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Old 31st Jul 2020, 5:51 pm   #61
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Default Re: Ferguson 621 U woes.

I have still got the pins bridged etc from the previous test that i have done ie valve is out.
R34 is out of circuit and have measured across grid 1 and the cathode sockets and I cannot get a stable reading at all, the meter is jumping from pos to neg milivolts??

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Old 31st Jul 2020, 6:05 pm   #62
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Default Re: Ferguson 621 U woes.

You don’t need a voltage or those links fitted.
Without the power applied check the resistance between the cathode and G1 on the socket, no valve installed. Use the highest resistance range on your meter, it should read open circuit.
If that is O/C then the valve is definitely the cause, the UL84 is more than likely faulty but we are trying to rule out all other causes.
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Old 31st Jul 2020, 6:18 pm   #63
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Default Re: Ferguson 621 U woes.

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Originally Posted by Nuvistor View Post
You don’t need a voltage or those links fitted.
Without the power applied check the resistance between the cathode and G1 on the socket, no valve installed. Use the highest resistance range on your meter, it should read open circuit.
If that is O/C then the valve is definitely the cause, the UL84 is more than likely faulty but we are trying to rule out all other causes.

No resistance between the pins whatsoever Frank.

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Old 31st Jul 2020, 7:37 pm   #64
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Default Re: Ferguson 621 U woes.

Well it’s what was expected but worth checking, see how the new UL84 performs.
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Old 31st Jul 2020, 8:41 pm   #65
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Default Re: Ferguson 621 U woes.

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Originally Posted by Nuvistor View Post
Well it’s what was expected but worth checking, see how the new UL84 performs.
Will let you know how things go when it arrives


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Old 1st Aug 2020, 1:38 pm   #66
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Default Re: Ferguson 621 U woes.

My valves have arrived today courtesy of Norman Raeburn (cheers Norman) and replacing the ul84 has made a massive difference. The hum is now very faint and the HT on filter resistor r37 is almost whats on the sheet.
The rustling is still there though and I still have a bit of pos voltage on grid1 96mv. I think the next thing I will do is get the board as clean as I can (can you clean a pcb safely with soap and water?) and go from there.

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Old 1st Aug 2020, 11:01 pm   #67
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Default Re: Ferguson 621 U woes.

96mv is ok as long as it doesn’t rise out of control. Never cleaned a PCB with soap and water but I thought Paxolin was absorbent and water may not be good for it.
Others have probably a better idea than me on what to use.
You are fixing the faults, well done.
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Old 1st Aug 2020, 11:20 pm   #68
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Default Re: Ferguson 621 U woes.

Quote:
Originally Posted by poppydog View Post
My valves have arrived today courtesy of Norman Raeburn (cheers Norman) and replacing the ul84 has made a massive difference. The hum is now very faint and the HT on filter resistor r37 is almost whats on the sheet.
The rustling is still there though and I still have a bit of pos voltage on grid1 96mv. I think the next thing I will do is get the board as clean as I can (can you clean a pcb safely with soap and water?) and go from there.

POPPYDOG
Can't remember whether you've replaced C54. Worth doing if you haven't. Also any capacitor (I can't see far enough to left from the schematic snip you posted earlier) between anode of preceding valve and bottom of R33.

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Old 2nd Aug 2020, 3:03 pm   #69
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Default Re: Ferguson 621 U woes.

Well that's something I wouldn't recommend, cleaning a pcb with fairy and warm water.
I tried making sure that it didn't go where it shouldn't but now I have lost lw/mw (it was very distant anyway) and have introduced a very nasty crackle that can be varied with the volume control. 2 steps forward and 10 back.

The black cloud is still over me

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Old 2nd Aug 2020, 6:42 pm   #70
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Default Re: Ferguson 621 U woes.

Leave the radio in a warm place to completely dry out, may take a few days.
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Old 2nd Aug 2020, 7:08 pm   #71
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Default Re: Ferguson 621 U woes.

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Originally Posted by poppydog View Post
Well that's something I wouldn't recommend, cleaning a pcb with fairy and warm water.
I tried making sure that it didn't go where it shouldn't but now I have lost lw/mw (it was very distant anyway) and have introduced a very nasty crackle that can be varied with the volume control. 2 steps forward and 10 back.

The black cloud is still over me

poppydog
I've had that problem even cleaning switchbanks using proper contact cleaner. Given a bit of time to dry out, everything went back to normal working. Maybe put the PCB alone somewhere warm to dry. It's a good excuse for doing something else for a while - like just nothing!

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Old 7th Aug 2020, 6:27 pm   #72
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Default Re: Ferguson 621 U woes.

The board has dried right out now and the scratching sound has gone, the rustling sound in the speaker still remains though.
Mw/lw are very faint, if I grasp the aerial coils on the ferrite with my fingers the stations can be heard very well.
I have cleaned the wave change switch outer wafer as the contacts were oxidised but I cannot get in there to physically clean the inner wafer and its contacts as there is no room, spraying with servisol does nothing.
There is quite a bit of unsoldering to do to remove it to clean it which I don't really want to do but I may end up having no choice, anybody have any other ideas?

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Old 7th Aug 2020, 7:13 pm   #73
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Default Re: Ferguson 621 U woes.

Orientate the receiver for max signal then touch the antenna coils with your fingers, an increase in signal strength would normally indicate that the tracking is out of alignment.

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Old 7th Aug 2020, 7:42 pm   #74
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Default Re: Ferguson 621 U woes.

Glad there is no major damage with the board cleaning. The Servisol will clean the contact area on the switch, the areas that are not in contact with the wiper blade don’t matter. Working the switch with the servisol applied and no power should normally work.
Leave for the servisol to evaporate before switching on.

I would follow Lawrence’s excellent suggestions for the weak signal.
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Old 8th Aug 2020, 8:34 am   #75
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Default Re: Ferguson 621 U woes.

Not sure if this has been covered already....the rustling sound....is it there at minimum volume? If so there are two possibilities. The original output valve has been proven to be faulty with excessive leakage. This may well have damaged the output transformer. I've had this several times on sets that have been run with a faulty output valve for long periods. Check the resistance across the primary of the output transformer...I would expect to see somewhere between 300 and 600 ohms. Most importantly it should be a stable reading.

Virtually any output transformer from a mains valve radio could be used for a quick test. If the crackle stops then we need to think about finding you an output transformer.

The other possibility is leakage across the PCB (if the crackle remains). Personally I'd check the transformer first.
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Old 8th Aug 2020, 8:58 pm   #76
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Default Re: Ferguson 621 U woes.

With regards to the questions asked in post 68 and 75. C54 (grid coupling) has been replaced as stated in post 1 and the rustling/whispering is there regardless of the volume also as stated in post 1.

Resistance across the primary of the output transformer is 375r and is stable. If I poke and prod R35 and R36 I can get the rustling to stop and start, I have remade the solder joints but I can still make it happen by poking and prodding, R35 looks like its had a hard life R37 next to it gets very hot. Is it possible there is an internal fault in either of these resistors?

Switched on this evening and there is nothing at all on lw/mw unless I touch the coils on the ferrite, so its worse than when I last switched on??, nothing on the tuning side of things has been touched by me.
Can someone elaborate on what is meant by “tracking”? Is it another word for alignment?

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Old 8th Aug 2020, 9:19 pm   #77
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Default Re: Ferguson 621 U woes.

Tracking as used in this thread has two entirely different meanings.

1. Tracking occurs when an insulating material becomes conductive, possibly because it's been contaminated with liquid or it's burned turning it into carbon which is conductive. Very common in car distributor caps, but we won't discuss that here!

2. When it comes to alignment, tracking refers to maintaining a constant difference between the frequency the aerial coils are tuned to by one section of the tuning capacitor and the frequency the local oscillator is tuned to by the other section of the tuning capacitor. The constant difference is of course the Intermediate Frequency or IF. If the set has an RF amplifier stage the tuning capacitor will have three sections all of which will have to track together.

Ensuring optimum tracking is part of the alignment procedure. In practice the tracking is only adjusted at two points, one at the low frequency of the band and the other at the high frequency of the band. Tracking is optimised by adjusting trimmer capacitors, padding capacitors, iron or ferrite cores, by moving coils along a ferrite rod, or even bending the plates of the tuning capacitor. That's why the vanes have radial slots in them.
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Old 8th Aug 2020, 9:41 pm   #78
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Default Re: Ferguson 621 U woes.

Thanks for the explanation. I think for now I'm going to concentrate on this wavechange switch as this problem is coming and going. Once I can make sure its clean and working properly then I will start to look into whats been previously suggested.

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Old 11th Aug 2020, 7:50 pm   #79
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Default Re: Ferguson 621 U woes.

The question I asked regarding the UL84 cathode and anode resistors r35 and r36, I seem to have answered it myself. Replacing them seems to have stopped the rustling, I’m not holding my breath though.
I have managed to clean the inner wafer switch contacts and the wavechange switch now works as it should, MW is still silent unless the aerial coil on the ferrite is touched and LW is faint but comes in when coils are touched.

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Old 13th Aug 2020, 7:18 pm   #80
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Default Re: Ferguson 621 U woes.

The rustling has not come back so I think that’s all sorted now , c34 (black hunts) has been replaced as the casing was cracked and when tested it was miles out of spec anyway.
I’m so glad I decided to do some voltage checks around the UCH81 before I started turning trimmers and moving aerial coils etc, although I did try c19 which made a little difference. Voltages that I took were not the same as those stated on the sheet and after some resistance checks I found that resistors r13 and r15 had gone high so replacements were put in making the voltages something like it.
I thought I would check all resistors in that area as there probably was more out of spec and that’s when I spotted r23 wasn’t soldered properly, you could push the lead back through the board. Looking at the sheet I saw where it went and got very excited, I knew that was it so I checked it was still in spec and resoldered it properly. Its much better now with regards to volume of the station but the stations could still do with bringing in a bit more, on lw/mw its picking up a hum and its echo-ee (microphonic?), not sure what I can do about that.
There is a replacement cossor uch81 valve in this, so I wonder if someone tried a replacement to try to sort this problem so they might also have touched those IF transformers, the aerial coils don’t appear to be touched.



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