Rig-Talk

Guitars, Gear, Tone!
It is currently Wed, Nov 21, 2018 11:25am

All times are UTC - 5 hours




Post new topic Reply to topic  [ 17 posts ] 
Author Message
PostPosted: Thu, Sep 13, 2018 7:28pm 
Offline
Plank Cranker Wanker
User avatar

Joined: Wed, Jan 21, 2009 4:43pm
Posts: 2105
Location: In a room surrounded by Wizards & Mesas
Are you human?: 951
Our subject in question: 1993 Mesa Triple Rectifier

... but what is this:

Image

Image

Image

Someone added a 15K ohm resistor off the last 30uf/500V preamp filter cap... then connected it to a small mini-pot... then to ground? Why? I've never seen something like this off a 30uf/500V large cap? Thoughts?

I think another resistor was replaced/added right next to the 2 orange ceramic disc caps too (right next to C52).

_________________
Excellent transactions with: sjk (S: Soldano SLO 100), glip22 (S: Gibson Historic LP R7), MrPlexi (S: Suhr PT100), Metalhead (S: PRS SC-250 AP), killertone (S: Diezel Herbert), tlingen (S: Engl SE EL34), fuzzyguitars (S: PRS Tremonti Trem & Gibson Historic LP R8), xzyryabx (S: Engl Savage 120), Devilinside (S: Randall Satan), DarkCide: (S: ESP M-II), Mizati20 (S: PV 6505+), bartmcartman (S: Bogner XTC 101B), thaifoo (S: Engl Savage 120), lester (S: Bogner UberKab 4X12), adrenalinejunky (S: Fryette UltraLead), gbsmusic (S: Fender EVH Wolfgang), savant421 (S: Bogner UberKab 4X12 cab), ams2ek (S: Mills Acoustics 4X12 cab), blastcap (S: Gibson Explorer), braciola (S: PV EVH Wolfgang USA), splawner (S: Wampler Plextortion), mhenson42 (S: Celestion V30 speakers), Gsxrbusa (S: Jackson SL2H), El Mariachi (S: Suhr Koko Boost), braintheory (S: Engl SE EL34), ChurchHill (S: Gibson Historic Custom BBR7), RKnight (S: Mesa Mark IV), and many more.


Last edited by Wizard of Ozz on Fri, Sep 14, 2018 11:17am, edited 1 time in total.

Top
 Profile  
Reply with quote  
PostPosted: Thu, Sep 13, 2018 7:43pm 
Offline
Rock God

Joined: Sun, Mar 25, 2012 6:51pm
Posts: 6697
Location: Wi
Are you human?: 951
Someone doing the unthinkable...making a Rev F a Rev G!!!!! AAaargh!!!!!

J/K. I have no clue. How does it sound compared to stock? More or different gain structure?

_________________
Many Toys in my Attic


Top
 Profile  
Reply with quote  
PostPosted: Thu, Sep 13, 2018 7:52pm 
Offline
Plank Cranker Wanker
User avatar

Joined: Wed, Jan 21, 2009 4:43pm
Posts: 2105
Location: In a room surrounded by Wizards & Mesas
Are you human?: 951
Racerxrated wrote:
Someone doing the unthinkable...making a Rev F a Rev G!!!!! AAaargh!!!!!

J/K. I have no clue. How does it sound compared to stock? More or different gain structure?



Not sure... yet ;) TBD. :yes:

Here's a stock 1993 Rev F Dual for comparison:

Image

_________________
Excellent transactions with: sjk (S: Soldano SLO 100), glip22 (S: Gibson Historic LP R7), MrPlexi (S: Suhr PT100), Metalhead (S: PRS SC-250 AP), killertone (S: Diezel Herbert), tlingen (S: Engl SE EL34), fuzzyguitars (S: PRS Tremonti Trem & Gibson Historic LP R8), xzyryabx (S: Engl Savage 120), Devilinside (S: Randall Satan), DarkCide: (S: ESP M-II), Mizati20 (S: PV 6505+), bartmcartman (S: Bogner XTC 101B), thaifoo (S: Engl Savage 120), lester (S: Bogner UberKab 4X12), adrenalinejunky (S: Fryette UltraLead), gbsmusic (S: Fender EVH Wolfgang), savant421 (S: Bogner UberKab 4X12 cab), ams2ek (S: Mills Acoustics 4X12 cab), blastcap (S: Gibson Explorer), braciola (S: PV EVH Wolfgang USA), splawner (S: Wampler Plextortion), mhenson42 (S: Celestion V30 speakers), Gsxrbusa (S: Jackson SL2H), El Mariachi (S: Suhr Koko Boost), braintheory (S: Engl SE EL34), ChurchHill (S: Gibson Historic Custom BBR7), RKnight (S: Mesa Mark IV), and many more.


Top
 Profile  
Reply with quote  
PostPosted: Thu, Sep 13, 2018 8:50pm 
Offline
Rock God Trainee
User avatar

Joined: Fri, Jun 30, 2006 8:19am
Posts: 4695
Location: California
Are you human?: 951
Hard to say. Would need a schematic to look at. You got one?

_________________
KSR Gemini
KSR Ares
Ceriatone Chupacabra
Mayones Duvell MBC


Top
 Profile  
Reply with quote  
PostPosted: Thu, Sep 13, 2018 8:59pm 
Offline
Plank Cranker Wanker
User avatar

Joined: Wed, Jan 21, 2009 4:43pm
Posts: 2105
Location: In a room surrounded by Wizards & Mesas
Are you human?: 951
FourT6and2 wrote:
Hard to say. Would need a schematic to look at. You got one?


Image

Not the clearest to see... but accurate.


Here's a better one:

Image

Image

_________________
Excellent transactions with: sjk (S: Soldano SLO 100), glip22 (S: Gibson Historic LP R7), MrPlexi (S: Suhr PT100), Metalhead (S: PRS SC-250 AP), killertone (S: Diezel Herbert), tlingen (S: Engl SE EL34), fuzzyguitars (S: PRS Tremonti Trem & Gibson Historic LP R8), xzyryabx (S: Engl Savage 120), Devilinside (S: Randall Satan), DarkCide: (S: ESP M-II), Mizati20 (S: PV 6505+), bartmcartman (S: Bogner XTC 101B), thaifoo (S: Engl Savage 120), lester (S: Bogner UberKab 4X12), adrenalinejunky (S: Fryette UltraLead), gbsmusic (S: Fender EVH Wolfgang), savant421 (S: Bogner UberKab 4X12 cab), ams2ek (S: Mills Acoustics 4X12 cab), blastcap (S: Gibson Explorer), braciola (S: PV EVH Wolfgang USA), splawner (S: Wampler Plextortion), mhenson42 (S: Celestion V30 speakers), Gsxrbusa (S: Jackson SL2H), El Mariachi (S: Suhr Koko Boost), braintheory (S: Engl SE EL34), ChurchHill (S: Gibson Historic Custom BBR7), RKnight (S: Mesa Mark IV), and many more.


Last edited by Wizard of Ozz on Thu, Sep 13, 2018 10:07pm, edited 2 times in total.

Top
 Profile  
Reply with quote  
PostPosted: Thu, Sep 13, 2018 9:46pm 
Offline
Plank Cranker Wanker
User avatar

Joined: Sun, Sep 10, 2017 1:50pm
Posts: 1091
Are you human?: 951
Not a clue... but were they trying to drop the voltage to V1A? Just a guess, and not a very educated one without knowing more about the B+ supply.

_________________
:rock: :rock: :rock:


Top
 Profile  
Reply with quote  
PostPosted: Thu, Sep 13, 2018 10:39pm 
Offline
Supah Stah
User avatar

Joined: Mon, Sep 07, 2009 1:20am
Posts: 2677
Location: Chicago, IL
Are you human?: 951
It's like reading hieroglyphs to me.....


Top
 Profile  
Reply with quote  
PostPosted: Thu, Sep 13, 2018 11:48pm 
Offline
Plank Cranker Trainee

Joined: Wed, Nov 18, 2015 9:39pm
Posts: 526
Location: Great White North
Are you human?: 951
Yeah, that makes no sense. The resistor and mini pot are connected to the ground side of the filter cap.
If the ground leg of the filter cap is still connected to ground, then the resistor and pot do nothing.
If the ground side of the cap has been lifted, then maybe it's a crude attempt to alter the filtering at that node :dunno:
Are you sure the other end of the resistor / mini pot is connected to ground and nothing else? Hard to tell from the pics.

As for the changed resistor @ C52: If you have high res shots of a stock amp, zoom in and see what the color code is on the stock resistor vs your amp. I can't tell from the pic you posted. Also, I don't see C52 on the scheme you posted. If we had a scheme showing C52 and what's in the vicinity, it would help.

_________________
Certified Ampaholic :D
Bogner Twin Jet
Diezel VH4
EVH 5150III 100watt
Friedman BE100
Marshall 1987xl (with V2a 80's mod board)
Peavey 5150 block letter
Peters Vega-FSM
Soldano SLO 100
Vox AC30HW
Wizard MCII

A couple Les Pauls, an SG etc...


Top
 Profile  
Reply with quote  
PostPosted: Fri, Sep 14, 2018 12:09am 
Offline
Plank Cranker Wanker
User avatar

Joined: Wed, Jan 21, 2009 4:43pm
Posts: 2105
Location: In a room surrounded by Wizards & Mesas
Are you human?: 951
fusedbrain wrote:
Yeah, that makes no sense. The resistor and mini pot are connected to the ground side of the filter cap.
If the ground leg of the filter cap is still connected to ground, then the resistor and pot do nothing.
If the ground side of the cap has been lifted, then maybe it's a crude attempt to alter the filtering at that node :dunno:
Are you sure the other end of the resistor / mini pot is connected to ground and nothing else? Hard to tell from the pics.

As for the changed resistor @ C52: If you have high res shots of a stock amp, zoom in and see what the color code is on the stock resistor vs your amp. I can't tell from the pic you posted. Also, I don't see C52 on the scheme you posted. If we had a scheme showing C52 and what's in the vicinity, it would help.



I’m guessing that the mini pot is going to ground as it’s going to a trace that runs under the board... I would think it runs to a common ground somewhere. You can see the open joint where the mini pot terminates in the stock pic. It doesn’t look like anything is protruding up from the bottom side of the pcb.

After further marination on the topic... what about some sort of hum trimmer? Signal shaper? Since the filter caps in the preamp are filtering the signal... the mini pot would have to be increasing, decreasing or shaping the signal. Many of the older techs are used to looking at a Marshall Plexi or Fender Black/Silver face on a scope... maybe he didn’t like the shape of the wave on his scope and added the pot to shape/smooth it?

The pot is too small to be a bias pot... definitely in the wrong section... it is not connected to any preamp tubes, and that would be the easiest/quickest way to add gain by swapping or adding a cap to a preamp tube socket leg...hmmm

The other extra added resistor near C52 is not present in the schematic or in the stock unit either. I guessing they are somehow connected in providing addition filtering/shaping... but why?

The amp was looked at by a very experienced tech... and I’ve heard clips of it and it sounds great. But I’m picky... and spotted this in the pics of the board fast. Just covering all my bases before buying. Lol.
:yes:

_________________
Excellent transactions with: sjk (S: Soldano SLO 100), glip22 (S: Gibson Historic LP R7), MrPlexi (S: Suhr PT100), Metalhead (S: PRS SC-250 AP), killertone (S: Diezel Herbert), tlingen (S: Engl SE EL34), fuzzyguitars (S: PRS Tremonti Trem & Gibson Historic LP R8), xzyryabx (S: Engl Savage 120), Devilinside (S: Randall Satan), DarkCide: (S: ESP M-II), Mizati20 (S: PV 6505+), bartmcartman (S: Bogner XTC 101B), thaifoo (S: Engl Savage 120), lester (S: Bogner UberKab 4X12), adrenalinejunky (S: Fryette UltraLead), gbsmusic (S: Fender EVH Wolfgang), savant421 (S: Bogner UberKab 4X12 cab), ams2ek (S: Mills Acoustics 4X12 cab), blastcap (S: Gibson Explorer), braciola (S: PV EVH Wolfgang USA), splawner (S: Wampler Plextortion), mhenson42 (S: Celestion V30 speakers), Gsxrbusa (S: Jackson SL2H), El Mariachi (S: Suhr Koko Boost), braintheory (S: Engl SE EL34), ChurchHill (S: Gibson Historic Custom BBR7), RKnight (S: Mesa Mark IV), and many more.


Top
 Profile  
Reply with quote  
PostPosted: Fri, Sep 14, 2018 12:15am 
Offline
Plank Cranker Wanker
User avatar

Joined: Sun, Sep 10, 2017 1:50pm
Posts: 1091
Are you human?: 951
Wizard of Ozz wrote:
I guessing they are somehow connected in providing addition filtering/shaping... but why?

Think you nailed it there... why? Filtering? Balancing? Shaping? Who knows... In my admittedly limited experience, I've never seen anything like it.

It does look like it'd be pretty easy to undo, though. Just curious... what did the tech you had say after looking at it?

_________________
:rock: :rock: :rock:


Top
 Profile  
Reply with quote  
PostPosted: Fri, Sep 14, 2018 12:28am 
Offline
Plank Cranker Wanker
User avatar

Joined: Wed, Jan 21, 2009 4:43pm
Posts: 2105
Location: In a room surrounded by Wizards & Mesas
Are you human?: 951
ChurchHill wrote:
Wizard of Ozz wrote:
I guessing they are somehow connected in providing addition filtering/shaping... but why?

Think you nailed it there... why? Filtering? Balancing? Shaping? Who knows... In my admittedly limited experience, I've never seen anything like it.

It does look like it'd be pretty easy to undo, though. Just curious... what did the tech you had say after looking at it?


The seller said the his tech told him it was 100% stock... but I spotted it in the pics pretty quick. I’m detailed like that lol.
:yes: :lol: :LOL:

I’m betting on some sort of hum trimmer. Not seen any sort of pot, unless added in any Mesa. It’s a clean job at least... should be easy to remove. I plan on replacing all the filter caps anyway... the 4 30uf/500V caps included. Just curious and was wondering if it was some sort of band-aid covering up a bigger issue.

_________________
Excellent transactions with: sjk (S: Soldano SLO 100), glip22 (S: Gibson Historic LP R7), MrPlexi (S: Suhr PT100), Metalhead (S: PRS SC-250 AP), killertone (S: Diezel Herbert), tlingen (S: Engl SE EL34), fuzzyguitars (S: PRS Tremonti Trem & Gibson Historic LP R8), xzyryabx (S: Engl Savage 120), Devilinside (S: Randall Satan), DarkCide: (S: ESP M-II), Mizati20 (S: PV 6505+), bartmcartman (S: Bogner XTC 101B), thaifoo (S: Engl Savage 120), lester (S: Bogner UberKab 4X12), adrenalinejunky (S: Fryette UltraLead), gbsmusic (S: Fender EVH Wolfgang), savant421 (S: Bogner UberKab 4X12 cab), ams2ek (S: Mills Acoustics 4X12 cab), blastcap (S: Gibson Explorer), braciola (S: PV EVH Wolfgang USA), splawner (S: Wampler Plextortion), mhenson42 (S: Celestion V30 speakers), Gsxrbusa (S: Jackson SL2H), El Mariachi (S: Suhr Koko Boost), braintheory (S: Engl SE EL34), ChurchHill (S: Gibson Historic Custom BBR7), RKnight (S: Mesa Mark IV), and many more.


Top
 Profile  
Reply with quote  
PostPosted: Fri, Sep 14, 2018 12:45am 
Offline
Plank Cranker Wanker
User avatar

Joined: Sun, Sep 10, 2017 1:50pm
Posts: 1091
Are you human?: 951
Yeah, the only pots I've seen in Mesas were added as part of the adjustable bias mod, which this one is quite obviously not. I'm curious as to what they were trying to accomplish. I mean, there's just not that much in that part of the B+ supply, just the filter caps and dropping resistors.

You definitely have a point about not wanting it to be a band-aid fix. Maybe they were trying to reduce hum or just had a bad batch of tubes. Can't think of anything else they'd be trying to fix there.

Now that (presumably) replaced or modified (and not added) resistor next to the two ceramic caps... maybe they had a bad filter cap that blew and took out that resistor? Maybe they were trying to modify the voltage to that filter cap in an attempt to keep it from happening again? This doesn't make sense, either, as it looks to me like all of those caps are the same age. Maybe they replaced them all??

All of this is just wild speculation on my part. I'm really clueless. As you said, at least it's a clean job and should be easy to remove. If you do find out anything more about this, let us know, OK? Now I'm curious, too... :)

_________________
:rock: :rock: :rock:


Top
 Profile  
Reply with quote  
PostPosted: Fri, Sep 14, 2018 4:35am 
Offline
Plank Cranker Trainee
User avatar

Joined: Fri, Sep 11, 2015 1:30pm
Posts: 592
Location: Jerkovski, on the Dutch-Polish border...
Are you human?: 951
Perhaps some additional power supply hum filtering?

Typically in DC powered guitar fx pedals, one would place a 100 Ohm resistor in series with a 100uF electrolytic, to minimize ripple and noise coming from the power supply.
Not sure if it would apply here, but who knows...

_________________
Amps:
Engl InVader 100 + Engl 4x12 Pro cab
Engl Ironball
Engl Savage 60 + Two Notes Torpedo Live
Engl e670 Special Edition EL34
EVH 5150 III 50W + Mesa Boogie 2x12 Vertical Slant cab
Fender '74 Princeton Reverb (w/ Eminence Legend 105-8)
Fryette Sig:X head + HB 212V cab (G12K85 +V30)
Marshall Lead 100 MOSFET + 1966A & 1966B cabs
Mesa Boogie Mark V:25 + Mesa 1x12 Thiele EVM cab
Roland Jazz Chorus JC-55 combo & JC-120H head
Axes:
Burny Les Paul (3x), Charvel So-Cal, Epiphone Wildkat, ESP Horizon NT-II, Fender '68 RI Strat, Gibson '67 RI Flying V, G&L ASAT Classic Tribute, Ibanez S540FM & Kramer SM-1 Guitars


Top
 Profile  
Reply with quote  
PostPosted: Fri, Sep 14, 2018 4:47am 
Offline
Plank Cranker Wanker
User avatar

Joined: Sun, Sep 10, 2017 1:50pm
Posts: 1091
Are you human?: 951
This wouldn't be an attempt at changing the heaters to DC, would it? The pot could be a hum balance for the heaters... :dunno:

_________________
:rock: :rock: :rock:


Top
 Profile  
Reply with quote  
PostPosted: Fri, Sep 14, 2018 7:45am 
Offline
Plank Cranker Trainee

Joined: Wed, Nov 18, 2015 9:39pm
Posts: 526
Location: Great White North
Are you human?: 951
ChurchHill wrote:
This wouldn't be an attempt at changing the heaters to DC, would it? The pot could be a hum balance for the heaters... :dunno:

Yeah I was wondering about this too.
Elevated heaters??
But it's connected to the wrong side of the cap.
If you figure this out, be sure to let us know WTF is going on here. :confused:

_________________
Certified Ampaholic :D
Bogner Twin Jet
Diezel VH4
EVH 5150III 100watt
Friedman BE100
Marshall 1987xl (with V2a 80's mod board)
Peavey 5150 block letter
Peters Vega-FSM
Soldano SLO 100
Vox AC30HW
Wizard MCII

A couple Les Pauls, an SG etc...


Top
 Profile  
Reply with quote  
PostPosted: Fri, Sep 14, 2018 3:40pm 
Offline
Plank Cranker Wanker
User avatar

Joined: Wed, Jan 21, 2009 4:43pm
Posts: 2105
Location: In a room surrounded by Wizards & Mesas
Are you human?: 951
Well... I heard back from someone very familiar with Mesas that it is indeed a bias pot. Never seen one placed here myself.

It is indeed sending the additional current to ground, lowering the current going to the power tubes. That’s why the pot is connected to a common ground. Most current production 6L6GC power tubes (and even many nos) run too hot (they draw too much current in the stock Mesa Recto circuit, which I’ve seen first hand myself). The pot must look a lot bigger in person, as it appears to be itty bitty in these pics.

If we were playing golf... Tim was closest to the pin. :yes: :thumbsup:

_________________
Excellent transactions with: sjk (S: Soldano SLO 100), glip22 (S: Gibson Historic LP R7), MrPlexi (S: Suhr PT100), Metalhead (S: PRS SC-250 AP), killertone (S: Diezel Herbert), tlingen (S: Engl SE EL34), fuzzyguitars (S: PRS Tremonti Trem & Gibson Historic LP R8), xzyryabx (S: Engl Savage 120), Devilinside (S: Randall Satan), DarkCide: (S: ESP M-II), Mizati20 (S: PV 6505+), bartmcartman (S: Bogner XTC 101B), thaifoo (S: Engl Savage 120), lester (S: Bogner UberKab 4X12), adrenalinejunky (S: Fryette UltraLead), gbsmusic (S: Fender EVH Wolfgang), savant421 (S: Bogner UberKab 4X12 cab), ams2ek (S: Mills Acoustics 4X12 cab), blastcap (S: Gibson Explorer), braciola (S: PV EVH Wolfgang USA), splawner (S: Wampler Plextortion), mhenson42 (S: Celestion V30 speakers), Gsxrbusa (S: Jackson SL2H), El Mariachi (S: Suhr Koko Boost), braintheory (S: Engl SE EL34), ChurchHill (S: Gibson Historic Custom BBR7), RKnight (S: Mesa Mark IV), and many more.


Top
 Profile  
Reply with quote  
PostPosted: Fri, Sep 14, 2018 4:41pm 
Offline
Plank Cranker Wanker
User avatar

Joined: Sun, Sep 10, 2017 1:50pm
Posts: 1091
Are you human?: 951
Wow... that's the strangest bias mod I've seen. Interesting... glad to know what it is, though. :)

_________________
:rock: :rock: :rock:


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 17 posts ] 

All times are UTC - 5 hours


Who is online

Users browsing this forum: IndyWS6, mchn13, Purerock7, technomancer, wIsEbLooD and 14 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group - Terms of Use