Resurrecting a Neglected DC-3

[bendo]

Yes, my old DC3 Combo ate a set of new Mesa tubes in 3 hours. Sounded great and then sounded like a jet engine on steroids.

This is when I made the switch to JJs.

Because of how hot the DC3 is biased, anything hotter than a -25 will red-plate almost immediately. Mesa EL84s are all in -30 range.

 

[jakep]

Greetings. I am the original poster on this.

After my last post on this thread I reconsidered whether I really wanted to try to fix the amp myself. I decided against doing so, and took the DC-3 to the local authorized Mesa service technician. I just got the amp back from him today, and it sounds FANTASTIC.

It turns out that the output tubes were *not* the problem. In a nutshell, the tech did the following:

- replaced a bad signal capacitor
- swapped out a preamp tube for one with lower gain (reducing the hiss to nearly nothing)
- re-soldered some connections
- replaced the reverb tube and fixed a bad reverb tank ground
- waved his mojo stick over the amp until it smartened up ;-)

Anyway, to me the amp now sounds better than it did when I bought it.

During the time that the amp was away for service I put some Duncan pups in my strat. It is a 1989 American Standard sunburst Strat, which had the original Fender pups in it. I replaced them with (from bridge to neck) Duncan stk-s6, stk-s4, and stk-s7 pups. These are hum-cancelling tapped-coil pickups.

As I expected, I lost a lot of my Strat quack by changing pups. But the Duncans have more output (and less hum, of course). They are not so "strat-ty" as the factory pups. However, the guitar was previously kind of a one trick pony paired with *any* amp. About the only position that sounded good was the neck+middle pup position. Otherwise there was lots of hum, and the bridge pup sounded like a dentist's drill going in without anesthetic. The newly serviced Mesa Boogie DC-3 loves these pups; a little more beefy output and no hum, and wow wow wow. I have dialled in a bunch of great tones that just were not available before.

Most importantly, somehow the combination of the work done by the tech on the DC-3 and the new pups has given me a *totally sweet* clean sound. I spent a couple of hundred Canadian dollars on the service bill. But now I feel like I just acquired a "new" premium amp for a very low price.

I do owe a bit of a debt to this forum for sticking with the DC-3. It pointed out to me that many people love their MB. Now I do too. This little giant will be rocking in my garage for a loooong time to come.

- Jake -

 

[bendo]

Nice dude! Glad to see you got it back up and running.

Which Duncan's did you get? I put a JB in my Std. Strat MIM that I just picked up today, and absolutely love it! It had a standard Fender Humbucker in it. I also put a nickel cover on it I had from an old busted BurstBucker, and re-wax potted it. Plus a laundry list of other crap.

 

[jakep]

Bendo:

That's a nice looking strat. I love the cover on the humbucker. Mine's a little plainer, standard tobacco sunburst with a white pick guard; see below.

The pickups I put in are:

bridge: Custom Stack Plus (stk-s6), highest output
middle: Classic Stack Plus (stk-s4), lowest output
neck: Vintage Hot Stack Plus (stk-s6), medium output

Since these have coil taps I replaced the volume pot with one with a push-pull switch. I had trouble pulling out the switch with the standard strat knob on it, so I put knurled chrome tele style knobs on it. This may offend strat purists, but I think it looks pretty good, and it does allow me to work the push-pull switch easily.

I almost opted for a humbucker in the bridge, but the one I chose was supposedly designed to produce a David Gilmour tone, which I like. My choice of pups was formulated after several hours of roaming around youtube for demos people using various pups. The original bridge pup sounded terrible to me, really thin. Now I can get a pretty beefy overdriven sound from it.

The main thing that I am happy about with the DC-3 is that it now does not sound "choked". It now breathes a bit on both channels. I even find the lead channel quite usable. Previously I could never dial anything good in on the lead channel, even before the amp started manifesting problems. I don't know which of the repairs caused this improvement. It is possible that the amp needs the new hotter pickups to come to life.

While the DC-3 was at the shop I spent quite a bit of time trying new amps at the music store. Most people say that it's the preamp the really defines a tube amp's tone. But having auditioned maybe fifteen different amps, I feel that I can distinguish a 6L6 outputs from EL84s (or similar). The DC-3 definitely has what to my ears is a characteristic EL84 tone, whereas the "fender tone" I had been wanting usually shows up in amps with 6L6s (or similar). However, now that the DC-3 has some "air" in its tone, I am not wishing I had a Princeton Reverb or something. I actually find the DC-3 to have a lovely combination of tight, warm, and just enough sparkle to make me happy.

 

[bendo]

I completely agree with you on the DC3 tone. You should look at some of the reverb mods, can be made to sound SWEET! Just a resistor change. EL84s just sound sweet and chimey. I play a DC3 and my rhythym guitarist plays an AC15 custom.

The reverb can also be made foot switchable rather easily. All that needs to be done is to take Pin 7 of V5 to ground. It can be done with a jack, and a shielded cable to a foot switch. I built a powered switching relay that is powered by the heater elements since I noticed the signal got a bit attenuated with a long cable. This way, the signal never leaves the chassis.

Digging the Strat. Make some music!

 

[jakep]

I am interested in being able to switch the reverb. The user manual and schematic that I have is for the earlier version of the DC-3, I think. If I am reading these documents correctly the reverb was switchable in the earlier DC-3 models, but is not on mine.

As shown in the schematic I have, V5 is the reverb tube, and the reverb foot switch would ground the input to V5b (whatever pin that would be).

Did this change with my model? You suggest that V6 is the one to alter. My schematic shows V6 as something else - I forget what it is, maybe a phase splitter? My knowledge of tube circuits is rustier than I had thought.

Because my DC-3 is the later rev, which does not match either the user manual or the schematic, I actually spoke to Mesa on the phone when I started all this to see whether an updated manual and schematic had ever been published. They said "no".

- J -

 

[bendo]

I am interested in being able to switch the reverb. The user manual and schematic that I have is for the earlier version of the DC-3, I think. If I am reading these documents correctly the reverb was switchable in the earlier DC-3 models, but is not on mine.

As shown in the schematic I have, V5 is the reverb tube, and the reverb foot switch would ground the input to V5b (whatever pin that would be).

Did this change with my model? You suggest that V6 is the one to alter. My schematic shows V6 as something else - I forget what it is, maybe a phase splitter? My knowledge of tube circuits is rustier than I had thought.

Because my DC-3 is the later rev, which does not match either the user manual or the schematic, I actually spoke to Mesa on the phone when I started all this to see whether an updated manual and schematic had ever been published. They said "no".

- J -

Sorry, edited my original post. Pin 7 of V5 is what get taken to ground. My DC3 is the later revision, the switch applies to all revisions. Mesa just removed the jack on the B.

The green wire in my previously posted photo is the one that goes to pin 7. There is an extra eyelet there you can use to solder the wire in place.

The parts for the powered switching setup can be bought from Hoffman Amplifiers. http://www.hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=Lamps&ORDER_ID=457117645 <-- with that all you will need is a jack (I used the slave out jack since I will never use the slave), a shielded 2 conductor cable ( a good microphone cable can be used for this), and a foot switch (I used a case from an old Metal Muff I had, and a standard SPST stomp switch).

With this configuration, you eliminate the risk of any attenuation of the signal, since the signal never leaves the chassis. My first couple of attempts used a wire from Pin 7 strait to the jack, and a ground from the jack to the common ground for the Output Power supply coupling caps. I then just used a cable to a switch. In this config, I was just grounding Pin 7 with a LONG cable. Certain cables attenuated the signal. Even a shielded 2 conductor affected how the reverb sounded, though it didn't attenuate it. The powered relay setup eliminated this issue.

 

[jakep]

Thanks! That mod should be within my capabilities.

 

[tonedragon]

Put your strat pickup selector on position 2 or 4. If that don't work shield the heck out of the strat. If that don't work I dunno what to say.

I set my DC up to break up a little with single coils and break up alot with humbuckers. That's on my clean channel. !!
My dirty side is set up with dirt on bout 3, treble 7 ,mid 9. ,bass between 2-4. My DC 3 is bass heavy.

I used to get all of though s sounds. Retubed with sovteks, the JJ/ Ruby's didn't last long.

 

[tonedragon]

Good luck with it ,nice strat. Hope u find the problem.


Cool looks like everything worked out. I just have a cheap fan facing the amp during a gig. If not I get a noise amp.

 

[SixVeeSix]

I just refurbished a DC-5 and now it sounds great.

Clean your jacks. I used a small piece of 180 grit sandpaper rolled up tight and spun it inside the jacks to break the corrosion free, then sprayed with electronics cleaner (an aggressive, non-residue type for jacks). Then while the cleaner was still wet I inserted and removed a 1/4" guitar plug repeatedly. Especially clean the Effects Send and Return jacks, these are famous for causing problems.

Caig Deoxit products are the best for cleaning, you need one type for jacks and tube sockets and another for pots.

Clean your tube sockets. Spray with the same cleaner you used to clean the jacks and then take one of the old tubes and insert/remove repeatedly while the cleaner is still wet.

Clean your pots. Follow the instructions on the can. I am waiting for my can to arrive, final part of my refurbishment.

The V90 is better than the V30 in a single 12" but a premium cast frame speaker like JBL G125-8 or EVM is much better still.

Try a 5751 tube in V1 if you want a smoother, sweeter clean tone. Also try a 12at7 in V6 (PI), this will improve clean tones as well.

One test you might make is to turn the amp on, turn it to a moderate volume, crank the reverb and then rock the amp on the floor. If there is a loud crashing sound then the return on the reverb is working. There is a thread buried deep on here about reversing the ends of the reverb tank to get the sensitive end away from the OT, I tried this and my reverb went from being quite noisy to nearly silent, a bit improvement in the noise floor.

Finally, as far as settings for a nice clean tone try setting the Main Master up high, 5-6. Set all your other knobs on the clean channel to 0 and make sure the push/pull on the Gain knob is pushed in. Set the channel master to 3-4 and then start creeping up the Gain and tone knobs. You may prefer to leave the mid at 0 or very low, this will help give a more Fender-like tone overall.

Don't give up, that is a GREAT amp once you get her up and running!!!!