minimum for the set. A 300 ma fuse seems to work fine.

RCA usually used a 7 amp line fuse on their consoles at about a 300-325 watt draw off the AC line, the portables had a 5 amp fuse with a wattage of about 225-250.

[jshorva65]

Chad: The 250mA rating is the one I use in a B/W sets' B+ Boost line. For horizontal output cathodes in color sets, the closest 5x20mm pigtail fuse I've found to 300mA so far is 315mA. I vaguely remember the 7A fuses from the RCA CTC22 and CTC36. No primary-circuit protection at all was included in any "roundie" RCA that I recall, only a PTR breaker in the secondary circuit to the doubler diodes. CTC27's and 31's IIRC had a "fuse link" in the primary circuit. I'd probably go with a 7A fast-acting 227-series pigtail to guard against a "hard" short like a bad rectifier, etc. and no larger than a 4A time-lag 228-series either pigtail or in a holder of some kind for "softer" overloads. In my experience, I've found that a time-lag fuse can be rated closer to the actual demand of the set without "false alarm" blowouts. Many guitar amps using a pair of 6L6 or EL34 and single 5U4 draw about 2A and have 2.5A slo-blo line fuses. That's only 25% over actual demand.

I knew a hobbyist/tech once who upped the fuse rating in a tube hi-fi amp because "It was blowing fuses every 1/2 hour but worked OK." Sure enough, about 2 days later, the real problem (a leaky 'lytic) overheated, blew its seal, then went to a dead short at which point the rectifiers and surge-limiting resistor smoked. I think that's called "finding the real problem the hard way" ... and cleaning up all that 'lytic goo couldn't have been much fun.

[Chad Hauris]

Oh no, I would not put a larger fuse than specified in a piece of equipment that is designed from the factory from a fuse...the only time I have increased the fuse rating is when I am retrofitting one into a set that doesn't have one and trying to find the best fuse rating. The time I have had the fuse blow after a 1/2 hr I was using a fast-blow fuse very close to the actual current draw when I was experimenting with the ideal fuse rating to add to a non-fused set.

Yes you are right, the round sets usually just used the circuit breaker in the power transformer secondary winding plus perhaps fusible wires for filament protection...no primary fuse.
The later RCA tube consoles like CTC-39 I remember as using the 7 amp fuse.

Also the later RCA tube portables like ctc-52 use a thermal fuse that is mounted near the HO tube to detect overheating, some of the earlier color portables run the HO cathode through a thermal circuit breaker that will open the ac line.

[jshorva65]

Yes, I vaguely remember the last of the tube sets (hybrids, actually). Of the hybrids, I seem to remember working on more Sylvania D12's, D14's, etc. back in the early 80s when most people had an all-transistor model as their main set and an older hybrid in another room. There were lots of CTC48, 58 and 68 chassis in living rooms around here at that time and an old D12, D14 or CTC38 in the "den" of the same house.

I started doing paid radio repairs for neighbors at age 8 and was being paid for fixing B/W tv sets by age 12 and learning to service color sets about the same time. That was how I paid for my audio gear, record collection, social life and gear to use in a series of nameless garage bands up through the college years. A 4-year EE Tech degree led to a series of temp jobs with contract engineering firms, more temp jobs in industrial machine repair, etc. with a few jobs at tv/vcr/audio shops in between the higher-paying industrial ones. I always had a preference for tube gear and did my first antique radio restoration at age 12. I still have that Atwater Kent model 40 in my living room. Still worked great last time I plugged it in about 2 weeks ago. The antenna I'm using is an old "loop" that was in with some surplus stuff and about half the size I'd like to have, so I can only pull in a few nearby stations.

Most of my "roundie" experience was with Zenith sets. My grandparents had two 24MC32's and a 25NC33. One of their neighbors had a 24MC32 and one of my neighbors had a 26KC20. All of those sets eventually ended up with me as their original owners switched over to remote-controlled cable-ready sets and I eventually sold them to people who liked the nostalgic look of the round picture at times when I was short on cash. I had a Sylvania D01 in the "den" of my previous house. Sold that set on eBay 2 years ago to help pay down the credit card balances that were run up by the remodeling I did before moving in here plus the company startup costs. Most of my credit card debt is hardware store and lumber yard purchases.

[jshorva65]

That 7.5-ohm resistor (R195) is actually a 10-watt "sandblock" resistor with its outer "block" removed leaving only the u-shaped core. This probably results in some derating of the resistor's spec from its 10-watts down to about 7. Scoring along the edges of where the potting material meets the block, clamping one side of the resistor body to the benchtop and then tapping the other side with a miniature hammer and chisel along the scoring will neatly split the "sandblock" and the "tapped" side will come off. Turn the resistoir around and repeat for the other side. I bought three 7.5-ohm 10-watt resistors. I cracked the core of the first one trying to split it, but the other two split nicely.

After soldering the resistor to its "plug" pins, I inserted it into the socket and connected the set to a Variac, a 4A slo-blo fuse and an AC ammeter and placed a #44 lamp in series with the 6CD6 plate connection as a plate current indicator. On this chassis, since the plate cap connector is uninsulated, I covered the cap connector with some heat shrink tubing. The line current rose smoothly as I raised the voltage and the speaker emitted the familiar inter-station noise indicating the presence of B+ and at least a semi-functional audio section. Shortly after that, I heard the familiar sound of vertical sweep. The brightness of the #44 lamp indicated that the 6CD6 plate current was above normal but not dangerously high. I did not see the raster in the mirror or hear the faint high-voltage "crackling" or the typical sound of horizontal sweep, but I also didn't see a red-plate condition in the 6CD6 and the #44 lamp did not burn out. The output tube, although not glowing red, did seem to be heating up faster than normal, so I shut down the test. What I found was that the HV cage was warmer than I expected near the 6CD6 after only about 2 minutes of "on" time and the 6CD6 itself, although not dangerously hot, was warmer than expected. The "warmer than usual" condition without obvious, dangerous overheating evidence (red plate) indicates the horizontal drive is probably insufficient but not totally absent. The most common causes of insufficient drive that I have observed are low B+ caused by the very common "open doubler 'lytic" condition and attenuation of the drive pulse due to poorly-performing paper capacitors in the sweep circuits. Open doubler 'lytics typically increase the ripple content of the lowered B+ and cause noticeably-increased audio hum. The symptoms I observed are consistent with paper capacitor trouble and I'd need to get under the chassis to troubleshoot further, so my next move will be to remove the chassis and begin recapping.