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 Post subject: Re: Tube testers
PostPosted: Sep Fri 10, 2021 3:23 pm 
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Joined: Sep Tue 07, 2021 6:41 pm
Posts: 6
I just purchased an EMC Model 215 off of eBay, and tried to test with NOS tubes compared to the tubes that was in both radios (one from eBay and one that was my grandparent's old radio both AA5 RCA 55U & 65U). I'm seeing where it says all of the tubes are shorted on PIN 7 which leads me to believe the tester may need repair. I can see where someone must have opened it up prior cuz a screw is missing and another flathead was replaced with a Phillips.

Can someone verify (I'm reading the schematic from reprint manual for the 213/215) whether or not I'm missing any capacitors / resistors as I'm fairly new to reading schematics:
Fixed value resistors of in ohms: 1 Meg, 1.5, 270, 2K, 100, 1.2K, 750 adjustable, and 1K
Capacitors: 50 MFD, 50 MFD, 0.02, 0.01
Ammeter 5 M.A. 350 ohms (this appears to be working)

Would a loose wire to PIN 7 / switch 7 cause the tester to show a short?

I'd also like to replace the shunt variable component and/or plastic knob, could someone tell me what I should buy as a replacement?


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 Post subject: EMC 215 Tube Tester Question
PostPosted: Sep Fri 10, 2021 6:26 pm 
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Joined: Oct Thu 04, 2018 2:11 pm
Posts: 864
Location: Suburban Chicago
The 0.02 uF cap in series with the shorts test neon bulb is likely to be the cause of the shorts test issue. Replace it with a modern 0.022 uF cap with a voltage rating equal to or greater than the original. There are no voltage markings on the schematic that would guide us. The voltage is probably marked on the cap. If you can't find any indication you can use a 630 V cap which is certainly overkill but they are common and cheap enough.

The variable shunt resistor probably dissipates some power, it would be a custom design most likely, and replacements are not easily obtained. Finding someone who is parting out the same tube tester is your only option unless you want to research the values used in similar tube testers in hopes of finding some that used the same pot and that would expand the pool of parted out tube testers that could serve as a donor, if you are lucky. So use the original if you possibly can.

If it is only the knob that needs replacing you can find something that will work. It is probably a quarter inch shaft and the one I see in an online picture is a chicken head knob with a set screw. Those should be easy to find.


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 Post subject: Re: Tube testers
PostPosted: Sep Fri 10, 2021 6:57 pm 
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Joined: Jun Sat 15, 2019 7:43 pm
Posts: 1516
Perhaps operator error, Have you thoroughly read the shorts test procedure in the manual and note the notations in the tube chart.
The other possibility is a short in the wiring to the sockets for pin 7 or a problem with the #7 selector switch.

DM


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 Post subject: Re: Tube testers
PostPosted: Sep Fri 10, 2021 11:14 pm 
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Joined: Jul Mon 06, 2015 11:25 am
Posts: 302
I have the same tester and I believe this is normal. Here's my explanation to someone who had the same question with his EMC 211:

"I have an EMC 215 which I believe has the same basic circuit as the 211. The instructions for the Short tests are confusing. When testing for shorts the neon light will usually illuminate twice -- when the switch for each pin of the tube filament element is flipped. This does not mean there is a Short, but merely reflects continuity of the filament. So, for the 35L6GT, the "Short" light will probably illuminate when switch 2 is activated, and again for switch 7 -- since these pins 2 and 7 are the filament. A Short would be indicated if there was illumination for any switch other than 2 and 7."

If pin 7 is a filament, then I believe you are OK.


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 Post subject: Re: EMC 215 Tube Tester Question
PostPosted: Sep Tue 14, 2021 1:14 pm 
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Joined: Sep Tue 07, 2021 6:41 pm
Posts: 6
I was testing tubes 35Z5-GT, 50L6, 12SA7, 12SK7 and 12SQ7. According to the documentation, the filament is not pin 7 for all of these tubes, but they all showed a short on pin 7. My guess and I'll find out later today or tomorrow when I open it up, is that either the tube slot has a bad connection for pin 7, or the switch does.

The knob is partially stripped out as it moves without moving the switch pot.

Anyone validate the resistors and capacitors were correct and complete other than the missing diode short light?


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 Post subject: Re: EMC 215 Tube Tester Question
PostPosted: Sep Tue 14, 2021 2:02 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 11150
Location: Long Island NY
Pin 7 is definitely a heater pin on each of those tubes. The instructions are highly confusing but they say that it is normal for the bulb to glow when only one of the switches is pressed to the "P" position ... indicating filament/heater continuity. Since the set-ups for your tubes have pin 2 as the heater selector switch position (and slide switch 2 should not be pressed to "P") then the other side of the heater is pin 7 and the bulb should light if the heater has continuity. You kind of need to keep a copy of the tube manual handy to figure out which switch should light the bulb until you become familiar with the tubes you are testing.

It would appear that your tester is functioning correctly and there is no need to rip it apart and start changing all the components unless you are having other problems with it. Replacing every part in it will not change the design of the instrument and it will still do what it does now.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


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 Post subject: Re: EMC 215 Tube Tester Question
PostPosted: Sep Tue 14, 2021 11:34 pm 
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Joined: Jul Mon 06, 2015 11:25 am
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deleted as duplicate


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