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Old 11th Sep 2019, 5:20 pm   #41
crackle
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Default Re: Kolster-Brandes MR10

I suppose R31 in my radio could be brown very dark green orange, anyway 10k - 15k not that much difference, and it is all back in the case so I cant take a closer look with more light.
The capacitors I sometimes use are the brown Polyester types, I try to buy ones branded "Suntan" as I found problems with the CBB branded ones, they didn't seem to live up to their voltage rating.. When I tested a 630 volt cap it started making faint crackling noises at about 400 volts.
Suntan ones don't seem so common now, everyone seems to be selling CBB caps.
They are a lot more economical to buy than the yellow axial ones. I do use the axial types sometimes if I am re-stuffing caps in an older 30's radio.

Mike
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Old 18th Sep 2019, 6:04 pm   #42
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Default Re: Kolster-Brandes MR10

Can anyone advise where I can find a replacement for the C40 electrolytic capacitor.

The KB Museum service manual shows C40 as being 2μF 150V - needs to be axial as well. I appreciate that a modern equivalent of 2.2μF would also suffice?

I've tried all the usual outlets and eBay but no joy??
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Old 18th Sep 2019, 6:48 pm   #43
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Default Re: Kolster-Brandes MR10

It's not axial, otherwise one of these will do, you won't get 150 volts across the capacitor in that circuit position.

https://www.cricklewoodelectronics.com/2U2H100.html

Axial (I've never used this supplier):

https://www.bitsbox.co.uk/index.php?...oducts_id=2369

Lawrence.

Last edited by ms660; 18th Sep 2019 at 7:07 pm. Reason: correction and additional link.
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Old 26th Sep 2019, 11:12 am   #44
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Default Re: Kolster-Brandes MR10

Made good progress with replacing any out of tolerance resistors along with the waxy paper capacitors and Hunts Mouldseals - haven't touched anything in the FM section though.

Some of those Hunts caps just crumbled when I tried to remove them - here's a picture of some of the casualties: -

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The good news is that I'm still getting a good strong signal on Radio 4 LW while I now have many stations available on MW that I never had before. Signal strength is now good on both LW and MW.

The bad news is that there is still absolutely nothing on FM?

I did have a minor mishap due to a rogue solder blob at the junction of R14 and C28 (Trader Sheet References) where the pin from L19 had been inadvertently earthed to the chassis. Removed the blob with solder braid and it turns out there is only about 1mm of clearance between the pin and the chassis at this point.

Voltages on V5, V4 and V3 are all much improved following the replacement of the Hunts caps but then things start to go awry when we come to V2. I was very careful when replacing components on the underside of V2 because of the very cramped space around the B9A valve-holder but there are no short circuits or dodgy solder joints.

For V2 (ECF82) and V1 (12AT7) the voltages I'm reading for AM and FM are: -

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The 12AT7 still has no signs of heating up and is cold to the touch even after the set has warmed up. Clearly something amiss here but not sure where to go next. A bit wary of going into the FM section to change anything as realignment may be required after that!
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Old 26th Sep 2019, 11:28 am   #45
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Default Re: Kolster-Brandes MR10

You've done your voltage table wrong.....swop the AM & FM (Column 4)

If the 12AT7 heaters aren't working it can only be one of two things, either there's no heater voltage supply to the valve or the valves heaters are open circuit (in effect)

Lawrence.

Last edited by ms660; 26th Sep 2019 at 11:33 am.
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Old 26th Sep 2019, 11:55 am   #46
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Default Re: Kolster-Brandes MR10

Quote:
Originally Posted by ms660 View Post
You've done your voltage table wrong.....swop the AM & FM (Column 4)
Well spotted Lawrence - I simply transposed my AM and FM - corrected table here: -

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Quote:
If the 12AT7 heaters aren't working it can only be one of two things, either there's no heater voltage supply to the valve or the valves heaters are open circuit (in effect)
A step to a hint please on how to check these out?
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Old 26th Sep 2019, 11:58 am   #47
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Default Re: Kolster-Brandes MR10

Quote:
If the 12AT7 heaters aren't working it can only be one of two things, either there's no heater voltage supply to the valve or the valves heaters are open circuit (in effect)
A step to a hint please on how to check these out?



Lawrence.
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Old 26th Sep 2019, 12:47 pm   #48
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Default Re: Kolster-Brandes MR10

Point taken ...
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Old 26th Sep 2019, 8:09 pm   #49
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Default Re: Kolster-Brandes MR10

A huge thanks once again to David Taylor (David G4EBT) for advice and guidance on how to identify the problems with this 12AT7 valve.

So what we found was that if you remove the valve and check on a low Ohms range first between pins 4 & 5 of the valve itself, then between 4 & 9 and 5 & 9 you get a reading of 1 - a short/open circuit?

Then with the valve back in place, the set turned on and switched to FM, checked if there was 6.3V AC between pins 9 & 4 (or 9 & 5). Got a reading of 6.5V AC so at least V1 is getting a heater voltage?

Can we therefore conclude that we have a duff valve?

If I do need to replace this valve should I just go for a like-for-like 12AT7 or go down the route of swapping it for an ECC81?

No matter which one is chosen, there are many variations of both of these valves so some further advice and guidance would be welcomed?
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Old 26th Sep 2019, 9:04 pm   #50
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Default Re: Kolster-Brandes MR10

Quote:
Originally Posted by DonaldStott View Post
So what we found was that if you remove the valve and check on a low Ohms range first between pins 4 & 5 of the valve itself, then between 4 & 9 and 5 & 9 you get a reading of 1 - a short/open circuit?
If the resistance reading is infinity the heaters are open circuit.

If the resistance reading is zero the heaters are short circuit.

If the series resistance when cold is between approx. 10 and 20 ohms the heaters should be ok.

Lawrence.
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Old 26th Sep 2019, 9:06 pm   #51
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Default Re: Kolster-Brandes MR10

Quote:
Originally Posted by DonaldStott View Post
So what we found was that if you remove the valve and check on a low Ohms range first between pins 4 & 5 of the valve itself, then between 4 & 9 and 5 & 9 you get a reading of 1 - a short/open circuit?
I am confused by your result of measuring the resistance of the valve heater. A reading of open circuit would normally be OL and of a short would be 0.5 or what ever the resistance of the meter leads is.
A reading of "1" does not seem likely.
Across pins 4 & 5 (both halves of the filaments) you should get a reading of about 13 ohms. Between 4 & 9 and 5 & 9 you should get about 6.5 ohms as you are measuring each half of the filament.
The heaters may be faulty but I would suggest it is a broken valve pin.
Carefully check the valve socket pins to see if you can see any broken pins.
I carefully use a solid piece of wire the same thickness as a valve pin to push into each valve socket hole to see if there is any friction from the pin making contact with the wire. What ever you do dont use a piece of wire thicker than the valve pins.

Mike

edit
I have just checked on a very cheap 3 meter and and an open circuit resistance is shown as 1.
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Last edited by crackle; 26th Sep 2019 at 9:12 pm.
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Old 26th Sep 2019, 9:17 pm   #52
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Default Re: Kolster-Brandes MR10

It shouldn't matter if you use an ECC81 or a 12AT7 and it shouldn't make any difference which make you buy. But do buy from a reliable source you can trust. Often ones sold on the popular auction site can be anything from dead to working, unless they say tested as good then you dont have much come back.
You might even be able to use an ECC83 in some sets but they don't work quite as well in this application.

Mike
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Old 26th Sep 2019, 10:01 pm   #53
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Default Re: Kolster-Brandes MR10

Looked through my collection of components using a magnifier and found a resistor with leads exactly the same diameter as the valve pins.

Checked all valve socket holes visually to ensure that nothing is broken and checked each one in turn with the resistor lead - in every instance there is friction with the resistor lead and it is gripped in place by the valve socket pins.
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Old 26th Sep 2019, 10:29 pm   #54
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Default Re: Kolster-Brandes MR10

Well if you are getting infinite resistance between pins 4 & 5 on the valve then it looks like a new one is needed.

Mike
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Old 26th Sep 2019, 11:16 pm   #55
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Default Re: Kolster-Brandes MR10

It's very unlikely that the heater is short circuit. It's much more likely that it's open circuit.

It doesn't matter if you fit an ECC81 or 12AT7, they are alternative codes for the same valve. If you need to buy one, just buy on price. There are various special quality and military variants, all of which should be fine. I agree with Mike that you should buy from somebody with a track record rather than any random seller. You may well find that a forum member has something suitable.
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Old 27th Sep 2019, 5:27 pm   #56
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Default Re: Kolster-Brandes MR10

Hello Donald,
I have a trade pack of NOS Mullard ECC81 valves. If you would like one FOC please contact me via PM with your details and I will post. Please don't pay silly money for one.
Regards, John.
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Old 27th Sep 2019, 7:15 pm   #57
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Default Re: Kolster-Brandes MR10

Quote:
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Hello Donald,
I have a trade pack of NOS Mullard ECC81 valves. If you would like one FOC please contact me via PM with your details and I will post. Please don't pay silly money for one.
Regards, John.
Hi John and thanks for your really kind offer, much appreciated.

But thanks to another Forum member I already have a replacement for the 12AT7 on it's way to me.

Best wishes
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Old 29th Sep 2019, 1:06 pm   #58
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Default Re: Kolster-Brandes MR10

While I'm waiting for the replacement for the 12AT7 to arrive I've moved on to to other areas that need attention.

1. Speaker Grill

I've removed, cleaned and re-sprayed the speaker grill which was in desperate need of some TLC as much of the gold finish was in very poor condition.

In my Post #1 in this Thread I mentioned the article "It Came From Outer Sidcup" by John Ounsted in the BVWS Bulletin volume 24 number 3 Autumn 1999 - in this article the author offers the following: -

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Despite my best efforts I only managed to save one of the plastic pegs when removing the metal brackets and, initially, couldn't understand why? Then I noticed that a tell-tale circle of glue also came away indicating that at some point in the past these plastic pegs had been stuck back on: -

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Don't know why this was done as there are spare, unused pegs. Good news for me though as I can utilise these unused pegs when refitting the speaker grill!

2. AM Aerial

I can also revisit the wired up external aerial - I'm assuming that this is an add-on and not something K-B rigged up themselves. This wire is connected to one end of the ferrite rod, see here : -

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The KB Museum Service Data notes "A short picture rail type of aerial will not in general give improved results over the internal aerial and may in some cases give rise to increased interference."

I also need advice on what these symbols mean - there are associated with the P.U. Sockets: -

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3. FM Aerial

The KB Museum Service Data also notes "For V.H.F. reception an internal plate aerial is fitted and the connection to this is a wander plug lead which should be plugged into aerial socket (A1 left hand socket on A-E panel."

I do have the little gold pip which appears to have been used to connect the internal plate aerial (aluminium foil) on the inside of the set - although the short length of wire attached to the wander plug is too short to plug in to any of the sockets on the back of the set:-

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The internal plate aerial is not attached at this time.
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Old 29th Sep 2019, 1:31 pm   #59
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Smile Re: Kolster-Brandes MR10

Hi,
I had one of these sets years ago, given to me by an uncle. It was a cream coloured one, just like the one that adorns the sideboard in the comedy series 'Mrs. Brown's Boys'.
I wish I knew what became of it when we moved.
I didn't know they were available in other colours too.
Cheers, Pete.
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Old 29th Sep 2019, 1:57 pm   #60
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Default Re: Kolster-Brandes MR10

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I wish I knew what became of it when we moved.
Hi Pete - if you ever do locate the set then keep me in mind: -

https://www.vintage-radio.net/forum/...d.php?t=159484
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