Sound City B120 MKIV restoration

[Mr. Foxen]

[quote name='Slipperydick' post='1271097' date='Jun 16 2011, 10:05 AM']Eddie Current... What a great name for a 50s Rock n Roll singer ![/quote]

Eddie current and the vorticies.

[Toasted]

How many of these do you have?

[Happy Jack]

He has more vortices than you could shake a stick at.

[Mr. Foxen]

[quote name='Toasted' post='1271208' date='Jun 16 2011, 11:17 AM']How many of these do you have? [/quote]

Nine SC120, although at least one has had the preamp gutted out of it and replaced. That one and another are with a tech I trust. Am fairly tempted to use many of them at once when they are working. Not sure all of them are going to be recoverable.

Edit: typos

Edited June 16, 2011 by Mr. Foxen

[Subthumper]

[quote name='Pentode' post='1269576' date='Jun 15 2011, 06:30 AM']Ooooo.... Is this Deoxit stuff as good as it's made out to be?

Might get some if it is. [/quote]


Yeah, I thought maybe it was snake oil but tried it and have been dead impressed. Seems to be more of a detergent than a solvent. First used it on an amp that was absolutely un usable and have not seen it since I gave it back to the customer. Follow the instruction and you cant go wrong. Main drawback is the price but if its just for the ocational use it should last you years as long as you dont let your guitarist get hold of it.
Cheers Just

[Mr. Foxen]

Overkill filter capacitors (modern ones are laods smaller, same value equivalents in 35mm don't even poke out the top of the clamps, I figured more is more so these are more than double value of originals, more punch or something. I'm told it is a worthwhile upgrade for my purpose, of bass, and the guitarist I lent my Burman with overkill filter caps in was loving it, so think it should be happy.

[Subthumper]

Dont forget to make sure the old ones are discharged. I promise you it really really hurts. Never trust a capicitor..even a small one.

[Mr. Foxen]

These things haven't been powered up for 20+ years, should be good to go. Replacing all the electros an other criticals before I even try turning it on. Been suggestions I switch out the diodes, sound like a goer, they are cheap, and apparently new ones won't need the snubber caps.

[escholl]

[quote name='Mr. Foxen' post='1272782' date='Jun 17 2011, 02:22 PM']These things haven't been powered up for 20+ years, should be good to go. Replacing all the electros an other criticals before I even try turning it on. Been suggestions I switch out the diodes, sound like a goer, they are cheap, and apparently new ones won't need the snubber caps.[/quote]
lol, diode technology hasn't changed much, I don't think -- can't imagine what changing them would do for you? You don't *need* snubbing caps, really -- however, they do help mitigate one aspect of the diode's switching behaviour. I would probably leave them in, but you might find they don't make much difference at all.

[Mr. Foxen]

Most of the caps I ordered have now arrived. What hasn't arrived is solder. FS. Mission out to try an find some proper lead solder in a local shop now.

[Mr. Foxen]

Got solder. Also found leftover caps from previous SC120 I worked on. Interestingly the red plastic job, that was hidden under other stuff in earlier pics, was a 1uf but on the previous amp it was a 4uf. I checked the schematic and that says 4, so getting a 4 in there. Took a ton of photos for this bit, because it involved disconnecting things do give me space to solder other things. Will try and pick out informative ones. Nutpains here were: The screws in the clamps were really corroded, so couldn't loosen the clamps much, and someone has wrapped one can in tape and stuck some sort of foam to the other to lodge them in, so they didn't come easily, ended up WD40 around them, and pushing the out from the inside with a blunt thing. Then I realised I had to do the exact same thing because the clamps wouldn't tighten either, I used some stick on gasket stuff, like weather strip for doors, but a bit finer, came with hifi drivers, 4 bits around the can made it a snug fit.

The objective: underneath the rectifier diodes (the smarty caps attached are snubbing caps to suppress noises from the diodes switching) Wrapped in black electrical tape.



Replaced bias cap on the left, tape wrapped smoothing cap, off shot the diodes from the rectifier have been lifted off the turrets along the bottom:


The other one, with resistors lifted out of the way, looks like someone was crushing the turrets to hold the components legs in place, bit of a ballpain.



New ones installed and bits stuck back down, lumpy soldering where the crushed turrets made a pain of themselves, they should have a nice slot on the top which makes stuff really easy:



The new caps have two false legs for securing them to PCBs, since they are chunky items.

Also, small electro I replaced on the preamp board, I used some stripped off sleeve to insulate the legs to avoid shorting fun with the inappropriate radial cap in an axial's place.

[Mr. Foxen]

The 33uf electros arrived today. Due to my refusal to use overpriced made for audio caps, these are totally the wrong size for the clips and clamps holding in the originals (we're talking £8 for one 32-32 450v cap in a big can, or £7 for ten single radial ones).

Here's the ones in there, and the new ones in the background:


Took a ton of pics in case I mess something up, and labelled the wires before I took anything off. A cluster of three caps looks about right to fit in the clamp where one was before, the originals are doubles, so the third one can replace the cap in the clip, making things much neater.

Here they are assembled, and everything labelled, floating cap and clip removed. Paused because I can't find my spanner to undo the clamp:

[Mr. Foxen]

This one involves loads of really similar pictures, where I hope anyone might notice stuff I may have cocked up. Turns out labeling things 'positive' and 'negative' relative to the lugs from which I detached them isn't great when the positives and negatives are sometimes connected together.

Old cap pushed out, new ones pushed in, wrapped in electrical tape, classy, but appropriate to the originals (stick on foam held it in the oversize clamp). Old wired trimmed of melted insulation from desoldering, and the ends curled round need nose pliers to secure to legs, since there aren't proper lugs, looks a lot like a paperclip sculpture due to nothing being trimmed:



Same again, with solder and poking out ends trimmed, smooth shiny soldering contrasting the horrible bodgery it is on (cleaning everything with a meths dipped cotton bu seems to help a lot). Insulation slipped over the last leg that is the cap that was in the clip so needs connecting to the board:


Connection to the board, nice trailing wires, faithful to the existing style or willy nilly cable routing. I don't know enough about lead dress to know if I can do this better.



And from the top, on the left, original cap, wedged in with foam you can see at the edge, middle my work with the tape, and on the right, nicely fitted big modern cap I put in earlier:



Replacing the last one should be much less trouble, gonna go for similar style, but with just two caps, and figure wedging them in the clamp.

[AttitudeCastle]

Are you trying to single handedly undo [topic="126658"]this!?[/topic]



Intresting thread, even with my lack of valve amp knowledge! If i may ask how much did the 9 amps cost in total?

Edited June 28, 2011 by AttitudeCastle

[3below]

Looking at the DIY can capacitor, I wonder if you could fit them inside 35mm plastic piping. If so you could glue a pipe end cap on and have a low cost tidy can capacitor. Might work, might not.

[escholl]

[quote name='3below' post='1285524' date='Jun 28 2011, 06:41 PM']Looking at the DIY can capacitor, I wonder if you could fit them inside 35mm plastic piping. If so you could glue a pipe end cap on and have a low cost tidy can capacitor. Might work, might not.[/quote]
i was trying to think of a suggestion last night but nothing good came to mind, I think yours is actually quite a good idea if he's up for it.

or possibly heat shrink could work too, if anywhere sells one big enough to cover all of them at once.

[Mr. Foxen]

[quote name='AttitudeCastle' post='1285481' date='Jun 28 2011, 05:57 PM']Are you trying to single handedly undo [topic="126658"]this!?[/topic]



Intresting thread, even with my lack of valve amp knowledge! If i may ask how much did the 9 amps cost in total?[/quote]

They are all hosted on photobucket so aren't taking up BC space.

Don't really want to talk money, it is pretty unlikely that I'll be keeping them all and I don't want people bringing it into it when I try and move them on.

[quote name='3below' post='1285524' date='Jun 28 2011, 06:41 PM']Looking at the DIY can capacitor, I wonder if you could fit them inside 35mm plastic piping. If so you could glue a pipe end cap on and have a low cost tidy can capacitor. Might work, might not.[/quote]

i consider pulling off the plastic sleeve from the existing cap, but it was too small anyway. Cooling was a possible issue that occurred to me, but I don't think they are supposed to get hot.

[AttitudeCastle]

[quote name='Mr. Foxen' post='1286694' date='Jun 29 2011, 05:23 PM']They are all hosted on photobucket so aren't taking up BC space.

Don't really want to talk money, it is pretty unlikely that I'll be keeping them all and I don't want people bringing it into it when I try and move them on.[/quote]

I was kidding my man!

And fair enough mate, was just a little curious, i'd be interested to see and hear the out come of this!

[bumnote]

[quote name='Mr. Foxen' post='1269211' date='Jun 14 2011, 09:02 PM']Bit of an update because I had some thoughts whilst wandering around town today.

Second, I bought a can of this stuff for shining up car interiors. Seems to make things blacker and shinier, but means any dirt stuck in the basketweave shows up more. Should probably take a brush to it if I seriously gave a flying one:



Actually, now I see it next to the original photos, it makes a fair bit of difference.[/quote]

Ive enjoyed reading this. Ive used dashboard shine before but there is silicon or some such in it and it makes the surface slippery. I did read on one of the us forums that wd 40 was good for cleaning up covering all though I have never tried it

[escholl]

[quote name='bumnote' post='1286952' date='Jun 29 2011, 08:57 PM']Ive enjoyed reading this. Ive used dashboard shine before but there is silicon or some such in it and it makes the surface slippery. I did read on one of the us forums that wd 40 was good for cleaning up covering all though I have never tried it[/quote]
does it not leave an oil residue behind?

[umph]

fair,

you done all your check ups before you fire it up?

clean all the sockets (inside and on top to prevent arking)

checked all caps to make sure they're not obviously leaking

check to make sure theres no shorts on the ht

check transformers for shorts

give all the pots a spray etc.

Then fire it up WITHOUT any valves, check that ht is on all the proper pins and that there isn't any anywhere it shouldn't be ie. tone stacks / grids etc.

Check to make sure bias voltage is there.

if all thats okay give it a blast with valves in and start the proper troubleshooting ;>

[Mr. Foxen]

Clening is done. The stuff involving a meter I haven't done, don't really know what I'm up to with it. how would I check the transformer for shorts?

All the electrolytics have been replaced.

Sop fire it up without valves in and stick the meter in the valve bases, what voltages am I looking for in there, on what pin numbers (actually caught myself there, then realised that is valid use of the phrase 'pin number').

[umph]

[quote name='Mr. Foxen' post='1287143' date='Jun 29 2011, 11:21 PM']Clening is done. The stuff involving a meter I haven't done, don't really know what I'm up to with it. how would I check the transformer for shorts?

All the electrolytics have been replaced.

Sop fire it up without valves in and stick the meter in the valve bases, what voltages am I looking for in there, on what pin numbers (actually caught myself there, then realised that is valid use of the phrase 'pin number').[/quote]

[url="http://tdsl.duncanamps.com/show.php?des=EL34"]http://tdsl.duncanamps.com/show.php?des=EL34[/url]

should have the HT on pin 3 - about 530 - 540V without valves in and a little less on pin 4

3.3v AC on pins 2 and 7

bias will be negative voltage on top end of that upside down cap, follow it along to bias pots etc.

to check transformers just measure resistance across the windings etc.

[Mr. Foxen]

What sort of figures should I be seeing on the transformers?

[umph]

[quote name='Mr. Foxen' post='1287179' date='Jun 30 2011, 12:01 AM']What sort of figures should I be seeing on the transformers?[/quote]
under 1k, basically though if you turn it on and theres voltages it'll more than likely be okay