Re: DRRI Upgrade ideas
- From: J.P. <jpasano@xxxxxxxxxxx>
- Date: Sat, 31 Mar 2007 18:21:01 -0500
On Sat, 31 Mar 2007 14:35:23 -0600, "Elvis Kabong"
"J.P." <jpasano@xxxxxxxxxxx> wrote in message
Well, My nephew and I are starting to look into parts for upgrading
his DRRI to a PTP Hoffman board with 6L6's. So far, we are looking
into using the stock PS, choke, RT, and replacing the OT with a multi
tapped unit that will handle 6L6's and maybe 6V6's also in case he
decides he wants to change back in the future. I want to install a
couple of bias taps for the output tubes with meter binding posts and
bias pots adjustable through the chassis bottom also..Probably behind
the tubes also so they are out of the way and not an easy access.
He is looking for something as nice sounding as his SRRI but in a
more portable box. He also wants to dump the bright switches and not
cut any extra holes in the faceplate. We will likely place the speaker
ohm selector switchplate on in the rear or mount it through the
chassis behind the tubes somewhere also.
Anyone have any suggestions that might give us improved tone or
other ideas that might make this a better upgrade.
Well you could replace the PT with a higher VAC secondary enough to
drive a pair of EL34s. Refer also to the Diaz version of a Vibroverb or the
first preamp tube of a Marshall with an 820 ohm cathode resistor
and 250 mfd bypass cap for V1A and for V1B a 2.7K cathode resistor
and a .68 mfd bypass cap. And leave out the tremolo circuit altogether.
Does that amp have bright switch? The originals didn't. Instead of a
bright switch and a 120pfd cap, there is a 47pfd cap wired to the vibrato
channel's volume pot.
Try to use a variety of coupling and tone caps from different manufacturers.
Make sure they're rated at least 600 volts and don't just use ALL Orange Drops
for mfd caps. Use only a few silver dipped micas for pfd caps but also
use a few ceramics. And no need to exclusively use metal films. Good idea
to up the rating from 1/2 watt to at least 1 watt and from 1 watt to 2 or 3 watt
especially in the power supply, but screen resistors should be 1 watt carbon
comps unless you use EL34s - then use 1K 5 watts typically or increase the
value if the supply voltage is too high for screen grid max voltage.
If you don't use the tremolo circuit you can use one of the pot holes for a mid
control. Just remove the 6.8K resistor that goes from the bass pot to ground
and install a 10K pot instead. And if you want to get kooky, install a higher value
than 10k like a 100K and notice the extra gain. However it will render the bass pot
useless when turned way up.
Here's hoping you have "happy accidents" instead of mistakes.
He does not want a
master volume on it. Any brands or part numbers of stuff might help
also. I forgot to mention he is replacing all the tubes. And this is a
budged project also. As reasonable as possible.I plan on using metal
resistors of double stock wattages and fireproof resistors of 1 extra
watt on the voltage divider circuit. (3 watts instead of the stock 2
He wants this to play around Austin at open mic nights and whatnot.
His preferred style is SRV and Hendrix stuff and I am trying to get
him stage time so he can continue to grow as a guitarist. Maybe he'll
make Antone's and a few of those clubs one of these days...and he
doesn't even get high or drink! But neither do I anymore.. lol ..J.P.
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