Argyll Minor reel to reel help needed.

[Nuvistor]

There is a possiblity that the grid circuit pin7 is still to blame, i.e. faulty valve or valve base, I should have mentioned that but at least you have narrowed the area down you need to check.
Don't go shorting any HT points to chassis, use a capactor if unsure say 0.1uf.
Frank

[sobell1980]

In your experience, Frank, what would you check next?
I don't have another valve to swop as that would be the quickest check to do first.
Do you think it's worth the resistor across the volume pot wires to be sure? Do you think my scope will pick it up?
Dave.

[Nuvistor]

My experience! its a long time since I fixed these.
I would disconnect C4 and from this result you can determine if its before or after C4.

Just isolate each stage or part of a stage until you find the culprit. You may see it on your scope, depends how sensitive it is.

If disconnecting C4 stops the noise try S/C pin 2 of the valve to chassis and note the effect. Once you only have two or three items that are suspect you should be able to decide which one.

Frank
edit. I have not looked back through all the posts but is C4 a good one.

[Cobaltblue]

I just wonder about R3 10M Ohm

In my previous experience anything over 1M Ohm tends to head for infinity

Cheers

Mike T

[Nuvistor]

Very possible, just trying to methodically isolate the trouble.

Frank

[sobell1980]

Appreciating all the replies and help. Can we all confirm which diagram we are using? Just there are several available for this.
Ive been using the Playmaster circuit diagram.
Dave.

[sobell1980]

This shows the volume control stage of the Fidelity Playmaster circuit I've been using.

[Nuvistor]

I am using the one on Pauls DVD, available from the link at the top of the page.

http://www.service-data.com/product....25/2914/a12225

If you are using the ERT one I think it is marked C5, its the cap from the anode pin 1 of the ECC83 and the 100K resistor connected to the V/C, on my circuit the 100k is missing, the cap goes straight to the V/C

Frank

[Nuvistor]

Originally Posted by sobell1980

This shows the volume control stage of the Fidelity Playmaster circuit I've been using.

That looks like the ERT one, I will use that in future.
Frank

[sobell1980]

Yes It is the ERT one. So when you said disconnect C4 did you mean c5 on the ERT diagram.

Does R3 form part of a time constant for its associated Cap? How could R3 cause me an issue?

[Cobaltblue]

R 3 is the Grid Leak.

If it gone high in value its likely to be noisy and the valve might Squeg.

Its whats prevents electrons collecting on the grid making it increasingly negative with respect to cathode thus cutting off the electron flow.

Cheers

Mike T

[Nuvistor]

Originally Posted by sobell1980

Yes It is the ERT one. So when you said disconnect C4 did you mean c5 on the ERT diagram.

Yes thats the one, it does not really matter whether you approach from the earlier stages e.g. R3 or the later stages e.g. C5. Just be methodical and have reason for testing/changing that part of the set, not just changing things as a guess.

Frank

[ms660]

Does it show up on a 'scope?

Lawrence.

[sobell1980]

Good morning. Good news. Disconnecting the various components working back from the volume control I found the fault. Like you guys I like to chase the fault and not blanket change components. So found the fault to be R3. It had gone slightly high to 12M ohms, so not enough I'd believe to cause a major issue but cured the noise when disconnected and a new 10M ohm fitted. I was greeted with silence and just the gentle hiss you get through the speaker at full volume. No heavy loud popping or sizzling sounds. It was a matter of process when the time allowed. I just don't get time in the weekday eves without interruptions. I tried a resistor across the volume connections to eliminate the volume pot but the problem remained. So working back, which didn't take long as there isn't that much to check I disconnected R3 and the noise went. Quickly dropping a new 10M Ohm in its place instantly solved the issue. My only worry when I found it was possibly R3 was that because that will effect the grid operation of the valve was that it could have been the valve itself. Disconnecting R3 could have just caused the valve operating conditions to change masking the fault in the valve and fitting a new R3 would have made no change. But I guess this would have then proved it was the valve at fault. I have to order a new mains braided cable and lubricate the mechanical moving parts and it can be returned to my friend for him to use.
Here is a link to it now working properly although not fully complete.
https://youtu.be/8eb5P6BjBkU

Many thanks.
Dave.

[ms660]

Good result.

Keep at it.

Lawrence.

[sobell1980]

Thankyou, Lawrence.
I know I can do it. Perhaps sometimes I should try thinking for myself a little bit harder before posting. I guess it's still a bit of lack of self confidence. I know that's why you push for me to think about the diagnosis myself.sometimes I'm just looking for confirmation I'm headed the right way or I'm doing the right thing. I appreciate yours and everyone's input. It's a great forum and everyone is so helpful. Thanks again.

[ms660]

No worries, the more you do the easier it should get, most circuits can be broken down to blocks or stages, eyes and ears and occasionally nose are the first weapon, followed by a multimeter followed by a 'scope for specific signal anomalies. Meanwhile keep swotting up on basic theory, it will stand you good.

Lawrence.

[sobell1980]

It's retaining it all. I do lots of reading of Tony Thompson books and reference material. As with anything though you need to then put it onto practice which helps retain it as then you can relate to certain repairs and faults. I have lots on the to do pile. Must keep at it. I need to have a tidy so I can get back on my HMV set if you remember that one.
I am awaiting a new braided mains lead for this Reel to Reel and it is finished. Hopefully this project will be boxed up and delivered to my friend by Wednesday.

[sobell1980]

Also thanks to Frank for the valve. Working perfectly when switched to record mode and lighting up beautifully now I've replaced the cap alongside it. I will make that agreed donation this week and let you know. As you can see the bench needs a tidy and some room making for the next project.

The link to see it working on You Tube.
https://youtu.be/8eb5P6BjBkU
I will put up some more photos of it completed.
Dave.

[Nuvistor]

Hi Dave,
Good job sorting the noise out. I am really pleased the DM70 did the job, may as well have it doing something useful rather than sitting in a scrap chassis.

Frank