So, yesterday I picked up an early 1970´s Laney Supergroup MK1. The dude gave it away for free because he was moving and was tired of storing it. I got the info that the amp powers up but it doesn´t make any sound. Well let´s see..
I took some photos outside that shows the amp has been stored quite well. It has a couple of really small dents in the corners but the vinyl is in very good condition. I also took the chassis out and set it up for some closer examination. Looks like this beast is pretty much original and I got some serious replacement work ahead. I will print out the schematics tomorrow and start taking some measurements. Luckily the inside are overall pretty clean so it´s not too had to follow the schematics.
I´m not powering it up. I´m thinking I´ll first go through measuring the coils of the transformers to see if there are any shorts. Also checking shorts in the tubes, couple of the power tube sockets feel a little loose.
I posted this thread because I know someone has some insight reagarding this particular amp and possibly can see the condition of this unit in a different view. Also any discussion regarding this amp is welcome.
K
I took some photos outside that shows the amp has been stored quite well. It has a couple of really small dents in the corners but the vinyl is in very good condition. I also took the chassis out and set it up for some closer examination. Looks like this beast is pretty much original and I got some serious replacement work ahead. I will print out the schematics tomorrow and start taking some measurements. Luckily the inside are overall pretty clean so it´s not too had to follow the schematics.
I´m not powering it up. I´m thinking I´ll first go through measuring the coils of the transformers to see if there are any shorts. Also checking shorts in the tubes, couple of the power tube sockets feel a little loose.
I posted this thread because I know someone has some insight reagarding this particular amp and possibly can see the condition of this unit in a different view. Also any discussion regarding this amp is welcome.
K
does the impedance selector link have continuity?
i'd also fix the ac line (looks like someone replaced that) and take the incoming ac ground off the controls and apply it to the chassis
check the output tubes section, it looks like one of the resistors was replaced, possibly to fix a previously shorted output tube.
bias supply cap looks like a replacement also.
i'd also fix the ac line (looks like someone replaced that) and take the incoming ac ground off the controls and apply it to the chassis
check the output tubes section, it looks like one of the resistors was replaced, possibly to fix a previously shorted output tube.
bias supply cap looks like a replacement also.
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How did you know where to go first?
There´s no continuity on the link piece. The resistors seem to be in surprisingly good condition, very well within tolerance. Yes, the bias cap has been replaced with a 25uf? Should I go back to 10uf which is in the schematic?
K
the picture gave it away (thanks to the close up) you can see the holes at the ends of the pins have no solder, but many an old Marshall with that style connector has the wire link sheared off from the head getting wedged in somewhere in the truck pack.
the bias supply cap should be fine as long as it's not an old "leaky" cap.
speaking of things in the picture the socket with "replaced" resistor looks to have been replaced as well, no?
standby switch too!
the bias supply cap should be fine as long as it's not an old "leaky" cap.
speaking of things in the picture the socket with "replaced" resistor looks to have been replaced as well, no?
standby switch too!
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I think it´s the original socket but the rivets have been taken out from the way of screws. The three remaining sockets are pretty loose. Those are attached with rivets.
I think it´s the power switch that has been replaced. Looking at all the images of other Supergroup units both the switches are those with metal toggles. The power switch toggle is plastic. I have those metal toggle switches in stock too so I might just replace that to meet the original look.
Also I have a lot of 70´s NOS resistors stored from my dad so should I see about replacing those that have drifted some?
K
I have all the necessary parts but I haven´t put one together yet since I wasn´t prepared to get a project in my hands with these kind of voltages any time soon. I mainly work with low voltages.
But I´ll first go through the very principles of this thing and surely before powering this beast up I will have one bulb tester ready.
K
Yes, the whole "reaching accross the board" type of approach to this looks a little hazardous to me. So I was thinking replacing the rubber "reinforcement" in the entrance of the AC line and anchoring the Earth to the chassis nearby the AC entrance.
This unit has been stored for 8-10 years on a shelf a dry space and has not been used since. I think I´m probably going to sell it in some point down the line because it´s not really my thing. It is awesome, but t´s a bit too much.
I´m trying to keep it as original as possible, but do a clean good job on the restoration on the parts so it´s in good working condition for the next owner.
There´s the other same type selector there for the mains voltage. The link piece is the very same and it conducts very well. No solder on that either, and that works. Should I start looking for a replacement for that link piece?
K
Man, that´s what I thought! And getting it for free, I´m going to take really good care of her
I´m glad I have a lot of 70´s electronics in stock so I can probably keep the resistors and such pretty much to that date and keeping the same feel of the amp. It would be a disgrace to update an amp like this more than necessary.
EDIT: And that´s one of the reasons for this thread, do it right. I´m asking a lot of questions about particular components to keep it in the right lane and not go overboard.
K
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are you checking that link/jumper out of circuit?
with respect to the power transformer i have a suspicion that it's been replaced and likely has the selector jumpered internally.(didn't see any in the pictures)
as to the impedance selector you could solder a jumper wire or if you think that's too ghetto than yes replace it
with respect to the power transformer i have a suspicion that it's been replaced and likely has the selector jumpered internally.(didn't see any in the pictures)
as to the impedance selector you could solder a jumper wire or if you think that's too ghetto than yes replace it
Checking iit out of circuit and it´s conducting. Here´s the selector without and with the jumper. The PT primary taps need the jumper link to work properly, so no conection without it.
It probably wouldn´t ghetto at all if it was any other amp than this
K
I think that is something thought out later on in the amps life. There´s a piece of clear film between the chassis and that selector. So when looking at the selector from outside it seems like there´s no access to it. It is the same type of selector as the impedance selector but the jumper has been set inside the unit. Probably so that anyone wouldn´t knock it off by accident and then bust out the whole unit with installing it in the wrong way.
K
The mains input should be using a 3 pin round 5Amp Bulgin. These were never hard wired and Laney have never used hardboard as a mains cable holder!
If you want authenticity bulgin 3 pin | eBay
Otherwise a standard IEC connector will fit after a fashion.
If you want authenticity bulgin 3 pin | eBay
Otherwise a standard IEC connector will fit after a fashion.
I will look to purchase this bulgin connector. I´ll go as close to the original as possible. Thanks for the information!
One question about the 16uf caps, they´re probably fine replaced with 25uf caps? Or even 15uf? The 15uf caps are readily available here in 500V rating as the 25uf sprague caps are only available in 50V rating.
K
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