Mercury Model 1100B Tube Tester.

[audion_1908]

I got myself a Mercury model 1100B tube tester for Chistmas, it was listed as not working, I finally got around to having a look at it, I was not expecting it to be much of a problem. In the past I have built a basic valve tester in a tupperware box! It is missing a knob and the switch goes all the way round that makes fitting the knob tricky, and it's had its top cap lead cut off? It was made for 115V I got an auto trasfomer for that.
It is also missing its case lid.

[audion_1908]

Inside it all looked OK, I did notice the wiring from the transformer to the middle rotary switch had been disturbed and then an worrying smoke mark on the case. I found one of the contacts has burnt away and one of the wires has been badly resoldered!
The tube tester wants 117V and the autotransfomer is 110V?
The contact has burnt away is connected to the 117V supply, and US plugs fave no fuse! So it would have been on a 15 or 20 amp circuit so the fault current could have been high

Any one know where I can get a new wafer for the switch?

[audion_1908]

The top part of the wafer switch is only used to switch it on and off, I can bypass that, but the bottOm contacts are used to select the filament supply from 1.4V to 110V using an auto transformer, the 110V is direct from the unfused supply it is a 12 way wafer switch but not all the ways are used.

I think if/when I get this valve tester working I will add some internal fuses and earth the case
http://www.radiomuseum.org/r/mercury...ster_1100.html made in 1967, 46 years old!

[audion_1908]

For now I could use the valve tester by bypassing the wafer switch, it would mean I would have to unplug it to switch it off and open it every time I want to change the heater voltage.

[Freya]

Have you checked the transformer, to do that to a contact would need a substantial amount of electrictity.
You should really have posted this in the workshop section.

Steve

[Heatercathodeshort]

For what it's worth I would not put that 'tester' any where near the tube in your Bush.
95% of testers either destroy or damage good tubes or reactivate them when nothing is wrong.
Apply 6v AC to pins 1 and 12, the heater pins of the tube and carefully observe the heater cathode assembly as in this picture. [58]

https://www.vintage-radio.net/forum/...t=74510&page=3

If you have a traditional meter it should register around 300m/a at 6v.
If this is correct I would leave it at that. Being a Mullard tube it will probably give a decent picture. Regards, John.

[audion_1908]

Originally Posted by Heatercathodeshort

For what it's worth I would not put that 'tester' any where near the tube in your Bush.
95% of testers either destroy or damage good tubes or reactivate them when nothing is wrong.
Apply 6v AC to pins 1 and 12, the heater pins of the tube and carefully observe the heater cathode assembly as in this picture. [58]

https://www.vintage-radio.net/forum/...t=74510&page=3

If you have a traditional meter it should register around 300m/a at 6v.
If this is correct I would leave it at that. Being a Mullard tube it will probably give a decent picture. Regards, John.

My basic tube tester is not meant for CRT's and I dont know if it is a Mullard CRT, as the damp has made all the stickers fall off! I dont want to risk the CRT so will take your advice and just test the heater, but if the valve tester has the currect heater voltage it should be OK to give a basic test of my unknown TV valves.
The shorted switch looks like it did not involve the autotransformer, I will test it

[Heatercathodeshort]

The tube in your Bush should be a Mullard MW36-24 or MW36-44. It may have had a rebuilt tube fitted but generally the labels do fall off. Don't risk the tester on anything that may be servicable. You will soon sort the odd faulty valve when you eventually power it up. Take care. J.

[audion_1908]

Originally Posted by freya2871

Have you checked the transformer, to do that to a contact would need a substantial amount of electrictity.
You should really have posted this in the workshop section.

Steve

The 230 to 110V auto trasformer puts out 117V open circuit and 116V when runing the valve tester, I tested the valve tester's auto transfomer for the heater and it is fully working but all the outputs are low? eg the 6.3V tap is 5.9V it could be my cheap DVM it only has a 600V and 200V range and the AVO is not calbrated and two resistors are charred
I don't like working on stuff connected to the mains with no current limiting or RCD, my flat doES not have one? but I am buying a plug in one.
I will try some ef80's in it

[Freya]

Could be your DVM on the AC, try the AVO, nothing to loose.

[audion_1908]

Originally Posted by freya2871

Could be your DVM on the AC, try the avo, nothing to loose.

The AVO has no leads and the DVM's will not fit, I used some hookup wire held in with twisted cardboard just to use the AVO to test the pots, I have a data sheet for the AVO and will test the resistors, and with a 1.5v battery.

Its an AVO Multiminor MK4

[Herald1360]

That AVO shunt looks a wee bit past it!

The DVM is the same as my own cheapy. You could check its cal to within a few percent by measuring a known low ac voltage- maybe scaled mains from a 100k/1k potential divider (240V > 2.38V) or 2.37 if you allow for meter 1meg input.

[audion_1908]

Originally Posted by Herald1360

That AVO shunt looks a wee bit past it!

LOL, I know but I want to get the AVO meter working, it could have done with a fuse in it.