I dont have another rectifier. But I was bidding for one on ebay which will end in few days.
I have some silicon rectifying diodes piv 1600. About 650mA each rated. But I dont know how to use them in tube set. Never done it before.
By the way, the set is the amateur radio transmitter Heathkit DX40-U.
I will get the current readings on the heater later.
I have some silicon rectifying diodes piv 1600. About 650mA each rated. But I dont know how to use them in tube set. Never done it before.
By the way, the set is the amateur radio transmitter Heathkit DX40-U.
I will get the current readings on the heater later.
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Use those two diodes wiring each anodes to the HV transformer ends, solder the cathodes together and trough a 100-150Ω power resistor to the filter cap and try. If voltage is too high, increase the resistor. Having the set working OK, then remove the diodes and wait for the rectifier.
If the valve has still got the silvery dark internal coating, as in my photo I posted and it is not white, it is not gassy.
My guess is a damaged valve base.
My guess is a damaged valve base.
I agree. My suspicion is that one or both of the heater's ends are cut near the base because of thermal fatigue of the wires. The noise from the base augments my suspicion.
As it is beyond the range of your DMM, the measurement is inaccurate. It should be much higher: 710V per phase.
The center tap on the power transformer is 0, end to end (anode to anode on the 5U4) should be 710+710 = 1420 Vac.
This device has some serious voltages.
Read this file and be careful.
This 5U4G has silver band at the bottom of the glass starting from the plastic base. It is shinny silvery band without any transparent gaps.
The silvery band is about 40% of the tube glass.
If your point is correct, then this 5U4G is definitely damaged one then.
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Later I spotted one of the pin from the smoothing cap was touching the chassis, and it is separated.
When the anode reading was made again on the 5U4G after that, the voltage went up to 1350 ACV.
But my vintage Fluke 25 can read only up to 1000V. How it went up that voltage was a bit of shock.
I have a few DMMs, but none of them can read more than 600 - 750 ACV.
The vintage Fluke 25 was rated highest ACV reading at 1000V.
Forget about how much AC voltage is reaching the valve.
Are the heaters lit?
If they are not and you have continuity across the heater pins, the valve base is not connecting to the valve properly.
If the valve has white inside on the glass it is gassy, if not it is not gassy.
Are the heaters lit?
If they are not and you have continuity across the heater pins, the valve base is not connecting to the valve properly.
If the valve has white inside on the glass it is gassy, if not it is not gassy.
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There is no white on the glass, but silver band on the glass bottom where it connects to the plastic base.
Above the silver band, the glass is totally clear everywhere.
Couldn't see the heaters lit at all.
The pins only 2 and 8 has continuity. No other pins has continuity all round.
Is a tube checking / valve checking device any useful? Saw a few for sale on eBay, but was very expensive.
Couldn't tell if they are worth the money.
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On other rectifying circuits in PSU, they seem used 4 rectifying diodes.
Each cathodes of 2 diodes are fed from the transformer HV, the diodes 2 anodes connected to the chassis, and then 2 more diodes connects to the end of the cathodes, and the 2nd pair of diodes get connected together then to the smoothing caps.
Is it the same way as the your option with the resistors instead of the 2nd pair of the diodes?
Ummm budkor
First the orange / yellow 'light' in the 5U4 (and the other valves) is from the filament or heater deep inside the valve. The filament or heater is supplied from a low voltage 5 volts AC for the 5U4. (Other valves use typically 6.3 or 4 volts etc.) The high voltages (710 volts AC) do not make the light inside the valve.
You measure 5 volts between pins 2 and 8 at the valve socket and have continuity between 2 and 8 on the valve pins, it should 'light'.
If it does not, the next check is to measure the voltage from pins 2 and 8 at the socket with the valve inserted.
If it is still 5 volts there is something wrong with the valve. Or it is not inserted correctly.
If the voltage drops well bellow 5 volts, you likely have a poor connection in the wiring or transformer.
Second, the rectifier in your set is a 'Bi-phase' rectifier. It uses two diodes (the 5U4) and 2 windings on a transformer (710-0-710). The Transformer has a 'centre tap' marked 0 on the diagram. Which is the negative connection for the rectifier so connected to the radio ground or negative line too.
The circuit you mention above is a 'Bridge rectifier' four diodes, but only one winding on the transformer. The negative connection is now the junction of the two anodes NOT the transformer.
You can measure the 710 volt AC windings with your 1000 volt AC meter, if you put one probe on the centre tap / chassis and the other probe to pins 4 and 6 in turn...
PS:- a bit late in the day but you are counting the valve pins from the under/component side not the top of the chassis?
First the orange / yellow 'light' in the 5U4 (and the other valves) is from the filament or heater deep inside the valve. The filament or heater is supplied from a low voltage 5 volts AC for the 5U4. (Other valves use typically 6.3 or 4 volts etc.) The high voltages (710 volts AC) do not make the light inside the valve.
You measure 5 volts between pins 2 and 8 at the valve socket and have continuity between 2 and 8 on the valve pins, it should 'light'.
If it does not, the next check is to measure the voltage from pins 2 and 8 at the socket with the valve inserted.
If it is still 5 volts there is something wrong with the valve. Or it is not inserted correctly.
If the voltage drops well bellow 5 volts, you likely have a poor connection in the wiring or transformer.
Second, the rectifier in your set is a 'Bi-phase' rectifier. It uses two diodes (the 5U4) and 2 windings on a transformer (710-0-710). The Transformer has a 'centre tap' marked 0 on the diagram. Which is the negative connection for the rectifier so connected to the radio ground or negative line too.
The circuit you mention above is a 'Bridge rectifier' four diodes, but only one winding on the transformer. The negative connection is now the junction of the two anodes NOT the transformer.
You can measure the 710 volt AC windings with your 1000 volt AC meter, if you put one probe on the centre tap / chassis and the other probe to pins 4 and 6 in turn...
PS:- a bit late in the day but you are counting the valve pins from the under/component side not the top of the chassis?
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Great explanation, thank you Alan.
Yes, I was counting the pins OK as per your diagram. The 5U4G has come on, and lit up, but it was sparking with blue flames in the glass.
It did that a few times, and now thee is no continuity between pin 2 and 8.
No power is coming out to the SC.
So I think it is now totally damaged. It was in its last legs of operation, I think, but the couple of bad arching may have killed the continuity.
Thanks for explanation on the diode rectifying. I was unaware of the difference between 4 phase rectifier and 5U4G rectifying system.
People were saying the 5U4G is under rated for the set, and must get it replaced with 5U4GB.
Yes, I was counting the pins OK as per your diagram. The 5U4G has come on, and lit up, but it was sparking with blue flames in the glass.
It did that a few times, and now thee is no continuity between pin 2 and 8.
No power is coming out to the SC.
So I think it is now totally damaged. It was in its last legs of operation, I think, but the couple of bad arching may have killed the continuity.
Thanks for explanation on the diode rectifying. I was unaware of the difference between 4 phase rectifier and 5U4G rectifying system.
People were saying the 5U4G is under rated for the set, and must get it replaced with 5U4GB.