26th Dec 2016, 12:49 pm | #61 |
Octode
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Re: My first valve radio project - Philips 462A
I know these are well covered service documentation-wise but if you need any relative measurements taking or need anything clarifying with photos please ask as I have one near my work bench.
Andrew
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26th Dec 2016, 1:28 pm | #62 | |
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Re: My first valve radio project - Philips 462A
Quote:
Regarding using a higher wattage bulb, is this because it will be able to draw a higher current through the system and therefore a higher voltage across the radio? |
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26th Dec 2016, 1:37 pm | #63 | |
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Re: My first valve radio project - Philips 462A
Quote:
I have already disconnected the C28. Will it matter in my tests that I have bypassed the volume pot and wired the mains straight to the transformer. Will I get any sound out the speakers like this. I'm hoping that with a good clean the on/off on the pot will start working again so I can rewire the mains though it. |
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26th Dec 2016, 1:38 pm | #64 | ||
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Re: My first valve radio project - Philips 462A
Quote:
A higher wattage bulb will have a lower filament resistance than a lower wattage bulb thus more current will flow through it, therefore in a lamp limiter set up lower wattage bulb = less current available to the receiver higher wattage bulb = more current available to the receiver. EDIT: Bypassing the on/off switch is ok for temporary work but don't forget it's been bypassed, this higher voltage stuff can bite hard even fatally so. Lawrence. |
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26th Dec 2016, 1:41 pm | #65 |
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Re: My first valve radio project - Philips 462A
As part of my tests I presume I could feed a signal into the pair of gramophone inputs (using Julie's homemade signal generator). This way I don't have to rely on the receiver part of the radio working to get an audio output from the speakers.
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26th Dec 2016, 1:45 pm | #66 |
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Re: My first valve radio project - Philips 462A
Yep.
Lawrence. |
26th Dec 2016, 1:56 pm | #67 |
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Re: My first valve radio project - Philips 462A
I have a double pole mains isolation switch close at hand to switch of power to the lamp limiter. I also have a single pole switch wired across the lamp so that full voltage can be applied to the radio under test when wanted.. This is all mounted on a board with a 13 amp socket for the radio to plug into.
Mike |
26th Dec 2016, 2:14 pm | #68 |
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Re: My first valve radio project - Philips 462A
42W sounds like a halogen to me. It's too high to be any sort of seriously energy saving type and I suspect it's sold as equivalent to a 60W GLS light level wise. It should be OK as it will likely have a lower cold resistance than a normal 40W since the filament will run quite a bit hotter at full output.
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26th Dec 2016, 2:51 pm | #69 |
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Re: My first valve radio project - Philips 462A
For newcomers/beginners, here's a good series of videos as an introduction to current flow, resistance etc:
https://www.youtube.com/watch?v=61bC56Gcjqs All done old style in a clear manner, worth watching them if in doubt, basics are crucial to progression, once learnt rarely forgotten, the videos run concurrently from the start, there are other excellent electricity/electronics training films on Utube as well, mostly designed to teach military students. Lawrence. |
27th Dec 2016, 1:54 am | #70 |
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Re: My first valve radio project - Philips 462A
Removed the lamp limiter to see if I could increase the current going into the set. The valves all light up more brightly. Still only about 2 V AC across the filament (pins 2 & 8) of the rectifer though. I can measure 4-5V AC across the screen bulbs (bulb filaments have detached so no illumination so need to find a couple more). No loud / crackles from the speaker when I move the wavelength selector. I even tried with a second external speaker connected and with signal input into the gram sockets and no signs of audio. I will start to carefully measure some voltages in the morning to see if I can spot anything out of spec...
What amount of voltage would I expect to see across the rectifier filament for this to working normally. A lot more than 2 VAC I suppose.... is this pointing to a problem with the transformer supplying AC to the rectifer? EDIT: I've just read the datasheet for the AZ31 rectifier and it says the filament Voltage is 4V so looks like I'm not too far off. I'll check voltages downstream of the rectifier next as look like the transformer is supplying voltage in the right range. Last edited by indigo.girl; 27th Dec 2016 at 2:22 am. |
27th Dec 2016, 8:14 am | #71 |
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Re: My first valve radio project - Philips 462A
Can you remove all the valves and turn on power to the transformer via your lamp limiter.
There should be next to no glow from the lamp. Then take out the lamp limiter and test the radio again with no valves and see if there is any sign of the mains transformer getting hot. Leave it for an hour, if it gets too hot to hold your hand on, or you hear bubbling or crackling from it turn off. If the transformer is getting very hot it indicates there may be shorted turns, which is a problem, and may require replacing it. If all seems OK after an hour, lets check some of the heater windings. First turn off and connect your meter positive to the positive (red) terminal of C26 (Trader) Connect the negative lead to the rectifier heater pins. (with no valve in) Measure the resistance on your lowest range, you should expect zero ohms on one pin and a little higher than zero on the other pin which will be the resistance of the rectifier heater winding of the transformer. Then connect the meter negative to a clean part of the chassis where there is no paint. Do the same measurements on each of the other valve base heater pins. The results should be similar to the last test. On one pin you will be measuring the resistance of the heater winding connections to chassis, and on the other pins you will be measuring the resistance of the heater winding for the rest of the valves in the radio. Let us know if you get any anomalous readings. Mike |
27th Dec 2016, 9:06 am | #72 |
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Re: My first valve radio project - Philips 462A
I would adjust the mains tapping to the setting which produces 4 volts on the AZ31 heater and 6.3 volts on the other heaters and go from there.
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27th Dec 2016, 9:09 am | #73 |
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Re: My first valve radio project - Philips 462A
I wouldn't, I would keep the transformer tapping to the correct setting for your mains voltage.
Mike |
27th Dec 2016, 9:35 am | #74 |
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Re: My first valve radio project - Philips 462A
For the mains voltage selector, 245 VAC should be the best setting.
If the receiver has been powered up without a lamp limiter and no smoke/signs of stress etc emerges then try taking a DC voltage measurement on the HT line between between chassis and C26 +ve (Trader sheet) without the lamp limiter. Lawrence. |
27th Dec 2016, 10:24 am | #75 | |||
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Re: My first valve radio project - Philips 462A
Quote:
Pin 8 to C26 = ZERO OHMS Quote:
Pin1 (heater) to Chassis = ZERO OHMS Pin8 (heater) to Chassis = ZERO OHMS Pin7 (cathode) to Chassis = ZERO OHMS All other pins to chassis = INFINITE OHMS ECH21: Pin1 (heater) to Chassis = ZERO OHMS Pin8 (heater) to Chassis = ZERO OHMS (same with both valves) Quote:
The set is now on (minus all valves) and will leave for a while to see if Transform heats up as suggested. Prior to these tests I also tested the voltage across the heaters of the output valve (EBL21) - with set on / lamp limiter removed. I could measure 5V AC across the heater pins. The specs say 6.3V for this valve so only slightly below whats expected. However, I find zero voltage across each anode to chassis (i.e. pin 2 to ground, pin 5 to ground, pin 6 to ground). So should I take it from this result that the EBL21 valve is not generating a current flow from cathode to anode even though the heater is heating up the cathode? |
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27th Dec 2016, 10:40 am | #76 |
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Re: My first valve radio project - Philips 462A
"Prior to these tests I also tested the voltage across the heaters of the output valve (EBL21) - with set on / lamp limiter removed. I could measure 5V AC across the heater pins. The specs say 6.3V for this valve so only slightly below whats expected. However, I find zero voltage across each anode to chassis (i.e. pin 2 to ground, pin 5 to ground, pin 6 to ground). So should I take it from this result that the EBL21 valve is not generating a current flow from cathode to anode even though the heater is heating up the cathode?"
We wouldn't expect any significant voltage on pins 5&6, they are the anodes of the detector and the AVC/AGC circuit, pin 2 however is the anode of the pentode, the pentode is the audio output section of that valve, under normal operating conditions that anode (pin2) would show a DC voltage reading of approx. 245 volts with respect to chassis, the fact that it's missing shows that something's amiss, measuring the DC voltage across C26 (Trader) would confirm if any HT voltage is being produced the rectifier valve, without a reasonable amount of HT voltage nothing will work. EDIT: The voltage for the pentodes anode is supplied from the rectifiers cathode (heater) via winding c/d (Trader) of the audio output transformers primary. Lawrence. Last edited by ms660; 27th Dec 2016 at 10:55 am. |
27th Dec 2016, 10:50 am | #77 |
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Re: My first valve radio project - Philips 462A
Yes, good result for those tests. With a more sensitive meter it may have been possible to read the resistance of the 2 separate heater windings, but as it is so very low it is difficult to destinguish from zero.
The HT windings are different, if you measure the resistance of those you will get a "DC resistance" reading on in the region of maybe 30 to 100 ohms. This may seem very low, but to the AC mains the windings will present a much higher resistance, or more correctly Impedance. Mike |
27th Dec 2016, 11:08 am | #78 | |
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Re: My first valve radio project - Philips 462A
Quote:
Before reading your post I also checked out the T1 output transformer that feeds the loudspeaker. No voltage across the secondary windings e and f and therefore nothing across the speakers to give an audio output. I also injected a signal into the 'gram in' but nothing generated across T1. So, looks like the fault is AZ31. Julie mentioned a work around if the rectifer is shot so I could be able to continue testing while sourcing a replacement. Can I put a HT output across the EBL21 valve without the need for the AZ31 rectifer? |
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27th Dec 2016, 11:14 am | #79 |
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Re: My first valve radio project - Philips 462A
Is the transformer hot or cool after an hour of being on with no valve heater load?
Mike |
27th Dec 2016, 11:17 am | #80 | |
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Re: My first valve radio project - Philips 462A
Quote:
If not then remove the rectifier and check the valves heater continuity (ohms test) between pins 2&8 of the valve, the resistance reading should be very low if the valve's ok, if it's infinity then the valve's heaters are shot. If the rectifier valve's heater check out ok for continuity the next thing to confirm is the AC voltage supplied to pins 2&8 of the rectifiers valve socket, should be approx. 4 volts AC if all's well (no lamp limiter) The next move would depend on the above findings. Lawrence. Last edited by ms660; 27th Dec 2016 at 11:27 am. |
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