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Old 23rd Jul 2016, 9:11 pm   #41
sobell1980
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Default Re: Argyll Minor reel to reel help needed.

So that's approx 20 volts ac across the pair of heater wires from the mains transformer disconnected from the pcb, I'm also getting 90volts ac from each heater wire to chassis. Reconnecting them back to pcb they read zero volts ac. Could I have a faulty mains transformer causing thus intermittent issue?
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Old 24th Jul 2016, 9:09 am   #42
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Default Re: Argyll Minor reel to reel help needed.

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Originally Posted by sobell1980 View Post
So that's approx 20 volts ac across the pair of heater wires from the mains transformer disconnected from the pcb, I'm also getting 90volts ac from each heater wire to chassis. Reconnecting them back to pcb they read zero volts ac. Could I have a faulty mains transformer causing thus intermittent issue?
What's the resistance reading across the heater winding ? (with the winding disconnected from the PCB)

Lawrence.
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Old 24th Jul 2016, 11:04 am   #43
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Default Re: Argyll Minor reel to reel help needed.

Made a little progress this morning. I'm not sure if I'd just got brain overload last night but this morning I've definately got 7.5 volts from the heater winding and approx 3.5 v from each wire to ground.
With the valves removed I've soldered back the two wires to the two heater tracks on the pcb. Plugged the valves in, applied power and measured again. Zero volts across pins and 4 to pin 9 of valve 1 and zero volts across pins 4 and 5 of valve 3. I removed the valves and applied power again. So both heater tracks should read 3.75 volts respective to chassis ground. One heater track to pin and 4 of valve one and pin 5 valve 3 reads 3.75 v always. The other heater track reads 10 v to chassis ground which is connected to pin 9 of valve 1 and pin 4 of valve 3. I unsoldered the heater wire from the pcb again. So neither track should be receiving any voltage. One heater track is as expected measuring o.00 volts. The other is receiving
10 volts to pin 9 of valve 1 and 4 of valve 3. I've checked for shorts to close by components and to the valve pins . No direct shorts.so one heater track is getting 10 v ac disconnected from the mains transformer heater winding.
Dave.
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Old 24th Jul 2016, 11:54 am   #44
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Default Re: Argyll Minor reel to reel help needed.

With the valves fitted check out post#28, you should have cracked this by now.

Lawrence.
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Old 24th Jul 2016, 5:24 pm   #45
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Default Re: Argyll Minor reel to reel help needed.

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Originally Posted by sobell1980 View Post
…...It burst into life after probing the circuit board valve pins……….
Dave
Hi, This suggests that you may have either a dry joint or valve bases which have poor connections to the valve pins. You seem to be getting very tied up with the various voltage readings on the valve heater pins.

Personally I would disconnect the valve heater feed from the transformer to the PCB and do some "cold" DC resistance checks from each of the pcb tracks which feed the valve heaters, even going as far as to check for DC continuity from the print side of the PCB to the appropriate socket on the valve holder.

Also check the DC resistances of the transformer windings which feed the valve heaters (If you haven't already done so)

I seem to recall someone else mentioning do a few DC checks in an earlier post.


Regards

Andrew
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Old 24th Jul 2016, 6:26 pm   #46
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Default Re: Argyll Minor reel to reel help needed.

Yes, both Lawrence and Andrew. I seem to have not followed a logical diagnostic path and got myself mixed up in multiple inconsistent voltage readings at the valve pins. One second they read good then they don't. I need to to take a step back and make a logical diagnostic path to follow. What does that part of the circuit need to work. What have we got and what haven't we got and go from there. As Lawrence said, I'm a bit embarrassed I haven't cracked this yet. It's simple LT heater circuit. Apologies all, seem to have gone off on a tangent on this one.
Dave.
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Old 25th Jul 2016, 1:25 pm   #47
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Default Re: Argyll Minor reel to reel help needed.

It would appear that the heater winding in the mains transformer is an intermittent open circuit. This will explain the inconsistent voltage readings.

If I measure across the the two heater wires disconnected from circuit it reads open circuit. If I then measure from each wire to ground (centre tap) I get 282R one side of the winding and open circuit the other side of the winding. Measuring across both wires it ranges very occasionally from open circuit to the 1.7 mega ohms then back to open circuit again.

This is why I have "a" voltage reading on the pcb, but the second any valve heater is plugged in the voltage dissappears. This is because the heater winding is breaking down the second the heater filaments require to draw a load from the heater winding. As soon as I unplug any valve the voltage appears again.
I hope you all concur. Many thanks.
Dave.
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Old 25th Jul 2016, 8:47 pm   #48
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Default Re: Argyll Minor reel to reel help needed.

If any one has any feed back that would be great. Seemed to have lost my self confidence this time round. Well, I guess it needs to have a fully functional mains transformer before I continue with the rest of the project and hopefully this will solve my issue.
I have found on EBay a donor Argyll which I may be able to salvage the mains transformer from. The only thing is I think it is a major and not a minor. Could anyone tell me if the major and the minor have the same mains transformer fitted? If so this maybe a cheaper option and will also supply me with some extra valves and other parts for this project and future ones. Many thanks,
Dave.
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Old 26th Jul 2016, 8:16 am   #49
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Default Re: Argyll Minor reel to reel help needed.

I don't know what the differences are between the Minor and Major power supplies transformer wise so no help there.

It's unusual for a heater winding to go O/C but if it is then it is, you might be able to peel back the outer insulation and find the break, nothing to lose if the transformer is duff.

Lawrence.
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Old 26th Jul 2016, 8:28 am   #50
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Default Re: Argyll Minor reel to reel help needed.

Or just put in an extra heater transformer. Often called "filament" transformers, these were commonplace in the '50s and '60s to power the CRT when it had gone heater-cathode short. (Hence some are described as low capacitance).

Seems a shame to part-out another machine - could you temporarily power the thing from 4 x 1.5V batteries while you fault-find the rest of it?
Graham
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Old 26th Jul 2016, 5:49 pm   #51
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Default Re: Argyll Minor reel to reel help needed.

Yes I did think about powering it up from a battery pack, like you say to confirm the fault is actually that and then to test the rest of the set. However, the heater wires from the mains transformer connect to two points on the pcb which go on to various heater pins and is ac not dc. If I were to connect a battery pack, being dc would it matter which way round on the two connection points on the pcb I connected it? May seem a daft question but the heaters are run from ac. Many thanks.
Dave.
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Old 26th Jul 2016, 6:41 pm   #52
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Default Re: Argyll Minor reel to reel help needed.

You can power the heaters from a suitable DC source such as a suitable battery, the polarity shouldn't matter, the DC source needs to be connected to the same two points on the PCB that the heater winding is connected to but make sure that the wires from the heater winding are disconnected from the PCB before connecting the DC source.

The DM70 heaters won't work with the said set up but that's no bother at the moment, you just need to see the other valves heaters illuminate to prove a point, be aware that the current draw of the heaters will be just over 1 amp from the DC source.

Lawrence.
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Old 26th Jul 2016, 8:47 pm   #53
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Default Re: Argyll Minor reel to reel help needed.

Hi, I think the transformer for the Argyll Major may be a different affair to that of the Minor.

I would take the advice mentioned earlier and fit a seperate heater transformer; it appears that there is already an 82 Ohm resistor fitted to reduce the voltage for the DM70's 1.5 Volt filament anyway so as long as you can find a centre tapped transformer you should be OK


A Playmaster or a Braemar (which is nowt more than a cosmetically modified Playmaster) transformer should also be a suitable alternative if you can find a donor machine.

Regards

Andrew
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Old 27th Jul 2016, 9:32 pm   #54
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Default Re: Argyll Minor reel to reel help needed.

To let all know who have kindly been involved that this evening I have 100% sussed it. I will give a proper description of the repair tomorrow evening as it's late now. I have also had the wife knocking on the man cave door so have had to call it a night. I will explain tomorrow but it wasn't the mains transformer or heater winding or any valves. Misleading wiring diagrams haven't helped or mods that haven't been documented. Got there in the end. Many thanks all, especially Lawrence and Andrew. You got me thinking it out for myself eventually in the end. I know they were only ever words of encouragement and to push me to think for myself.
Dave.
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Old 29th Jul 2016, 11:05 am   #55
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Default Re: Argyll Minor reel to reel help needed.

Glad you sorted it out, we'll await your report.

Lawrence.
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Old 7th Aug 2016, 5:34 pm   #56
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Default Re: Argyll Minor reel to reel help needed.

I still haven't forgotten to report on the fix. I will write a report once I've completed the tape player and I can cover all the faults I've found. It's now working perfectly except I've got what sounds like a very noisy volume pot.
It sounds like someone is welding, through the speaker and popping, sizzling bacon sounds. I've taken apart the volume pot and cleaned the tracks with servisol.
I have rectified the dodgy speaker wiring that was hanging on for dear life. I've sprayed into the tone pot. Didn't dismantle it because it's also the on off switch. Both pots now feel beautifully smooth and free. I've even bypassed the recording / playback switch to see if it was a poor intermittent connection . It looks identical to a wave change switch, this also has been cleaned.
I was convinced a clean of the pots would solve this but it remains. The noise can be turned up and down with the volume pot and the tone control. I haven't changed any electrolytics on this set yet as it didn't suffer any hum. I suppose I could bypass the pots with fixed resistors? This would eliminate those . Any ideas? Other than this it's working beautifully now and is the last remaining fault.
Many thanks.
Dave.
P.S.
Forgot to say it does this not playing a tape, so the heads are not being used and the machine is just idling with nothing engaged.

Last edited by sobell1980; 7th Aug 2016 at 5:55 pm.
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Old 7th Aug 2016, 10:30 pm   #57
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Default Re: Argyll Minor reel to reel help needed.

If you short pin 7 of the ECC83 to chassis does the noise stop?

Frank
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Old 8th Aug 2016, 7:04 am   #58
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Default Re: Argyll Minor reel to reel help needed.

Thanks, Frank. I will try this tonight after work. Won't this test just completely kill the audio signal, not just the noise I'm suffering with? Pin 7 also connects to the output of the volume control. Will this prove it's the volume pot or the valve? Many thanks.
Dave.
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Old 8th Aug 2016, 9:23 am   #59
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Default Re: Argyll Minor reel to reel help needed.

Hi Dave,
The reason I suggested the S/C was that I was unsure if the noise is there all the time or only when you rotate the V/C. It will stop the audio but as this occurs when no tape is playing there will be no audio to stop.

When you S/C that grid to chassis if the noise stops it a good chance of being generated before that point, if not you can rule out the V/C and look elsewhere.
If the noise is only when you rotate the V/C, have you replaced C4, 0.01uf, a leaky cap will put DC onto the control and that can make them noisy.

The R/P switch has HT on some points, a tracking switch wafer could be the culprit, you have isolated the switch but did that include removing HT from it?

Another item that can generate noise are resistors, more noticeable in the early amplification stages. After that you have the valves/valve bases etc, quite a few items really. At least there is not a lot in the electronics on these machines.

Apologies, turned into a bit of a ramble.
Frank
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Old 8th Aug 2016, 6:51 pm   #60
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Default Re: Argyll Minor reel to reel help needed.

Good evening.
I have shorted out pin 7 to chassis ground. The noise completely dissappears. So does the normal hiss that you can hear at full volume alongside the irritating popping and noise I'm getting.
To clear things up, the noise is there without adjusting the volume pot. The set is switched on and is idling. Then the popping and sizzling and crackling comes and goes without any adjustments of the controls. The noise though can be adjusted with the volume and tone controls. So the crackling and popping can be turned up and down but has no relation to movement of the volume /tone controls. What I'm saying is that operating the controls doesn't seem to suddenly make it happen or suddenly start doing it.
All the caps have been changed except the electrolytics.
So it could also be this. I didn't change the large cans as it wasn't suffering any hum. I could try fixed resistors across the volume and tone pots? This will definately eliminate them? As you say the fault is now before that grid pin. But it's also poss that the HT DC could be creeping in . Perhaps it's worth trying the fixed value resistor across the volume pot next? Then would it be possible to keep trying the short circuit on the audio signal line to see at what points the noise is coming in or dissappearing?
Many thanks.
Dave.
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