DC-3 questions???

[bigjav]

Hi to everybody! I am new here, so will appreciate every input.

I bought a DC-3 combo from the U.K., hardly used. I have so many questions. I will try to list the most important as clear as possible to make answering them easier. I play an Ibanez S 1520 with 2x Dimarzio Air Classics:

1. On the rear panel it is written DYNO-Watt, not DYNA-Watt. Any comments?

2. What is LDR and where are they in the PCB?
http://amp8.com/guitar/mesa/jpeg/dc-3-6.jpg

3. On the rear it says the amp is wired for 240V - 50/60Hz. I am running it at 230V - 50Hz. I noticed the pilot blue light is something tamed when the amp is on, not as bright that I see on pics here. Could there be a mismatch and tone sucking?

4. There is low hum noise when Lead channel activated, instrument unplugged. Any ideas?

5. Everybody here is talking about JJ EL84. How do you know they fit the amp bias range and are safe and tone beneficent to use?

6. On the PCB stays written Mesa DC 2B (1993). Is this some sort of an updated DC-2 or is DC-3 model?

7. When I first tested it I noticed the Lead channel was too honkey, closed, boxed. The mid and bass pot weren't doing nothing and the treble almost nothing. Then I saw one of the legs of the treb pot was broken. Replaced the pot (not the original, but with a good one A250K LOG I had at home). Now the tone pots respond OK, the sound is much better, more responsive, but still low mid oriented. I am still missing that typical Marshall-y, lovely presence that EL84 and el34 used to give.
Look at this video for a good example of tone I'm talking about - http://www.youtube.com/watch?v=cCCvN5jfZkU

Mine is much more muddy, flabby, even lacking gain (I have to put it on 9 to get a good amount of it, but then it goes into a mush. I changed the v1, v2 and v3 preamp tubes. Any suggestions?

Thank you very much for your time!

 

[Jimmy74]

Hi and welcome to the board, just answer a few of your questions, there are 3 LDR's on the board, chunky black plastic parts with four legs, 2 on each side. 2 LDR's are sitting right next to eachother above the mid pot wires.

I think, but I'm not sure, that Mesa DC 2B (1993) just indicates the board version, mine has Mesa DC 23C(1993). As for the different power rates, I live in Italy and wall AC is rated at 230v, the amp is wired for 230vAC 50hz. If I were you I would leave it at 240v because that seems to be the main rating for the UK. There shouldn't be much difference, probably just a little less power to the power tubes.

As for your "mushy" tone problems, could be bad power tubes.

hope that helps

 

[bigjav]

Thanks a lot, Jimmy74!

But what these LDRs are used for?

I noticed that when the EQ/reverb footswicth is conected the LEDs are not working. The footswitch seems to do its job ok changing EQ & reverb, but no lights. I assume something is bad in the amp, because conected to my other amp everything is OK with the LEDs. I should keep testing it also, because it seems that the sound is not the same when footswitch is used than when only the knobs on the front and rear panels are used to change channels, reverb and EQ. Any idea?

Also, do you have any idea about this:
1. On the rear panel it is written DYNO-Watt, not DYNA-Watt as seen usually ?!?!?!

 

[Jimmy74]

I have no idea about that dyno watt mistake....

Make sure you're using the right sort of footswitch for this model, in this amp LDR's are used in the switching matrix for changing the channels and engaging the EQ/footswitch.

 

[bigjav]

Well, I think that every standard dual footswitch with stereo cable and jack should be ok for the EQ/Reverb input in the rear panel, or I am not right?

 

[Jimmy74]

Not so sure about that, the instruction manual states "Mesa dual footswitch" is to be used

 

[bigjav]

..., there are 3 LDR's on the board, chunky black plastic parts with four legs, 2 on each side. 2 LDR's are sitting right next to eachother above the mid pot wires.

Yeah, I think I found them. They are three in the board, so I assume they are for
1. channel switch
2. EQ on/off
3. reverb on/off

Do you know which one is 1, 2 and 3? Can you tell me the full definition of LDR?

One more thing that bothers me is when I have the footswitch conected to the rear panel and then the switching pot on the same panel set on LEAD (the EQ switch on only on the Lead channel) I still can swicth the EQ on & off in both channels. Also, the range of the GEQ sliders is not the same when the footswitch is conected than when it is not. I am sure there is some problem, but I don´t know where it can be. Do you think I could have a fault LDR? Any other way to check them (for example, when switching between channels there is well audible click inside the amp, almost no click when switching the EQ/reverb. Is this OK)?

Regards

 

[Jimmy74]

LDR = Light Dependent Resistor

The LDR's are used for channel switching (lead and rhythm channels) and 1 for the EQ, I'm not sure which is 1 2 or 3.

As for your footswitch problems, I would suspect the footswitch itself not being the correct type for this model.

 

[Jimmy74]

PM sent

 

[apak]

hm.. Mine says Dyno-Watt too on the back. With an "o" and not an "a"

 

[wizard333]

1. No idea, wouldnt worry about it.

2. Already covered.

3. A <5% mismatch is not bad. Your heaters will run ok, and if anything the tone will be maybe a hair softer and there will be a tad more gain. Here in the US a +/-5% mismatch at the wall socket is common. I've seen actual wall voltage here anywhere between 115 and 125VAC pretty regularly; in some older clubs it can be lower than that and cause issues with anything sensitive (most tube amps are not sensitive unless there are also solid state and digital components in there to). Tube amps just sound a bit different when the voltage is a tad off.

4. Bad tube would be my first thing to check. Could be a few other things to; check caps if its not a tube.

5. Order them in a "medium bias range" from your supplier and mention what amps its for. Or get a Groove Tube EL-84 S (jj) that falls in the 4-6 range. JJs are a very robust tube, I found they improved the sound on my DC (and just about every other amp I use them in). They'll also stand up to a lot of abuse.

6. Already covered.

7. Have you replaced the tubes yet? Given that its a used amp, thats the first thing I'd do. It should have a ridiculous amount of gain; at 5 on the gain knob mine is in complete melt down. As far as having Marshall sparkle; it does not unless you adjust at the GEQ; its a fairly dark amp due to a couple .001uf caps to ground at the end of the gain channel. It shouldnt be flabby are farty though; its pretty tight in the low end. If you have replaced the tubes and still get that effect, there is something else wrong. I'd check the entire circuit path on the gain channel given that you've already found a problem there. Also double check and make sure that new treble pot you wired in is wired correctly.

 

[bigjav]

Thank you very much for the input guys!

I have one more question: I am curious about the speaker the DC-3 came with, what brand and model is it? The sticker on it was removed and there is nothing written. Only this number in the backside of the membrane: 1257-1

?!?!?

 

[GD_NC]

The stock DC-3 Combo Speaker is a Celestion V-30