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Chris55000 · 16th May 2019, 10:44 pm

Hi!

This looks like slight heater/cathode leakage in the video amplifier or detector stage or possibly even the CRT, and unfortunately needs something like a Mullard HSVT or a Sussex that will measure the heater/cathode insulation at working voltage with the heater at working temperature!

If you have no valve tester it's a ****** faff to do in series heater lines, but if you have a bench power supply, you can at least rule the CRT out by feeding it's heater at d.c., temporarily disconnecting the original heater leads and short–circuiting them to maintain continuity in the chain, then testing the set again.

If the bar is now cleared, unfortunately the CRT is at fault, but if the fault is still present another valve may be responsible, and it's quite possible the RF stage or mixer/osc could be the culprit, so if the above test rules out the CRT, begin with trying the RF, mixer/osc and video amplifier valves by substitution first, then work thro' the remainder along the signal chain.

Don't forget there may be one or more smaller electrolytics across the h.t. feeding the r.f. strip or video amplifiér stage that may be partially or completely o/c!

I think the TV53 used a metal h.t. rectifier, but I suspect that will have been modernised a long time ago with a diode & surge–limiter, so I wasn't immediately thinking of rectifier problems at this stage!

Chris Williams

PS!

Don't forget any anode or screen–grid decoupling in the frame TB amplifier as well by the way, and if the frame amplifier is a PL84 this has known to be responsible for strange tricks, see "Valves & Their Habits" written by Harold Peters, available from Jan 1965 issue of "Practical Television", A.R.H. site!

16th May 2019, 10:44 pm	#5
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,873	Re: Bush TV53 hum bar problems Hi! This looks like slight heater/cathode leakage in the video amplifier or detector stage or possibly even the CRT, and unfortunately needs something like a Mullard HSVT or a Sussex that will measure the heater/cathode insulation at working voltage with the heater at working temperature! If you have no valve tester it's a ****** faff to do in series heater lines, but if you have a bench power supply, you can at least rule the CRT out by feeding it's heater at d.c., temporarily disconnecting the original heater leads and short–circuiting them to maintain continuity in the chain, then testing the set again. If the bar is now cleared, unfortunately the CRT is at fault, but if the fault is still present another valve may be responsible, and it's quite possible the RF stage or mixer/osc could be the culprit, so if the above test rules out the CRT, begin with trying the RF, mixer/osc and video amplifier valves by substitution first, then work thro' the remainder along the signal chain. Don't forget there may be one or more smaller electrolytics across the h.t. feeding the r.f. strip or video amplifiér stage that may be partially or completely o/c! I think the TV53 used a metal h.t. rectifier, but I suspect that will have been modernised a long time ago with a diode & surge–limiter, so I wasn't immediately thinking of rectifier problems at this stage! Chris Williams PS! Don't forget any anode or screen–grid decoupling in the frame TB amplifier as well by the way, and if the frame amplifier is a PL84 this has known to be responsible for strange tricks, see "Valves & Their Habits" written by Harold Peters, available from Jan 1965 issue of "Practical Television", A.R.H. site! __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! Last edited by Chris55000; 16th May 2019 at 10:52 pm.