I'd like my DRRI to break up earlier...

[Blues Jr]

Hey there...
I'm not totally interested in "clean" headroom. I'd like my DRRI to get crunchy sooner on the volume knob. The amp starts to break up now around 5-6. Anything I can look into? Tubes? Speaker? I was planning to order a full set of JJ's, but I'd thought I'd ask first.
I have the stock tubes right now, and a Jensen P12Q.

Thanks:)

[zook]

Originally Posted by Blues Jr

Hey there...
I'm not totally interested in "clean" headroom. I'd like my DRRI to get crunchy sooner on the volume knob. The amp starts to break up now around 5-6. Anything I can look into? Tubes? Speaker? I was planning to order a full set of JJ's, but I'd thought I'd ask first.
I have the stock tubes right now, and a Jensen P12Q.

Thanks:)

Swap the 12AT7 Phase inverter for a 12AX7. That's the tube next to the 6V6.

Winnie

[tonytrout]

What do y'all mean by "amp break up"?? Please explain.....in simple English.....

[Jeffscreamedcorn]

When the amp starts to distort.

[teXum]

Mine (SFDR) actually starts to break up at 2/3 on the volume dial. No idea why it does this, but it still sounds great, so I've never bothered with trying to "fix it".

The Weber Mass works great with the DRRI. Since the amp is pretty small to begin with, you don't really have to attenuate that much to bring volume down, while still having the amp break up nicely. Highly recommended.

[Wally]

The bias may be set 'cold'. When you get your JJ's, have the bias adjusted to something around 70% of plate dissipation. Zook's suggestion on the 12AX7 will heat up things, too. IF that doesn't get it going for you, there are other things to do. Adjusting the resistance in the negative feedback loop gets an amp up into the hot and rich zone. Changing the PI cap from
.001 to .01-.02 brings in more mids. The preamp cathodes can be separated and gain increased. all sorts of things to do....of course, the PCB RI is not as easily worked on as a vintage DR, but there it is.

[Glen W]

What guitar are you using? For instance, I can plug a Strat into my PR, DR, or SR, and stay pretty clean to 4 or 5. Plug in a Tele, and it may get greasy a little sooner using the bridge p/u. If I plug in the P90 Les Paul, I'm getting the grit at 3.

[PhatTele]

1) Make sure it's biased correctly. If it has the factory bias, it's probably too cold. Use the following table to set the bias (w/a GZ34 rectifier, I usually set it up around 21-23mA per tube):

http://members.shaw.ca/house-of-jim/...as_tables.html

2) If that doesn't do it, try a 5V4 or 5R4 rectifier and rebias. This will drop the plate voltage and allow you to bias hotter (using the tables above) and will create more sag...don't use a 5U4 in your amp. I don't think the power transformer is set up to handle the extra current draw those require.

3) Figure out how to add a midrange control. Basically, you will replace the resister tied to the Bass control pot (a 6.8K value) with a audio taper pot (I like 25K). Stick the pot in place of the ground switch (the ground switch doesn't have anything connected to it anyway in those reissues...it's just there for show).

4) As someone mentioned above, swap the phase inverter tube (the 12AT7 next to the power tubes) with a higher gain 12AX7.

5) Remove the first preamp tube (the one furthest away from the power tubes). This will increase the bias on the preamp tube tied to the reverb channel, thus giving you a bit more gain.

If it were a SF or BF version, there are other things you can do (easier to get at the components).

[Mike Simpson]

Turn the bass and treble down to 2 to 4...

[Blues Jr]

Hey thanks for all your suggestions.
My amp is probably biased cold, it's a few months old now and never had it worked on. Maybe a good set of tubes and rebias to start and go from there.
Are certain tubes higher gain than others? For instance, are JJ's any different than Tungsol or TAD?

Thanks.

[zook]

Originally Posted by Blues Jr

Hey thanks for all your suggestions.
My amp is probably biased cold, it's a few months old now and never had it worked on. Maybe a good set of tubes and rebias to start and go from there.
Are certain tubes higher gain than others? For instance, are JJ's any different than Tungsol or TAD?

Thanks.

It's not neccessarily the Brand as much as the tube type. The greater the amplificatrion factor, the more gain you'll get. Check this out:

Tube substitutions


Drop in for 12AX7
Tube type - Amplification factor
12AT7- 60
12AU7- 17
12AV7- 41
12AX7- 100
12AY7- 44
12AZ7- 60
12BH7- 16.5
(draws twice the filament current)
12BZ7- 100
(draws twice the filament current)
12DM7- 100
12DW7- 100/17
12DT7- 100
5751- 70
5814- 17
5963- 21
5965- 47
6072- 44
6189- 17
6201- 60
6679- 60
6680- 17
6681- 100
6829- 47
6913- 18
6955- 16.5
7025- 100
7247- 100/17
7318- 16.5
7728- 60
7729- 100
7730- 17


Winnie

[PhatTele]

For now, Don't worry about getting "hot" rated power tubes. Just get your amp biased properly with the tubes that are already in it. I'm sure they're fine, whatever brand they are. Use that point as your benchmark to adjust your tone. If you change too many variables all at once, you'll never know what "the fix" was.

[zook]

To check the Phase inverter swap you can do that quite easily. Take the 12AX7 from V1 (that's the non reverb channel) and the 12AT7 fro m the phase inverter (the one next to the 6V6) and swap them. Play through the Vibrato channel and see how it sounds to you.

Winnie

[slideman]

might really do the trick, if you're not satisfied with all the great suggestions on the tube swaps.

For my PJ, I tried all sorts of tube changes as well, but nothing really nailed the early breakup tone that I was looking for, until I swapped out the stock speaker for a Weber Alnico -- which was specifically designed for providing earlier breakup. The combination of the output tubes with the earlier breakup of the speaker enhanced my tone significantly.

Just my two cents.

[The Radium King]

the RFT 12AX7 (an east german tube) has lower headroom and will break-up sooner than most other 12AX7's.

[Mike Simpson]

Originally Posted by Blues Jr

Hey there...
I'm not totally interested in "clean" headroom. I'd like my DRRI to get crunchy sooner on the volume knob. The amp starts to break up now around 5-6. Anything I can look into? Tubes? Speaker? I was planning to order a full set of JJ's, but I'd thought I'd ask first.
I have the stock tubes right now, and a Jensen P12Q.

Thanks:)

What are your tone controls and reverb set on when "The amp starts to break up now around 5-6."