Hi all. I have an EMC tube tester which I have persisted in using, though I have data for testing only tubes popular in the US, which means I am constantly having to generate new test data for Australian and European tubes. However recently when trying to use it I was unable to get the tubes to heat up. The nearest schematic I have ever been able to find is for a model 200, which is a little different from the 206. However by patient tracing with pad, pencil and ohmmeter, I have concluded that I had two problems, the first being the "GAS" switch, a two-position slider, had a contact resistance of about 62 ohms. Since the tester came with a brand-new NOS spare, that suggested that the previous owner may have had trouble with it. So I replaced it, half-expecting the problem to be solved, as it is in the heater circuit, one contact of it connected to the end of the heater winding of the power transformer. all heater current being through its contacts.
But the problem persisted, and further checking revealed that the power transformer heater winding is in fact, open-circuited. This is the winding with MANY taps, to supply a large range of heater voltages to the tube being checked.
The first tap on the winding is for 0.75 volts. The winding between this tap and the common end of the winding appears to be open.
I searched for a replacement transformer. The part number appears to be 903P1. I DID find a tranny for an EMC tube tester but it didn't look too flash in the photo, and seemed to be a lot simpler than mine.
Not too keen to start unwinding the brute, I put the brain in gear to come up with an alternative.
I have on hand a 240 to 6.3,7.5,9,10.5,12.6 and 15 volts multi-tapper. If I was to use the part of the secondary between 7.5 and 9 volts, I will have 1.5 volts available. But if I use the tranny on 110 volts, I will have 0.75 volts, which is the required voltage. The tester is 110 volt operated.
Then, if I take the end pigtail of the original transformer from the "GAS" switch and tape it up, and connect the new transformer's 0.75 volts between the original transformer's 0.75 volt tap and the GAS switch, I think we might have something that will work. I will have to connect it in the correct phase, or all other voltages, other than .75 will be out by 1.5 volts.
Does anyone have a BETTER idea?
But the problem persisted, and further checking revealed that the power transformer heater winding is in fact, open-circuited. This is the winding with MANY taps, to supply a large range of heater voltages to the tube being checked.
The first tap on the winding is for 0.75 volts. The winding between this tap and the common end of the winding appears to be open.
I searched for a replacement transformer. The part number appears to be 903P1. I DID find a tranny for an EMC tube tester but it didn't look too flash in the photo, and seemed to be a lot simpler than mine.
Not too keen to start unwinding the brute, I put the brain in gear to come up with an alternative.
I have on hand a 240 to 6.3,7.5,9,10.5,12.6 and 15 volts multi-tapper. If I was to use the part of the secondary between 7.5 and 9 volts, I will have 1.5 volts available. But if I use the tranny on 110 volts, I will have 0.75 volts, which is the required voltage. The tester is 110 volt operated.
Then, if I take the end pigtail of the original transformer from the "GAS" switch and tape it up, and connect the new transformer's 0.75 volts between the original transformer's 0.75 volt tap and the GAS switch, I think we might have something that will work. I will have to connect it in the correct phase, or all other voltages, other than .75 will be out by 1.5 volts.
Does anyone have a BETTER idea?
