Repairing a SoundCity 120

[Zozobra]

A friend had an SC120 that was making all sorts of noise and misbehaving. First notable thing was one of the 6(!!!) EL34s was redplating and was for the bin.


When I pulled the chassis I was greeted by this. Yup, the safety ground and become disconnected, leaving the amp at risk of causing electric shock should there be a short to the chassis and also leaving the circuit floating.



I repaired the safety ground and also added some much needed strain relief with a couple of cable ties behind the cable gland.



I stuck a spare EL34 in and rebiased to around 60%. Ideally I'd want to stick a full fresh set in but that's not an option for my friend right now. The spare I have is matching okay with whats in and the quiescent current on each half of the output transformer is reasonable balanced.

The amp is sat idling for an hour on my bench to test it. I can't crank it right now unfortunately. So far no bad noises or redplating.
The big blue cap in the top of the photo was also secured into the clamp as it had become loose.

I should hopefully be able to drop this back with my friend soon. It'll get cranked of course.

[ajaxlepinski]

Charge him $400 for Bench Time and $50 for the tube!

Just kidding!

Man, I'd still have a few old amps if I knew that some issues wer easy to fix.

[Zozobra]

Amps aren't that hard to diagnose and repair. Most of the time it's going to be something simple like bad tubes or blown screen grid resistors. After that you're looking at the power supply or bad wiring. Actual wacky shit that takes a lot of effort to figure out is pretty rare.

[trey85stang2]

Charge him $400 for Bench Time and $50 for the tube!

Just kidding!

Man, I'd still have a few old amps if I knew that some issues wer easy to fix.

Every so often if i want to make some cash, I post up on craiglist offering to buy broken tube amps. You would be surprised at the stuff you can get for less then $100 bucks, 90% of the time its something very very simple.

[MikeO]

Every so often if i want to make some cash, I post up on craiglist offering to buy broken tube amps. You would be surprised at the stuff you can get for less then $100 bucks, 90% of the time its something very very simple.

A few years ago I got a Peavey Ultra Plus for $100 because the guy said it didn't work and he didn't want to bother with it. It ended up being a 12AX7 that needed replacing. Thank goodness for lazy people.

[ajaxlepinski]

Charge him $400 for Bench Time and $50 for the tube!

Just kidding!

Man, I'd still have a few old amps if I knew that some issues wer easy to fix.

Every so often if i want to make some cash, I post up on craiglist offering to buy broken tube amps. You would be surprised at the stuff you can get for less then $100 bucks, 90% of the time its something very very simple.

What a great idea!
Been studying amp repair as a hobby for a couple of years... I think I need to give this a go right now.
My plan was to supplement my Social Security (when I retire in 10 years) by fixing other people's amps.
But, it never occurred to me to advertise for broken amps to fix and resell.
Cheers!!!

[trey85stang2]

Every so often if i want to make some cash, I post up on craiglist offering to buy broken tube amps. You would be surprised at the stuff you can get for less then $100 bucks, 90% of the time its something very very simple.

A few years ago I got a Peavey Ultra Plus for $100 because the guy said it didn't work and he didn't want to bother with it. It ended up being a 12AX7 that needed replacing. Thank goodness for lazy people.

My best one was a guy that had a fender pro jr. He was so excited to get rid of it he drove it across town to my house and I gave him $20. It intermittently would power off. It was two broken solder joints from the transformer to the board. I had it sold for $300 a day later.

[ajaxlepinski]

$280 profit on a couple of drops of solder! Amazing!

[Riffraff]

I have 4 amps in my collection that were intended to be fix and flip amps. I fixed them all, it's the flip part I seem to have a problem with.

'65 Danelectro DM10 $50 broken tube (value $150)
'67 Silvertone 1482 $185 loose speaker lead & broken volume pot (value $400)
'59 Stromberg Carlson AU10 $100 bad power switch (value $250)
Peavey 6505+ $275 burned ribbon cable connector (value $450)

The only one I actually fixed & sold was a '70s Earth G1000 head I got for free (Dual Showman clone). It needed some rewiring to replace wires mice had completely eaten and a few tubes from my stash. I sold that for $250.

[Zozobra]

Alas this amp has now developed another fault and will be back on be workbench when I have time. I'm gonna go through the whole damn amp as it's most likely a bad wire/solder joint that has gone microphonic. SC120's can be a massive pain in the ass!

[Riffraff]

I feel your pain bro.



There are so many possible rabbit holes to go down under the hood.



I recapped mine then chased ghosts for a few years before giving up and selling it.

[long standing member]

I have 4 amps in my collection that were intended to be fix and flip amps. I fixed them all, it's the flip part I seem to have a problem with.

Brother from another mother!

Do you know how many laptops and desktops I have (and there's only me, wife, and 2 kids)?

I'd much rather be fixing amps!

[Pepi]

I've owned one Sound City head and fixed another plus mine. I will say they are a bitch to troubleshoot. Fucking intermittent problems with both