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 Post subject: DC-3B Firebreather Mod!
PostPosted: Sun Apr 10, 2016 11:05 pm 
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Joined: Sat Oct 01, 2005 2:27 pm
Posts: 5423
Location: Maui Wowee!
I've been a little bored with my DC-3 lately, so I thought I would come up with a new set of mods for it.

My DC has a full set of Mercury Magnetics transformers, including a choke. Not sure how these mods will work with a stock amp, but I bet they'll sound great!

I wanted the following from my amp:
Warmer/Fatter cleans - this was brought on by my Rectoverb 25. The cleans on the RV are warm and fat, but still very sparkly.
Liquid Gain - The DC3 has always sounded a little boxy to me.

I apologize now if uploading snapshots of parts of a schematic is offensive to anyone.

Before you try this, DISCHARGE THE FILTER CAPACITORS!!!!!!
If you aren't comfortable working in a tube amp, or if you do not have any experience doing so, please take it to someone that does.
The DC voltages in the amp can kill you, even when it is off and unplugged!


Warmer/Fatter cleans:
V1a - Change Cathode Bypass capacitor from 3.3uf to 15uf
- You can also lower the Slope Resistor value in the tone stack from 150K to 100K
Image



Liquid Gain:
V1b - Remove both 1.3K and 1.5K resistors from pin 8 (my amp had 2 - 1.5K resistors)
- Replace one of the resistors with a jumper
V1b - Replace 150K resistor with 220K
Image

V2a - Remove 56K resistor
- Remove 500pf capacitor
- Remove 2 - 100K resistors
- Install .022uf capacitor from the node of the 56K resistor (the side that connects to pin 1 of V2a) to the 750K resistor
Image

V3a - Replace 6.8K resistor in Tone Stack with a jumper
- You can also play with the Slope Resistor. I left mine at the stock value of 82K
Image

If someone tries it, let me know what you think!
It is very important to leave the rest of the face Tone Stack parts in the circuit just after V2a. If the rest of the parts are removed, there will be too much gain, which will cause the circuit to squeal if the Gain is turned above 8.

I like this mod much better than the previous gain boost mods.

_________________
Elvis said.......
Quote:
Amp techs do get shocked. :shock:


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