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Old 19th Apr 2019, 3:31 pm   #121
Boater Sam
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Default Re: Ferguson 382U Firefly not playing ball

Voltages on the valve please.
Explain please, the signal sounds OK on the grid of the UL84 but after the valve it is distorted - is this correct?
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Old 19th Apr 2019, 3:48 pm   #122
el gringo
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Default Re: Ferguson 382U Firefly not playing ball

Hi Sam,

That wasn't terribly clear, apologies!

If I use the Ferguson's detected and preamp'd signal present on the UL84 grid ( i.e. just before it gets amplified for the speaker ), it is loud and clear fed to my mp3 mini speaker.

If I use say, an iPod as an Audio signal feed to the external "gram" input, or (decoupled) to the UL84's grid, the resulting audio coming through the Ferguson's speaker is quiet and very distorted.

UL84 voltages:

1 = (n/c) 0V
2 = 0V
3 = +27V
4 - 5 = 38V
6 = (n/c) +196V
7 = +220V
8 = (n/c) +218V
9 = +193V

Ta,

Pete
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Old 19th Apr 2019, 4:04 pm   #123
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Default Re: Ferguson 382U Firefly not playing ball

Pin 3 is the cathode with 27V and that is across R28 (150 ohms) and corresponds to a current of 180mA! As that is not a realistic current, check the voltage on pin 3 again and try measuring the resistance of R28.
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Old 19th Apr 2019, 4:19 pm   #124
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Default Re: Ferguson 382U Firefly not playing ball

Measure the resistance between the cathode pin and chassis, should be approx. 270 ohms.

Lawrence.
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Old 19th Apr 2019, 4:41 pm   #125
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Default Re: Ferguson 382U Firefly not playing ball

Good work chaps! That 270 ohm Cathode resistor was open circuit!! Replaced and we now have clear sound! Vk = 7.3V

Also, feeding the iPod (decoupled) too the UL84 grid gives me loud and clear audio!

Getting there....
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Old 19th Apr 2019, 5:06 pm   #126
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Default Re: Ferguson 382U Firefly not playing ball

The cathode voltage still isn't right, measure the UL84's voltages again and also measure the DC voltage across the primary of the audio output transformer.

Lawrence.

Last edited by ms660; 19th Apr 2019 at 5:16 pm. Reason: addition
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Old 19th Apr 2019, 5:29 pm   #127
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Default Re: Ferguson 382U Firefly not playing ball

If there is an electrolytic across that 270 ohm resistor (cathode bypass), it's worth checking it since an O/C cathode resistor will make the cathode of the valve rise towards HT. As you were measuring 27V on the cathode with an O/C resistor, the capacitor (if fitted) may have been damaged and could now be acting as a low value resistor thus bringing the cathode voltage down. Most UL84's run with a cathode voltage of somewhere between 9 and 12 volts. What does the circuit voltage say?
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Old 21st Apr 2019, 10:22 am   #128
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Default Re: Ferguson 382U Firefly not playing ball

Thanks to everyone on here, I'm getting close to finishing this restoration off now! FM is working ( even with the internal dipole - although I made an external one yesterday - which is louder ).

MW although of course "muddy' by comparison to FM, is coming out clear, my main concern now, is this symptom of FM stations being "squelchy" ? ( can't remember the proper term ) Like, I need to be slightly off centre tuning to get a clearer tone - although still got a clipped overdriven sound to my ears. This happens with both the internal and the external FM aerial.

Anyone have any suggestions?

Pete
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Old 21st Apr 2019, 11:58 am   #129
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Default Re: Ferguson 382U Firefly not playing ball

Did you replace the discriminator capacitor? Usually about 4uF, 25V to 50V and POSITIVE to chassis/OV!

If not, then the discriminator coil may have been tweaked. Easy to sort with a wobbulator, otherwise use 10.7 MHz signal generator. Normally carrier off, but later you can turn on AM to see rejection.
The centre of the 10.7MHz needs to be at the middle of the slope of one side of the discriminator coil, not at the peak. If that's been peaked at 10.7MHz, then you have to tune off centre on the IF and creates distortion.

Great you've made good progress.
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Old 21st Apr 2019, 2:39 pm   #130
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Default Re: Ferguson 382U Firefly not playing ball

Hi Mike, thanks for the tip, will investigate now..

Pete
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Old 21st Apr 2019, 3:05 pm   #131
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Default Re: Ferguson 382U Firefly not playing ball

Well, the good news is that I had indeed replaced it, however I had it reversed polarity (DOH!) and now it's connected the right way around, we've got better sensitivity and, the quieter stations are reasonably clean sounding ish? The strongest signals are still crunching though..?

I've not unfortunately got any RF sig gen stuff and def not got a wobbulator! Anything else I can sniff around to test stuff?

Ta, Pete
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Old 21st Apr 2019, 3:17 pm   #132
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Default Re: Ferguson 382U Firefly not playing ball

You can get away with no sig gen for MW alignment using broadcast stations. However you can't do a very good job on FM without at least a signal generator. Some discriminator circuits can be tricky to balance even with the correct gear but without it.....! A lot of twiddling MAY get it acceptable but it will never be right. It does sound as if the discriminator is a bit off but I've never tried to balance one without a sig genny.
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Old 24th Apr 2019, 3:09 pm   #133
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Default Re: Ferguson 382U Firefly not playing ball

Been reading up and trying to understand a little about FM discriminators and ratio detectors and found an article which certainly looked interesting, given the specific issue I'm seeing. The "loudest" stations are the most crunched/distorted and this comment I thought was interesting:


"...In some cases, significant distortion will be heard on some stations, particularly the local commercial programmes, even though the set is correctly aligned. The reason for this is that these transmissions use a greater amount of modulation than the earlier transmissions. The increased use of audio compression also means that the sound is louder and the modulation reaches the limits much more often. The problem will not occur on the BBC stations, apart from possibly BBC Radio 1, because they use higher quality transmitters and less compression, and care more about the transmission quality. This fact allows you to establish that you do indeed have this problem by checking the reception on BBC Radio 2.

If you want to use the set to receive the programmes that give this problem, it is necessary to widen and flatten the response of the IF stages. This can be achieved by connecting a resistor in parallel with the primaries of the VHF IF transformers. You may need to experiment with the resistor values, but generally 18K across the final IF primary and 27K across the others is a good starting point. Note that the lowering the resistor value will flatten the IF response but the gain will also be reduced. Depending on the design of the set, you may not be able to totally remove the distortion without adversely affecting the reception of other stations. The advantage with this sort of modification is that it can easily be reversed in the future if necessary...."

which I found here: http://www.vintage-radio.com/repair-...rf-stages.html

Just wondered if anyone else had come across this and, what they decided to do - given in the case of the Ferguson, the connections would need the IF can/cans removed to access the primaries?

Pete
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Old 24th Apr 2019, 10:54 pm   #134
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Default Re: Ferguson 382U Firefly not playing ball

hmmm......well whilst what they say has an essence of truth I've never found it necessary to ever change anything....as for the 'better quality transmitters' apparently used by the BBC, I don't think that is quite true. I know very little about broadcasting techniques other than the fact local stations tend to use more compression than national stations. However although these stations tend to sound louder than the nationals (with the possible exception of Classic FM) I've not noticed distortion. My main receiver is a Leak Troughline tuner from the mid-sixties and that receives all available stations in excellent quality. I have several early FM sets and in the past have also had a Ferguson 383A which is basically the same as the 382U. I don't remember having a problem with distortion on the locals.

What is more likely to be the problem is the fact that older receivers need a good FM aerial (by 'good' read 'outdoors'). Most are far less tolerant of poor signals.
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Old 25th Apr 2019, 7:56 am   #135
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Default Re: Ferguson 382U Firefly not playing ball

Hi Sideband - interesting.. That's a pretty good sample of receivers!

I know when I tried my home made Dipole it produced even louder reception etc. - although I did still get the distortion/crunching..

I've had a look around the associated detector/discriminator components and, they seem to be okay - so guess there's not gonna be a lot that can be done with it now?

Pete
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Old 25th Apr 2019, 10:56 am   #136
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Default Re: Ferguson 382U Firefly not playing ball

Does it suffer from that sound distortion on AM?

Did you sort out the reason for the low cathode voltage you measured on the UL84?

Lawrence.
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Old 25th Apr 2019, 11:32 am   #137
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Default Re: Ferguson 382U Firefly not playing ball

Hi Lawrence thanks, yeah it’s actually pretty clean on AM, so I’ve not spent any more time on the audio output stage.

If I ‘mis-tune’ slightly then it’s def cleaner, it nowhere near as clean as it used to be back in the day ��.

Pete
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Old 25th Apr 2019, 11:57 am   #138
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Default Re: Ferguson 382U Firefly not playing ball

An imbalance of the detector diodes in the EABC80 can cause this.
I note you have replaced that valve already but maybe try another if you have one?
What was wrong with the original?
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Old 25th Apr 2019, 12:01 pm   #139
el gringo
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Default Re: Ferguson 382U Firefly not playing ball

Hi Sam, the original turned out to be low emission and my first replacement turned out to be completely duff! I don’t have another one to try unfortunately.

Thanks Pete
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Old 26th Apr 2019, 5:29 pm   #140
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Default Re: Ferguson 382U Firefly not playing ball

Update: discovered one more Hunts brown capacitor C47. Looks to be amongst the discriminator / detector areas so went ahead and replaced. Now seem to get even more stations ( which is great ) however still have the annoying crunch - more so noticeable with lower frequencies? and, at any end of the tuning cap range.

Anyone have any suggestions please?

Ta, Pete
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