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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 15th Apr 2009, 3:09 pm   #1
jamezx88
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Default HMV Minigram Mk. 2

So once again I have another item that needs fixing
Firstly Id just like to say a big thanks to Peter (petervk2mlg) who has extensively lent a helping hand in order to fix my Kriesler Radiogram. He is still actually helping me on it so anyway a big thanks

OK so now to the HMV minigram
This was actually one of the first things my mum bought with her paycheck in late 1968/early 1969, so I am somewhat eager to fix it
Also a search turned no results so always good to add a bit of info for others who are looking

It seems to be turning fine, and can hear a really low sound coming from the needle when it's on, just the speaker seems to be not working properly.
However when the volume is turned up to the max, there is the humming sound you would normally hear from a working speaker.
Attached is a few photos. Any one have any ideas? Could it just be a dry soldier joint? If so which one?

Ive attached a few pictures to give everyone an idea
Thanks
James

Edit: thought I'd also say a few years back I took it to an electrical repair man, and he said it needed new parts in the tone arm and wasn't fixable.
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Old 15th Apr 2009, 3:22 pm   #2
Darren-UK
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Default Re: HMV Minigram Mk. 2

It sounds as if the cartridge has failed; do you know if this machine has been stored out of use for a long time?

I note the cct shows TR4 and TR5, at least, as being Silicon transistors; on your image they look like Germanium jobs to me. Maybe I've got that wrong?
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Old 15th Apr 2009, 3:26 pm   #3
jamezx88
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Default Re: HMV Minigram Mk. 2

It was stored out of use for a while, but when I got it a few years ago it was working. Just a few months after that it worked intermittently, then now fails to play.

Oh and TR4 and TR5 look like they have metal caps on them or something (pic attached)

Quote:
Originally Posted by darren-uk View Post
It sounds as if the cartridge has failed; do you know if this machine has been stored out of use for a long time?

I note the cct shows TR4 and TR5, at least, as being Silicon transistors; on your image they look like Germanium jobs to me. Maybe I've got that wrong?
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Last edited by jamezx88; 15th Apr 2009 at 3:34 pm.
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Old 15th Apr 2009, 3:29 pm   #4
AlanBeckett
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Default Re: HMV Minigram Mk. 2

Darren,
If I read it right TR4 & 5 are silicon and TR6 & 7 are germanium.
Further to another thread this one is cute
Alan
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Old 15th Apr 2009, 3:35 pm   #5
Steve_P
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Default Re: HMV Minigram Mk. 2

Right - The turntable works, so there is power getting to the set. Might need a clean though.

Anyway - Volume up and see if you get any hum when you touch the wiring to the cartridge. If you do, try the Cartridge and the Stylus.

If not, make sure the amp is receiving power.

We'll take it from there if we need to.

Cheers,

Steve P.
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Old 15th Apr 2009, 3:43 pm   #6
jamezx88
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Default Re: HMV Minigram Mk. 2

Yes when playing with the wires connected to the cartridge, it does work well. Only for a short time though then reverts back to the silent humming. new cartridge?
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Old 15th Apr 2009, 3:54 pm   #7
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Default Re: HMV Minigram Mk. 2

Tighten the connections and try it then.

Cheers,

Steve P.
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Old 15th Apr 2009, 3:54 pm   #8
Darren-UK
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Default Re: HMV Minigram Mk. 2

Those transistors are indeed Silicon; I can see the BC markings on the closer images James has posted. I always though the BC186, at least, had that 'D' shaped case.

I raised the issue not as an OT drift, but because I wondered if transistors had for some reason been changed and incorrect biasing had killed the audio. In fact, what James describes in post #6 does suggest a biasing problem.
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Old 15th Apr 2009, 3:57 pm   #9
jamezx88
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Default Re: HMV Minigram Mk. 2

Yes seems to be working now
Easy fix this time!
Thanks heaps
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Old 15th Apr 2009, 4:11 pm   #10
julie_m
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Default Re: HMV Minigram Mk. 2

I have definitely seen silicon transistors (B means silicon) in metal cans.

Quote:
Originally Posted by jamezx88 View Post
thought I'd also say a few years back I took it to an electrical repair man, and he said it needed new parts in the tone arm and wasn't fixable.
That's a red rag to a bull, that is!

If you're getting a hum from the speaker, then that means that the amplifier is getting some power. So try injecting a signal across the ends of the volume control potentiometer RV1. If this comes through the loudspeaker, then it indicates the pick-up cartridge is faulty.
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Old 15th Apr 2009, 6:05 pm   #11
AlanBeckett
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Default Re: HMV Minigram Mk. 2

AJS,
Errrrrr. Is that post backwards? Most (early) silicon transistors came in metal TO18 cans - BC107, 8, 9 for example, and lots of BFs
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