I´ve started this thread for a better overview about some useful mods out there.
My Peavey Ultra is still stock but from now it´s the guinea pig of mods
I bought it new (in 1997), and everything works fine, loaded with new standard JJ preamp tubes and a pair of TAD 6l6str.
It´s a great amp, without a doubt, nice clean, nice crunch, nice heavy, nice reverb, so why mod this thing ?
"I would called it a personal fine tuning"
Easy Mods:
Try different speakers or cabs with the amp and u will hear the biggest difference of all mods coming up underneath.
I tried many different cabs with different speakers and the Ultra always sounds differently.
Actually i play it with an Eminence V12 speaker, nice versatile, good for crunch and metal tones.
Tubes....there are many posts here about Ultra tubes, read it.
CR1 CR2 Mod:
These diodes are in many Peavey preamps as a "noise reduction" on higher gain settings.
A bit mystical and controversial mod, some people say the diodes also clip, some people say they don't clip.
These diodes are only activated in the signal path when the gain boost switches (crunch/lead) are enable.
It´s a noise reduction and it works very good on the high gain settings.
You can make it switchable (isolated switch) if you want.
There is a tiny bit sound and dynamic difference between diodes on/off, more noise without the diodes, but if u roll your guitar volume down to clean
there is more dynamic and no sound cut without CR1/CR2 !It´s up to you...i leave it switchable.
Here is the CR1/CR2 Video:
https://www.youtube.com/watch?v=pWwTeH1w0oo
Two Crunch Channel Mod
Changing VR7 1M log (Ultra Gain Pot) to a 50K log pot gives you two Crunch channels.
If you don't need so much gain, the 50k log (Crunch Gain Pot value also) reduce it and
you can finely, precisely regulate the gain.
No effect to the sound except -> loosing the Ultra Channel, getting two Crunch Channels
Anti 80ies Midhonk Mod
1 swapping out the C76 coupling cap after V1b from the (overly shrill) 1nf -> 2.2nf film
2 changing the parallel C75 470pf/R502 470k before V2a to 2.2nf/470k
3 upping the V1b C15 0.47uf EL cathode bypass cap to 1uf film
>tested, verified<
I´ve done this on my Ultra, sounds good:
https://www.youtube.com/watch?v=1n8lFymOUG4
Expert Add for this Mod
Changed the plate resistors to 100k(R3 and R13 only) This will give less distortion but a rounder gain.
The stock voltage the preamp tubes are seeing is 260v give or take. This is not the best sounding voltage for a preamp like this. 320 or so is much better.
Change R90 and R91 out for 4.7k resistors. This will bring this preamp to life.
NOTE: I think he's referring to the plate voltage feeding the preamps. This will raise the current going through the tubes, and should cause more grid-current-limiting which is what you get when you bias warmer.
>tested and verified<
I´ve done this on my Ultra too, sounds good:
https://www.youtube.com/watch?v=1n8lFymOUG4
Clean-Channel-Mod
This small mod has made a pretty dramatic change in the clean channel on the units I have done them too, providing that the amp was well maintained & serviced with decent tubes.
1) Ground the bottom end of C15 & raise the cap value 10uf or 22uf (if you put the larger cap in parallel it can be removed pretty easy if you dont care for it.
Also with a little bit of caution you SHOULD not have to remove the board
2) Try putting a 1.9k ohm resistor across R14.
>not tested, not verified<
Bias wazz Mod:
wazz wrote:Ok, getting back with some news. I sort of made up the above tripler circuit (from TripleXXX/JSX) around the existing doubler circuit of my Ultra 60 and it works fine. I am now able to vary the bias voltage towards cooler and hotter settings, ie from -61V (very cold) to -49V (very hot). I finally set to a 40mA cathod current (bias voltage around -53V) and, with 486V measured plate voltage, everything now seems ok.
So to me, the final answer to the question in this topic title is "yes you can".
Cheers.
______________wazz wrote:Ok here is the final "before/after" circuit. This is kept to a minimum of mods. All was done from the top, cutting and soldering on existing components, without removing the main board. So all together, I only had to change two resistors (the original voltage divider), add one more diode, one more cap and add the trim pot plus the limiting resistor on the right. Hope this helps.
Bias wazz Mod
Most of this Mods are copied from the internet.
WARNING:
Please note that Amp-Modification are not a beginners project and only for experienced amp builders !
Voltages inside tube amplifiers can exceed 500V and can cause serious damage and can even kill!
OK, post your mods here if u want or pm me.
