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

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Old 23rd Mar 2018, 11:19 pm   #21
Sideband
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Default Re: Leak Stereo70

I have one of these amps giving very good service. Mine needed some electrolytics changed in the preamp modules...the ESR meter showed they were very poor. Once these were changed, the performance was greatly improved and I also set up the Q current. The pots were OK on mine but it might be worth checking them again (two years since they were touched) just in case they've drifted.
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Old 24th Mar 2018, 9:14 am   #22
nutteronthebus
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Default Re: Leak Stereo70

I have used in the past on Quad 33 pre amps BC550 to replace the BC109 ( as recommended by DADA ) they seem a good lo noise transistor
Ps I also need a 200 ohm pot for bias adjustment as mine fell apart on setting the thing

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Old 27th Mar 2018, 1:42 pm   #23
PatMorgan
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Default Re: Leak Stereo70

As well all do when we repair something- I think the reason my preamp board blew was because part of the track on one of the power amp boards broke, leaving a driver transistor collector unconnected- this would have done a good job on the previous/earlier section. Before Id reliased this, I swapped the pre-amp boards within and meagrely transferred the fault! But I have no shame sharing this as others might learn. I migth of course be wrong, but it was working fine then i lost one channel.

The tracks on the boards are not particularly heat sensitive- and Ive gone back to my small Antex, rather than 25w one for any board-repairs.

As nutteronthebus has found- 200 ohm trimmers are like gold-dust to the wattage these amps need. I notced yesterday a S70 on Ebay in a very poor condition but seems to be there electronically-speaking. Its had its 4 diodes repalced for a 3amp bridge, but the boards are there. One of the big caps has been repalced- it might be a source of spares, but I bet it works or wouldnt need much to get iot working! A new mains lead, sleeve and a few covers might help- and some Letraset.
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Old 27th Mar 2018, 2:06 pm   #24
PatMorgan
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Default Re: Leak Stereo70

Quote:
Originally Posted by Sideband View Post
I have one of these amps giving very good service. Mine needed some electrolytics changed in the preamp modules...the ESR meter showed they were very poor. Once these were changed, the performance was greatly improved and I also set up the Q current. The pots were OK on mine but it might be worth checking them again (two years since they were touched) just in case they've drifted.
My IQ reference had gone from 35ma to 120ma in the space of a month- You can generally tell if its drifted for the worse as the heat from the output transistors is obvious when you put your hand on the top of the amp- even if its only been running for an hour or so. The trimmers, Im sure are the culprits.
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Old 23rd May 2018, 12:19 pm   #25
PatMorgan
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Default Re: Leak Stereo70

I have a distinctive 'crack' through the speakers when I turn off one of my Leak Stereo 70's- any suggestions please? ive not changed the output or PSU smoothing caps (which I suspect one or other is the culprit)
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Old 24th May 2018, 7:54 pm   #26
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Default Re: Leak Stereo70

That 'crack' noise might be coming from the mains switch.

You could try a snubber network across the mains transformer primary.
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