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Author Topic: GE 102 AMBC radio tube problems  (Read 23945 times)
N4NYY
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« on: August 14, 2011, 07:47:01 PM »

Before I go look for these, I have question on 1 tube.

3 tubes measured bad, 12SA7 (no deflection), 12SK7 (weak), 12SQ7 (weak)

The 12SK7 and 12SQ7 both were well within the bad area of the meter. However, the 12SA7 converter did not deflect at all. It was pinned bad, all the way to the left end of the meter. I double checked. Is this common or unusual?

I do not have any of the 3 or crosses for them. Some before I put in a call to my radio club to see if they have them, I wanted to see what is up with that 12SA7.
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AC5UP
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« Reply #1 on: August 14, 2011, 08:12:47 PM »

I double checked. Is this common or unusual?

Three situations come to mind that might do that...

1) Filament open (you'd have noticed, right?) or the filament voltage switch on the tester was set too low.
2) Gassy tube. When you push the test button, did you notice any arcing going on inside the tube? Blue or purplish glow on the inside of the glass?
3) Operator error.
. a] The 12SA7 is a pentagrid converter with more internal elements than a pentode. On some tube testers you have to run multiple tests (each with different switch settings) to test all the grids & screens. One of the tests might be for internal shorts where zero deflection is a good thing. (?)
. b] On a tester like the Hickok TV-7 and its predecessor there are two octal sockets. Any chance you're in the wrong socket?

What kind of a tube tester are you using, and don't say Heathshkit!

BTW: One of my perverse ways of testing a tube is to do the usual test(s) per the book, then reduce the filament voltage by a click or two to see if the tube still tests good. A marginal tube will tend to be far more sensitive to filament voltage than a healthy example.
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N4NYY
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« Reply #2 on: August 14, 2011, 08:14:32 PM »

Quote
Three situations come to mind that might do that...
1) Filament open. (you'd have noticed, right?)
2) Gassy tube. When you push the test button, did you notice any arcing going on inside the tube? Blue or purplish glow on the inside of the glass?
3) Operator error. The 12SA7 is a pentagrid converter with more internal elements than a pentode. On some tube testers you have to run multiple tests (each with different switch settings) to test all the grids & screens. One of the tests might be for internal shorts where zero deflection is a good thing. (?)

What kind of a tube tester are you using, and don't say Heathshkit!

Filament open makes sense and I do not think any of the tube lit up when they were in the radio.

And yes, it is a Heathshitz! LOL. I just got a TC-2 and just upgraded it with new resistors, shorting cap, 1N4007 in place of selenium diode, and cal pot. I did the cal on it and it was balls on. The resistors were way out of whack.

« Last Edit: August 14, 2011, 08:17:35 PM by N4NYY » Logged
AC5UP
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« Reply #3 on: August 14, 2011, 08:25:07 PM »

.

WELL, DUH !

IF NONE OF THE TUBES LIGHT UP IN A SERIES FILAMENT STRING AC / DC RADIO WHAT DOES THAT TELL YOU, SEYMOUR ?
.
.
.
.
BTW: Forgot to mention that I threw out a bunch of tubes like that last month..... Also, good to hear that your Heathshkit is "balls on".
.
.
.
At least someone in that house is.
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N4NYY
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« Reply #4 on: August 14, 2011, 08:37:28 PM »

LOL. These were not see thru tubes. 2 of them were opaque black, including the 12SA7, so I could not verify. And stop making fun of my balls! And also, I lived on Seymour Ave at one time! And please stop telling me about all that stuff you threw out last month!

BTW, is the Heathkit that shittzy?
« Last Edit: August 14, 2011, 08:39:57 PM by N4NYY » Logged
AC5UP
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« Reply #5 on: August 14, 2011, 09:00:50 PM »

Observe the basic elements of a proper workspace:

http://www.hickok-inc.com/hickok90/hickoktubeguy.jpg

1) A complete selection of quality test equipment.
2) Proper lighting with adequate storage space.
3) Conveniently located reference material.
4) Drawers make access to hand tools convenient while reducing clutter.
5) The complete and total absence of anything made by Heathshkit.

BTW: The device in the technician's hands is in fact an AC / DC tube-type AM table radio.
The technician noticed that none of the tubes are lit and plans to ask someone what that means.

 Roll Eyes
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N4NYY
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« Reply #6 on: August 14, 2011, 09:04:29 PM »

I have the following:

1. Wavetek RF genetor
2. FET VOM (11 megaohm)
3. Tek scope (80MHz) 1980's vintage
4. Extech True RMS DMM
5. BK freq counter
6. BK audio gen
7. Heathshitz TC-2 !!!!!!!!!!!!!!!!

BTW, I could not see the filament failure because I did not know which tube's filament was kaput. The tester told me that with the black tube. However, being I am new to tubes, I needed to know if this is common, as this is the first tube I have tested that did not deflect.

And why did they make black tubes?HuhHuhHuhHuhHuhHuh What good is a tube you cannot see thru?

BTW, the 2 boxes of tubes that my friend from my radio club gave me, seem to not have many AA5 tubes. Isn't that a bit strange?



« Last Edit: August 14, 2011, 09:07:45 PM by N4NYY » Logged
KA5N
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« Reply #7 on: August 15, 2011, 01:45:40 AM »

Vinnie,

You can test the filaments for continuity with an ohmeter.  Also just leave the tube in the tester and see it it gets warm.  Black tube?  Do you mean metal tube?  There are plenty of metal tubes usually painted black but sometimes other colors and even varnished and left metal colored.
You need to get off those acky-dacky (AC/DC) BC sets and get into "real boat anchors".
Then the fun begins.
Allen
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AC5UP
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« Reply #8 on: August 15, 2011, 02:37:45 AM »

Long ago and far away in a place called the late 30's your friends at RCA developed what's called - THE METAL TUBE - and radio lover's everywhere rejoiced.

They look like this: http://i221.photobucket.com/albums/dd293/meoutbidu/2011/met3.jpg

The big advantage over an all-glass tube was a metal shield for lower noise, increased thermal dissipation (black body heat radiator) for increased service life, and (allegedly) less tendency toward microphonics as the internal structure was better supported by the smaller envelope size. All this was true. Even something as lowly as an AA5 could be improved and metal tubes were used as a selling point. Buy this model, it comes with metal tubes and they're better. It is also true you can't see the filament and maybe that's why other tube manufacturers offered the 'GT' version which meant 'glass tube'. An RCA 12SQ7 is a metal tube, a Tung-Sol 12SQ7GT is the glass version.

In the case of your 12SA7 you can test the filament by hanging your Extech ohmmeter across pins 7 and 8. Should read wide open, and all kidding aside, it is unusual for a filament to open like that. Usually they go the way of your 12SK7 and 12SQ7 where the transconductance value drops low enough that it just doesn't work any more.

The reason the box of tubes given to you has no AA5 pieces for your particular radio is because:

1) They were picked out before you got the box. This ain't Halloween.
2) The AA5 has been around long enough to cover Octal, Loktal and Novar tube types over three decades. Your radio is 40's flavor Octal. The box of tubes could be more like 60's vintage Novar miniatures.
3) The box of spare tubes may have come from a two way radio or TV repair shop that rarely saw an AA5 and was glad for that.

BTW: Your Heathshkit TC-2 is a basic transconductance tube tester that uses a simple circuit to tickle the tube with enough current to measure how well it conducts. Even though the testing is done at DC, this is OK as it was understood back in the day that a tube checker was a basic GO / NO GO test device useful in weeding out the dead, the dying, the shorted and gassy. Performance against a known good tube in the actual circuit was the real test. It is possible for a tube to test good but perform poorly in a specific circuit, especially in VHF / UHF amplifiers & oscillators.

Oh......... And while we're bragging........ I have three tube testers (all Hickok):

An I-177 formerly owned by Unca' Sam... http://home.hccnet.nl/piet.blaas/groot/i-177-b-groot-boven.jpg
A TV-7 formerly owned by Unca' Sam... http://www.audiotubes.com/testtv71.jpg

And, the king-kat daddy of them all, previously owned by AT&T Long Lines and built like a stretch Cadillac with another Cadillac in the trunk...
The legendary Hickok Model 1234 Cardmatic: http://members.iquest.net/~finchum/1234.jpg

What a beast. Show up at a Hamfest with that bad boy and you will get noticed. Two big aluminum transit cases. One for the tester, the other for the punch cards, and it makes every other tube checker seem....... Inadequate.

Like the typical Heathshkit with "ED". (electron dysfunction)  Grin
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G3RZP
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« Reply #9 on: August 15, 2011, 02:44:11 AM »

If you want to pay the cost of shipping, and have a good postal address, I can send you a 12SA7 and 12SK7. The XYL is coming to the US on business next month, so it would be mail from Oregon.
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W8JI
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« Reply #10 on: August 15, 2011, 03:09:05 AM »

Years and years ago we used B and K 707's I think, or a very similar number B&K  tester. There were about 18 inches square, and had an upper row of fully prewired sockets for common tubes and a lower row of switch set sockets.

I owned a large expensive Hickok, and it sometimes would pass tubes that would not work in some critical circuits. The 707 and 747 on the other hand would reject tubes as low emission that often would work.

The reason I settled on the 707 was I would rather change a marginal tube needlessly than drag something in for bench service or have a tech spend hours just to find a bad tube. With the 707 we pretty much would weed out tube problems without spending hours substituting tubes that tested good.

 I still have a B&K smaller tester, I think a 747 or similar.

Metal tube patent? It was for a smaller more rugged tube.

http://www.google.com/patents?id=g9l5AAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q&f=false

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W8JI
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« Reply #11 on: August 15, 2011, 03:11:15 AM »

If you want to pay the cost of shipping, and have a good postal address, I can send you a 12SA7 and 12SK7. The XYL is coming to the US on business next month, so it would be mail from Oregon.

It's OK, I'm closer if he needs one and I probably have some.
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N4NYY
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« Reply #12 on: August 15, 2011, 06:31:20 AM »

KA5N - Yes, metal tube. This is my first experience with them and any octal tubes. (I learn new terms on a daily basis). I have not done real boatanchors because of the cost factor. Even old rigs have tremendous parts value, hence they are expensive to buy, and then you have to restore. I am going to graduate to them at some point. I would like to get to an SWL boatanchor net. These 2 (GE and RCA) were free handoffs from Hollingsworth, as he did not have time to restore them. He is typically traveling on his speaking tours. So he just gave them to me.

AC5UP - This tube tester was a gift from an extra at my club, from his silent key dad. His dad would have also given me the tester based on wanting aspiring hams to learn. My problem is that I am 44, and about 30 years behind in ham years. BTW, my tester is balls on (I think I got that from an This Old House episode). I see alot of these around and hamfests and such, but the bigger duty ones are hard to find and expensive. I did check those websites out that explain them in detail. Lastly, it is more entertaining to read your anti-Heathshitz post, that makes it worth keeping them. I get an education and a laugh.

G3RZP - I will check locally. Some old timers at my club usually have them. And yes, I will always pay for shipping.

W8JI - Don't worry about looking yet. Let me see if I can get them here. Again, I will pay for shipping. BTW, check your email. I sent a yard layout to see what antenna I can change to in the fall. No rush.

« Last Edit: August 15, 2011, 06:34:07 AM by N4NYY » Logged
AC5UP
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« Reply #13 on: August 15, 2011, 07:40:35 AM »

BTW, my tester is balls on (I think I got that from an This Old House episode).

http://www.youtube.com/watch?v=BrjC1E1TBdg

(if you need any help translating the dialect ask someone from New Jersey)

Quote
Lastly, it is more entertaining to read your anti-Heathshitz post, that makes it worth keeping them. I get an education and a laugh.

You're like the retarded little brother I never had............   Grin

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KE3WD
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« Reply #14 on: August 15, 2011, 09:49:24 AM »

Advice from an old coot who lived through the daze when tube sets came across the test benches with regularity, MEMORIZE THE PINOUTS of the basic tube types. 

When looking for an suspected open series filament string, the fastest method is to simply leave all tubes in the set and use the AC voltmeter, one side connected to the Line where the series string starts and use the other probe to "walk" through the filament pins, in order if you can decipher the connections.  You should easily find the point where the circuit is open and thus suspect that tube.  Another way to go about that one is to simply use the AC voltmeter to measure the voltage drop across the filament pins of each tube. 

Old trick tip:  Not always the case, but every once in awhile you may find an old tube where the filament appears to be open but in reality it is the connection to the filament at the base pins.  Try resoldering the base pins to be sure, tube upside down, like held gingerly in a bench vise, then heat the pin on the side of the edge by the hole and apply small amount of new resin core solder to the hole, let it flow a bit and repeat on the other pins.  BTW this method has also worked to save tubes that appeared to have problems other than filament open and won't test on the tube tester.  Tube testers are nice, but in actual practice I used to use the checker rather rarely, because it is a lot faster to "test" them in the circuit where they live, using mostly the VTVM or these days, the DMM.  Of course, that means that you have spent some time in learning what to expect from the healthy tube circuit.  A very good drill is to do some voltage checks on a set that is operating properly to get a good idea of what "healthy" looks like.  Schematics show voltage checkpoints referenced to Common, the savvy tech learns to also think in terms of Voltage Drop across components as well. 

Used to have a little penlight cell driven injector that was called the "Mosquito".  Shirt pocket size, the thing contained a simple one transistor squarewave oscillator output at a needle probe and a short lead with gator clip to chassis of the five tube wonders and such of the era.  One could use it to walk backwards from speaker, injecting the little bweeep into each section (another reason to know your tube pinouts from memory), injecting tubes at their inputs and simply listening for where the signal stopped.  Because it was a square wave, rich in harmonics, it worked right on through both AF and IF and RF sections to quickly spot where the signal stopped.  Wish I still had one, but today will sometimes use the Function Generator to provide a square wave, through a homemade coax probe that has a series DC blocking capacitor to protect the generator from the high tube voltages (a high WVDC cap that can pass the rather low audio frequency of the square wave) and can use it on the test bench in the very same way. 

If you don't already have an AC Isolation Transformer on your bench, get one.  Use it always on any power transformerless set.  The savvy tech does not have to spend a lot of money on a specialized isolation transformer for the bench.  You can get the same result by hooking the Secondaries of two identical filament transformers to each other and using their respective Primaries as input and output to AC plug and socket.  This method actually provides a bit more isolation than the single and more expensive dedicated Isolation Transformer.  Feed it with a Variac, add AC voltmeter and AC ammeter along with a 100W lightbulb that can be switched in series with the ac line and you have a very nice setup that will allow you to even troubleshoot those high current eating fuse blowers.  The bulb will light brightly when you bring up the variac to the halfway point or so when the Unit Under Test happens to have a fault that would otherwise blow fuses or make smoke.  You can even locate a short condition quickly using this method by leaving the variac at some point lower than the full AC line with the lightbulb glowing in series with the set, simply use the voltmeter to look for where the show stops.   


73

Keep at it, experience is the mother of expertise. 


73
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