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Old 29th Sep 2019, 1:49 pm   #61
ms660
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Default Re: Kolster-Brandes MR10

That AM wire antenna looks to be connected to the hot end of the MW tuning coil so far as I can make out, if it is it's a bit of a fudge, if it was a decent length antenna it would upset the tracking for sure due to the antenna's capacitance.

According to the schematic the external antenna socket is bottom coupled to the RF tuning coils, that arrangement would have minimum effect on tracking.

There's a good article here explaining the two methods of antenna coupling in respect to shunt and series connected starting on magazine page 389:

https://www.americanradiohistory.com...ld-1975-08.pdf

The circuit in Fig.8 is basically the original arrangement in your KB and the circuit in Fig.11 is in effect what you have at the moment with that antenna wire connected.

Lawrence.
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Old 29th Sep 2019, 2:03 pm   #62
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Default Re: Kolster-Brandes MR10

I cant think of a reason why the original grille was removed, I wonder if the original had been broken and replaced with a not perfect substitute.

Mike
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Old 29th Sep 2019, 3:27 pm   #63
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Default Re: Kolster-Brandes MR10

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That AM wire antenna looks to be connected to the hot end of the MW tuning coil so far as I can make out, if it is it's a bit of a fudge, if it was a decent length antenna it would upset the tracking for sure due to the antenna's capacitance.
Thanks Lawrence - I suppose I could just remove the AM wire antenna and see (hear) what happens?

The Wireless World link looks interesting as well - more useful stuff for me to assimilate!
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Old 29th Sep 2019, 3:56 pm   #64
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Default Re: Kolster-Brandes MR10

No problem, another common method back in the day of coupling the antenna to the first tuned circuit was by configuring the RF tuned circuit as a transformer with a high inductance primary, the primary was designed to broadly resonate just below the low end of the band with the antenna's capacitance, the secondary being the inductive part of the receivers RF tuned circuit, amongst other things it reduced the effect of different antenna capacitances on the RF tuned circuit, sometimes folks can get confused by them thinking its a long wave coil assembly because of the size of the winding when in fact it's a medium wave coil assembly.

There's a not too involved article about the high inductance primary in the link below starting at magazine page 463:

https://www.americanradiohistory.com...ld-1937-11.pdf

Lawrence.
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Old 29th Sep 2019, 5:11 pm   #65
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Default Re: Kolster-Brandes MR10

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

Attachment 191029
Apologies should have it made it clear that I know that the P(ick) U(p) socket is used with the set in the Gram position - my question was more related to what the symbols are meant to represent?
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Old 30th Sep 2019, 10:39 am   #66
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Default Re: Kolster-Brandes MR10

The one on the left is a representation of an old style gramophone pickup head, the one on the right is supposed to be a representation of a turntable unit with its pickup and arm fitted.

Lawrence.
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Old 30th Sep 2019, 12:34 pm   #67
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Default Re: Kolster-Brandes MR10

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Quote:
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That AM wire antenna looks to be connected to the hot end of the MW tuning coil so far as I can make out, if it is it's a bit of a fudge, if it was a decent length antenna it would upset the tracking for sure due to the antenna's capacitance.
Thanks Lawrence - I suppose I could just remove the AM wire antenna and see (hear) what happens?
Well I removed the rogue AM wire antenna and am very pleased that this has cleaned up most of the distortion on both MW and LW - quite an amazing difference!

Let's hope we get a similar result with FM when I fit the replacement 12AT7 ...
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Old 30th Sep 2019, 1:03 pm   #68
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Default Re: Kolster-Brandes MR10

The internal plate antenna is pretty useless in these unless you live next door to the transmitter - they aren't the most sensitive of sets on VHF anyway. If you have a reasonable signal you can expect acceptable performance from a homemade dipole or one of the Poundland dual telescopic aerials.
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Old 30th Sep 2019, 4:46 pm   #69
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Default Re: Kolster-Brandes MR10

Thanks Paul - do you mean this: -

https://www.poundland.co.uk/signalex...v-aerial-30-cm
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Old 30th Sep 2019, 4:48 pm   #70
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Default Re: Kolster-Brandes MR10

Yes, anything like that.
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Old 30th Sep 2019, 5:50 pm   #71
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Default Re: Kolster-Brandes MR10

Ribbon cable FM aerials are also widely available, such as these:

https://www.amazon.co.uk/Pro-Signal-...CX85WXJC1K7E08

I've got one pinned up in my workshop for testing FM receivers - it works fine.
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Old 30th Sep 2019, 6:13 pm   #72
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Default Re: Kolster-Brandes MR10

Both my MR10's, Mk1 and Mk2, work fine on FM, I am about 33 miles from the Wrotham transmitter.

Mike
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Old 3rd Oct 2019, 4:57 pm   #73
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Default Re: Kolster-Brandes MR10

Thanks once again to the generosity of Forum member David G4EBT I received an 12AT7WA which I have used to replace the "faulty" 12AT7 - you may remember that FM was completely silent on this set.

The great news is that I now have FM - quite good reception with just a single wire connected to the A1 aerial socket. The volume is, however, quite low and I have to turn it fully round to get a decent audible signal - gave me a fright when I switched back to AM!

Here are some voltage readings for the replacement 12AT7WA with the set switched to FM and at a quiet spot on the dial (no signal): -

1. Firstly, the heater pins - across Pins 4&5 we have 0.05V AC, across Pins 4&9 and across Pins 5&9 we have 6.62V AC.

2. Secondly, we have - Pin 1:132V - Pin 6:130V - Pin 3:0.85V

I note from previous Posts/Threads on the KB-MR10 that " ... they aren't the most sensitive of sets on VHF anyway" so I'll wait until I've rigged up a decent dipole (or Poundland dual telescopic aerial) before investigating whether or not I need to look at increasing the gain on FM somehow?

I'm only 16 miles from my local FM transmitter at Black Hill at an angle of 77 degrees from North in an Easterly direction. This transmitter is chucking out all the main BBC FM stations at 250kW and is horizontally polarised so I'm assuming that would be better for any picture rail dipole??

https://www.aerialsandtv.com/blackhilltx.html

All good news (I think?) but as usual comment and feedback welcomed.
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Old 3rd Oct 2019, 5:47 pm   #74
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Default Re: Kolster-Brandes MR10

All you can do is experiment. What is FM reception like on other radios?

You do sometimes get areas of poor reception even quite close to big transmitters.

I haven't checked, but it's very unlikely that Black Hill is using exclusively HP for FM. The transmitter network was re-engineered for slant or mixed polarisation several decades ago to better serve people listening in cars and on portables.
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Old 3rd Oct 2019, 6:50 pm   #75
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Default Re: Kolster-Brandes MR10

That aerialsandtv info link is for TV transmissions which are Horizontal, as Paul says, Mixed for FM:

http://downloads.bbc.co.uk/reception...tlandtrans.pdf

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Old 4th Oct 2019, 5:56 pm   #76
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Default Re: Kolster-Brandes MR10

Thanks to everyone for their helpful feedback.

Currently contemplating and assessing options for an indoor FM dipole, dual telescopic aerial or ribbon aerial - I'll report back in due course on my findings.

Meantime I had problems early on with the on/off switch tone control with dead areas that hummed as you rotated the control. De-soldering and re-soldering the tags to test the switch/pot and several doses of DeOxit seem to have cleared that problem but I'm left with a tone control that is is very bright and harsh with a lot of sibilance! You can only turn the control a very small way round before the audio becomes too harsh to listen to!

Don't really want to think about replacing this switch/pot so what are my options to alleviate this issue? From the Trader Service Sheet 1233 I note that between the Anode of V5 and the Output Transformer we have R23 (4.7kΩ) and C44 (0.01μF) in series. Would increasing the value of any of these help - if so, what values would be recommended??
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Old 4th Oct 2019, 9:00 pm   #77
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Default Re: Kolster-Brandes MR10

Are your voltages measured with an analogue meter or a digital one.
They are slightly down on the ones I noted on the KB schematic for your type of MR10 mk2.
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Old 4th Oct 2019, 9:21 pm   #78
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Default Re: Kolster-Brandes MR10

Thanks - all voltages have been taken with a digital meter as my Avo Panclimatic Model 8 Mark 4 is on my ToDo list.

I understand (thanks again to David G4EBT) that it " ... will originally have been measured with an analogue meter (AVO 8 - 20,000 Ohms per Volt), and would probably have measured nearer 6.3V. However, your digital meter won't 'load' the circuit, so is probably why it reads slightly higher."

What voltage should I expect on V1 Pin 3 (cathode) - there is nothing shown in the KB Museum Schematic whereas on Trader Service Sheet 1233 it states that this should be 1.3V?

I'll be looking at other causes of the HT being down specifically around V1, now a 12AT7AW.
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Old 5th Oct 2019, 10:27 am   #79
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Default Re: Kolster-Brandes MR10

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What voltage should I expect on V1 Pin 3 (cathode) - there is nothing shown in the KB Museum Schematic whereas on Trader Service Sheet 1233 it states that this should be 1.3V?
The cathode voltage for V1 is given in the manufactures manual, it's given as 1 volt in the valve voltages table....The voltages quoted were measured using a 20kohm per volt meter.

The voltages given on the Trader sheet were measured using an AVO electronic meter (VTVM)

The difference in the loading effect on V1's cathode voltage for all intents and purposes will be zilch, ditto for the heater voltage.

Lawrence.
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Old 5th Oct 2019, 4:52 pm   #80
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Default Re: Kolster-Brandes MR10

Yes, there is a voltage chart for the Mk1 on page 11 of the KB service manual, I don't expect there to be much difference for the Mk2 version you have with regard to V1.
I didn't make any note regarding V1 cathode voltages on my Mk2.
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