Dear all,
I hae browsed around the interned for a while now and I think I understand most the problems with my amp so I am just trying to hear from you before I start to work on it. Maybe doing so I will avoid some mistakes.
My unit sounds OK but one problem I have found is a strong channel imbalance, in order to have balance between the two channels the knob has to be rotated 45 degrees, I therefore think there is a problem.
I will start de-oxing the knobs but I have few question to you before I proceed.
1- This is the most important one: when do you actually have to replace the capacitors? I photographed some capacitors that I think need replacement [1] [2] and some other that I they do not [3] [4], do you confirm? Is there an actual test one can do in order to make a judgment or do you just use eye inspection? I am especially in double for [4].
2- I think that the main plug is an aftermarket fix and I also this is dangerous because the amp is not earthed, do you advice in just replacing the plug by cutting the wire? Or should I just leave it and earth the amp from the casing?
3- There are some part which have particularly bad oxidation (also here), in these cases do you remake the connections or just give it a clean?
Here is the link to the full album of pictures.
Thanks a lot guys, I will of course keep you posted whit any news...
Best regards,
Leo
I hae browsed around the interned for a while now and I think I understand most the problems with my amp so I am just trying to hear from you before I start to work on it. Maybe doing so I will avoid some mistakes.
My unit sounds OK but one problem I have found is a strong channel imbalance, in order to have balance between the two channels the knob has to be rotated 45 degrees, I therefore think there is a problem.
I will start de-oxing the knobs but I have few question to you before I proceed.
1- This is the most important one: when do you actually have to replace the capacitors? I photographed some capacitors that I think need replacement [1] [2] and some other that I they do not [3] [4], do you confirm? Is there an actual test one can do in order to make a judgment or do you just use eye inspection? I am especially in double for [4].
2- I think that the main plug is an aftermarket fix and I also this is dangerous because the amp is not earthed, do you advice in just replacing the plug by cutting the wire? Or should I just leave it and earth the amp from the casing?
3- There are some part which have particularly bad oxidation (also here), in these cases do you remake the connections or just give it a clean?
Here is the link to the full album of pictures.
Thanks a lot guys, I will of course keep you posted whit any news...
Best regards,
Leo
Are they noisy? - if so clean them, if not don't bother.
I would however clean the edge connectors, as always I'd use WD40 (as it's proved to be more effective over many decades) - squirt along the edges of the PCB, and wipe it off with a clean cloth - and a gentle squirt along the sockets.
You need to signal trace, or signal inject to find where it's losing the signal (assuming cleaning the edge connectors doesn't cure it).
In my old Leak Stereo 70 the fault turned out to be one of the preamp transistors, but I've seen very few other faults on them apart from that once, and (as I've mentioned already) poor connections on the edge connectors.
There are no 'popular' failing type capacitor types on those boards, so they could quite easily be perfectly fine.
A random picture of a plug doesn't help anything 😀
Two or three pin plugs depends on the market, and if it's a class-I or class-II device.
I can't even remember what mains lead my Stereo 70 had - but it DID have American style two pin mains outlets on the rear.
No oxidation in those pictures, leave it alone 😀
I presume you're referring to the flux residue?.
Dear Nigel,
Thank a lot for your detailed answer, it is very clear! Below I have two or three questions for clarification then I will buy the WD40, massage the boards and report back to you.
Thanks again!
Leo
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Thank a lot for your detailed answer, it is very clear! Below I have two or three questions for clarification then I will buy the WD40, massage the boards and report back to you.
Thanks again!
Leo
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They are not particularly noisy I just thought that the balance know could be the cause of such an imbalance.
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That is interesting I did not think about that! Which WD40 do you suggest? On Amazon I can find a million of them.
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OK that is reasonable but how on earth do you do that? Have you got a link to a guide or something? I have ammeter voltmeter and ohmmeter but not sure on how to proceed.
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Sorry my bad, that is the plug of my LEAK and since you can see the earth wire sticking out it looked strange to me, in the US where you only have to pin how do you earth? (Here in Italy we have three pins) Does one of the two pins do two jobs?
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What do you mean by flux residue?
Analog VOM is adequate to to some useful tests, with a load on the amp.
First excite the amp with some music with the same volume all the time, say a transistor radio tuned to a pop or rock station. The beats of the music will be louder, that is somewhat useful in screening out RF oscillations - you can see the beats on the pointer. Use a RCA wye cable to both inputs from one channel of the radio to excite both channels with the same voltage.
Look at the good stage on the 20 VAC scale, or on the first stage the 2 VAC scale, and see where the voltage is getting lost on the bad channel versus the good channel. Your bad component is in that stage. Pots, resistors not from the USA mil-spec factories post 1960, e-caps, bad solder joints or connections are all usual suspects. Resistors can be cheaply measured if one end is not connected to a semi-conductor.
After voltage to both driver transistors is the same, then you can ask questions about the main supply and caps. Are they up to rated voltage? Is the AC ripple on the main caps too high?
With 10000 hour service life rated small caps running $.09 each, and the big ones for 3000 hours service life running $4, I just replace the **** things instead of doing a lot of analysis. The freight on the box ($9 from NC) is usually higher than the parts costs. No, I don't live within 180 miles of a Fry's, nor do I live in London. On shelf stock caps, outside the original bag you can't tell what service life you are buying anyway. I had to replace some e-caps from local suppiers 4 times in the life of my Dynaco ST70, due to low B+ and bias voltages.
Good luck on this old classic. See this thread about some other opinions and experience: http://www.diyaudio.com/forums/soli...-70-attempt-diy-overhaul-buy-another-amp.html
First excite the amp with some music with the same volume all the time, say a transistor radio tuned to a pop or rock station. The beats of the music will be louder, that is somewhat useful in screening out RF oscillations - you can see the beats on the pointer. Use a RCA wye cable to both inputs from one channel of the radio to excite both channels with the same voltage.
Look at the good stage on the 20 VAC scale, or on the first stage the 2 VAC scale, and see where the voltage is getting lost on the bad channel versus the good channel. Your bad component is in that stage. Pots, resistors not from the USA mil-spec factories post 1960, e-caps, bad solder joints or connections are all usual suspects. Resistors can be cheaply measured if one end is not connected to a semi-conductor.
After voltage to both driver transistors is the same, then you can ask questions about the main supply and caps. Are they up to rated voltage? Is the AC ripple on the main caps too high?
With 10000 hour service life rated small caps running $.09 each, and the big ones for 3000 hours service life running $4, I just replace the **** things instead of doing a lot of analysis. The freight on the box ($9 from NC) is usually higher than the parts costs. No, I don't live within 180 miles of a Fry's, nor do I live in London. On shelf stock caps, outside the original bag you can't tell what service life you are buying anyway. I had to replace some e-caps from local suppiers 4 times in the life of my Dynaco ST70, due to low B+ and bias voltages.
Good luck on this old classic. See this thread about some other opinions and experience: http://www.diyaudio.com/forums/soli...-70-attempt-diy-overhaul-buy-another-amp.html
We actually use Servisol 40+ - but normal 'official' WD40 works fine as well.
You really need a scope (and a signal generator) for something like this, or an audio millivoltmeter and a signal generator.
If you're confident enough in your hearing accuracy you can get away with a signal generator or signal source, and a simple 1KHz or so multivibrator makes a handy signal injector, plus it works for radio as well.
You first need to download a schematic for it, it's essentially the same as the Stereo 70.
But again, simply cleaning the edge connectors could well cure it without the need for anything clever.
Yes, that's a three core lead with a two pin plug bodged on, you should replace it with a three pin one.
We have three pin plugs (and only three pin) in the UK.
There are a few brown traces (on the pot connections for example), that's flux residue, I couldn't see any corrosion anywhere.
Friend was enamoured by Leaks.
Spent ..Years... trying to Tame his Copies.
Finally gave up as there were simply TOO many inbuilt issues to patch
Spent ..Years... trying to Tame his Copies.
Finally gave up as there were simply TOO many inbuilt issues to patch
Forty year old electrolytic caps? As indianajo posted - for the cost of them, rid your amp of these suspect parts that have finite shelf and service lives. Even if their capacitance value is still in tolerance, most will have an ESR going through the roof. i.e near useless.
Sure, you'll have a hard time finding the original axial leaded types shown in your pics but a little ingenuity (they will be much smaller) by substituting the now universal radial leaded types and you'll soon have cleaner sound with fewer troubles.
Sure, you'll have a hard time finding the original axial leaded types shown in your pics but a little ingenuity (they will be much smaller) by substituting the now universal radial leaded types and you'll soon have cleaner sound with fewer troubles.
axial caps are in ready supply. BC (ex philips) still makes them. available from Mouser in US, others in Europe (or Mouser still)
Vishay / BC Components Axial Vishay / BC Components Capacitors | Mouser
Vishay / BC Components Axial Vishay / BC Components Capacitors | Mouser
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