HT Valve rectifier


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HT Valve rectifier

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DKendall
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Oct 11, 2005, 6:27 PM

Post #1 of 15 (1610 views)
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HT Valve rectifier	Can't Post

I have a bush tv53 tv set in which the ht rectifier valve has blown its heaters. I dont care for the set much but it would be nice to c something on it. Is there a way of replacing the rectifier without using another valve?

stocksie
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Oct 12, 2005, 10:49 AM

Post #2 of 15 (1605 views)
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Re: [DKendall] HT Valve rectifier [In reply to]	Can't Post

Use a 1n4007 with a 10 2w carbon resistor in series across A & K of the valve base. Cathode to cathode!

stocksie
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Oct 12, 2005, 10:53 AM

Post #3 of 15 (1604 views)
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Re: [DKendall] HT Valve rectifier [In reply to]	Can't Post

Sorry, was in a rush with previous answer. put ohm after 10. It might be a good idea to add a standy switch in the cathode line and allow all the other heaters to warm up before switching the HT on. With a set that old things are likely to break down!

DKendall
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Oct 12, 2005, 7:43 PM

Post #4 of 15 (1597 views)
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Re: [stocksie] HT Valve rectifier [In reply to]	Can't Post

Cathode to cathode! ???????????? I have some old microwave ht diodes. Will they do?

stocksie
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Oct 14, 2005, 9:32 AM

Post #5 of 15 (1591 views)
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Re: [DKendall] HT Valve rectifier [In reply to]	Can't Post

Leave the faulty valve out in case it has other problems. Fit the replacement solid state diode (cathode to valve base cathode, K-K) include a limiting resistor (say 10-20 ohm) in series with the diode and standby switch. Better still make the limiter 100 ohm 10W variable and set it to max then let the other heaters warm up before slowly reducing the limiter and hope the electrolytics etc dont break down. Keep the resultant HT below 200v as a precaution. If you do get any action from the CRT leave the HT at that level. The diode you speak of should be OK but bear in mind modern solid state devices have no self limiting action like the valves did. Good luck.

rrobor
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Oct 16, 2005, 11:10 AM

Post #6 of 15 (1583 views)
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Re: [stocksie] HT Valve rectifier [In reply to]	Can't Post

If memory serves me correctly there was a modification to replace that valve, it was just a valve base with pins, across the anode cathode was a diode and across the heaters was a 7 ohm resistor. you just pulled the dud out and pushed this in. As I think this is a UK unit the heaters ar likely to be in series so you must bridge them, use a 7ohm 5W. again stretching the memory I think there was a fair bit of inductance before the valve so a resistor in that line was not needed then. Now, yes I think i would have a 10ohm + in the line. I would doubt if you have a variac but one of those would be handy to crank the power up first time as the electros in that are liable to need forming, good luck and watch the eyebrows are not singed with the flash.

DKendall
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Oct 16, 2005, 10:10 PM

Post #7 of 15 (1578 views)
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Re: [rrobor] HT Valve rectifier [In reply to]	Can't Post

I mean the HT rectifier has gone. There is a valve sitting on top of the lopt. The lopt generates a nice big voltage that jumps nicely to a screwdriver but it does not get rectified because the valves heater has gone. The voltage im talking about is the crt anode.

stocksie
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Oct 17, 2005, 11:24 AM

Post #8 of 15 (1575 views)
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Re: [DKendall] HT Valve rectifier [In reply to]	Can't Post

The valve on top of the transformer is the EHT rectifier (Not HT). Its heater is supplied by a few turns around the line output transformer core thus keeping it isolated from the normal set heater chain. The EY86? heater should read low ohms (disconnected) but doesnt glow very bright as far as I remember. Try checking the Line output valve screen volts but do not try to measure the valve anode volts as the line energy will damage your meter.

rrobor
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Oct 17, 2005, 11:52 AM

Post #9 of 15 (1574 views)
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rrobor
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Oct 17, 2005, 12:05 PM

Post #10 of 15 (1574 views)
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Re: [stocksie] HT Valve rectifier [In reply to]	Can't Post

funnily enough there was a replacement for that as well it was a stick rectifier that plugged in and the top cap fitted on that. I would think you could use 2 microwave diodes in series to do that. They are usually 15000v so one will be almost ok but very close to spec, 2 will give you miles of margin. I would be checking across the heaters of the valve though with an ohm meter, that was not a common fault with these valves. If the valve is stuffed just pull its top cap off and fit your diode to that, you should be able to get to the bottom of the valve base so just stick the diode through the base like a pin and solder it on

DKendall
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Oct 24, 2005, 5:28 PM

Post #11 of 15 (1558 views)
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Re: [rrobor] HT Valve rectifier [In reply to]	Can't Post

I have put the two diodes in but still nothing. The ac eht from the lopt sparks around an inch from its terminal to a screwdriver held by me (not to earth). This appears like a nice high voltage so I think that is working well. The tube has shown brightness at some point since Ive had it so i think that is ok. The only thing I can think of that could be stopping the thing is the diode set up. The microwave diodes are rectifying the eht but the rectified voltage jumps a measly couple of mm's. The diodes worked in the microwave but read open both ways. I have no idea why that is.

Wiz
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Oct 25, 2005, 11:29 PM

Post #12 of 15 (1548 views)
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Re: [DKendall] HT Valve rectifier [In reply to]	Can't Post

The ohm meter that you are using needs to be using at least 6v to measure the resistance with. If your meter isn't giving this much voltage for the resistance measurements, then the diode will read open both ways round. You will need to replace the battery in your meter to one that gives its full voltage output.

rrobor
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Oct 26, 2005, 12:16 PM

Post #13 of 15 (1543 views)
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Re: [Wiz] HT Valve rectifier [In reply to]	Can't Post

Agree with last post but also think you may not be using a diode. A microwave often has 2 diodes, one normal and the other a protector. The protector is marked with 2 lines then the diode symbol, are you using one of those?

DKendall
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Oct 26, 2005, 5:43 PM

Post #14 of 15 (1535 views)
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Re: [rrobor] HT Valve rectifier [In reply to]	Can't Post

Im 99% sure they are diodes ( -|<- ) They do seem to rectify the voltage but the final dc volts will only jump a couple of mm. Does this mean one of them is dead? If I assume thay are fine what else could be at fault?

rrobor
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Oct 27, 2005, 9:16 AM

Post #15 of 15 (1530 views)
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Re: [DKendall] HT Valve rectifier [In reply to]	Can't Post

Chances were your flyback transformer has died. Also as an olDER tech the valve base of these things died and did all sorts of nasties, look at that carefully.

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