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HMV 1890 Tuning fault

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Marc
 Marc
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Hi all,

I have an HMV 1890 that works beautifully on all band III channels but is really snowy on all Band I channels
I cleaned all the contacts in the tuner which were really grotty but it's made no difference.
Any ideas welcome :)

Cheers,
Marc.

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Posted : 31/01/2015 4:54 pm
Anonymous
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That looks like co Chanel interference but from where?
Rob T

 
Posted : 31/01/2015 6:03 pm
Marc
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That looks like co Chanel interference but from where?
Rob T

Hi Rob,

The fault is within the set and not transmitted to it, this set just doesn't like Band I. :cch
I've changed the PCC 89 and the PCF 80 on the tuner to be on the safe side but it's made no difference.

Marc.

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Posted : 31/01/2015 6:20 pm
Alastair
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Is there any advantage in using Band 1 over band III?

 
Posted : 31/01/2015 6:22 pm
Marc
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Is there any advantage in using Band 1 over band III?

Hi Alastair,

Simple answer is I have a distribution system that runs all over the house that transmits Band I CH2 to all my sets so I don't want to have to keep changing the Aurora each time I want to use the HMV.

Marc.

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Posted : 31/01/2015 6:27 pm
Terrykc
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First thoughts are : most likely problem is a fault in the aerial isolator, possibly an open circuit connection to the inner of the coax, a break in a track or a low value capacitor - don't forget that Ch.10 will be about four times the frequency of Ch.4 and the variation in capacitive reactance between the bands can make a lot of difference!

If you can run the set from an isolating transformer, you could try bypassing the isolator and its connecting cable for a quick check.

Do you have the circuit diagram of the tuner we could look at?

Is this a tuner that might have had an option of two aerial sockets, one for each band and there is a missing or open circuit link?

When all else fails, read the instructions

 
Posted : 31/01/2015 7:12 pm
Marc
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Hi Terry,

Here's a photo of RATS 1960/61 page 410.
Sorry my scanner is out of action, hope the photo is clear enough.

Marc.

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Posted : 31/01/2015 7:31 pm
Terrykc
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Thanks Marc.

Nothing likely that I can see - I'm still pinning my hopes on the isolator ...!

When all else fails, read the instructions

 
Posted : 31/01/2015 7:44 pm
Marc
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Hi Terry,

I'm going to take another look at the isolator later this evening though nothing looks physically amiss from what I've seen around that area. :aaq

Marc.

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Posted : 31/01/2015 7:47 pm
Cathovisor
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Just a thought Marc - are there separate AGC and local/distant settings for Band I/III, like many a Bush has?

 
Posted : 31/01/2015 7:48 pm
Marc
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Just a thought Marc - are there separate AGC and local/distant settings for Band I/III, like many a Bush has?

Hi Catho,

It only has the one Local/Distant control so I guess single AGC there again remember it's me at this end and I could well be wrong !
You haven't got the 60/61 RATS book handy have you ?

Marc.

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Posted : 31/01/2015 8:00 pm
Cathovisor
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You haven't got the 60/61 RATS book handy have you ?

No, still buried in the store.... :cch

However, you said it only has one AGC setting and nothing to equalise gain between Band I and Band III, so... :aaq

 
Posted : 31/01/2015 8:06 pm
Marc
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I'm still pinning my hopes on the isolator ...!

Hi Terry,

No problems round the isolator, both caps check fine as do the resistors.

Marc.

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Posted : 31/01/2015 10:27 pm
slidertogrid
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I'm not familiar with the chassis but assuming it has a turret tuner rather than a band switch. I would check the connections to the contact strip that connects to the biscuits in the turret.
I can't remember what set it was but I had a problem similar to this years back that turned out to be a disconnected wire on one of the coils on the turret this only affected the one channel rather than the whole lot of channels on that band.
Back then I had the luxury of a spare set of biscuits to prove the point but if the biscuits on yours are easily removed (ie it's not a fireball tuner) it should be fairly straightforward to check them.
Regards,
Rich.

 
Posted : 31/01/2015 11:01 pm
Marc
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Hi Rich,

I think this maybe a "fireball" if that is the type that has all the tuning coil biscuits arranged like multiple hands on a clock face . (please could you confirm that for me ? :aaq )

I have checked all the connections on each tuner segment and all are fine as are the contacts on the other side also they making good contact with their counterparts in the tuner body.

I have replaced the two short wires (75mm) from the aerial socket to the tuner with a piece of screened and that has massively improved the picture on band 1 but the sound is low no matter how much twiddling of the fine tuning is done. (The two wires were not of my doing by the way, most annoying !) so next is where do I go from here to get a reasonable sound level like that achieved on band III channels ?

Just noticed that there is a quiet "ringing" noise on the sound too. :aaq

Marc.

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Posted : 31/01/2015 11:23 pm
slidertogrid
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Yes it sounds as if yours is a fireball tuner, there is a picture of one on this thread http://www.vintage-radio.net/forum/show ... hp?t=63667
I have heard a faint ringing on sound when using an aurora when I had reduced gain due to a faulty rf lead, the picture was very slightly grainy and the sound had a faint ringing noise like a microphonic valve, so I wouldn't worry too much about that at this stage.
See if you can measure the anode volts of the first valve in the tuner, you may have a anode load resistor gone slightly high.
Then I would look at the agc line to see if the voltage varies from band I to band III .
Hope this helps
regards, Rich

 
Posted : 01/02/2015 12:15 am
Marc
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Hi Rich,

Thanks for the info and yes it's "Fireball"
I shall have a look tomorrow at the other things you've suggested and report back.

Cheers,
Marc.

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Posted : 01/02/2015 12:20 am
Marc
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Hi all,

Still having fun and games with the Fireball tuner.
As mentioned a couple of posts back the picture is now fine but sound is very low however some times if you rock the tuner control just off channel you can get full sound so it is looking like a mechanical fault rather than electronic.
The coil disc is in good order with clean contacts, the mating tuner contacts are also clean and in good order. The coil disc is aligned to the tuner body...it's keywayed into position.
Does any one know if there are any possible adjustments that can be made ?

Marc.

EDIT.... on close inspection whilst rocking the tuner control the sound comes loud as the contacts in the tuner hit two neighbouring biscuits at the same time ! Back to the drawing board :bbd

Marc
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Posted : 01/02/2015 3:19 pm
AidanLunn
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Hi all,

Still having fun and games with the Fireball tuner.
As mentioned a couple of posts back the picture is now fine but sound is very low however some times if you rock the tuner control just off channel you can get full sound so it is looking like a mechanical fault rather than electronic.
The coil disc is in good order with clean contacts, the mating tuner contacts are also clean and in good order. The coil disc is aligned to the tuner body...it's keywayed into position.
Does any one know if there are any possible adjustments that can be made ?

Marc.

EDIT.... on close inspection whilst rocking the tuner control the sound comes loud as the contacts in the tuner hit two neighbouring biscuits at the same time ! Back to the drawing board :bbd

Could it be an effect of the screened cable you've fitted? When you fitted that, that's when the picture went OK but the sound remained weak - maybe the cause of the sound remaining weak is different now you have fitted the screened cable?

 
Posted : 01/02/2015 4:44 pm
Marc
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maybe the cause of the sound remaining weak is different now you have fitted the screened cable?

That's what I've already said, screened cable has cured picture but there is still a sound fault somewhere round the tuner which I can't find.

Marc.

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Posted : 01/02/2015 4:54 pm
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