Mercury Model 204 Retail Tube Tester?? - Videokarma.org TV - Video

Tubejunke · #1 10-05-2007, 01:36 AM

I recently purchased one of these units that once would have been in a store. It has a couple of bugs to work out and I'm wondering if anyone here knows anything about repairing tube testers in general or better yet this type in particular.

This unit is really cool looking with the lamp lit sign at the top of the scroll saying "Quality Tubes Sold Here". I would like to get it working properly because it is new enough to have settings and sockets for most generations of tubes.

I will not go into the problems it has until hopefully someone chimes in that knows something about the subject.

mrclassicman · #2 10-05-2007, 02:11 AM

Most of those "Retail testors" Eico's Lafeyettes, Knights were just basic emission testers. A voltmeter would tell you where the most likely area to check would be. The switches control what pins get what voltages. so take a known rube like a 12ax7 (which will have two settings 1 for each triode section). Pin one should have a plate voltage ( which on these testers is generally pretty low 150-180 volts). pin 2 will be 0 volts and pin three will have the bias voltage which will be rather low also around 1 to say 5 volts. The second triode pin numbers will be plate -6 grid-7 cathode -8. The filaments are pins 4-5 & 9. If the tester puts out 12.6 volts then pins 4 & 5 will be incircuit with pin 9 open. If the tester puts out 6.3 for the filaments then pins 4 & 9 or pin 5 & 9 or 4-5 & 9 . If all the voltages check out then it is probably the meter and or dirty contacts. When the test button or swithc is closed a small voltage is applied to the grid causing the tube to conduct, which the meter is in circuit to read. These testers are so straight forward I think you will have no problem ferreting out the problem.

Terry

Tubejunke · #3 10-07-2007, 12:28 AM

Thanks Terry, really the tester basically works but there is no way to set the meter to a cetain # off of the chart before the tube is inserted, per instructions. In other words the rheostat that you use to select this setting no longer has an effect on the meter. I know the rheostat itself is good because I can hold down the TEST button and turn it and see its effect on the reading. The effect on a tubes result is a lot with little turn of the rheostat so this is a critical setting.

Probably like most things there is some bad resistor or capacitor causing the trouble. If anyone has parts for old testers I would like to replace the meter assembly. My needle is broken, which throws the calibration off quite a bit.

I don't think this unit is one of the cheap emissions only testers. It has a gas and a shorts test. The Lafayette price tag is still on it for $349.95. I don't know its exact age. I do know that I carried bags of tubes to that store and used it back in the late 70's and it wasnt new then.....

mr_fixer · #4 10-07-2007, 02:52 AM

I was lucky, I was on the tail end of that era. There was a Radio Shack that had one of those during my high school days. there was nothing quite like the satisfaction of deducing that a problem with a radio/tv had to be a bad tube and confirming it with the know-all, all seeing tube tester. Those were glorious days indeed. I felt like I had arrived when I owned my own tube tester. Logan

Carmine · #5 10-07-2007, 01:10 PM

I can barely remember the days when drugstores/7-11's had them. Then it was just radio shack. Then there were none.

I'd love to own some kind of retail store today, just so I could have one of those things to confuse people.

Boobtubeman · #6 10-07-2007, 04:30 PM

I remember when THRIFTY store had them and those brochures with the number tabs you apply to the tube and the sockets. When they closed, i remember seeing the unit sitting behind the store. By the time i got ahold of a pickup truck, it was gone... I saw it a week later at the local auction

Steve

mrclassicman · #7 10-07-2007, 06:19 PM

If you have looked at the under side of your tester, see where this rheostat is wired in. Most generally it is wired in on the primary side of the transformer. If it is then try this, set everything else up on the tester for the tube you want to test. Then put the tube in the correct socket and then center the meter using this rheostat. When the meter is centered and the tube is warmed up press the test lever and read the meter. I do not see any reason they would have this adjustment made before the tube was installed. But if I knew everything I would be making a lot more money than I am! If you can post a couple of pictures of this treasure you have. You do have a piece of history!

Terry

Tubejunke · #8 10-07-2007, 11:36 PM

I'll do what I can about posting some pics in the next few days. I can take some fairly crappy pics with my existing older Cannon set up with NO flash. I would rather see if I can figure out how to use my brand new Polaroid to upload pics. Either way I'll do something. I have to reassemble it first......

kx250rider · #9 10-08-2007, 10:56 AM

Those tube testers are what got me into old TVs! I was always fascinated by seeing people testing tubes at the Sav-On Drug in West LA. There was a tube tester in every drug store, and also Pep Boys and Radio Shack. Sav-On sold GE tubes, and the other stores sold various brands. But none seemed to sell RCA.

Anyway, I bought a no-name retail tube tester on eBay a couple years ago, but it was big and didn't "do it' for me. So I resold it about a year later. I suppose I'd be more interested in keeping a GE one if I found one.

Charles

classicradios · #10 10-08-2007, 06:22 PM

I really like those old store tube testers. I barely remember them in radio Shack and 7-11 being born in the late 60's. I have a U-Test-M that I use mostly for tube storage. I use the U-test-M for quick tests and a Triplett mutual conductance tube tester for serious testing. I've owned a couple of these U-Test-M's and must say they have always been reliable and accurate.
Jim

Tubejunke · #11 10-08-2007, 11:33 PM

I may be amoung one of the first or at least youngest tube equipment buffs. This thread enden up making me think back a bit to the memory of tube testers in most drug stores and some dime stores, and of course Radio Shack. I too was born in the late 60's so I did start pretty young. I was thinking about the last time I could find a store tester easily anywhere I went and it must have been around 1981 or so. Even then I was buying 50's sets from all of these people who probably thought I was just some stupid kid wanting a tv bad enough to pay them for their aging junk. And thats what the 40's-40's stuff was at that time, JUNK.

That was good to me. I regularly found 30's-50's radios and old TV's for $5, or even better FREE.. Once I bought a 50's RCA portable. One of those space age metal things with the knobs on the side and a handle on top. The set had a couple of small issues and I remember bagging up all the tubes and getting Mom to drop me off at the drug store. No problem, in and out with my $2.89 purchase in no time. It seems like most of the testers I remember were like the ones pictured in post #10.

The testers along with the 8 Track tape vanished somewhere in the 1980's. I was overseas in the service during the late 80's and I remember thinking that quite a lot had changed in America since I had been gone.

Since then I drifted away from the hobby a time or two but whenever I did need to test some tubes the Mercury that started this thread was ALWAYS kept on the sales floor until the roof leaked and got it wet according to the store owner. I dont know how the meter needle got broken from rain. That probably happened when they moved it to the store room. The needle has not been pegged and broken and the meter still works, so that is good. A dab of super glue will fix that needle if I can get inside there. The pieces are floating around inside the meter face. Yes PIECES!! It broke in 3 I guess you would say because there are two pieces laying there. The loss of weight causes the meter to be quite a bit off in calibration so I need to do something there. If I can only get the initial setting rheostat working correctly...

Tubejunke · #12 10-09-2007, 12:01 AM

Quote:

Originally Posted by mrclassicman

If it is then try this, set everything else up on the tester for the tube you want to test. Then put the tube in the correct socket and then center the meter using this rheostat. When the meter is centered and the tube is warmed up press the test lever and read the meter. I do not see any reason they would have this adjustment made before the tube was installed. Terry

Hi Terry, the method I mentioned is clearly stated on the tester. Plus I remeber using it quite a bit through the past 20 or more years. It was the last one in any store around here up till the day I brought it home in disrepair.

The instructions say to find your tube on the chart containing two settings only. The first setting being a rotary switch with ABCD or whatever on it. I'm fairly certain that is a filament voltage switch. The second setting is where you set the meter via the rheostat BEFORE the tube is inserted. The last thing you look at is the socket# and any footnotes. Pretty simple, and quick.

The way the tester is messed up the only way that you can see the rheostats effect is when the TEST button is mashed and the tube is inserted and warmed up. This is when you are not supposed to be moving the setting. The good thing is that by this fact alone I know that all major components are working. Something is stopping the rheostat from passing voltage when the button is not depressed. I think it is the test button its self. It is a rather complex multi connection slide switch that opens and closes several circuits at specific times. Kind of the heart of the tester it looks like...

Tonight I did some continuity and resistance checks on the rheostat to meter circuit. I found nothing odd or off value. I cleaned the switch with some cheap electronic parts cleaner and nothing changed. I can probably study how the switch works and do some continuity checks pretty easily. Maybe I'll come up with something......Don't know what else to do.

Ebay???

mrclassicman · #13 10-09-2007, 03:35 AM

Well when you get the camera up and running take a "as high a resolution" as you can picture of the whole underside. Maybe a couple more eyes can help come up with something! I would hold off on Ebay as it sounds like you could use this tester, and would enjoy it! What you describe sounds like there is something "open" in the in the circuit in the non test mode. But hey at this point I am drawing at straws. You may be on the right track with the test switch. Since this was a commercial unit that saw a lot of service the contacts may have just been worn out! May have a bit of an issue finding a replacement if you need one but that is another story. Later.

Terry