| Author | Message | ||
| Rory Coupland (bigjilm) Username: bigjilm Registered: 06-2013 |
Hi chaps. I was wondering (& thought sensible / also may be good general info for anyone) if I could be reminded of the best procedure to bleed filter caps (& bias caps/ others) discharging them safely to ground before removal. I plan to recap my 9 basic caps in an old MM 130 (2275). Ive got all f&t caps at correct or higher voltages ready, & I've built 3 amps before -but a good while ago- so a reminder seems sensible preparation. Any other tips welcome. Thanks, B-JiLm. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Well, I use a 50k resistor of about 2 watts fixed on a probe and go around and hit all the caps themselves and randomly on the circuit. Some guys use a bigger resistor, kind of depends on what you have. Some recommend a 100k, some 200k. Even 1 meg works good, just slower. After I drain them, I usually clip a test lead from the caps to ground because caps have a little memory and will sometimes build back up a little so I keep them grounded while I work. Just remember to REMOVE the jumper before firing up! Mike. | ||
| Rory Coupland (bigjilm) Username: bigjilm Registered: 06-2013 |
Thanks Mike, I had this planned but -always- good to be reminded. I shall also be using a chopstick, and have one hand in my trousers, such will be the excitement involved. I did read s'where on here about an added 'bleed' involving unplugging the mains plug from wall, whilst on standby.. or whilst still 'on'.. or s'thing? I dont suppose it would add any | ||
| Rory Coupland (bigjilm) Username: bigjilm Registered: 06-2013 |
..thing to the bleed process over what you knindly suggested, would it? cheers B-Jilm. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
They say that yes, turn off amp while NOT in standby, play guitar through it until you stop hearing anything. May work, may not. I folow the x files credo-TRUST NO ONE (or anything). Measure, drain, measure again. | ||
| Rory Coupland (bigjilm) Username: bigjilm Registered: 06-2013 |
So "turn off amp while NOT in standby, play guitar through it until you stop hearing anything" is just the normal way to turn off the amp, no? (ie amp playing away with stby in the down/65w position, then turning amp off at the back shuts the whole mumma down. One just has to remember next time to flick stby switch to centre b4 turning on again at the back). Is it the actual playing s'thing / putting a signal into the input which is the point to this? | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
It's more of an indicator. I STILL don't suggest it. I don't trust anything like that. MEASURE THE VOLTAGE on the caps and be safe. Mike | ||
| Rory Coupland (bigjilm) Username: bigjilm Registered: 06-2013 |
Aha I get it.. I think I'll just go the normal way you suggest / I had in mind. One other thing: once amp is on its back the cap-can Im not quite so used to (tweed amps Ive made, filter caps inside etc).. I was thinking if some DC left in a cap and unluckily the can touches a + end when removing, my trousers might have not so much room in. Is there extra special care needed to lift this off? is it easy without any prizing or tugging involved? Any tips on removing this? or is there plenty of room each end undernesth to prevent such an unlucky mishap. One hand makes sense here Id say. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
The cap cover USUALLY is kind of stuck from the padding in there but there is plenty of room. Just lift it up amd make sure you mark each cap position with a sharpy or something before removing. You can just grap the cover from the outside and wiggle as you lift and it should come off. If you have drained the caps from the open side, you can clip a jumper from someplace like pin four on the power tubes to ground and that will get you safer. Mike. | ||
| Rory Coupland (bigjilm) Username: bigjilm Registered: 06-2013 |
Cheers Mike- that gave me the inpetus to go for it, and nice & roomy it was: 6 of the 9 caps you suggested Ive replaced.. .. but which 3 of the 5x 20uf caps on the B2 board Im meant to be redoing? do you know by visually referencing? (schematic is not easy w'out getting clear vision underneath: not so easy at all). Thanks B-JiLm. Also Is there any pic of the 2 filter cap board I can check anywhere? (I marked the + and - on the board but forgot to mark the red/white lead and the green lead which attatch looking as I was to the RHS of the caps.. daft ejut so I am). | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
I suggest doing ANY eletrolytic caps. TWO filter cap board? The main PS caps under the cap cover-there should be 4, not 2. Which amp did you have? I thought it was a 130. The on;y board that has two caps on it is the bias supply board. If that is what you want, here you go.  | ||
| Rory Coupland (bigjilm) Username: bigjilm Registered: 06-2013 |
Hi Mike, the amp is a MM 130 (2275) and I expected to see 4 caps under the cap-cover.. but only TWO large (Mallory) 100uf 450V hooked onto its fibreboard. Im sure too no-one had opened that up since it was new too. The amp looks completely unserviced, or even opened tbh, all orig caps, nothing unoriginal anywhere. The bias supply board as above (thx) I have indeed done. Just the 3 20uf to fit s'how in the bias (trimpot etc) board.. but which I cant work out, or fit as theyre too big! maybe some sprague 25/25v Ive got a few of? | ||
| Rory Coupland (bigjilm) Username: bigjilm Registered: 06-2013 |
Im confused now. On the schematic it has 2 100uf/450v filter caps. Under my cap-cover I did indeed find 2. Removed (Message edited by usermod1 on July 07, 2013) | ||
| Rory Coupland (bigjilm) Username: bigjilm Registered: 06-2013 |
\ Removed (Message edited by usermod1 on July 07, 2013) | ||
| Rory Coupland (bigjilm) Username: bigjilm Registered: 06-2013 |
Mike I cant figure out how to add a pic- or to erase a post: could you erase these two last posts? I dont want folks trawling tru my 'photo album' particularly. thanks B-JiLm |
Tue, 03/25/2014 - 09:54
#1