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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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29th Aug 2012, 11:23 pm | #1 |
Pentode
Join Date: Jan 2009
Location: Bury, Greater Manchester, UK.
Posts: 103
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Early HMV electric pickup help needed
Hi again
I am in the process of bringing my HMV 532 radio-gramophone back to life and would really appreciate s little help. The amplifier works brilliantly and packs a punch but the radio and gram sources are problematic, I can however use an external source (namely a portable cd player/radio) and get great results. Currently I am trying to get the pickup working. I have replaced all the wiring from the pickup to the pre-amp and across to the power amp but the pickup produces exceedingly little sound. All the rubber in the pickup seems fine and I am now wondering whether the coil is the culprit. This is where I am in need of help. Does anyone have any experience of re-winding the coil in the pickup head. This is the HMV electric pickup no 15 in the metal shell that contains one coil. Any help and guidance as to what I need to use and how to go about removing and replacing the wire would be greatly appreciated. Steve |
29th Aug 2012, 11:31 pm | #2 |
Octode
Join Date: Jul 2006
Location: Solihull, West Midlands and Beaford, Devon
Posts: 1,626
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Re: Early HMV electric pickup help needed
Hi Steve.
I'm not an expert on record players (or anything else if it comes to that) but I had a similar problem with my HMV radiogram (I don't know the model number but the pickup head was a big brown metal box which you could rotate 180 degrees to change the needle). Although the rubber looked kind-of okay, it was very tough and the needle couldn't move it far at all. I replaced it with the thick rubber from the top "handle" portion of a hot-water-bottle and everything was fine after that. Anyway that's just my experience. Thanks Steve. Kind regards. From Mike.
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G7TRF |
30th Aug 2012, 8:34 am | #3 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
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Re: Early HMV electric pickup help needed
Hello Steve,
The first thing you need to do is measure the actual resistance of the coil. Most HMV pick ups are high impedance with a coil resistance of around 1.3K. Some AC/DC models have a very low resistance of only around 40 0hms. They are matched to the high slope output valve via a matching transformer. If the 532 has a triode preamp stage such as the MHD4 your coil will be the 1.3K type. These are wound with very fine hair like wire but is surprisingly strong. The coil usually goes O/C where it joins the lead out wires due to 'green spot'. If the coil is definitely O/C it may be possible to unwind it taking care to store the wire on a cardboard former as it is very difficult to see and tends to knot. [Very frustrating] You will then be able to form a new lead out wire and hand rewind it with the aid of a small dowel placed through the circular coil former. The coil former is very delicate and brittle, take great care with it. If damaged it can be repaired with VERY thin fibre washers. As Steve mentioned the square damping rubber on top of the needle holder and the two small tubular sections on the needle holder pivot have to be 100% with the holder set dead central to the magnetic poles, difficult to describe. If the needle holder is 'stuck' to one of the poles the result will be zero output. John. |
30th Aug 2012, 12:57 pm | #4 |
Pentode
Join Date: Jan 2009
Location: Bury, Greater Manchester, UK.
Posts: 103
|
Re: Early HMV electric pickup help needed
Thank you for the quick responses. I shall take a good look at this this afternoon.
John, I'm sure that the 532 does have the MHD4, thank you for the info on the resistance - that is so helpful. I shall change all the damping rubbers anyhow as this will no doubt make an improvement. Steve |
1st Sep 2012, 7:58 am | #5 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
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Re: Early HMV electric pickup help needed
You will need to cut a tiny slot in the top damping rubber to enable the top of the needle holder to locate. Set the needle holder gap between the pole pieces at equal distance with the securing screws. This is most important. Make sure you actually have a magnet in the pick up....If the coil reads OK it must work. Use silicon rubber sleeving for the bottom damping if your local friendly cycle shop ran out of valve rubber in 1961.
John. |
13th Sep 2012, 4:37 pm | #6 |
Pentode
Join Date: Jan 2009
Location: Bury, Greater Manchester, UK.
Posts: 103
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Re: Early HMV electric pickup help needed
As suspected the coil was broken. There was nothing registering on the meter what so ever. So after much meddling I thought I'd have a go at taking all the wire off the coil. I made a rights pigs ear of it. The kept sticking to the coil and snapping, and I eventually ended up with an empty real and a huge mess of what I can only describe as hair! Thankfully I've another pickup somewhere.
Out of interest has anyone found an alternative wire that could be used to replace the hair like stuff? Steve |