Dating from around 1974, and mostly valueless... eBay prices these at about £30 at the time of writing.
Still, there's no point in it just sitting in a pile...
It's been through the wars a bit, but that's OK. I need something to practise my veneering skills on, for a forthcoming turntable project, so this may do as a test bed...
Typical 70's construction.
I'd labelled the amp up "Hums" ....
There's something unpleasant oozing out of the top of the positive rail smoothing cap... It's a 6,800uF 40V part....
... I have some 10,000uF 63V parts, which are slightly fatter, but much shorter. The fit in the clips OK, so they'll do....
Powering up instantly blows both 5A fuses on the main board. You can see in the photo, I've lifted R3 and R5 on the small vertical PCB. This is the protection board. It's purpose in life is to blow fuses by shorting out the supply rails with a triac in the event of there being more that 0.5VDC on the speaker outputs. A sort of crowbar circuit.
Powering up again, with new fuses and checking the speaker outputs (with no speakers attached) for DC shows everything in order.
R3 and R5 are soldered back into position and power is applied again. All is well. I wonder if one rail came up before the other due to the new/larger caps?
I check round the caps on the main board for ESR. Remarkably, they all check out OK. Every last one of them! I even checked the calibration on the ESR meter because I doubted it!
The power indicator lamp on the front doesn't work, because, well... it's missing. I'll make up some white LED's to go in...
I had a short length of LED strip left over from when I fitted some lighting in my kitchen, so I cut off a short length. The voltage supply for the lamps is half wave rectified, with no smoothing. It peaks at around 20 volts, so I added a 470 ohm resistor to limit the current a bit, and added 100uF to smooth the supply a bit, so the LED's don't flicker.I removed the original lamp holder, and fixed the strip in place with a spot of hot-melt.
Looks good....
After a prolonged test in the workshop, the amp remains well-mannered, and sounds decent. It's quiet and produces around 30 watts into 8 ohms. I'm actually quite taken with it, so much so, I'm going to put it in the main hifi set up for a bit.. one issue though... the input sensitivity. It's a tiny 140mV for line inputs. We'll need to fit an attenuator on the input I intend to use for the CD player. Thankfully there's an attenuator switch fitted to the Tuner input, which is switched on the back for two different levels. Looking at the circuit, my calculations show it'll do as it stands. Good news!
Now to make up some 5-pin DIN to RCA leads, and order some veneer!
Talking of 5-pin DIN plugs... this Leak doesn't quite follow convention....
1 is Right input
2 is GND
3 is Left input.
4 is Right output for Tape/cassette
5 is Left output for Tape/cassette....
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