MKIIC+ - Looking inside my DRG

[Dasein]

Hi Guys

Pulled my amp out -- it's been a while -- I let it warm up in standby and turned it on. The magic is still there but I'm getting some noise. I'm also smelling what I'd call an electrical smell -- NOT BURNING -- more like Ionization. For the first time in my life I pulled it out of the body and had a look (just felt I should look in case I had some obvious bad caps). To be honest -- I see nothing alarming. Any thoughts? I've always (since I bought it in 84 associated a smell with using the amp - a combination of the wood and the tubes and electronics but It's been a while so I'm not sure if this was what I used to smell or if it's something else. My wife thinks it's just dust. Although in my life I have brought it into an amp tech twice in my city for "service" I see no evidence of work (I was getting some ghost notes in the very early 90's) I've essentially only logged about 10 to 20 hrs on this since I retired from active playing in 93 and have lived lots of my life since then either overseas or in places where it wasn't feasible to drag out my gear. I wonder about getting a full check-up and service done - I'm absolutely paranoid about loosing it (in shipping or otherwise). Here's a picture. I can take more, including higher rez and better lit. Any thoughts? This is my original, fully loaded MKIIC+ combo/hardwood from 1984. Here's a link to the photo in it's original size as well: http://www.dogsoverlava.com/images-for-web/Boogie-1.jpg

 

[Allen]

Hi Guys
Pulled my amp out -- it's been a while -- I let it warm up in standby and turned it on. The magic is still there but I'm getting some noise. I'm also smelling what I'd call an electrical smell -- NOT BURNING -- more like Ionization.

Hello Dasein-

Probably years of dust in the chassis, but then again...

The amp may need a full refreshing of all the electrolytic capacitors. Electrolytics don't like to sit unused for years on end. They need to be used regularly to be at their best. Even with continual use, they won't last forever.

Just like you, I recently pulled my DRG IIC out of "retirement" for some afternoon fun, and even though I initially warmed it up on a 100 watt voltage limiter (to soften the power surge to the caps), after an hour or so I started smelling something too. I had refreshed the high voltage and bias caps back in 2005 but I apparently missed a few of the smaller electrolytics.

Not sure what pre-amp board your C+ has, but on the RP11A pre-amp board, in the rear corner, tucked down underneath the edge of the high voltage supply board, is a small DC power supply section for the Rhy/Lead footswitch LED and relay. There is a 470uf/16v cap there that is fed by a 680 ohm 1w resistor. I think the cap finally just could not hold a charge and the power resistor was over-worked to the point that it burned itself open.





Anyway, the point is, you might want to get a good local tech on it or send it over to Mesa for a full re-cap. It will sound beastly again and might just inspire you out of your "retirement." 8)

Hope this helps.

 

[b00g13mk2B]

Check the electrolytic caps. The ends may be bulging (the three blue ones were on mine). My amp had a very hot smell (not ionization), there was blue glow at the base of the power tubes and a crunchy/crackle sound when I hit the side. Replaced all the electrolytics, they were original from 1980. Problem solved. Luckily, no resistors or other parts damaged.

 

[gts]

Fwiw his has the RP11A pre-amp board.
If you zoom in on the pic in his link you can see it.
It's a little out of focus but it can be read easily enough.

Yes a recapping might do the trick. I wonder if Boogiebabies is around. He'd probably know for sure what it needs

Not sure what pre-amp board your C+ has, but on the RP11A pre-amp board, in the rear corner, tucked down underneath the edge of the high voltage supply board, is a small DC power supply section for the Rhy/Lead footswitch LED and relay. There is a 470uf/16v cap there that is fed by a 680 ohm 1w resistor. I think the cap finally just could not hold a charge and the power resistor was over-worked to the point that it burned itself open.

Anyway, the point is, you might want to get a good local tech on it or send it over to Mesa for a full re-cap. It will sound beastly again and might just inspire you out of your "retirement." 8)

Hope this helps.

 

[dodger916]

Fwiw his has the RP11A pre-amp board.
If you zoom in on the pic in his link you can see it.
It's a little out of focus but it can be read easily enough.

Yes a recapping might do the trick. I wonder if Boogiebabies is around. He'd probably know for sure what it needs

.

George: I heard a "rumor" that Ed is back in upstate NY, probably somewhere between us.

 

[gts]

Fwiw his has the RP11A pre-amp board.
If you zoom in on the pic in his link you can see it.
It's a little out of focus but it can be read easily enough.

Yes a recapping might do the trick. I wonder if Boogiebabies is around. He'd probably know for sure what it needs

.

George: I heard a "rumor" that Ed is back in upstate NY, probably somewhere between us.

It's not a rumor. ;-)

 

[McBarry]

G'Day,
"noise" is a pretty wide description...
hum.. static.. pops.. burps... farts... - do any of these seem to apply ??

Re smell... I'm with the other guys re dust.. esp on the bases of the inverted tubes.. and as heat rises the dust and crud gets MIGHTY warm.. esp if a little moisture is mixed there.. heaven knows how it get there, but it does..

I've also had annoying hum and pops that were un-traceable in a couple of my own Mark II's - a thorough clean of the preamp board with methylated spirits (actually, it was almost a wash :lol: ....) and silence returned. Admittedly, the 100w IIB was bloody filthy.. but the point remains..

A bit more info and we might be able to throw some better ideas.. and have you rectify some or all of the symptoms before a tech visit for a final look and probably cap job...

Dave

 

[Boogiebabies]

Late to the party as usual.

That resistor is the dropper for the LDR/GEQ supply along with a 15V Zener diode.
THEY GET HOT !!!!! The diode case is most likely split too.

Try a 680 Ohm 3 Watt fireproof cement power resistor.
470 UF Cap looks newer.