this is just a question:

i just got a furman spring reverb rack thing and it wasnt working right and i opened it up and there is that amber-looking gunk all over the PCB solder joints.

an amp i fixed recently had the same stuff that was causing intermittent noise and when i cleaned it, it got all better.

now what IS that gunk? and why sometimes when i re-flow solder on an older board does it seem to appear?

is it rosin? but if it is, is it bad? it certainly seemed to be in the case of the amp....is it nicotine (i think roly maybe mentioned that) or other noxious residue? or just oxidation?

just curious.....

alright heres where im at:

did some resoldering - power supply, phase inverter - even put in new preamp tubes and a new phase inverter tube - problem persists.

after some extensive mix/match (including other amps and speakers) testing today, im pretty convinced the problem is in the deville's power amp.

if i play the amp's clean channel, it sounds good, but it still breaks up in a boxy,jagged,unpleasant kind of way. the drive channel, on the other hand, is not only quieter, but also kind of hollowed out (no low end) and much much much more jagged/boxy. not pleasant tube saturation but kind of gnarly, clipping, farty and grainy kind of distortion.

if i plug in a diffeent preamp direct into the deville's power amp, i get the same problem - gnarly, boxy, congested distortion

these are new powers tubes, as well.

testing wise, the only voltage that looks off is the phase inverter cathode voltage - its about 10 volts too low. could that be causing the symptoms? seems like it could, since the phase inverter directly feeds the power amp....

where is the cathode bias on that tube coming from???

we did it!

replaced the main filter caps and we are all good.

sounds great, actually!

quick question: so i know there is no biasing this amp (i read on another thread here that its got a self-adjusting control grid voltage circuit thing) - does that mean anything for matching tubes? i did not number the tubes when i took them out and im wondering if i should do any measurements to see if i paired them back wrong or not.....

the cap in series didnt work - my meter read 0VAC in that configuration....but like i said, its a cheap meter. or maybe cap didnt get it cause its too low frequency (i used an 0.04 uf).....

BUT i scoped it and i got a nasty looking 8 V p-p ~150Hz ripple...asymmetrical trapezoid shape.  thats too big of a ripple, right?? on lo-power its more like 2.5 V p-p - but still too big, right? shouldnt the ripple be quite small, less than a volt?

EDIT: wait a second my probe was on x10 - so thats 80 V p-p!!! (right?)

change the filter caps?

meter shows AC on B+.....800V?!

its not a super fancy meter so let's hope thats just a little fluke (no pun intended....really). should i scope it there and see what the scope says or go ahead and change the filter cap?

EDIT: dont waste your time giving me any advice on this yet. im trying to nail down a clear, repeatable symptom and am getting all kinds of stuff (including a weird octave down effect......). ill post again when i have a more clear symptom description.

okay EDIT EDIT: watch the video i posted.

heres whats up: the hum is not a hum. rather, the issue is, when the amp is played (with a guitar) it makes a weird puttering, almost octave down-y kind of farty noise underneath the note. this is with the preamp shorted, straight to the power amp in.

the video above is a 1K sine wave into the input. the 1K tone comes out fine but it has a lower, buzzy/farty kind of tone underneath it (thats the phantom waveform you see in the video). oscillation?

heres a better clip (this time signal goes into main in): http://dropcanvas.com/#G8A159j2k59a09

ill keep this one short (schematic attached)

this amp has a weird hum. higher pitched than 60 Hz. i checked power supply - looks okay - except plates are only getting ~363 volts (according to schematic should be 525). other DC stuff looks okay, but i didnt go through everything yet.

i scoped the hum (with a 1K test tone....ignore the shuffling sounds, they are unrelated. the hum kind of blends in with background noise, but you can hear it):

http://dropcanvas.com/#9i6BMjZ3oBMzr4

any ideas?

with no input signal: the amp hums with the controls all the way down. the controls in that case have no effect on the hum. if i scope that (with scope leads across speaker tabs), though, the scope seems to load it down (or ground it?) and it disappears....if i crank the amp up the scope picks up a (quieter hum) that just looks like noise (no discernible waveform) - cant tell if thats just noise floor of amp then.

the bigger problem is that this amp has a snow camo design. i wish there was a repair for that....

ohhhh

now i see! i thought that switch ddint make sense.....i thought it was an internal thing - of course its not working!! i wonder if it's always been missing that part........

alright ill just hard wire for 115V, then! let me know if you guys see anything the pix i should take note of....and whats the best way to hard wire it??

http://dropcanvas.com/#oykJ406u48IJ9y

those work okay?

EDIT: this link works now - fixed it

jesus what a simple solution to such a pain in everyones....

http://dropcanvas.com/nl0yl

thanks, Gonz!!

(i edited my previous post with the correct corresponding file titles)

can you download/open this file:

https://drive.google.com/file/d/0B96d2ZNKqmsHWUljZG1wU1ROT0E/edit?usp=sharing

?

if not ill upload them a different way (easiest this way but you know......lazy way isnt the only way....)

EDIT: i removed the stupid links! for pix see this site: http://dropcanvas.com/nl0yl

QuoteIt sounds like the white and black are reversed at the switch.

i thought so, too....isnt the Black wire supposed to be L(ine)? remember, the 120VAC readings im getting are BLACK wire to chassis (meaning I am reading from the bottom of the pilot light to chassis). I get 0VAC from the white wire (mains fuse) to chassis.......?

Quoteusing green+yellow stripe for anything other than a mains safety ground is an absolute nono

if you look at the pictures marked "Standby wiring" you will see that the green/yellow striped wire was cut from that bundle and possibly spliced (?) onto the pilot light side, where it now goes to the pilot light....its hard to tell whats going on and why. where SHOULD that wire (or a wire of that sort) go to/from in the normal amp world?

Quotehave a look at the resistance of the leads coming out of the mains side of the tranny

with the amp unplugged, i did this, but the results were not encouraging. first of all, there are no leads that are not connected to something - where do the other (245V/225/105,etc) taps go normally when they are not in use? the only transformer taps that were readily available were the ones attached to the mains selector switch and two blues ones (as in the file "PT 1"), one lighter blue and one darker. the darker one goes back to the mains switch - switching to the black mains lead and the pilot light - and the lighter one to the grounding selector switch (the file "grounding cap"). with my DMM hooked to the node where these two blue wires connect to a thick black wire from the PT (common point on primary winding?), i get 0 ohms/dead short to BOTH sides of the mains selector switch - the side that goes to a fat yellow wire into the PT and the side that goes to a thinner red wire that goes into the PT (that node also goes the green/yellow stripe that goes back to the pilot light).

i am getting a short between the fat yellow and the thin red wires going into the PT.

my hope, i guess, is that the mains selector switch is shorting things together, not the PT! remember, i get NO connection between the outer nodes of the mains selector switch and the middle pin (which goes to the mains fuse).

there are a few other pix that are more for your interest at this point, seeing as the amp has bigger fish to try. one other thing i will mention is that (as per the picture "fuse_to_ground") i disconnected the wire that goes from the fuse to the grounding selector switch, thinking that, since the amp has a 3 prong mains plug, i didnt need that. death cap, right?? why would an amp that was built stock with a 3 pronger have that, anyway?

alright so i did some mixing and matching and have come up with the frustrating conclusion that the problem is maybe in both the pre and the power amp (is there a possibility of it being kind of between the two? the phase inverter??)

IF i take the preamp out and connect it to another amp, i get the same kind of boxy and congested, even grainy sounding break-up.

IF i play my guitar directly into the power amp in, the amp sounds better but still has an element of the problem - a kind of unpleasant breaking up/distortion that verges on crackliness.

basically it seems like more of the preamp acting up, but its hard to be sure that the power amp isnt also a part of the problem, somehow....

additonal detail i forgot to mention: some months ago the amp was doing this weird thing where it would make and sustain a loud hum whenever id hit an F#. it would sustain the note in a loud, hum similar it 60Hz power stuff, but not exactly (it would just hold the F#!). the third preamp tube (phase inverter?) would amplify the noise if i tapped it (microphonic?). i figured it was the problem so i switched it out for a new one. the problem went away BUT strangely enough when i switched the old tube back in (out of curiosity) it did NOT come back, nor was it microphonic anymore.

ill try some tube swapping just to see if that changes anything, but otherwise:

does it make sense to troubleshoot the phase inverter given the symptoms?

ookay - so:

no voltages on the amp side of the PT.

i tried to untangle the mess thats been made of the wiring coming in from the mains. the mains plug and lead itself seems all good, with the earth wire properly grounded to chassis.

first issue is the mains switch:

the white wire from the mains plug (is that the L connection?) goes to a brown wire, via the mains switch, that then goes to the mains fuse.

the black wire from the mains plug (the N connection?) attaches directly to one side of the pilot light, and then goes to a blue wire, via the switch, that goes into the transformer (bottom of the primary,  i assume, at least per the schematic). should i rewire the pilot light onto the transformer side of the switch?

the other side of the pilot light goes to a green/yellow wire that then hooks up with an orange wire that disappears into the transformer (top of the primary, depending on the mains voltage switch?).

IF i take an AC reading with my DMM, i can only get 120VAC reading from the BLACK wire to chassis. nothing if i read the white wire to chassis. is that normal?

i get ~35VAC from the pilot light to chassis ().

second (bigger) issue:

the reason im not getting anything inside the amp is because the mains voltage selector switch does not seem to be working. there is NO connection between it and the mains fuse. it looks like there should be, but either the switch broke internally or it needs to be turned. i have to say it scares me a little bit - seems like if i turn it the wrong way im misinforming the power transformer as to the voltage its going to get....would that be catastrophic? im not sure what to do. should i take a picture of the switch??

heres a description: the center pin connects to the fuse. around it there are 6 pins. a pair is connected together and connects via a fat yellow wire into the transformer. another pair is connected together and goes to the green/yellow wire that hooks up to the other side of the pilot light and ALSO to another wire that goes into the PT. NONE of these pins have a connection to the center pin (DMM tested)

i get 0VAC from the mains fuse to chassis.

quick question before i get into it (thanks again, Roly!):

the mains fuse (3A) tests okay (short) with meter but has a little bubble on it - that okay?

is that just a variety of slow blow?