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Just joined, lots to read about the TD125

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Just joined, lots to read about the TD125

Postby p38arover » 18 May 2018 06:43

Hi,

I am the owner of a second hand TD125 (Mk1) with an SME 3009 arm and Shure V15 cartridge that I picked up about 25 years ago. It has languished, unloved, and wrapped up brown paper in the garage ever since. (Don't flame me!)

It came from a radio station where I worked for a while as a tech. It was sitting in the equipment storeroom and excess to requirements, so I bought it with a view to getting it going.

The motor doesn't spin up - maybe that's why it was in the radio station storeroom - so checking the electronics will be the first job. :D

I finally decided that maybe I should finally do just that. If I don't, then I know that when I die, my daughter will toss it in the rubbish with all my other good stuff. She won't know what's good and what's not - and there's a lot of good stuff - electronic test equipment, workshop tools, woodworking machinery, etc!

The turntable needs a plinth as it came without one - I'll hunt around for dimensioned diagrams and will get my trusty table-saw to work.

Cheers

Ron
Western Sydney, Australia
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Re: Just joined, lots to read about the TD125

Postby Tonybro » 18 May 2018 07:24

Interesting back story there, Ron!

There's an absolute wealth of information here. You're in the right place! :D
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Re: Just joined, lots to read about the TD125

Postby p38arover » 18 May 2018 07:32

Thanks Tony.

My first turntable in 1969 was a Garrard SP25 Mk II. That was followed by an APAN BRU121 belt drive (I think it's out in the garage, too). My current TT which I've been using for many years is a Pioneer PL-51 direct drive with a Shure M91ED cartridge.
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Re: Just joined, lots to read about the TD125

Postby p38arover » 19 May 2018 04:07

The radio station had replaced the Thorens with two Technics SP10 Mk2 turntables but I can't recall the tone arms. I should because I also hosted the Friday night request programme. :)
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Re: Just joined, lots to read about the TD125

Postby p38arover » 20 May 2018 11:47

It is now running - I replaced the two 2200uf electrolytic caps as a matter of course as the ripple voltage was a bit high and the caps were quite old.

But I have an issue with the power supply voltages (the issue was there before replacement of the caps).

The transformer, P/N B830-10 is supplying +- 19.4VAC. The resultant DC voltages are +-23.9 VDC. They should be +-16.5 VDC.

The transformer P/N appears correct as seen in the exploded view in the TD125 manual.

My first thought was that the transformer was wired incorrectly and 240VAC was being applied to the 117V winding but the AC wiring is correct albeit a little imbalanced. My AC mains voltage tonight is 246 VAC into the 230V winding and the split across the transformer winding has 126VAC on the 117VAC lead (which is correct if you do the maths (i.e., 246/230 * 117 = 126).

The transformer DC resistances for the windings are odd, too. 71 ohms across the 117V winding and 144 ohms across the nominal 230V winding. I'd have expected both to be the same (or very close) for a centre-tapped transformer.

Any thoughts welcome.

Cheers

Ron
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Re: Just joined, lots to read about the TD125

Postby p38arover » 22 May 2018 02:55

Just an update.

I powered up the TT via a Variac adjusted to give 230VAC. The voltage on the 117 volt tap of the transformer was exactly 117VAC.

The transformer secondary voltages were 18.1VAC on both outputs.

The resultant DC voltages on the power supply rails were +- 22VDC.

I called my brother-in-law and he measured the AC from the transformer on his TD125 Mk 1 and got similar results to those that I got earlier, i.e., 19.7VAC. His DC voltages were also similar at 24.4VDC.

So based on a sample of 2, one could infer the 16.5 VDC markings are wrong or the transformer specs were changed during production. It would be nice to have some measurements from other owners.

Threads I have read on this forum where people have queried the transformer specs with a view to replacing their dead transformer have all speculated on the transformer voltages by working back from that hyperthetical 16.5 voltage.
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Re: Just joined, lots to read about the TD125

Postby p38arover » 22 May 2018 04:25

Curses! Blasted iPad changed "hypothetical" to "hyperthetical"! (above). I'm going to have to turn off auto-correct! Yesterday it changed "Nakamichi" to "malamute"! Gaahhhh!
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Re: Just joined, lots to read about the TD125

Postby p38arover » 05 Jun 2018 11:56

Received new Thakker drive belts (one for me, one for my B-I-L) today.

I mentioned earlier about ripple on the power supply. It's a pretty basic unregulated supply and the ripple varies according to the speed selected.

The basic ripple is, as you can see from the oscilloscope settings, 50Hz (2 divisions at 10ms/div = 20 ms or 50Hz). The amplitude varies due to ripple but is about 2 divisions or 2 volts. The gap in the trace is due to the trace flyback.

Image

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Image
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Re: Just joined, lots to read about the TD125

Postby p38arover » 09 Jun 2018 05:38

p38arover wrote:That was followed by an APAN BRU121 belt drive (I think it's out in the garage, too).


That should have read Apan BFU-121
Attachments
Apan BFU121 1.jpg
Apan BFU121 2.jpg
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