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Old 1st Oct 2018, 11:07 pm   #21
Argus25
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Default Re: Help Identifying Capacitor

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Originally Posted by Maarten View Post
But we'll have to wait until we hear if the capacitor is really the problem here or just a "let's replace all capacitors so the set will surely work again" (no offense, but this happens a lot and is often the cause for additional defects).
I agree, the type of 2uF capacitor that it is seldom fails, since it is not an electrolytic. So provided it had the correct uF value on testing(or close) and showed zero leakage on a meter, I would trust it, initially at least and not seek to replace it as a first move.
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Old 2nd Oct 2018, 3:17 am   #22
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Default Re: Help Identifying Capacitor

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the test would be to measure the voltage across the valve heaters after it's been fitted.
Philips explicitly specifies that with series string valves, the current should be measured (100mA) as the voltage can vary a bit more than with parallel heaters.
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Old 2nd Oct 2018, 9:52 am   #23
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Default Re: Help Identifying Capacitor

It won't vary that much with a 12.6 volt heater.

Lawrence.
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Old 2nd Oct 2018, 10:21 am   #24
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Default Re: Help Identifying Capacitor

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Regarding R31 does a 5W resistor suffice? and can you tell me in what pins to take the voltage measurement and what voltages to expect?

Do the lamps take any active role in the working of the receiver? Or in other words can it work without them?

The thermistor is definitly not good barely touched it and it cracked in half almost looks like a fuse but the core is solid looks almost like carbon, will post a photo tomorrow.
Personally I would fit a 10 watt resistor for R31.

When all's well the AC voltage across the UF89 heater should be approx. 12.6 volts, the pin connections for that valves heater are pins 4 and 5.

The bulbs (lamps) are in series with the heater circuit, if they are open circuit the heaters will not work, if that turns out to be the case you will have to replace them or fit a suitable resistor in place of them, I've no idea of the actual bulb voltage but I would have thought either 6.3 volt or 12.6 volt.

The thermistors definitely toast then, it might be similar to the Mullard VA1010 thermistor, the data for that one can be found here:

http://www.electrojumble.org/DATA/Mu...o%20VA1040.pdf

Lawrence.
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Old 2nd Oct 2018, 10:55 am   #25
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Default Re: Help Identifying Capacitor

I'll keep the C45 capacitor.
This is the photo of the NTC if any one can help identifying it or help finding something to replace it.
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Old 2nd Oct 2018, 11:50 am   #26
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Default Re: Help Identifying Capacitor

Probably it is a CZ1A or perhaps a CZ2 , have a look at this data sheet:

http://www.electrojumble.org/data/st...s_gen_info.pdf
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Old 2nd Oct 2018, 4:08 pm   #27
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Default Re: Help Identifying Capacitor

Well i think i have most of the parts sorted out should have them in a couple of days, the only problem is really the NTC, from the looks of it that CZ1A seems very similar, any modern replacement?
Can for instance a fixed value resistor be connected just for testing purposes?
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Old 2nd Oct 2018, 11:54 pm   #28
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Default Re: Help Identifying Capacitor

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Originally Posted by mindvhsfi View Post
Well i think i have most of the parts sorted out should have them in a couple of days, the only problem is really the NTC, from the looks of it that CZ1A seems very similar, any modern replacement?
Can for instance a fixed value resistor be connected just for testing purposes?
As you could see from the data sheet the resistance starts very high over 3000 ohms and drops low at the running temperature. This eliminates the surge currents because when the valve heaters are cold they have a very low resistance, compared to the resistance when they are at red heat.

So the thermistor (NTC resistor) prevents the current peaking above the heater's operating current at turn on.

You therefore cannot put a plain resistor on place of it. One option though, could be to get something like a 1k or 2k Ohm maybe 5 or 10W rated wire wound potentiometer with a series 47 Ohm 5W resistor, set up on an insulated panel with insulated knob, have it at max resistance and slowly adjust it after turn on, to a low value (zero ohms) to just leave the 47R in circuit, until you can find a real thermistor to replace the dud one.... but if you turn the set off and on again later, don't forget to reset the pot to its max resistance initially.

The real reason the thermistor is needed relates to the internal resistance of the power supply supplying the heaters. The mains power has a very low internal resistance, and also in a series heater chain, the more physically massive heaters take longer to heat up, giving a very uneven voltage distribution unless the warm up process is slowed down. On the other hand, when heaters are in parallel, driven by a set's power transformer, the total load resistance at turn on, on the transformer's heater windings is very low, this transiently overloads the the transformer, crashing the starting voltage to an initial low value with cold heaters and all the heaters get a nice slow start and no thermistor is needed. Often this gets neglected when people decide to run a valve heater off a low internal Z DC supply, then they are greeted with a bright heater flash at turn on, just like in a series heater chain when the Brimistor is inadequate or not there.
Also the idea of using a capacitor as a series dropping device in a heater chain is to drop voltage in a Wattless manner and not have the heat of a larger value series resistor.

Last edited by Argus25; 3rd Oct 2018 at 12:16 am.
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Old 3rd Oct 2018, 2:40 pm   #29
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Default Re: Help Identifying Capacitor

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Originally Posted by mindvhsfi View Post
Well i think i have most of the parts sorted out should have them in a couple of days, the only problem is really the NTC, from the looks of it that CZ1A seems very similar, any modern replacement?
Can for instance a fixed value resistor be connected just for testing purposes?
I would fit a 250 ohm 5 watt resistor in place of the NTC thermistor to start with, then measure the heater voltage of the UF89 valve and adjust the value as needed for 12.6 volts AC.

Lawrence.
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Old 3rd Oct 2018, 3:38 pm   #30
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Default Re: Help Identifying Capacitor

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It won't vary that much with a 12.6 volt heater.
In practice, maybe not on this particular type but since the valve designation explicitly begins with a U, Philips is very clear on how this should be measured. Why deviate from that if it isn't necessary? The easiest way to measure current is to measure voltage across the series resistor and calculate the current. Not more difficult than measuring across a heater and probably easier to access.

Last edited by Maarten; 3rd Oct 2018 at 3:47 pm.
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Old 3rd Oct 2018, 3:53 pm   #31
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Default Re: Help Identifying Capacitor

Thanks for all the help and explanations.
I was able to find a CZ1 on sale so i will go with that and see how it goes.
Have to wait a couple of days for the parts but i will report back as soon as i get them.
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Old 3rd Oct 2018, 3:55 pm   #32
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Default Re: Help Identifying Capacitor

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In practice, maybe not on this particular type but since the valve designation explicitly begins with a U, Philips is very clear on how this should be measured. Why deviate from that if it isn't necessary?
I didn't say it wasn't necessary, I was just saying that a voltage measurement would probably suffice, I quoted measuring the UF89 heater voltage (12.6v) for that reason as opposed to the UCL82 (50v) or the whole heater chain (81.6v)

Lawrence.
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Old 5th Oct 2018, 1:39 pm   #33
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Default Re: Help Identifying Capacitor

I would agree with Lawrence (above) regarding the heater voltage measurement.
There is not much point in aiming for an "extremely precise" voltage, as one is unlikely to always get an "extremely precise" mains voltage going into the set.
Those dial lamps in the 'photo look like Christmas decoration lamps to me. The "fusable" types, that go short-circuit at the bead inside when the filament goes open-circuit. This would explain why they measured a near-short circuit on test. Tony.
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Old 6th Oct 2018, 11:04 pm   #34
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Default Re: Help Identifying Capacitor

It isn't about 'extremely precise voltage', but about making sure the current is somewhere around 100mA. I do agree that measuring across the lowest voltage heater will most of the times give a better indication than measuring across the entire string or another heater, but this is in no way guaranteed by the valve manufacturer.

I'll do some calculations just to get a feeling of the possible accuracy.

In any case, measuring the voltage across the series dropper and then calculating the current, is probably the easiest way in terms of accessibility so the discussion remains a bit theoretical.

Last edited by Maarten; 6th Oct 2018 at 11:23 pm.
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Old 6th Oct 2018, 11:38 pm   #35
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For the sake of simplicty I won't take into account any PTC characteristics of the heaters. I'll assume a 89V heater string on a 117V mains supply with a 280 ohms series resistor.

Assume the UF89 heater actually passes 100mA at 15.6V instead of 12.6. This would lead to the conclusion that there's 125mA passing through the heater chain.

Let's say you don't do any further calculations or measurements (because in this experiment the voltage accross the heater is a reliable way to determine the current) and increase the 280 ohms series resistor to 350 ohms.

The actual current through the heater chain is now 117/(350+890) = 94mA. Not too bad, only just outside the 5% tolerance for optimal operation.

Of course, mains voltage can vary by at least 6% both ways, the PTC effect will help a bit and who cares about spot on performance or optimised valve life in consumer electronics, maybe not even the original designer, so not really a problem. Question remains what is better, a solid repair (with less effort), or a "not really a problem"?

I forgot, let's see what the effect is on the nominal heater chain of the 3V surplus in factory original condition. This would give 117/(280+920)=97.5mA.

All in all, I think this was a nice excercise to get a feeling for the ballpark figures.

Last edited by Maarten; 6th Oct 2018 at 11:46 pm.
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Old 6th Oct 2018, 11:43 pm   #36
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Default Re: Help Identifying Capacitor

Using the dropper resistance as a current measuring shunt probably is the simplest method to measure the actual heater curent; but ideally you should measure its resistance with your multimeter immediately after switching off, so you get the actual resistance reading at its actual working temperature.
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Old 17th Dec 2018, 5:06 pm   #37
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Default Re: Help Identifying Capacitor

Hi,

Parts took a while to arrive.
So after putting all together the set works.
Took some measurements of the voltage across UF89 - 12.5v
I'm using a 270ohm 10w resistor instead of the 180ohm because of the mains voltage difference.
Now the temperature of the 270ohm resistor and of the UCL82 valve is very high is this normal?
Thanks

Last edited by mindvhsfi; 17th Dec 2018 at 5:12 pm.
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Old 19th Dec 2018, 4:01 pm   #38
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Hi again,

I have been doing some more measurements and would apreciate any input on this.

So measuring power draw at the Wall, when the set is turned on i got
16W witch rises to 28W in a few seconds and then 45W when the tubes start glowing and you can hear sound.
Current measured after the brimistor when the set is working is 100.8 mA (observed a brief maximum of 114 mA during the startup)
Voltages at the Heaters:
UCL82 - 50v
UF89 - 12,68v
UCH81 - 21
These tend to drift a bit up the more time the set is on.

Temperature of the mains resistor gets very hot >120ºC
Brimistor also gets very at 100ºC and UCL82 >120ºC.
This is like after 2 minutes of operation at with point i just shut it down.

Ins't the set drawing too much power?
Any insight is apreciated thx.

*Edited to make some spelling corrections.

Last edited by mindvhsfi; 19th Dec 2018 at 4:07 pm.
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Old 19th Dec 2018, 10:14 pm   #39
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Default Re: Help Identifying Capacitor

The UCL82 will get too hot to touch. It's an output valve and this is normal. Measure the voltage across the UCL82 cathode resistor and divide the measured voltage by the resistance and the answer will be in amps....for instance if the resistor is 150 ohms and the voltage measured is 6 volts, it's 6 / 150 = .04A (.04 amps = 40mA). Note that this is the TOTAL current drawn by the valve which includes anode and screen grid current. According to data for the UCL82, screen grid current is max 5.5mA and anode current is max 35mA so the total voltage across the cathode resistor should work out to a total current of no more than 40.5 mA. In practice you should measure a voltage equating to something in the region of 30 - 35mA.

The dropper resistor will get very hot....just make sure that it is capable of handling the power.
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Last edited by Sideband; 19th Dec 2018 at 10:27 pm.
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