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Old 9th Aug 2020, 1:34 pm   #1
Gabe001
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Question Raymond Electric F17 voltage drop help please

Good afternoon

I was wondering if I could get some advice regarding the most likely culprit for the fault I'm experiencing

I am currently working on a Raymond electric f17 which was destroyed in transit! Luckily the chassis seems unharmed

I started working on it this weekend and the problem is this. With v4 in place the voltage at the positive end of BOTH smoothing caps relative to case is about 90-120v. Current draw at v4 anode 16mA calculated using the voltage drop at L15. Cathode voltage around 3v.

Without v4, the voltage is steady at 210v.

Resistances of r18,17,16 and L15 fine

L18 measured by placing meter probes on positive ends of c22 and c23 reads grossly out of spec at 3k (should be 350)

Caps c17-23 are new. In fact I've replaced all wax caps except one.

With v4 in situ, when I switch the radio on, the voltage tends to rise rapidly to >200v, then drops to 80 then increases very slowly up to a max of around 120

Relevant section of circuit diagram attached for reference (I hope I'm not breaking any rules). Need to add that the rectifier is not the original u50 and the markings have gone so I can't identify it (see attached)

I'd like to ask where the problem is likely to lie? Is it down to L18 resistance being high (but surely then c23 would measure 280v regardless) or does the problem lie with the rectifier which cannot cope with the load, or even with v4 or with the transformer?

I'm afraid I don't have spare valves to try out instead

Thanks in advance,
Gabriel
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Old 9th Aug 2020, 2:47 pm   #2
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Default Re: Raymond electric f17 voltage drop help please

The rectifier certainly sounds tired from that description. Possibly the EL33, too- its normal anode current would be around 35mA with 250V dc supply.


What is the ac voltage from the TX HT secondary? The datasheet is somewhat lacking in any voltage or current indications.


Is the output TX primary OK? Could explain low EL33 current though not the low HT.
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Old 9th Aug 2020, 3:29 pm   #3
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Default Re: Raymond Electric F17 voltage drop help please

Sounds like a tired rectifier ? However , best to measure the ac volts to chassis for each rectifier anode. The dc resistance of the smoothing choke as you point out is incorrect (recheck?) but then you should still get full HT on the reservoir.
You could Recheck HT current by measuring the voltage across the smoothing choke but likely to be low if your resistance reading is correct.

Chances are the EL33 maybe OK

Andy
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Old 9th Aug 2020, 5:52 pm   #4
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Default Re: Raymond Electric F17 voltage drop help please

Thanks Chris and Andy. The AC voltage from transformer ht secondary measured on the rectifier pins is 240-245v AC. They are somewhat difficult to get to so may be a slight underestimate.

Service sheet says 255v AC, so not too bad.

It does look like I need to look for a new rectifier.

Voltage drop across smoothing choke is 11v, but that's with the voltages being about half what they should be. Trader sheet says the drop should be around 20v, so that may not be too far off either. I think I need to disconnect the wires to the capacitors to get a true reading of the smoothing choke resistance, but that may not be necessary if the voltages tally once I replace the rectifier.

Output transformer primary is fine.

Thanks for your help,
Gabriel
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Old 9th Aug 2020, 6:34 pm   #5
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Default Re: Raymond Electric F17 voltage drop help please

On further testing, ive taken the recifier out and it seems I'm only getting 1-2v AC on the filament pins which doesn't look good at all. Would that explain why the rectifier is struggling?
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Old 9th Aug 2020, 6:49 pm   #6
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Default Re: Raymond Electric F17 voltage drop help please

Yes.Should be 5 Volt heaters.Is it lit normally or a bit dim I wonder?
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Old 9th Aug 2020, 7:06 pm   #7
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Default Re: Raymond Electric F17 voltage drop help please

I can't see it, the valve is fully metallized. Is it repairable?

There is good continuity across the transformer heater circuit with only about 1-2 ohms resistance (in keeping with the service sheet) although on closer inspection there seems to be some old melted wax on the bottom of the transformer so I wonder if something happened to it in the past.
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Old 9th Aug 2020, 8:17 pm   #8
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Default Re: Raymond Electric F17 voltage drop help please

Dripping wax is some times not a good sign,could mean shorted turns.The valve is not repairable unless the pins need re soldering.Sounds as if it could be transformer shorted turns,if only a low voltage coming out and the rest are ok.
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Old 9th Aug 2020, 8:32 pm   #9
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Default Re: Raymond Electric F17 voltage drop help please

Hi, I meant is the transformer repairable, not the valve. I reread the post and my wording was misleading, so apologies.
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Old 9th Aug 2020, 8:56 pm   #10
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Default Re: Raymond Electric F17 voltage drop help please

Hi Gabriel, it's rare for a transformer heater winding to fail in this way. There was a case on the Forum a few months back with a Quad II amplifier where there was a bad joint between the rectifier heater enamelled wires coming out of the winding and the transformer terminal posts. Not sure if your transformer has terminals but, even if the wires are coming straight out of the bobbin, it is worth checking the solder joints at the valve pins.Make absolutely sure that your meter is measuring correctly on the low voltage AC range by checking the 6.3v supply to the other valves. As a last resort, you might be able to get away with using silicon diiodes in lieu of the rectifier. Cheers, Jerry
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Old 9th Aug 2020, 10:00 pm   #11
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Default Re: Raymond Electric F17 voltage drop help please

posts #5 and #7 confuse me as you refer to the U50 rectifier as being fully metalized. The U50 is a glass rectifier with very visible tape heaters from the top !?, normally.
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Old 9th Aug 2020, 10:16 pm   #12
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Default Re: Raymond Electric F17 voltage drop help please

Agreed, the red made in USA 'tube' is not a U50 and unfortunately the type number seems to be illegible. It might be a 5Z4?
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Old 9th Aug 2020, 10:34 pm   #13
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Default Re: Raymond Electric F17 voltage drop help please

From post #1 -

Quote:
Need to add that the rectifier is not the original u50 and the markings have gone so I can't identify it (see attached)
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Old 9th Aug 2020, 10:55 pm   #14
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Default Re: Raymond Electric F17 voltage drop help please

I'll recheck the readings on the rectifier heater tomorrow and report back. I'm convinced the problem is with either the transformer supply to rectifier heater or the rectifier itself.

As previously mentioned the rectifier valve is not the original u50 which is why I posted a picture of it.

Gabriel
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Old 10th Aug 2020, 6:27 pm   #15
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Default Re: Raymond Electric F17 voltage drop help please

Good news. I've recheck the voltage across the rectifier heater and it's spot on 5v so it's just a tired rectifier. Phew!
I'll ask around for a replacement. Hopefully the radio won't throw any further nasty surprises and she'll sing again.

Thanks for the tips. Apologies for the confusion caused by the inaccurate voltage reading yesterday

Gabriel

Last edited by Gabe001; 10th Aug 2020 at 6:53 pm.
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Old 10th Aug 2020, 7:03 pm   #16
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Default Re: Raymond Electric F17 voltage drop help please

you could always use some diodes and a resistor in the mean time whilst tracking down a sensibly priced rectifier. You can progress with any other work needed.
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Old 10th Aug 2020, 7:50 pm   #17
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Default Re: Raymond Electric F17 voltage drop help please

Quote:
Originally Posted by Freya View Post
you could always use some diodes and a resistor in the mean time whilst tracking down a sensibly priced rectifier. You can progress with any other work needed.
Funny you say that, I was researching this earlier in case tranny was faulty, and ran some simulations on an online site. I was after 280v RMS at smoothing choke, which is after the first smoothing cap. Ignore the 1n4007 diode designation I hadn't decided on the most suitable yet

I was dreading having to go down this route to be honest

Gabriel
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Old 12th Aug 2020, 7:12 pm   #18
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Default Re: Raymond Electric F17 voltage drop help please

Your 'red' 5Z4 appears to be an AMERTY Mullard/ American metal version date coded 1948. They are very good valves and rarely fail.

I have managed to dig out a RCA version which yours probably is. I've checked it both on my AVO Mk3 and my home constructed amp and it checks out 100%

If you would like it FOC please let me have your details and I will post ASAP.

Regards, John.
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Old 12th Aug 2020, 8:28 pm   #19
Gabe001
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Default Re: Raymond Electric F17 voltage drop help please

Yes John thats it, spot on.
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Old 14th Aug 2020, 8:48 pm   #20
Gabe001
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Smile Re: Raymond Electric F17 voltage drop help please

Just an quick final update. I received the u50 rectifier from Richard (Dickie) today and it works great. A steady 260v and good voltages on the valve pins.

I'm posting some before pictures of how I received this after parcelforce got their boots in it. Case was hard work and has been reglued, reinforced with milliput and fibreglass resin and sprayed in Brazil brown. It's not perfect but it's more than acceptable.

Video of it playing some royalty free music via pickup (Bluetooth) here:
https://youtu.be/97goDunKSBM

Thanks for your spot on diagnosis and help.

Admin can close this thread.

Gabriel
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