Peavey PAG 120 - Suggestions for change

[marvintm]

1st Post.... Yay-me.

As an opener, I will contribute one schematic that I dont find posted on the NET... Peavey Triumph PAG 120. Different schematic than the regular Triumph. Peavey Triumph PAG 120 Schematics.pdf

Then I shall ask for some opinions. (Thanks in advance)

Got a pawn shop PAG 120 that was non functional due only to a missing speaker cable. Got em down to $150. With a wash, wax, and repainted black trim, it now looks like new and proved to be fully functional and very clean.

Had original tubes. Couple scratchy pots. As good measure, I have done the following:

• Replaced preamp tubes with JJ 12AX7.
• NOT replaced 6L6 ...yet.
• New peavey pots where needed.
• Replaced all electrolytics with identical values.
• +/- 17v rail is less than 0.5 v variance to Gnd.
• Have not touched the Bias.

I played the amp for about 4 weeks before digging in. But the typical "honk" or half throttle wah pedal attack that the Triumph is known for is still there. Had hopes - but didn't really expect it to change much.

So with the attached schematic in hand, I am wondering where this sound comes from and can it be edited? I expect that someone here thats familiar with the design of tube amps can identify a coupling cap, or filter somewhere that would be the likely source of a pronounced mid-bass. You can hear more mid than bass come in when rotating the Low pot. I am thinking about comparing the 5150 stages to the PAG for possible changes, but dont want to get into a cascading mess of changes. I have read Nashvillebills posts about his regular Triumph, but dont glean much from them.

That said, I am also considering a simple speaker swap for the LARGE magnet scorpion. I tried an Eminence Delta Pro 12a, and it helped a tad but sounded like you were listening to the amp through a pringles can. Distant, thin. Too much power handling for good response in home use I suspect. I am considering a Celestion Classic Lead 80 now.

I like 70/80s hair and classic rock. My solid state Bandit 112 sounds far better and has bass and mid controls that respond like you'd expect. The Triumph sounds best suited for that country "twang".

So.... In order of preference:
1. Circuit mods/value change suggestions?
2. Speaker suggestions?
3. Power tube suggestions?
4. Tube Bias or not Tube Bias?

Gary

[nashvillebill]

Glancing quickly at the schematic, it appears this might have some common features with the Classic 50 preamp--the use of the IC for the reverb driver, for example. Perhaps some of Steve Ahola's mods on his blueguitar site The Blue Guitar may carry over ????

edited: nope, looking closer, it's a lot different. The "bottom" "body" and "edge" controls???? Weird, well to me at least.

[Enzo]

Bottom, body, and edge are what PV calls the tone controls in their active EQ stages. Their regular old passive EQ are labelled high, mid, and low like anyone else. SO when both types of tone controls are on one of their amps you can tell what is what. The active EQ is usually only on the OD channels.

The bias on this amp is not adjustable anyway, so good thing you didn't try to adjust it.

Power tubes are like car tires, they wear out just doing their job. Any used amp purchase really deserves a fresh set of power tubes right off the bat. It is doubtful anyone put nice new tubes in the amp before selling it to a pawn shop. Fresh 6L6s should liven up the sound. I don't think the brand of 6L6 will have near the effect that brand has on preamp tubes.

[olddawg]

If you play classic rock you might want to convert it to EL34s. If you like your Bandit have you tried the Bandit line out into the main amp in or effects return on the Triump? If you are adventurous you might want to gut the thing and make it into a JCM800.

[marvintm]

So what makes the triumph sound like it does? I there is a roll-off filter or anything in the path to make the response more mid-bass / mid-nasal than a typical amp? This character is present on all channels so its not from the active EQ, nor the ultra/crunch stages.

Any comments on the Celestion Lead 80 (or any other speaker) to loose the honk?

[Gtr_tech]

I think the Scorpion speakers sound liks ass for guitar. Tried it with something different yet? Them Scorps have little going on in the tone department. Try it with a closed back external cab and see if that is more to your liking....

[Gtr_tech]

The schematic looks real...*real* similar to the Ultra amps. Did you remove/jump out the coring diodes (CR1,CR2) from the signal path? That makes a noticable difference in sound quality.

[Gtr_tech]

Oh yea.....what does the "PAG" make different from the regular Triumph?

[nashvillebill]

Well, the PAG stood for Parallel Axis Geometry, I think...a fancy way of saying some of the tubes were mounted horizontally rather than vertically, if what I read was correct.

The design also differs a lot from the original Triumph. The original was all-tube, the only transistor in the entire amp was used to power the Standby LED, whereas the PAG has several transistors and IC's. Also the PAG had separate user-adjustable EQ for the Crunch/Ultra gain channel--the original only had an EQ in the Normal channel, which was bypassed (instead using the factory pre-set EQ) when switched to the Crunch/Ultra channel.

[Enzo]

That's what the PAG meant alright.

The solid state stuff in the PAG is the reverb drive, plus a couple JFETs for the "clamp" muting and signal control at the reverb output.

[marvintm]

Yes the Triumph PAG mounts the preamp tubes horizontally out of sight in the amp chassis. Then cools the chassis + preamp compartment with a tiny fan.

I think I am going to tweak one of the coupling caps and Cathode Bypass cap for a bit more low end. New JJ 6l6GC's are in my hands as well.

Does anyone have a suggestion for a speaker for this 100 watt amp with a more scooped mid? The Eminence Delta Pro 12a just isn't much better, and less presence. Keep thinking the Celestion Classic Lead 80.

[Gtr_tech]

No speaker swap is going to get you into death metal chug-fizz territory. Just stick an EQ pedal in the loop and suck out all the mids that way.

[tedmich]

check out the eminence sites samples; you can choose the speaker that sounds best (or several which sound best together) Eminence - The Art and Science of Sound

You want more scooped mids? Trade it for a Randall? The 10 band eq in the FX loop is the quickest way to getting the tone you like without potentially destroying the amp (or zapping yourself)

Also many think they have died and gone to heaven on old PVs when they put in new tubes and a decent speaker, and sealed cabs (like the Mesa Thiele) are easy to make and amazing sounding vs. std guitar cabs.

To learn tube amp electronics, go slow, know about bleeding caps and safety etc. also make sure you have a good temp control iron to avoid lifting the pcb traces. Subtle coupling cap changes are best (0.015uf ->0.022uf) and sometimes you can just "piggyback" on the existing cap to add values in parallel (same with cath bypass). Recording clips and documenting everything with a digital camera are godsends to getting it working again and truthfully telling if you prefer A or B.

As fun as messing with amps is I find a ratio of about 98% practice: 2% hacking the PCB bears the best fruit....IMHO.

[marvintm]

PAG is much improved!!

Well a few coupling and bypass cap alterations (as others have had some success with), and it made a huge difference!
The PAG is now much clearer sounding with a touch of bite. It has opened up quite a bit and is very playable now. Doesn't sound like Charlie Browns teacher anymore. The active EQ on the PAG is nice to have too.

My Bandit is now an orphan

These changes move the bass roll off "knee" further downrange. This makes midrange less prominent (flattening the curve by bringing up the low spots).
V1B cathode bypass cap (50volt E.L.) C15 from .47uf factory to 1.0
V2A input coupling cap (630volt Poly) C14 from .001uf factory to .008
V2A cathode bypass cap (50volt E.L.) C17 from .47uf factory to 1.0

I started the coupling cap at .0022, and worked up to 008. It makes the biggest difference of them all, but the coupling/bypass sort of go together in tone adjustment. I note that this does not change the response of the clean channel (much), as I did not change the coupling cap/s involved in that stage.

New JJ TUBES all the way around did not yield any difference. ~$120
RECAPPING the electrolytic's did not yield any difference. ~$50
I'm sure that an O-scope or really seasoned musician could tell a difference, but not me. The kick in the @#!*% was the cap mods.

I think the slam dunk would now be a different speaker, or better yet an external cab. Will post those results if I ever do it.

Thanks everyone!

[marvintm]

Power Stage question... what are these diodes for?

On my PAG, I see diodes on the power tube inputs that I don't see on other amp schematics of any make. What are they for, and would they affect tone appreciably?
Full schematic is on first post.