keep waiting for the catch ... but so far so good. I've just left the presets in with blobs of nail varnish to stop em moving
the sealed presets are usually for the bias setting.
But the Cyrus has fixed resistor bias.
Are they for output offset?
Well hopefully there isn't one 🙂
(When you fit the new fuses, make sure the fuse holders are reasonably tight)
(When you fit the new fuses, make sure the fuse holders are reasonably tight)
We modified the amp to adjustable bias to cover the possibility that the replacement transistors might be different in terms of turn on voltage. It does happen with older stuff as semiconductor doping processes might have changed.
I added the presets across the solder posts next to R81 after removing R81
I expect mission provided the posts fir service convenience ?
Ice just swapped out the old 470uF caps on the preamp psu side for nichicon finr gold 100v jobs. Panasonics I wanted to git are a bit too big. And putting fine golds in where the 22uF polarised caps are on the preamp side. Have nichicon muse forcthe bipolars
How it going ?
My Cyrus 1 got fixed by this thread and the brilliant help within it.
How are you getting on with yours ?
My Cyrus 1 got fixed by this thread and the brilliant help within it.
How are you getting on with yours ?
Cyrus 1 might get back on the road again
Hi and thanks for asking about my Cyrus 1. I have to admit that I have been following this thread until the final chapter before I jump in myself. OK, I could blame the Christmas festivities but that's not true. The thread reads like a crime novel and fortunately has a happy ending. I've made notes from all the posts and will be ordering some goodies from Farnell soon. I have also unearthed my old Sinclair meter to complement my other cheapie meter. All I need to do now is tidy the shed, cut the grass, paint the house and then jump in with both feet.
The support you have been given is amazing, and my faith in humanity somewhat restored by those prepared to offer assistance patiently and without recourse to bitchy comments. I may not be as speedy as you but I reckon that with all this info I should be able to do something.
Actually, I am going to build a bulb tester first seeing as many posts indicate its importance.....
Watch this space, but don't hold your breath. Have a great 2018
Hi and thanks for asking about my Cyrus 1. I have to admit that I have been following this thread until the final chapter before I jump in myself. OK, I could blame the Christmas festivities but that's not true. The thread reads like a crime novel and fortunately has a happy ending. I've made notes from all the posts and will be ordering some goodies from Farnell soon. I have also unearthed my old Sinclair meter to complement my other cheapie meter. All I need to do now is tidy the shed, cut the grass, paint the house and then jump in with both feet.
The support you have been given is amazing, and my faith in humanity somewhat restored by those prepared to offer assistance patiently and without recourse to bitchy comments. I may not be as speedy as you but I reckon that with all this info I should be able to do something.
Actually, I am going to build a bulb tester first seeing as many posts indicate its importance.....
Watch this space, but don't hold your breath. Have a great 2018
If you do have a go then just take it slow and steady. Gathering all the evidence first is always the best way to proceed and never assume anything with fault finding. Always measure and confirm.
Good luck 🙂
Good luck 🙂
You can build a super/duper Bulb Tester following the assembly instructions of Member Decdun
Building a Gainclone chip amp power supply.
in the section "Testing" where he has added an ON/OFF switch and a Bypass/limiter switch.
If you do add these switches then at least for the Bypass I would use a Push to hold type so that you can't accidentally bypass the bulb on first power up.
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Thanks for that. This forum gets better and better. I might even dust off my box of LM3886 chips, but first things first.
Definitely make a bulb limiter.
I'm not quite out the woods yet.
I took the made the mistake of replacing a whole load of old electrolytics and de - sulphiding the selector switch overnight.
Confident ice done a good job on the switch. Pics to follow.
Checked the insulation of the outputs from the heatsink etc they're ok.
On firing up, using the bulb limiter thankfully, all seemed ok. Little glimmer on switch on, that then fades.
I've both 3.15A fuses out and the front panel switch is off.
But after about 10 seconds the bulb grows brighter and brighter and i switched off.
puzzlement.
Switched on again and checked the voltage at the fuse holders.
150v ! wtf !?
off again.
the two big 470uF caps on the preamp psu are pretty warm I don't recall that before.
why on earth would i suddenly be getting big voltages off the secondary windings ?
any ideas folks ?
I've checked all the polarised caps are correctly oriented and looked for stray solder and braid
curiouser still it's actually just c68 that's hot and the top may even have bulged up a tad (or its my paranoid imagination) whereas c67 seems only warm
Before I look at the circuit, just confirm that the 3.15A fuses are removed (so that whatever has happened has not damaged the power amp circuitry).
Caps getting warm suggest either they are fitted back to front or that they are no what they seem (fakes).
Caps getting warm suggest either they are fitted back to front or that they are no what they seem (fakes).
Here is what you need to do:
(its an odd circuit because the part of the power supply you are working on is powered 24/7 and not affected by the power switch position)
1/ Make 100% sure the caps are fitted correctly. Where were they from ? Are they of 50 volt or higher working voltage ?
2/ Connect the black lead of the meter to ground. Use a circuit ground and not the metalwork of the chassis. The negative of any of the speaker terminals should be a good point.
3/ With your meter on AC Volts measure the voltage on the striped end of D19 and D20. You should see around 20 to 22 volts AC.
(its an odd circuit because the part of the power supply you are working on is powered 24/7 and not affected by the power switch position)
1/ Make 100% sure the caps are fitted correctly. Where were they from ? Are they of 50 volt or higher working voltage ?
2/ Connect the black lead of the meter to ground. Use a circuit ground and not the metalwork of the chassis. The negative of any of the speaker terminals should be a good point.
3/ With your meter on AC Volts measure the voltage on the striped end of D19 and D20. You should see around 20 to 22 volts AC.
They were from hifi collective about a year ago when i fixed my brother's cyrus 2
fuses are out.
I'm going to refit the original 470uFs
bit non-plussed by the high voltage reading
fitted with the black stripes facing each other ie connected together centrally