Deluxe Reverb - want earlier breakup

[LooseChange]

What are your thoughts on getting a Deluxe Reverb to breakup earlier without using some sort of Power scale or VVR??

Change the PI to a 12AX7?
Cathode Bias the amp?
Mess with the PI circuit?
Tweak the preamp?

Thanks!

Schemo: http://www.el34world.com/charts/Schematics/files/fender/DELUXE_REVERB_AB763.pdf

[sluckey]

Replacing the 6.8K under the tone stack with a RAW control (50K-250K) is very useful and may be all you need.

[Boots Deville]

Speaker swap?

[tubenit]

A very simple mod is to change the 3.3M resistor to a 2.2M or maybe 1.5M.
I tried that on the PR I owned and it did allow sooner breakup.

The 12AX7 in the LTPI would help also.

Sluckey's idea is a good one also.  I think most of the overdrive in an (that is smooth sounding) is from the mid tones.

With respect, Tubenit

[LooseChange]

Raw control is not a bad idea but all that midrange sometimes just kills the tone. I will play with that, tho'.

Man, I hate speakers! I just never know what to try and they are alway expensive..The amp has a Eminence Patriot Cannibas Rex. Good, Bad? What's your choice?

Thanks!

[Boots Deville]

I hear ya on the speaker deal... I've seen things on the Weber site like "early breakup" and "later, smooth breakup" and the like, but I haven't had the means to be able to get a large collection and A/B them with the same amp.

Eminence lists their "Break Up Modes" as "Slow", "Medium" and "Fast", and the C-Rex is listed as "Slow", which to me means a later break up.  The only "Fast" one listed is a Legend 10", but the others in the Legend series are "Medium" and I've heard others say good things about those in blackface amps, and as speakers go, they're pretty reasonable, price-wise.  No personal experience. 
http://www.eminence.com/support/tone-guide/

[tubenit]

I have a Cannabis Rex that I use with the TOS & SoLow Watt .  I like that speaker. My son has the same speaker in his amp which originally had Marshallish topology.

The Cannabis Rex does not impress me as a slow break up speaker compared to something like the Weber 12F150. I'd probably leave that in there. I think it's a good speaker. I'd certainly try other less expensive mods first.

I find when I boost the mids alot on an amp that I definitely have to lower the cathode caps on the preamp to something like the 5uf-2.2uf range. Having a 22uf cap and boosting mids is a tone killer, IMO. It just sounds like mud to my ears.  One of the guys on TAG talked about leaving a 22uf on V1-3 but dropping down to a 2.2uf on V1-8 & still being able to keep the Fender tone. Haven't tried that myself, though.

With respect, Tubenit

[spacelabstudio]

I'd be tempted to convert to cathode bias, personally.

[skeezbo]

Remove negative feedback?

Skeez

[phsyconoodler]

Remove negative feedback,lift the 6.8k resistor off ground on just the normal channel or do a marshall mod on that channel,change to a low wattage alnico speaker,bias the amp hotter,lower the voltage with a 5Y3 rectifier,remove the trem ground wire,separate the shared cathode resistor/cap on V1-V2.
  Change V2's plate resistors to 220k and the bypass caps to 1uf.
Lots of stuff!

[LooseChange]

Thanks for all the great ideas.... I'll line them up wit the owner of the amp and guitar in hand and we'll have some fun.

[tubeswell]

Man, I hate speakers! I just never know what to try and they are alway expensive..The amp has a Eminence Patriot Cannibas Rex. Good, Bad? What's your choice?

Thanks!

I am a huge fan of Weber speakers (altho' I have only bought 1/2 a dozen of them). I would just go by how they describe them on their website. The smooth-cone varieties definitely break up sooner

[jjasilli]

Probably the simplest thing to try is a higher mu tube for the PI.   Also, 12bz7 in the 1st stage, or in tone recovery stage, or PI, would surely sizzle. 

More invasive: First, I'd drop input resistor values down to 10K - 33K.  Then, preamp stages: increase plate resistors to 220K; cathode resistors to 3.3K (try 2.7k -  3.9K).  Reduce preamp bypass caps to 1uF.  Maybe boost voltage to the PI.  These things should preserve the tone of the amp, but increase its overdrive capability.  (If not enough, get mote radical from there.)

[skeezbo]

Here is something more radical, but many of us might consider it cheating: mid-range diode bounding.  It works, sounds very natural, and the parts cost less than a dollar.  On the Deluxe I think you would put the diodes (two rectifiers in parallel but out of phase) on the bass pot in parallel with the 6.8k midrange resistor.  I have only tried this on cathode follower TMB stacks; with the three controls you can balance the overdriven mids with clear highs and still solid bass. As you jack it up, you of course get more tubey distortion artifacts, too. The diodes do seem to dampen the dynamic range of the mids, so with the Deluxe tonestack you may need to increase the 6.8k to 10k or 15k to taste. It may also be worth trying a resistor (1k-5k) between the diodes and ground, which supposedly rounds out the clipped signal, but with only the mids clipped you may not hear the difference.
Skeezbo

[Platefire]

MV 

[HotBluePlates]

More distortion, or more distortion at lower acoustic volume?

Lower volume distortion will require some kind of change to the power section; cathode bias seems like a decent method, depending on the actual B+ in your amp.

Depending on your setup, you would like to be able to reduce the bias of the output stage, ideally also reduce the B+, make less output power, all of which allows the preamp to drive the output stage easier and at lower volume. It will also make the other suggestions more effective.

Or you go Platefire's route, and add a master volume.

[Ed_Chambley]

I removed the Negative Feedback wire and capped it off.  Replaced the Bass pot with a 100k and reduced the 22uf caps.  I cannot remember what I ended up with, but they are 1uf or less.  I have weber blue.  Begins to sound nasty good at around 3 on the volume knob.  Didn't sacrifice the great bass fenders have either.  I do have to back off the treble quite a bit now.

[Colas LeGrippa]

5Y3 and 20uF reservoir cap

[LooseChange]

Is the 5Y3 rated to handle the current of all 8 tubes?

[Willabe]

Looking at the tube cheat sheets you and tubenit posted that's cuttin it darn close. Probly be fine playin at 3-4 on the volume, but if you push it?    

http://www.el34world.com/Forum/index.php?action=dlattach;topic=13299.0;attach=28564
                      

                               Brad  

[jim]

Dan--You need to discuss the LP mod with jfet switching with your customer--he can have it all. Forget speakers--they will ruin the Fender chime.  Alternatively--I have built the one-stage attenuator that
GW lays out in his book "Understanding Tube Amps"--It is the book with the red cover.  I use it in my DR
for living room jams.  Perfect amount of hair on the tone. Jim

[GroundhogKen]

I use a 5Y3 in my vintage DR.

Using an inefficient speaker is a good option too if you find one with the right sound.

I use an Weber 12F150 25watt -- the 50 watt version might be a SLIGHTLY less efficient option.


If you really want to reduce the volume, you're probably going to need an attenuator.  It's a loud amp considering it's size.



Ken

[duke of earl]

Replace the .001 coupling cap at the PI with a .02 and look out bro! Great Fender Mod. Also try a 15k NFB resistor.

[stingray_65]

The NFB circuit is intended to raise the clean headroom.

It does not have to be eliminated completely, add a 100kL  pot in line and try dialing some more resistance.

[LooseChange]

Thanks Guys!  I was supposed to have this amp in this week but the guy went on vacation.