Gibson Falcon Amp Debugging?

[endorphin]

I know this is a stompbox forum but i gotta try being its the only technical forum i belong to 
Alright i've been doing the research on this amp i've hear some similar problems but no answers.most people seem to say " hey recap the power supply caps or filter caps replace the tubes"
The problem is when playing clean through it if i hit a certain note it gets real distorted and volume goes up sometimes but this is mostly with the reverb turned on. The tremolo doesnt work at all whether footswitch on or off, depth or intensity turned on. Ive been readin and readin especially the tube amp debugging from geofex. I feel ready to take this on

I would like to know where are the power supply/filter caps are and which tubes control what and whether this is cathode-biased or fixed-bias

http://www.drtube.com/schematics/gibson/ga-19rvt.gif

But on my amp the tube orientation is a little different
     V1        V2         V3    V4     V5         V6                V7
   6EU7     6EU7      6C4  6EU7  6V6  BLACKED OUT?    5Y3
SOVTEK  SOVTEK  RCA  USA  USA                            RCA

[foxfire]

looks like there should be 1) 20uF, and 3) 10uF filter caps. the 20uf is directly off of the PT. the first 10uF is after between the 470R and 4.7K. the second 10uF is between 4.7K and 10K. the third 10uF is between the 10K and the 470K. all of the electrolytic caps should be replaced.

the 6V6s are cathode biased.

as for what tubes do what and i may be wrong about this, half of V1 is the initial gain stage and the other half is a gain stage going to the reverb driver. V2 is the reverb driver and recovery. V3 is a gain/recovery stage after the tone control. half of V4 is the PI and the other half does the tremolo. V5 and V6 are the power tubes. V7 is the rectifier. i'm pretty sure i got everything right there but there may be a better name/description for a few of the stages.

not to be preachy but based on your questions i would suggest you do a little more reading and question asking before you open the amp up. i have been bitten a few times and it sucks, but i was lucky in that i'm not dead. one time it was enough to instantly burn the hair off of my finger. there are more than a few more than qualified people here that will help you but you may want to consider heading over to Music Electronics Forum if you haven't already. the Guitar amps section is loaded with very helpful people and posts.

one more thing, i'd suggest new tubes before you get too involved in opening the amp up. if the tubes in the amp are the originals then there is a fair chance that they could be worn out. if a tube swap doesn't change anything then you have a backup for the future...   

For the sake of being responsible i'll say it again, tube amps can KILL YOU!

[R.G.]

most people seem to say " hey recap the power supply caps or filter caps replace the tubes"

In general, that's right. The first step in debugging tube equipment is *always* to make a semi-intelligent guess and replace tubes with known-good one. Back when TVs used tubes, there was at least one guy in every town that made a living hauling a box full of tubes to people's houses and easter-egging in tubes.

There is a reason they're in sockets. 

And every tube amp owner with any sense of urgency about keeping his amp going will buy a spare replacement set to keep around for when - not if - the next tube fails. I think I wrote that up in the tube amp debugging stuff at geofex.

The problem is when playing clean through it if i hit a certain note it gets real distorted and volume goes up sometimes but this is mostly with the reverb turned on. The tremolo doesnt work at all whether footswitch on or off, depth or intensity turned on.

There are a large number of things that can do that. A big one is a bum or microphonic tube, or faulty filter caps.  If the filter caps are more than 20 years old, they probably need replacing.

Ive been readin and readin especially the tube amp debugging from geofex. I feel ready to take this on

Be really, really, really certain you know how to fritz around inside a live chassis with multi-hundred-volt DC and AC voltages on most of the wires before you dig in. Think hard about that one. We don't want to lose a technically capable guitarist. I was serious about those safety warnings.

I would like to know where are the power supply/filter caps are

The filter caps are the 20uF/10uF/10uF/10uF caps to ground from the plate circuits. They may be physically there as four sections of a single can capacitor. They will be rated for and carry 300-400Vdc at enough current to kill a human if they touch it and can't let go.

and which tubes control what

In the schematic you post:
V1 = first preamp and reverb gain
V2 = reverb driver/recovery (an unusual use of a 7199, by the way)
V3 = half used for volume recovery after the tone/volume controls; I don't see the other half used in that schematic
V4 = tremolo and phase inverter
V5/6 = power output tubes

and whether this is cathode-biased or fixed-bias

Cathode biased.

But on my amp the tube orientation is a little different
     V1        V2         V3    V4     V5         V6                V7
   6EU7     6EU7      6C4  6EU7  6V6  BLACKED OUT?    5Y3
SOVTEK  SOVTEK  RCA  USA  USA                            RCA

That mismatch is so substantial that it's clear that witehr (1) the schemo you show is not the same as your amp or (2) someone has "improved" your amp from the original.

Please don't take this wrong, but I have a bad feeling about your poking around in there given what your questions indicate about your skill level. I could be wrong - I often am - but please get skilled help unless you have high voltage experience. I would not like to see you get shocked or killed. Better to have more advice than you really need than less - right? Be careful and don't try this unless you're sure you can do it safely.

[G.Neyrey]

http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/gibsonamps/ea_28rvt-pathfinder.pdf

Here's your "Falcon" schematic...disguised as an Epiphone Pathfinder! I've got one of these Falcon amps too.

George

[R.G.]

That's more like it, George!

@endorphin:
The rest of the advice stands, I think. At least this one has comparison voltages. I'd restate and sum up with this new info:

1. Be very realistic about whether you can do any work in there safely. Get help unless you already know you can. We don't need to lose anyone to electrocution or fires.
2. Get a spare set of tubes. If you keep the amp, you'll need them. They will also be hugely useful in debugging.
3. If you pass yourself on (1), consider replacing all the electros to start with. Your problem may be a bad cap. If it is, replacing only one at this amp's age is not good economy. The next one may fail at any time. If it were mine, I'd do this to start with.
4. When and if you get to testing voltages, test with a DVM for the recommended voltages. VTVMs had an even higher input impedance than modern DVMs, but the DVM will be OK as an indicator.
5. Consider having a competent tech replace the AC cord with a three-wire safety grounding cord, redoing the input fuse and switches to make this right. This is yet more dangerous if done wrong than the high voltage DC, so reconsider (1) before trying this yourself.

Finally, once everything is running OK, the 6EU7 is a low noise, high gain duotriode somewhat like the 12AX7, but with a different pinout. It is possible to rewire the 6EU7 sockets to take 12AX7s to make getting tubes easier. This is a fussy detail to consider after you've worked through the amp first.

[endorphin]

Appreciate the help! yes certainly before going near the caps again. already looked inside the chassis to look for any defective looking components and to clean the pots and any foreign materials. Ha i've read several times about the high voltage and risks so i've been trying to read/learn about discharging the caps. Replacing the caps and tubes with NOS parts shouldn't be difficult as for the price I've got some good resources in this city and an amp tech i could get some help from as we're always talkin.

I'll look around more for tube amp info. I've got all the tools i need really just some more knowledge bout all methods to diagnose and safety believe me i don't wanna skimp out on nothing.

so how the hell do you insert images? i know theres a button but i dont get it.

[petemoore]

  New-new stock for capacitors makes sense, they have a shelf life like batteries, for the troubles involved with getting them in there, new/unused is as good as they get, they work for a long time [longer if power-cycled with regularity], then dry-up or otherwise leak/fail, old is sometimes worth the trouble or expense to get the 'vintage-vibe', but not necessarily with capacitor replacement, with new caps, a good solid/reliable power supply ~means no worries about recapping again any time soon.
   I'd suggest look for the original 'fatpin' type tube to replace any of themm instead of converting the socket/position/circuit to 12a_7 'skinnypin' type.

[R.G.]

i've been trying to read/learn about discharging the caps.

There is one "mod" that makes this a lot safer to work on in general is to put a high-value resistor across the first filter capacitor.  This resistor guarantees that the capacitor will, in fact, run down to zero even if the tubes are not conducting at all, or are all pulled out of their sockets.  Something like a 470K/1W across this cap ensures that the caps will drain. No worrying about discharging caps - if you wait for some short time, they're guaranteed to be discharged. The load of this resistor on the power supply is negligible in operation.

I have a whole suite of "mods" that I suggest for anyone that wants to listen. They are not what the guys who pop up and say "Hey, anybody got some cool mods for..." have in mind. All they do is make your amp work more reliably and safely.

Replacing the caps and tubes with NOS parts

What Pete said. "NOS" means "we couldn't get anyone to buy these when they were still new" in most cases. Caps have a shelf life.

just some more knowledge bout all methods to diagnose and safety believe me i don't wanna skimp out on nothing.

Good. Become close friends with that amp tech and ask him how many beers it would take to convince him to give you some instruction in safe wiring (before the beers, just to be sure...  )

so how the hell do you insert images? i know theres a button but i dont get it.

You put them somewhere else on the internet and link to them. The forum doesn't host them.

[endorphin]

Alright then what would be some good caps that i could use to recap the amp and also does this go the same for the tubes because where im thinking about gettin them they are likely to carry them plus they have a tube tester which i do not know how to use.

As far as the amp tech cant do the beer ha i can't buy beer But before i do anything ill see if this guy can look at it for free and what not.

Also i'd like to point out that i read it in the geofex tube amp debug but forgot what the symptom was anyways i looked at the tube in the dark and Valve 5: 6V6 has that blue fluorescence look burning in it.

I'll put up a pic and label what i believe is the right caps and values in the amp chassis.

[endorphin]