Power transformer replacement??
 

I have mentioned this before but I was a bit unsure. My RCA TCS-127 needs a power transformer. After much hope of this not being the problem I have come to the conclusion that it is. :tears: I borrowed a Megohmmeter and verified that my primary is shorted to ground. Along with at least one secondary winding. I stopped checking after that. I dont know how hard this is going to be to tackle. Not doing the work but getting the replacement part or having the existing part repaired.

Are there places that rebuild iron core transformers?

Are there places that sell N.O.S. or replacement transformers?

I have never had to replace any of my transformers so this is new to me. Any help or advice would be greatly appreciated. Here are the part #s on the trans: 970972-1-3
138012

The chassis # is KC534B

THANKS :thmbsp:

I would take the covers off the transformer and make sure the insulation on the hook-up leads isn't disintegrated inside...we have repaired some with bad insulation on the wiring by covering the old wire with heatshrink tubing all the way to the core.

If the transformer is really bad places like Radio Daze have general replacements
and on Steves site someone rewinds them and with a old sub book maybe a parts set has one like the 9T246 on Ebay for $20.00??
Item number: 150050438486

Hi. These sets have two line capacitors, and a resistor going to chassis that can fool you. I'd just remove those parts. On secondary, they sometimes had a negative bias supply ending to chassis with a resistor, and a positive secion of an electrolytic on the chassis. You may be actually measuring those two sources.

Bill Cahill

What I did was remove the rectifier. That its self deisconnects 3 leads. Then I removed the two leads going to the small strip with a B+ fuse (I thiink). I removed a lead that goes to one of the filters and I think one that supplies the heater string. I also disconnected the ground side if the line filters. This should have eliminated the short if it were in any of those circuits. I applied AC from the wall and still have a heavy current draw. The transformer hums like it is working its a** off what little time I can leave it on, which is a matter of seconds. The line chord will get hot and there has been a burning smell. I have nearly every indication that the trans is bad.

The megohmmeter does not help as much as I thought. I have compared the readings I get against other sets with known good transformers and they are similar. I was told that I should see no more than around 10M Ohms on the 250v scale and if I saw low readings that would indicate a short. I get nearly the same reading from say either side of the line input to ground. Also I get the same reading from one of the secondary leads going to 5u4 and to ground. The rest seem to be isolated. I will say that the motor tech that loaned me this hand crank megohmmeter is not a television repair man but he is trained decently and spends a lot of time finding shorted field coil windings in electric motors. We thought that a power transformer would not be much different.

Also I have to watch swapping from other sets because I have noticed that even though many RCA chassis use what looks like and many times are the same value components, it is not a given. This ct-127 has a different trans than my 8T-243. Probably the ebay 9T set will have the same one as my 8T. Hopefully something will pop up. On another thread someone said these trans. are pretty common. Hope so!!

My next step would be to remove the power transformer from the set (but keep track of what lead went where, especially the primary). Once the transformer is removed, I'd try applying line voltage to the primary briefly again to see if the short is still there. Check the insulation of the wire leads; if it looks brittle and crumbly, the short might be there. Carefully remove the end bell the wire leads come from (if you didn't already do that to remove it from the set) and check further, and slip heat shrink insulation on the problem leads. Of course, if the transformer smells like toast, it might be toast, but don't give up easy on it.

If the transformer in the set is drawing so much current that it makes the line cord get hot, I'd wonder about the circuit breakers or fuses in the house. Check that nobody stuck pennies behind the fuses....

I totally agree. I also don't see alot of similarity between motors, and transformers. The transformer sounds very shorted, alright, but, I'd agree you should remove it, and physically check the wiring first. If the transformer is making a bad odor, it probably is burned. I'd also suspect something in your house isn't right, as this should trip a breaker, or blow a fuse. The fuse in the tv is only a boost fuse for hv section. You eliminated one possibility by pulling 5U4's. I think this set uses two, but, I could be wrong.

I still say your filters are shot, and reming you there is usually a resistor from line to chassis as well as the grounding capacirots.

By the way, those two line caps were supposed to eliminate line interference, especially from medical devices, which are not even used any more. In most cases, removing them permanently will not affect the performance of the set, and actually, make ths set electrically safer.

Do now, however, attempt this on a ac dc set with out a transformer, as they are a different animal all together.

If the tube line up is the same as yours, chances are a replacement transformer would be fine. Make sure of every wire on both new, and old one. Colors don't always match.

By the way, it might be safer to put a light in series with the primary of the transformer. Under normal circumstances, you'd need a fairly high wattage, but, for this kind of shorts test, 60-100 watt should be plenty. If butl light full blast, no doubt about it, you have a major short. You obviously do, anyway, just, where is it?
It is a fairly common set, so shouldn't be hard to find the correct transformer for. But, consider this.
What is the physical condition of your set?
What type of cabinet does it have?
Are you really in love with the set?
Are you willing to put what ever it takes into bringing the set back to life?

By the way, there is still the resistor network going from B- to the chassis, and will still show a "short".

In all fairness, I love the old sets myself, but, don't destroy a better one for what you have.. It's a nice set, but, RCA used this chassis in many models. By the way, what is the exact chassis no? It would have a KCS in front of it.

KCS stands for Kinescope chassis set.
If anyone is wondering, The CT in RCA's color line stands for Color Television.

Bill Cahill

I'll try to sum up some things that are on other threads and this thread. When I first got the set naturally I used the 100watt bulb to reduce line voltage. Things seemed very hopeful as the bulb dimmed like it should and the tubes all glowed dimly. Perfect. I only did this for like 3 hours. I probably should have done it all night. This set seemed to be in real good shape so I didnt expect to have major trouble. I found that the LV rectifier was open so I replaced that. Then I applied 110V. That is where my troubles began. Instant major transformer hum and WARMING of the line chord, along with the bad smell. I would say that if I had left it plugged in for more than the 5 or so seconds that I did then the breaker would have took over.

At that point I hoped it was bad electrolytics so I went and bought new ones. I really felt good except for the fact that NONE of the existing caps gave ANY indication of anything that would cause a major draw. A cap that bad should be noticable with an analog ohm meter. Needless to say my second thoughts were right. Plugged her in and had exactly the same problem. That leads up to my using the Megohmmeter from work this weekend and pretty much determined that my primary winding is shorted to ground. The needle pegs when you crank the generator. I get the same effect from one of the secondary leads to ground. My wires are in great shape. Sounds pretty shorted. The transformer does not have RCA painted on it like my old 8T-243. Instead the #'s are stamped into the housing. Maybe the factory was trying to save a buck.

As far as the set being worth it. Yes! I have been wanting a roundie with a double d mask for ever. Not a lot around my area. Most people say the first TVs were in town around 1952. Many sets I read about have the 10BP4 like my 8T-243. This set has a larger tube. I forget the exact size. That makes it kind of unique to me. I love the doors as well. I would say the set shows average wear and tear but polishes up very pretty. Also, it has a rebuilt GE crt which is a positive aspect I think. It was installed in the 60's so it may not have much time on it. Such sets pretty much retired through the 70's. Thats how I gained interest as a kid. They were still siting in the corners of local repair shops and easily obtained cheap or free. Some 50's sets were in my high school electronics shop. That was cool. Even a Predicta that I would tinker with. Nobody cared about the older junk. We now had SOLID STATE!!

Hopefully this set will come together well. I want to reduce my collection to some degree and focus on a select few favorites. I really hate getting rid of anything. Y'all know how it is. I still have a late 50's Montgomert Ward's Airline for free if anyone can pick up....

Hmm. Sounds like it's worth saving. I wonder if this is a 16" set?
I have the power transformer from one of the early 16" sets. It has bad leads,but, I think transformer is still good. Can you get me the chassis no, and a good picture of the back of the set? Thanks. Bill Cahill

Thanks Bill, the chassis # is KCS34B. The c.r.t. is a 12LP4. I don't have a pic of the chassis as we speak but I may get one soon. You seem to be familiar with the old RCA's. Well I'm not as familliar but got some experience working with the "ugly" 8T-243 that I have mentioned and the chassis seem to LOOK identical. Really it LOOKs as if I could trade c.r.t.'s and swap chassis if I wanted to. I suspect there are some component value differences. I really don't want to change the subject to chassis swaps. Right now power supplies are the issue. My 8T had power supply problems as well but they were cured with caps. Not so with this TC-127.

How much difference is the desirablilty in relation to c.r.t. size, if any? It just seems like every other set mentioned has a 10BP4. I know that is a common tube. Again my 12LP4 is a G-E rebuilt with no brightener so I think I am good to go there. I know it would be smart to find out before getting all involved in restoration but unfortunately my tube tester all works fine, exept the c.r.t. test. It used to work fine and suddenly stopped. Sometimes I think it is crazy to use diagnostic equipment that may need as much diagnosis as the repair job......

I not sure just how much voltage the megohm-meter is putting on the wiring. Are you sure it isn't more than the insulation can take?

If you have a short that is causing the transformer to pull enough current to cause the line cord to heat up you should be able to measure that easily with a standard ohm-meter.

This may give you and idea of what you should see on the different windings resistance wise: http://www.radioremembered.org/xfmr.htm

Glad you're gonna save it. An early RCA with a newer CRT is a recipe for an excellent picture. :yes:

Please try what the others suggested and disconnect it. Test it on the bench. The forums over on antiqueradios.com are full of old threads where someone was convinced the transformer was shorted, and the problem disappeared when the transformer was totally disconnected. Shorted tube sockets, dial lamp sockets, and such. I'll admit what you said sounds really bad for the transformer, but humor us and try it. If it's bad, it's gotta come out anyway.

Even if it's bad you still might fix it by replacing the insulation under the end bells like Chad suggested.

I don't have a crank megger. I use a HV power supply and a VTVM. You don't happen to have these two items, do you? I suspect this is doing exactly the same thing as your megger anyway. If you have this stuff laying around, post back, I'll tell you how.

Ok, if it *is* toast, I don't know of anyone rewinding, but I've heard Heyboer will make you new transformers to original size and specs. This might be a good option if a universal one wont do for some reason, or you want an exact fit.

Good luck,

John

The good news is I have a KCS 34B. The bad news is I might need it's transformer. I picked up a T-120 that someone has messed up the power suppyly, replaced power transformer with possibly the wrong one, then, wired it wrong.I still have to check. However, I do have an extra one with bad wires,that I believe is not toast. It's a commontrhasformer in RCA's, and was used on a number of chassis'. Voltages, approx., follow:

Pri. 117volts ac. 50-60hz. Hv. Winding. 730volts AC Center tapped.
Sec.2 5volts AC 4 A.
Sec. 3 6.3 AC. I belive that one is 11A.
Sec. 4. 6.3 AC 2A insulated for 1200 volts. This fil. alone is used for the 6W4 fil. , which is not grounded, as it is connected to cathode to cut back on danger of arcing. Never ground this, or connect it with other filaments, as I guarantee it WILL cause major dammage.

If I am wrong about that winding, and your damper tube just happens to be a 5V4 The fil. specs follows: 5.0volts, 3A. Insulated for 1200 volts. On our inflated ac voltage of 120-124volts ac, The voltages will be somewhat higher.

I hope this helps.
Bill Cahill :banana:

Generally with early sets the smaller the screen size the more desirable the set. 12" isn't far from the standard 10" and is still very desirable. Really, any round tube sets are. When you start getting into rectangular tubes the interest starts to fade.

To Chimes, I'm not sure how much voltage the megohmmeter puts out either. The guy that loaned it to me said something about 4 times the operating voltage. He could have meant that the meter puts out 4x or that is what I needed. There were three ranges, 200v, 600v, and 1000v. I used the 200v. I seriously doubt that the momentary spike would damage anything. Nothing got hot. Also thanks for the link! Everyone should be able to use that info. I find the color coding confusing as my transformer does not seem to follow suit with what they show.

To Bill, no I don't have the items you mentioned. However I feel like simple resistance readings should tell the tale of a major short like I have. I should not have resistance readings from disconnected wires to ground in places I am getting them. A few minutes ago I took some readings. Here are some examples. These checks are to ground. Pin 4/5U4=1,300 ohms, pin 6=1294 ohms, the lead that goes to the switch has 91,000 ohms. I get 1.8 ohms across the ac line with the filters disconnected. Thanks Bill!!

To Bryan, I kind of knew round was better but I wasnt sure about size. I know any of us would like to have one of those huge DuMont Royal Sovereign sets with some ridiculously large crt, so I guess size is not necessarily a rule of thumb. Also I have a couple of the 50s rectangulars that I know are good finds. I always thought that interest started falling off around the early 60s with old TVs. The early Color sets then take over. There really are no guidelines as the hobby has expanded somewhat and there are some who find 70's stuff interesting. Some of this is relative to a persons age if you think about it. One day someone may find nostalgia in the plastic junk Walmart calls TV's. Go figure!!

Thanks for the help everyone. Still open to ideas and suggestions....

The way I would do this is to remove the transformer from the chassis, put a 60 watt lamp in series with the primary. Connect to 110 volt ac. No secondary leads connected to anything. Bulb glows bright=short. Remove end bells, check for bad insulation. Bulb glows diim=short somewhere in the chassis wiring.
There can be carbon tracks on a tube socket or some other elusive issue causing a short. It's a waste of time to keep trying to troubleshoot it without completly removing the loads from it.

I don't get into the whole how much is it worth thing but you will often have to spend more to repair something than you could sell it for. That only matters if you're going to sell it, though.

The criteria for collectable sets is pretty much confined to those with round tubes, especially for black & white sets. Post 1951 for black & white and maybe not until after 1960 or so for color is when sets go from truly collectable to merely interesting.

I doubt the meg-ohmeter will put out enough current for anything to get hot.

This would be the hv windings to center tap. I am assuming the center tap is grounded to chassis. Since both measure within a few ohms of each other they are probably OK.

That should not cause enough current draw to make the line cord heat up.

That seems a bit low. What filters are disconnected? I would do what chad suggest. Disconnect all secondary leads and see if the problem persists. If so, then there are probably shorted turns in the primary.

Bill H.

1.8 ohms isn't outside reason. I just measured the primary of my RCA TV set (it works quite well, other than a weak CRT that wants a brightner to work well) from 1957 and got 2 ohms (using a DVM on ohmmeter mode across the power plug pins with the set's power switch turned "on", which presents to me the transformer primary without having to take the back off the set). The impedance of the primary winding of the power transformer at 60Hz is what limits the current to a lot less than a pure 2 ohm resistor would draw.

ALL DC electrolytics, the two AC line filters, along with everything else are disconnected from circuit. I admit that as I stated before I simply pulled the 5u4, which automatically takes 3 or 4 transformer leads out of circuit. On one pin you have to remove the smaller wire that goes to the filters. I checked for pins shorted to ground. No problems. I also left a lead going to the on/off/volume potentiometer-switch. I checked the switch for short to ground. No problem. There is a lead going to one side of the AC line connection. That is not shorted.

Someone made the point that the transformer will likely end up coming out anyway so why not remove it from the chassis. Good point. I guess I took some "short" cuts while waiting to see if I can secure a direct replacement. Sometimes I take stuff apart and get sidetracked or disgusted and it sits in pieces way to long. Or the pieces may get lost. I shouldnt be able to lose a transformer though.

Again I have a good trans in my old 8t-243 but evidently that set is more "collectable" and it is kind of dumb to scrap a good set to fix another. Also although the chassis are identical there are different part #'s on the two transformers. I don't need to confuse the situation any more with thoughts of swapping.

Thanks to everyone for trying to protect me from hastily going and purchasing a transformer to find out that it was never the problem. Last I still think that there should simply be a resistance measurement that would tell the tale of a large short. Transformer checking has always confused me a bit because you usually don't have a set measurement that you are looking for on the particular transformer. Sometimes the winding resistance is listed on the schematic. The 8t schematic is all I have and it is not listed.

You may find another set that has a bad CRT or cabinet that could serve as a parts set...I haven't found the task of removing a power transfomer from a chassis to be too bad. It's pretty non-destructive so you wouldn't be destroying another chassis to remove the transformer.
I have not used resistance measurements very much as a troubleshooting tool except in cases of components completely removed from the circuit.

Resistance measurements are almost never any good to fault isolate a problem in a power transformer, unless it is an open circuit in a winding.

In the case of a short, usually what happens is adjacent turns in one of the layers in a windings short together. This only reduces the overall resistance of that winding by a fraction of an ohm, which is undetectable. But the effect on the transformer is dramatic. All the power in the transformer is delivered into that one shorted turn. That shorted turn overheats and causes the symptoms you describe. But a short EXTERNAL to the transformer will cause much the same results. You need to unhook ALL the secondary windings of the transformer. For the B+ circuits, this can be accomplished by simply removing the rectifier tube(s). For the filaments, you would need to unsolder at leas one of the wires on each of the filament secondaries.

Once you have done this, apply 115VAC power to the primary, and if the transformer still groans and gets hot, it has an internal short.

No need to disconnect the electrolytics, pulling the 5U4 will isolate them.
You shouldn't need to pull the transformer to find the problem. Do as John suggests, that will prove it one way or the other. If it proves bad, then you can remove it.

Great explanation of what happens when a short exists in a transformer John Folsom. Thanks!!

About the DC electrolytics, I guess I said it wrong. I meant that by pulling the LV rectifier I had eliminated the electolytics as a possible cause of the heavy load. Still thanks Chimes for backing up the no need to remove idea.

I think I have a line on a NEW Merit replacement. Wish me luck...........

Well I have the Merit replacement. I am going to need some help from someone who can pinpoint where each secondary leg will go. Reason being the replacement has a different color code. If I had a GOOD schematic I could look at where the various voltages are applied. For now I have no correct schematic. I have a Sams for a similar RCA and it does not show the voltages. The Merit replacement is quite a bit smaller as the end bells are not as tall, but it looks like it mounts up the same. Its a Merit P-0370 and the supplier insured me that it was a direct/drop in replacement. I hope he was right!

Even the way the color code breakdown on the box is confusing. I think it has something to do with the center tap. You can plainly see that black is 117 VAC, Green is 6.3v, yellow is 5v @3A, brown is 6.3v @2.7a. The two reds and the red/yellow say 350-350 vac @ 225 m.a.d.c.

If anyone can help pinpoint my connections and/or verify that this transformer is correct it would be greatly apreciated. Also some explanation of the red and red/yellow wires would be nice. Does this have to do with a "center tap"?

Thanks folks!!

Is your set a KCS-38 chassis?

I assume you mean the two reds are the secondary and the red/yellow is the center tap of the secondary. A center tap is just an wire connected to the mid-point in a winding. For this set, it is the return for the -120V supply. An ohmmeter can verify this, and check all the other windings and verify all the windings are isolated from each other.

The original transformer has a 6.3V 1.2A winding for the damper tube, a 6.3V 9A winding for all other filaments, except the rectifier, which uses a 5V 3A winding.

So I would assume yellow is for your rectifier, brown is for your damper, and green is for the other filaments, though you did not say what its current rating was. It better be close to 9A. If it is something less than 9A, then you can add up all the tube currents from data-sheets to calculate the actual current requirement to see if you green winding provides enough.

Good luck

Hi John, thanks for the info. I think this thing will work out and most of what you said was close to what I had in mind. Yes the green lead is rated at 10A. Now my unit has the Brown damper lead reated at 2.7A. Will thet present a problem? As far as the "two reds" go I mean I have 2 reds and a single red/yellow stripe. I have two of every color.

I measure 1.7 ohms between the blacks, .2 between the greens, .2 between the yellows, 65.2 between the reds, and 34.1/31.2 from either red to a red/yellow.

The chassis is a KCS-34b.

Do you have a schematic for this particular chassis? I already know other models that look the same have diffferent value components. I need to find out exactly where to solder every wire. The damper, rectifier, and other filaments should be simple enough. All of the red or red/yellow still confuses me. I'm asking for quidance because I want to be sure on this and not cause more problems.

Maybe these readings and more info will help you decipher some of this stuff. Efforts greatly apreciated!!!!

Thanks

There should be 3 wires on the b+ winding, and the different one will be the center tap. This is the red,red,red/yel probably. The red-yel will be the center tap.

So, just using the way the old one was hooked up as a guide, hook it up. What I mean by this is that the old one must have also had 2 leads the same and one different. Use this as a guide.

Another way: Hook the two wires that are the same color to the rectifier plates, and the different one where the old third wire was.

John

PM me your address. I am certain that I have a Spare SAMS 93-9 for your set.

polaraman

Tiubejunke,

What blue_lateral said. The two red wires go to your rectifier plates, the red/hello0w to the -120V bus return (where your old transformer denter tap wire went).

I can scan you jpeg images of the RCA schematic next week, but you shoud take polaraman up on his offer to send you a Sams for your set.

Let me know next week if you want me to scan the RCA schematic.

Good luck!

Heres the latest on the TC-127. I finally got around to unbolting the original transformer. I removed the endbells. Now I know where the burning smell came from. No bare wires shorted. Just burnt. Really that is good since I have invested in the Merit P-3070. The Merit unit is a bit smaller which means less weight. That always helps.

There are some differences in specs from the original to the Merit. John said that the original damper winding was 6.3v 1.2a. for instance. The Merit is 6.3v 2.7a. There are other differences but my Merit specs out at more than the original amperage in all cases. I would think that would be OK. Somebody make me feel good on this one.

Since I have real nice cloth wire I am thinking of simply connecting to everything up near the mounting point. I will not have to thread and tuck away new wire if I do this, plus the aspect of a more original apearance. I have to locate a big 2 watt 100 ohm resistor before I fire up the old thing. I noticed one that was cracked in two. Not really burnt, but cracked.

Now that I work a regular 9 to 5 its hard to get to one of the FEW electronics suppliers around here. Too bad Radio (joke) Shack aint what it used to be...

They probably wouldnt know what a resistor is.....Remember buying and testing tubes at the Shack? Those were the days!!

Yep, more amps is more better!

Tubejunkie,

The SAMS went out today. I have the same set in storage.


polaraman

Thanks friends. I'm going to start the install tonight.

Just for the sake of conversation here are some resistance measurements from the old (fried) transformer. Pretty weird!!

First I notice that none of the windings are color coded like my replacement. Merit had sense enough to group the windings in code. Like wire colors are seperate windings in this crazy thing. You get infinity across all but yellow to yellow.

Now between the Blue/yellow stripe to a Black I measure .7 ohms, 1.4 on the other set.
Between a Brown and one of the Blue stripes I measure .4 ohms, same on other.
Between one Yellow and a Green stripe I get 9.2, to the other yellow I get 14.2. This is weird because my measurement between the two yellows was 15.2.

I thought I had found the winding with center tap. Actually I probably have but I must remember that I am taking measurements from a faulty unit.

No wonder in the beginning I was having trouble taking resistance measurements. I was trying to match colors as far as windings go. Live and learn....

Well, the replacement bolted in fine. My game plan was to cut the old leads up near the old transformer and using a minimal amount of the replacements wire as it is rubber instead of the better looking cloth. On top of that I think this would be the best way to go in terms of common sense. The replacement did not have enough lead to go to the various connection points, so either way you would have to add some wire. Why not use what is there AND already routed real nice?

So, everything is now wired in. (Hope its all right) I went ahead and purchased enough caps to replace the whole power supply filter section and MOST other electrolytics. I also got a bunch of orange drops to replace most of the wax coated paper caps. Now I see why a lot of pros say change all of the caps. Tonight I noticed a 100 ohn 2 watt resistor burned in two in one of the horizontal circuits. There was a .0022 near by that measured like .012 and also there was a .22 that measured .001. I'm not sure about the mathmatics or exactly how much tollerance is allowed without noticable performance issues, but a measurement is a measurement and that is way off from the new stuff I put in. At least I will have peace of mind. I did not fool with the crazy stripped black caps which I have heard are troublesome as any, if not more. I may regret this move...

I'm trying to do this right so I have not yet applied line voltage to the set. I may break out the 100watt bulb again. I believe you are supposed to pull the horizontal output tube when doing the reduced voltage run. Anybody know?

I should have some results this week. I have a goal of seeing a picture by Christmas. Unless I really screwed up some wiring I should be a winner. Hopefully the power supply was the major problem area back in the sets use. That way all the RF coils and other odd ball things will be ok. No mysteries....

Hopefully!!

Yes you will regret it if you leave those striped caps in, please replace them or you will be asking for trouble...you can end up with hard to diagnose troubles or even if the cap holds together now it will decide to crap out and cause damage when you have it all back together.

Chad is right... change those black caps! All kinds of quirky little problems go away when you get rid of them. Also, I've had those blow out... and it will certainly cause you to soil your britches... they sometimes sound like a 22 pistol going off.

...

Good info.. Thanks folks!! No progress today. I feel like I can try the set with the black caps still in place. Sure there will probably be less than perfect performance but I can kind of check my progress so far with the whole power supply being replaced. Actually I went for a long time leaving those things alone in other sets because of that stupid color code. I have a book now that helps decipher what value thet are. Before that I just changed electrolytics, tubes, and bad resistors.