DSL 50 Not Working

[Lane Sparber]

Well, the main filter caps have nothing to do with the bias circuit. I'm not sure if that's what Asp was driving at, but it's doubtful that those are a factor in this issue. They could, depending on how they fail, contribute to crackling. That being said, because the filter caps act globally (for Asp's intents and purposes here) and this crackle is ONLY on the green channel, once again I doubt that they're a direct cause of any of his symptoms. If, on the other hand, a BIAS filter cap were to develop a dead short, it would certainly affect the bias voltage. It's extremely rare, but it can happen. Once he posts his unloaded bias voltage range like I asked him to, then we'll have a much better idea as to what's going on.

At any rate, should the amp proves to be more then 10 years old, then ALL electrolytic caps should be replaced, IMHO. It's not fun by any stretch of the imagination, but it's what's best for the amp.

-Lane

 

[aspguitars]

I've got a white barcode type sticker with the number : M-1999-20-1207A

 

[Lane Sparber]

Your amp was made the 20th week (last week of May/1st week of June) of 1999. As I said, IMHO, time for a complete re-cap. That's one question down!

Please click on the following link and scroll down to post #132 for a detailed series of blogs wherein I detail this exact re-capping process on my OWN DSL:

http://www.marshallforum.com/workbench/23877-lanes-corner-one-techs-blog-5.html

-Lane

 

[aspguitars]

Hi! Lane,
readings with V6 and V6 removed from pin 5 to chassis
V6 44.3v DC max
33.5v DC Min

V7 44.2v DC Max
33.7v DC Min

 

[aspguitars]

Hi! Lane,
just read your thread on the re-cap as recommended. Really very informative. If you don't mind me asking, what sort of price are you looking at to replace all the caps. I can source them myself, but as you say, easier to buy a kit. I just don't think I'll get one in the UK though. Perhaps I can get one sent over. I've got hundreds of components, but guaranteed not to have the one's I need.
Thanks again
Ade

 

[Lane Sparber]

Your bias voltages look great! Dead on. Try a different set of power tubes, and bias according to the method I lay out in the blog you just read.

As to the caps, there's an appendix to those posts in my blog where I link to the caps I used from Mouser. I don't know if the links are still good, but it's worth a shot. JCM on this forum sells a kit with the HT caps, so hit him up for a price. As to the other elkos, to the best of my knowledge you're kind of on your own. Do your own counts and see if my links will work for you.

In the meantime, try a known good set of power tubes and see if they'll bias up. Then you can start looking at your green channel as I outlined above.

-Lane

 

[Lane Sparber]

Your bias voltages look great! Dead on. Try a different set of power tubes, and bias according to the method I lay out in the blog you just read.

As to the caps, there's an appendix to those posts in my blog where I link to the caps I used from Mouser. I don't know if the links are still good, but it's worth a shot. JCM on this forum sells a kit with the HT caps, so hit him up for a price. As to the other elkos, to the best of my knowledge you're kind of on your own. Do your own counts and see if my links will work for you.

In the meantime, try a known good set of power tubes and see if they'll bias up. Then you can start looking into your green channel issues as I outlined for you above.

-Lane

Edit: CRAP! Sorry for the double post. That's what I get for posting from my cell phone.

 

[aspguitars]

Hi! Lane,
when I took these measurements, I measured from pin 5 to chassis as recommended. When I try to set the Bias with the tubes fitted, I use the three bias pins at the back of the amp. Do you thing perhaps it could be a problem on those pins, and could I actually set the bias by testing at pin 5 to chassis?
Ade

 

[Lane Sparber]

You could buy a bias probe and test that way. You can't really measure straight from pin 5. Try an alternate set of power tubes first using the pins in back.

-Lane

 

[aspguitars]

Hi! Lane,
will try some new tubes as suggested and try again. Thanks Ade