Leak Delta 70 service and repair advice requested

Hi there, I am hoping that a kind forum member (or members) might take pity on an electrical illiterate, and assist me with the above topic.
To give a very short overview, at the end of last year I decided that I would go back to the future and get some 1970's hi-fi. I already had two KEF Chorale speakers which I have used for years, and before Christmas happened across a Leak Delta turntable (Lenco L75) which I have refurbished (after a fashion - new V blocks etc). Anyway to complete the picture I have bought a Leak Delta 70 amplifier off eBay, which arrived yesterday. It is a 'one careful owner' model that has been in a loft for years, and cosmetically is very clean. Before I even thought about turning it on I had a look inside, and although there are a number of capacitors that are bulging, and one small leaking one, I decided to throw caution to the wind, and connect it to some other gash speakers. Incredibly it all seems to work, although I have lost the right hand channel a couple of times.
I have not run it for longer than an hour at a time, and it is not getting hot or smelly, but before I put it into proper use I feel I should service it as best I can, given that I am an electrical incompetent.
I have read the useful thread on this site regarding the restoration of a Leak Stereo 70, and can confirm that the inside of mine looks almost identical. I would be very grateful for advice on the following:-
1. Safety. As I don't want to electrocute myself, can I be advised as to whether there are any dangers in removing items such as the 4 PCB cards, or any of the large capacitors that are attached to the chassis. Obviously it will be unplugged, but do the capacitors need to be discharged, and is there an accepted 'best practise' method for this?
2. All the controls seem to work smoothly and without any crackle or hiss, but should I try and introduce deoxit (or similar) into the switches and controls?
3. Replacing capacitors. I am hoping this is not beyond me, as I have used a soldering iron, and can make careful notes/photos of the connections, but at this stage I only want to replace items that are clearly bulging. Certainly from the Stereo 70 diagrams, parts C2, C3, and C4 need to be replaced, as might C6 and C7.


I have shown the leaking capacitor above, and the large silver ones to its right also have some discolouration on the top, and a small lump. Is there any way to test these items, without having a proper capacitance tester?
The firm Farnells is mentioned as the best source for bits but the choice is unbelievable. Could I be advised on where to start looking? i.e. am I looking for Aluminium Electrolytic - leaded, or SMD, or snap in etc. If possible I would want to keep items of the same dimensions, so that they will fit into the clamps provided.
4. Practical soldering advice. I have watched some youtube videos on this topic, but are there any hints or tips about how components are replaced on the PCB cards - are they held in a jig, how do you ensure the capacitor stays put before you solder it - that sort of thing.

Anyway, I apologise for such a long first post, and will not be offended if members just point me to places on the internet where I can answer the above questions myself!
Many thanks, Steve

 

Hi Steve,

Welcome to the forum!

I'm the guy who did the Leak Stereo 70 restoration you have been reading. The Delta 70 is virtually the same amp but with few refinements such as a different faceplate and better heat sinks.

Restoring a Leak Delta 70 makes a nice DIY project but go steady if you aren't experienced at this sort of thing.

First of all I would recommend that you practice removing and soldering components from an old scrap PCB. It's easy to damage a PCB by overheating if your technique is a bit rusty.

Have you got a decent soldering iron and a multi-meter?

 

Hi there. I have got a basic multimeter with Volt, Amp, resistance and diode check functions, and a soldering iron with adjustable temperature (100 to 500 C), but that is about it! I was wondering if it was worth buying a capacitance tester, albeit the cost would be more than I paid for the amp......
I spent an hour going cross eyed looking at the Farnell's site yesterday, and I think the best capacitors to use to replace those at C2/3/4 would be code number 1198618, Panasonic 100V 560uF. From what I have read it would appear that I should try and keep capacitance similar, although I can up-spec voltage. Is that fair comment?
My amp was repaired in 1978 at the grand cost of £10.88 when it started to exhibit distortion on the right channel when hot, and although I cannot say what was done, my output capacitors are not the same as were fitted to your Stereo 70.


If possible I would like to keep as many original components as I can, provided they are working, not least so that the original clamps can be used to hold everything in place. As regards C2/3/4, do they affect the sound quality greatly?
Thanks again for any input.

Steve

 

Hi Steve,

Those Panasonic capacitors with the Farnell order code 1198618 will be perfect for C2, C3 and C4. They are the same as I used on mine. As a bonus they are the same diameter too so will fit into the original clamps. Upping the voltage is not a problem and can actually be beneficial in adding longevity.

My friend has a Delta 70 which has the same speaker coupling capacitors fitted as yours (C34L/R) so I think yours could well be the originals.

I definitely recommend replacing the two potentiometers (P5) with some nice quality multi-turn types and then resetting the quiescent current. Be sure to follow the correct procedure though or you'll blow your output transistors.

I'd be happy to undertake the work for you if you don't feel happy doing it yourself.

 

"but do the capacitors need to be discharged, and is there an accepted 'best practise' method for this?"

Yes it's a good idea. I just us a high power rated resistor (e.g.10w 22R) and connect it across any large capacitors to discharge them for a few minutes.

I've soldered mine to some short leads which are terminated with some small insulated/shrouded crocodile clips. I leave this in my toolbox with my soldering iron so that's it's handy.

There are other ways but this works fine for me.

 

Thanks for the offer, and suggestions. I want to do the work myself, as a bit of a 'project' if I can. The info regarding discharging the capacitors is very helpful, and I can make up a similar piece of kit for my own electrical tool box.
Cheers, Steve

 

It makes a nice little project

"All the controls seem to work smoothly and without any crackle or hiss, but should I try and introduce deoxit (or similar) into the switches and controls?"

I used deoxit to clean up all of the RCA connections on the back of the amp, the contacts in the source selecting knob (front far left) and the row of switches along the bottom.

For the tone controls and the volume knob I recommend Faderlube as this is safe for use on carbon tracks and provides some lubrication.

Lift out the four cards and give the contacts a scrub with deoxit and replace them. These contacts are often the source of problems on these amps and simply removing and replacing the cards will usually be enough to clean the contacts and fix the issue. Chances are that this will sort out your right hand channel gremlins. If the problem swaps channels if you swap the cards over then you establish which card the fault is on (i.e. L or R and pre-amp or power amp).

 

Thanks. I have had a 'play' with the power amp cards, and my right channel is performing fine now. I will add Faderlube to the list of bits to buy!

 

Glad to hear you've fixed the R channel issue.

I've been rummaging through my notes for you for any helpful information and I think the trimpots I used where these: http://www.digikey.com/product-search/en?mpart=3296P-1-201LF&vendor=118

And the two big smoothing caps I used where Pansonic ED series 2200uF 200v Farnell order code 2357441. They were narrower in diameter than my originals which meant I had to get some different capacitor clamps and drill new mounting holes in the chassis floor. To secure the clamps I recommend 'J nuts' and self tapping screws like Leak used to keep the authentic looks.

 

Many thanks. The order codes are just what I need, as it gives me a clue what to look for! My list grows longer.....

 

could you undertake a repair job for me on my Delta 70 LEAk stereo amplifier?

 

I'd be happy to do it. Any idea what's wrong? I'm located in Suffolk UK if that's convenient for you.

S