[ARC5] Tube Question

[Randy Randall]

Hello Wayne, if you are setting the line Adjust without a tube in the circuit this could very well explain why it's reading low. You definitely have to check with the instruction book but some testers want the tube in there when you make the line adjustment. Others do not.  

I just found a copy of the 205 manual on the web and it does require the tube to be in circuit while adjusting the line setting. The other thing I can see glaring on the tester is it uses a selenium rectifier. The internal resistance of a selenium rectifier tends to go up over time. Unfortunately in the instructions I did not see how to calibrate the tester other than a warning not to move the shunt control knob as it was set at the factory.  You can replace the selenium rectifier with a silicon one, but you also need to insert a resistance to bring the voltage down to a correct level as the silicon diode is more efficient than the old selenium unit and has a lower internal resistance.  Unfortunately there are no voltage readings on the schematic so trying to figure out The size of the resistor will be harder.

Sent from my iPhone using speech to text technology.

> On Sep 20, 2015, at 1:00 PM, Robert Eleazer <releazer at earthlink.net> wrote:
> 
> Okay, its an Electronic Measurements Corp Model 205.  It does indeed use a line voltage calibration control, and I have been careful to adjust that.
> 
> It uses a roller type test data chart (like the drugstore tube testers we all recall) which is a fine means of verifying your abilities to read small print and line up rows of letters and numbers.
> 
> Thanks,
> 
> Wayne
> ----- Original Message ----- From: "Randy Randall" <randy.ab9go at gmail.com>
> To: "Robert Eleazer" <releazer at earthlink.net>; <ARC5 at mailman.qth.net>
> Sent: Sunday, September 20, 2015 12:53 PM
> Subject: Re: [ARC5] Tube Question
> 
> 
> You did not mention the model and brand of the tube tester so I'm going with some generic suggestions. Since it is a simple tester you can calibrate using a resistor of a  value usually specified in the owners manual to set the calibration.  Do a search on the make and model on Google and I'm sure somewhere you'll find an owners manual with those instructions. The only tube testers instructions I've seen that was suspect was a Mercury Model 1100. Calibration instructions on that unit was to take 5 new 6ab6 tubes and test them all and take the average of all of them and set the meter to that point. Seems hokey but that was their calibration procedure.  Also back in the day some less than reputable TV and radio men would deliberately misadjust the tester to read low to sell more tubes.  Also if your tester has a line Adjust setting make sure that you set that with the tube in the tester in the filament lit with the correct settings. To be sure follow the directions in the manual.  One last thought if you own an Eico tester model 666 or 667 the tube charts were notoriously inaccurate. Do a search and you if you own this tester and you can find updated charts, but even the newer ones had errors.   Good luck Randy.
> 
> Sent from my iPhone using speech to text technology.
> 
>> On Sep 20, 2015, at 11:43 AM, Robert Eleazer <releazer at earthlink.net> wrote:
>> 
>> I finally got out the tube tester I bought a while back and stared learning how to use it.  It is simple emission tester.
>> 
>> I found something puzzling.  I have two 6AW8A tubes that were sold to me as good and a 6AN8A tube still in its original military box; these are basically the same type tube.
>> 
>> In the tube tester all three test as bad, the meter needle in the high area of the "replace" range.  Also, the meter needle wavers.  However a slight upward adjustment to the Shunt control shows the tubes as good. This is true for both sections of the tubes.
>> 
>> Anyone have any ideas on this?
>> 
>> Thanks,
>> 
>> Wayne
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