greetings. new to the forum. I have an old original Peavey 212 Classic hybrid SS front end with 6L6GC output. after playing for awhile the tone control cuts out. jumps to a high frequency and stays there until next time after being off for awhile. the control turns UP/DOWN but no change :loco
any thoughts
likes/dislikes this amp
whatever
I am familiar with working on tube amps, radios and some with transistor radios
first attempt at attaching schematic. check it out
by tone control I mean treble. see in first section solid state
maybe R45 going short
The schematic you posted is for a Classic VT. Is that what you have? Peavey also made Classic (and there were A and B series of those) as well as Classic VTX.
R45 going short? No, resistors do not short. They open or change value, but not short.
First suspect is the control itself. If pot R47 goes open at the bottom end - the end that meets R48 - OR if the solder is cracked so it acts open, you get your symptom.
Then again... when this happens, do the bass and mid controls still have any effect, or are they dead too?
While you are at it, check the solder on all the other tone stack components.
greetings Enzo. thanks for your reply. I see that this is an active forum. great. new here
that should be the correct diagram VT Series. bought amp used back in the 70s. got the print from the factory more recently but some time ago. factory pretty good about sending a diagram.
from memory I thought TREBLE but checking today it is the MID that suddenly has no control. plays fine for awhile then MID quits. no control but no scratchiness. the sound becomes treble although there is control with BASS and TREBLE. I would guess that the MID pot is bonkers stuck at the high side but I am not a solid state person. I know that tone stacks are tone stacks and pots are pots but maybe something kooky unknown to me going on. any further circuit analysis appreciated
I have a 79 Peavey Classic VT 212 with phaser with original footswitch and cover. <3)
I personally think it is a great amp for what you can get them for. I bought mine from a local guy about a year ago super cheap because it wasn't sounding great at the time but I put Winged C 6L6 tubes in it, had a tech check it out and replace filter caps and some other minor worn circuitry bits and basically brought it back up to new specs.
It also currently has an Eminence Swamp Thang and WGS Vet 30 in it and it sounds GREAT! :dbtu:
Fixed up right, it is a reliable and awesome-sounding amp for not much $$- and one that nobody will try to steal from you. :lmao:
yes phase shifter temolo. different speeds different effect. great reverb. select and combine switches. all in the original foot switch. check out the schematic attached to see how they do the switching with transistors. mine is all original. I have a lot of tubes to swap out. not much difference really. everything works fine except for the MID cutting-out
The earlier versions had "tremolo" but later versions had "phase." You can kind of make the phase sound like tremolo at the right settings. Which does yours have?
Distortion channel at low volumes isn't all that but when the volume is up and your pushing the power tubes, it sounds really good.
If you haven't already considered it, think about upgrading the stock speakers. It will make a HUGE difference. I started with two WGS Vet 30s and was really amazed at the difference. Then swapped out one of the Vet 30s for a WGS Reaper 30 watt and it gave it a bit more of a vintage sound with more speaker breakup from the Reaper. Again, great sounding just different.
The current Eminence Swamp Thang / Vet 30 combo is just brutal. Super tight low-end resonance you really feel in the bones with no mush whatsoever still plenty of mid and sparkle and a little breakup from the Vet 30 when pushed.
I have another Swamp Thang I may put in there but that may make it more of a bass amp than a guitar amp! But would sound AWESOME!
:dbtu:
Forgot to mention that I also like that I can run my Randall Commander head through the power-in of the Classic VT. Makes the Randall sound great with that tube power section.
I have one of these that I got for $20. It had a bad cap (the last node 10-350V on the power supply) and the two 22K resistors before it were bubbling and making a sound like frying bacon. I replaced those, and now it appears to have all functions, although some of the controls are noisy (i ran out of deoxit and am getting some more). It also had a hole in one of the speakers ( I have the original peavey square magnet ones) which got the white-glue-tissue repair treatment. I also removed the two-inch palmetto bug corpse from inside the cabinet. The cabinet is actually solid pine wood, the baffle is chip-board. It also looks really convenient to work on if you had to, the ics are all socketed, there are a lot of connectors, so you could easily remove the board with just a couple of screws and the pot nuts. All in all a solid piece of gear, I think.
thanks for the input guys. it has phase shifter with speed intensity and color control. high speed = tremolo. all original with square magnet speakers. no need to change them because you can use the 4ohm 8ohm output jack to any cab you want. I have tried different speaker cabs with some noticeable difference. the input/output loop is a nice feature. I did play around with both once upon a time.
shorting power supply filter capacitors will fry any resistors in the circuit. dry shorting electrolytic capacitors = high current. better fried resistors than output transformer. I have used coffee filter and Elmers glue to mend speakers. Elmers is water soluble, flexible and strong. coffee filter paper is tuff and flexible. repairs still going strong.
the issue with my unit is that it suddenly goes into a treble sound with the MID pot losing its control. almost like a heat component failure. like electronic switching. I am thinking now that maybe one of the small electrolytic capacitors is dried-out and grounding some signal in one of the op amps. not knowing characteristics of op amps I am only guessing. yes it does have the original capacitors in it... ::)
short op amp tutorial would be great :dbtu:
Quote from: tubeAMPI am thinking now that maybe one of the small electrolytic capacitors is dried-out and grounding some signal in one of the op amps.
I agree with
Enzo that you most likely have an intermittent open in the Mid pot path. Caps are always getting fingered but the fact is that broken tracks and solder joints (in the case of controls due to the amp face-planting on the floor at some point) is more likely.
Looking at the circuit there is no cap that presents itself as a likely cause of such behaviour, and I will even go so far as to nominate either one of the solder joints on the Mid pot, or possibly a rivet that connects the pot track to the pot connection lug.
so if R46 low side is going open neither C29 or C58 is never grounded. that might account for the highs being amplified. funny how the amp operates normally then suddenly has failure. let it rest it goes back to normal then operating awhile fails again. no static no noise more like an electronic component failing. but I have been fooled before :loco
Quotefunny how the amp operates normally then suddenly has failure.
Well. that's why those failures are called "intermittents".
Quote
more like an electronic component failing
Not necessarily.
Amps (and circuits in general) are made out of *parts* and *connections* .
"Bad parts" explain only half of the problems.
All parts may measure perfect and the amp may still develop a problem.
Quote from: tubeAMPno static no noise more like an electronic component failing
I don't think there is any basis for that conclusion at all. I've had components such as transistors fail like they have been switched off, and others that have made all sorts of fuss as they flake out; and I can say exactly the same for dry joints, cracked PCB tracks, socket contacts, and so forth.
One of the reasons I suspect an open, perhaps thermal, in the Mid pot path is your observation that the level of trebles rises. The Mid pot going open will reduce the tonestack insertion loss, in other words the overall signal level should rise.
you would think that 1.6v at U5A would not be enough to cause thermal issues at R46 pot. but it acts thermal by nature after running normally then 'yoink' high frequency time with no MID control. plugged guitar out/in to every input, switched foot switches, change control settings. same thing. turn OFF amp come back later back to normal.
BTW diagram doesnt say about the two ground symbols. one is chassis the other is BUSS for CT at 0v
I think you misunderstand "thermal issues." The whole amp warms up. That means the metal chassis and mounting hardware warms up, metal expands some. The solder on the connections warms up and metal expands. The thermal issue at the pot is more likely the solder connection widens up a micron or two as the whole thing warms up, and poof: your symptom. It isn't about 1.6v somewhere heating anything.
Quote from: tubeAMPyou would think that 1.6v at U5A would not be enough to cause thermal issues at R46 pot.
No, I certainly wouldn't, I was thinking of indirect heating from some other section (e.g. a zener dropper for the preamp power supply).
But whatever, at some point you have to stop mulling over the circuit and discussing how many teeth a horse has, and go out to the stable and count them. This fault isn't on the circuit and will only be found by close investigation of the actual assembly, and there is only one of us who can do that.
true. discussion redundant. thermal. solder. got it :duh
for those interested in the ugly beast
http://www.sacmusic.de/amps/reload.html?pea_cl.html
now you know what were talkin about :dbtu:
what did I know about amps back in the day. thought that it was longer ago than 79 but I must have just been coming out of the fog of the 70s. a favorite gig piece borrowed frequently by a buddy locale venue musician. the clean channel or BRIGHT in Peavey land is pretty good actually when the thing is working. NORMAL whatever that is channel is kind of gritty by tube amp standards. I am now learning solid state after favoring tube amps, old radios and such for so long. hope you dont mind the dribble but I am having fun with new interests :lmao:
still more to come :duh
this may be helpful for anyone trying to find Peavey parts
http://www.ampix.org/albums/userpics/10003/PV_Semi_Cross_Ref.pdf
this is pretty cool op amp illustration
http://www.williamson-labs.com/480_opam.htm
I may get a chance to bench the Peavey this weekend :dbtu:
For what it's worth, I had an "intermittent" failure going on with my Randall head that is the same age as your Peavey. It would drop volume and go fuzzy sounding. Sometimes come back to normal, sometimes not until after switch-off. Almost always failed after a bit of playing at above a certain level of volume.
Roly and DrGonz helped me diagnose and it turned out to be a bad solder connection on one of the filter caps. I cut fresh leads and resoldered and so far (fingers crossed) it hasn't failed again and sounds great.
Just took a lot of poking around and testing.
still trying to figure out the foot switch with the OP amp and CMOS data. looks like COMBINE has something missing in the foot switch diagram. combine what. connects pin-1 to F.S.-1 at Q2 then SELECTOR selects between pin-2 and pin-3 connecting F.S-2 or F.S.-3 at U3 and U4 CMOS.
all I can figure is that plugging into J4 AUTOMIX is always connected through J3 BRIGHT. U4 is switched ON/OFF cutting BRIGHT amp U1A into U5A or U2 that mixes or not with NORMAL amp U1B. U3 switches NORMAL ON/OFF. the foot switch does this somehow while making hard connections between F.S. points. something else U2 has pin-9. there is no pin-9 in a CA3094 OP amp. must should be pin-4 Vcc-
HOLD THE PHONE! One problem at a time (per thread) you are going to get bamboozled and confuse us as well. Stick with your intermittent Mid problem, then start a new thread about your footswitch (problem). This also makes problems/repairs easier to locate for those who come along later.
Agree^^^^^
Nothing is missing, I will be happy to explain how all that works, but let's not go there until what we are already working on is fixed.
interesting. another forum says do not start a new thread for the same device. different strokes folks. the only confusion is keeping the trends straight :loco
otherwise Im pretty good with discernment. probably bench the amp this weekend and practice with the pot connections as small and delicate as they are on PCBs.
but knowledge of operation flow wouldnt hurt.
I see that AUTOMIX plug lifts CT GND off of Q2 base turning it ON that turns Q1 ON.
must be sending + voltage to either FS-2 or FS-3 through FS-1 to operate the CMOS switches ? this is what is confusing to me. the switches, CMOS and foot :loco
pretty straight forward after signal hits U5A then its OP amp to hop amp til it gets to the power amp stage. goes through two driver/phase inverter IQ1 and IQ2. one is getting inverted signal from OT secondary. then 6L6GC pp output :duh
PS: at the same time AUTOMIX Q1 ON is sending bias voltage to U2 that beefs-up the signal from U1A while U4 is OFF...
hmmm... more thinking. maybe Q2 is sending CT GND to FS-2 or FS-3 through Foot Switch. U2 does the combining while foot switch connects FS-1 GND to either FS-2 or FS-3 turning each OFF/ON
I don't think we said start a different thread, we just want to work on one problem at a time, so we don;t get confused by references to various unrelated sections of he amp. In other words we fix channel 1 before we start on channel 2. Once the first issue is solved, I will be glad to explain in detail how the footswitch and automix work.
just sitting at my desk killin tyme looking over this schematic waiting for the next request to go on. lots of tyme to put to good use 8|
Have you tried cleaning and resoldering the mid pot yet? If so, what was the result?
I am going to get to it this weekend. it is good to have feedback for best focus :tu:
you guys must have done this before. I dont want to say that its working so it doesnt quit when I go check it again. but its been working for at least an hour now with all controls functional. there I said it knock on wood :trouble
took it down to the PCB for a solder touch-up and pot cleaning. probably didnt get enough cleaner in there because I didnt take all the connections off to be able to turn the board up-side-down. they are working well enough turning smoother after lubing the shafts and some in the pot openings. the solder job is the main attraction and is doing well.
so now Im a candidate for more knowledge 8|
this means that I get to learn the flow of operation through the AUTOMIX jack to at least the tone stack hopefully :dbtu:
muchas gracias
Sometimes I need to clean pots, and I see looking inside that the pots stick up from the board, so I would have to spray cleaner up into them from underneath somehow. A simple trick is to flip the chassis over on the bench, so the open side is down. Knobs facing away from me. Now I lift up one end of the chassis, so I am now looking up into the chassis. Now the pots are hanging down from the board, and the opening is on top.
With the extension tube on the sprayer, I put the end of the tube against the exposed edge of the pot wafer - where the legs come out. I gently spray, and the liquid then dribbles down into the opening. Turn the pot back and forth, et voila, clean pots. Forgive me, but it is not unlike pissing on a cement wall and seeing the fluid roll down towards the ground.
OK< Classic VT footswitching.
Note the reverb and phase footswitches common to ground, as you might expect. The channel switches common to R34 over by the automix jack on the drawing.
The channel switches do not enable the channel in question. Rather they kill the other channel. YOu want channel A? Then kill channel B, or vice versa. You want both? Then kill neither.
The two input channels are more or less identical. The output of each is switched on or off by U4, U5. After those the paths converge to one path through the amp. There is a footswitch control input to each of those ICs. grounding either of those turns off the corresponding IC, so it kills the channel. That would be simple enough. You can plug into the individual channel ins, and play through just one channel. But then you'd have to be careful not to have that channel turned off - killed. Plugging into a channel input pretty much means you want it on, so there is no need for channel switching then.
Automix allows you to play through both channels at the same time.
Note the Bright input jack has its ground shunt through the automix jack. Plugging into the automix ungrounds the bright in, which will be the input channel used. More on that in a moment. The automix jack also keeps the base of Q2 grounded. That turns it off, so the collector and thus R34 rise to +15v. Since that is the common for the kill switches, they too will have the positive voltage on them, so the channels remain live. But when you plug into the automix, then the ring contact shunt opens and the base of Q2 is pulled up by R31, turning the transistor on. That drags the collector down to ground, or at least close enough to it. That means R34 and the kill switch common are now grounded. NOW the kill switches work. You only want kill switches working when both channels are available, ie when using automix. And that combiner? It simply breaks the ground connection so neither channel can kill.
Back to the signal path. Automix only feeds the bright channel, but we need to get that signal over to the other channel too. The signal from the bright input is also routed through U2, to cross feed to the normal channel input. We don;t want that crossfeed all the time, so The Q2 controls the footswitch, but it also controls Q1, which turns U2 on and off.
That was a conceptual overview. If I glossed over anything too thinly, let me know.
Thanks Enzo. I think that I was getting it more or less in my second analysis. close anyway. looks like the ICs are held-up with voltage until the FS kills the power source with Q2 ground. not used to these logic circuits. hurts my brain. I did see the simple ground (CT not chassis) circuit at FS-G for REVERB and PHASE. sounds better when someone else says it as well. keeps me focused. confidence mo bedda :dbtu:
it is pretty cool design using transistors and IC switching :duh
thanks for taking the time with the walk through
happy trails to you
thought that I would check it before chassis going back into cab. failed :grr
good thing that I can recreate the trouble by moving TREBLE and MID pots. PCB flexes too but is isolated to this area. checking continuity between resistors and capacitors looking for opens. nada. thought maybe a voltage change might indicate intermittent... poking C28 while amp is ON is creating the trouble. reheat solder joints. no improvement. found a 600v .03uF in my stash for a replacement. big and fat but fits. Ragu, its in there. is working good senior. maybe problem solved. C28 must have been going open. everything mo bedda :dbtu:
tomorrow a new day will make some more checks before reassembly. while testing the amp without C28 in the circuit the trouble is recreated exactly. so I am pretty sure that was it but wont hurt to check it-out once more
Quote from: tubeAMPwhile testing the amp without C28 in the circuit the trouble is recreated exactly.
This is the sort of check back we like to do wherever possible. If you can re-create the fault on demand you can be pretty sure you've found it. :dbtu:
all the parts that I have are high voltage for tube radios and tube amplifiers. these low voltage solid state pieces are tiny and delicate. looks like it was an electronic component failure after all. capacitor replacement is noticeably larger but functional.
PCB is kinda flimsy. makes crinkling noises when flexed. I wanted to re-seat the connectors but not coming off easily. crinkle-crinkle
thanks for the input guys. looks like we are on our way
the old beast was looking kinda dusty. cleaned it up with some cleaner, brushes and a sponge. vacuumed it out. brushed-in a coating of ArmorAll into the Tolex then polished with a towel. looking like a brand new 70s combo now. sounding great. in a godda da vida baby. actually more like Howlin Wolf and Elmore James tunes 8)
Quote from: tubeAMPPCB is kinda flimsy. makes crinkling noises when flexed.
We try to avoid doing that because it can lead to hair line cracks in the PCB traces. :(
yes we do :loco
the thickness of the board to its length ratio is flimsy. pots mounting is delicate. connectors are tight fitting. there is no way not to stress the board when touching it. this is what was partially responsible for finding the trouble area. the board flex when moving it. closer inspection revealed the trouble. in this case a failed capacitor :duh
checking the amp this morning it cranks. looking good sounding good. I am much more familiar with it now :dbtu:
this is what I am working on lately. attached is 8- transistor radio. had an open IF transformer T4. repaired it with a strand from 24AWG stranded CAT6 patch cable. screaming loud now :dbtu:
Transistor radios are addictive. Stop now before you end up with a box full. :tu:
it is getting to where I am working on more solid state than tube type apparatus. its all good :loco
BTW I do have a variety around the house. some people decorate with vases and lamps. I decorate with radios and amplifiers from the early 30s to mid 60s :duh