FDP Home Page / FDP Forum / FAQ's

Fritz_D_Cat's photos: "Fritz" mod 2 - DeFLUB the bass on your DRRI

Here's another dirt simple DRRI mod for anyone that can run a soldering pencil. We're going to hotrod the DRRI first power filter stage to Blues Deville specs. Big BIG improvement to bottom end delivery, here, at any volume!! For this power supply mod, cost is about 20 bone$.

Parts List - P/N's for Mouser included:
You'll need a couple 220K 1/2 watt resistors at about $ 0.10, each. It's important to use 1/2 watt ones, because they will be carrying a bit of current. Don't use carbon comps; they are noisy and break down over time. Metal oxide resistors or Go Home. Appropriate P/N 273-220K-RC. Get a couple caps at almost $5 each and then there's the $10 in shipping. If they have Xicon 100 uF @ 350V caps, P/N 140-XAL350V100-RC in stock, they will fit without any mods to the doghouse cover.

Proper cap discharging technique can be found in original "Fritz" mod post under this profile.

Remove chassis from amp.

Under the doghouse (4 screws): Lift the power supply daughter board (4 screws). Remove (desolder) the 47uf and 220uf caps. Remove R65 and R66. Replace R65 and R66 with the two 220K 1/2 watt resistors. Replace C31 and C32 with the 100uF 350V caps, observing polarity.

That's it, you're done and can bolt her back together. It's a good idea to check tube bias. I like 16 to 20 mA per tube for all 6V6's except the JJ where I like 18 to 22 mA.

Tung Sol 6V6's have a classic tone without the cla$$ic price. JJ's will give you a bunch more headroom and punch like a 6L6 amp. They are about 24 bone$ for a matched pair, plus the shipping.

One more thing. Big caps in the first stage of filtering can put some startup stress on your rectifier tube. Get a Weber WZ68 Copper Cap. It will be supremely reliable. If you like the GZ34 better (I do), just keep the copper cap as a spare.

A WS1 Copper Cap will offer a bit more headroom. The Copper Cap also eliminates some filament power draw - good for a cooler running amp. Also good if you want to try your hand at 6L6's in the power tube spots. That's another story, tech discussion at this link.....


[YMMV and Fritz_D_Cat or any of his likenesses is not responsible for any damage or injury because you messed with a perfectly good amp]