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Hameg 307
Still progressing. Very helpful comments from Wavey Dipole about range of brilliance control in #111 (exactly as I suggested in #46).
1. When something is not working, you can forget all these fine calibration and set up adjustments as you mention in #112. You must get the machine working first. Then you can do the fine adjustments and calibration. The makers manual always assumes the machine is working , and just needs tweeking. After all, no machine they ever made fails or suffers from faulty components, even after 20 years.

We now have:
1.No change brightness when ExtX is moved in/out (3 #107). Which should be caused by change in cathode voltage p3.
2. Yet 40v change at R366 (Edit # 100).
3. So somehow variation you report at R366 does not reach CRT cathode p3.
4. Cathode p3 is not locked to heater and 900v rail, as cathode-heater insulation appears good (#112).
5. We have voltages around CRT:
cathode -900V unblanked (#100)
grid -910V (assuming by TB off you mean ExtX)
so grid on -10V with respect to cathode. This should give a fully bright spot.
6. I seem to remember you have confirmed the anode of the CRT p8 is somewhere around 0 to +100V and the focus control (-600V to -700V on p4) changes spot from fine to fuzzy.

7. But as WD says in last para of #111, CRT not responding to voltage changes at cathode p3.

8. Confirm you are changing the cathode voltage by switching ExtX on and off. And that when in the off position, the TB is not operating by AT off and no Y input signal, so there is just a spot. (para 2 #104 and para 2 #96).
9. To be sure, check voltages at tube base itself.
10. We have to resolve point 7 above, as WD says.
If all voltages are valid, then the only conclusion is that the tube is faulty. Though I am still doubtful.

At this stage, I should not worry too much about a HV probe, provided you are using your Avo on 2.5kv range, which restricts the current drawn. And I suppose a 10M DVM will draw a similar current when measuring 1 kv.
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