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hugeshows hugeshows is offline
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Default Restoring a TV-7/U Tube Tester

Hello again,

I've made some more progress on the TV/7. It was very important to pause and really read over the instructions carefully in order to make sure that I was reading the correct procedure for this particular unit.

After reading the calibration steps several times, it became fairly obvious that resistors R123 and R125 are very important, since they form the meter bridge circuit. They are 1K 2W resistors in my unit, and they measure out at 1.084K and 1.175K. That's fairly close, but not as close as I want. I started digging around in my stash, and found a nice box of NOS Mallory 1K 5W precision wirewounds. Out of a box of 5, I figured I'd get a pair that were well tighter than .5% I actually lucked out and found a pair that both measured exactly 1009 ohms. Here's a pic of them sitting on top of the transformer before installation:

https://www.dropbox.com/s/kx8o2sccse..._Resistors.jpg

R125 and R125 are the two 1K resistors on that turret board in this picture..

These had been messed with before and the results weren't very clean, so I decided to completely de-solder those terminals before putting the new resistors in. Here they are installed:

https://www.dropbox.com/s/3sb6ytcmes..._R123_R125.jpg

They fit quite nicely. In case you're wondering, I did check first to make sure they wouldn't bottom out once the tester goes back in its case. A quick measurement shows that they're still matched perfectly, so on to line check and bias adjustment.

The first step now that we have a good meter circuit with new diodes and resistors is to power the tester on for a couple hours and let it burn in. Then we will start adjusting the bias voltage.


That's all for today probably. Cheers!


-forkinthesocket