#1
By now, 3 times to the tech, a good solder job on some weak joints, has proved my 6505+ 112 was a friday job definitely

I took it in yesterday, after it had been dead for a little while, as the power tubes were not lighting. When I took it in IT WORKED (sods law eh?), my tech had a 30 minute look at it, and checked it out, nothing seemed wrong.

When I took it home and put it back in the case, played through it for a while, all was fine. Powered it down and later on plugged it through a bass cab I had acquired from a friend. Didn't know anything about the cab really, but assumed it'd be enough ohm rating & watt rating given it's a bass speaker. It didn't make any sound, so I turned it off as soon as I could. In the end, only had it on for about 20 seconds max.
When I plugged it back into my guitar cab, power tubes weren't lighting.

I should mention i've always run it correctly (right wattage & ohm rating speakers, not turning on without a load)

My only guess as to what's wrong, is the power tubes getting old (not changed since I brought it used a year ago, can't find the manufacture date). Can power tubes wane like this? I can't imagine that they can light some days and some days not, my guess is it's an issue with the circuit.

Luckily, my tech as given some nice prices, only £25 per hour, but still, should I possibly get another amp?

Thanks
#2
The stock tubes in those amps are crap, retubeing the second you buy one is almost mandatory for any Peavey amp. Also, if you don't know the ohm rating of your cab, DO NOT plug your amp into it. The 6505 combo isn't built with the best materials and it's possible all it could take was a few seconds of incorrect ohms to fry the output transformer.

But it's most likely the tubes just died. Tubes wont just work some days and work others, either they die violently, or you'll have volume swells and weak sound.
#3
Redone all the the preamp tubes, but okay could grab a set of 2 6L6s. I just want to rule out if it's tubes or not before I drop the cash on em.

My only thing that wards me off the idea that the power tubes are dying/died, is that this happened twice now, exactly the same thing happened before. I play it night before, then next day suddenly won't work, then I take it to the tech and it works again. Plus as far as I remember, haven't really been any volume swells, or nor has it sounded especially quiet.

I had the amp on 4ohm mode, and as it's a 15" speaker, I expect it's 60w rated or more. Either way, I'm not sure if I've fried the transformer.
#6
I don't know a whole lot about amp circuitry yet, but if your tubes don't light, you might have blown a fuse somewhere. I'm not sure if there is a fuse for the heater circuit or not, though it could have been the main fuse too.
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#7
Could be the tube heaters. The 6505+ combos are notorious for the heaters going shit, mine did it in the preamp but it could happen in the power amp too. Could be something as simple as a loose wire that got jostled around when you moved it around, this causing the intermittence.
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#8
Ah, that's where mine went wrong before, preamp had failed, due to a heaters connection being screwed. Thing is, I didn't move it at all in between it working & not working.
I'll take it out of the case AGAIN, for the 15th time or something stupid

Have to say, given all the issues i've had, temped to for the moment, run a pure POD setup, and buy a magnum 44 power amp pedal and leave the amp till I get round to fixing it. As this is probably my plan for my uni setup in a years time.
#9
Just an update, After I had taken it out of the case and inspected it visually last night, Plugged it in just now (outside case) and it seemed to work again

EDIT:
another update, was just playing through it, and it suddenly cut to a whisper. I went to standby then, and looked at the power tubes. The right one was glowing very abnormally, with the glow covering most of the tube.
From this, i'm assuming that the issue all along was the tubes were f**ed, but weren't showing any signs.
Hooray!
Last edited by ambler3 at Sep 14, 2014,
#11
Interesting problem Ambler3. Keep us posted. A fresh set of good matched tubes wont' hurt but it seems your issue is more related to the heaters as mentioned. I'm not an amp tech guy though.

Quote by Offworld92
I don't know a whole lot about amp circuitry yet, but if your tubes don't light, you might have blown a fuse somewhere. I'm not sure if there is a fuse for the heater circuit or not, though it could have been the main fuse too.

FYI - If it was the mains fuse, then the amp would NOT work sporadically it would just be dead dead until the mains fuse was replaced. If it was the HT fuse, then the amp indicator lights would light up, but the tubes wouldn't work. Again, that fuse either works or doesn't work, but not sporadically.


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Last edited by 311ZOSOVHJH at Sep 14, 2014,
#12
Quote by 311ZOSOVHJH
Interesting problem Ambler3. Keep us posted. A fresh set of good matched tubes wont' hurt but it seems your issue is more related to the heaters as mentioned. I'm not an amp tech guy though.


FYI - it was the mains fuse then the amp would work sporadically it would just be dead dead until the mains fuse was replaced. If it was the HT fuse, then the amp would light up, but the tubes wouldn't work. Again, though that fuse either works or doesn't work, not sporadically.


thank you
Spin 'round carousel when your horse isn't screwed in.

My band:
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(For fans of Death/Groove/Prog Metal)

Ibanez RGA42E
Ibanez S420
LTD H-301
Ibanez RG520
Peavey Predator USA
Douglas Grendel 725
Line 6 Pod HD500X
#13
Quote by 311ZOSOVHJH
Interesting problem Ambler3. Keep us posted. A fresh set of good matched tubes wont' hurt but it seems your issue is more related to the heaters as mentioned. I'm not an amp tech guy though.



I hope it isn't a heater problem, as that'd be another £35 i've spent on trying to sort it out
As much as i'd agree with you there, the thing that seems glaringly obvious is the tube, when the volume died suddenly, started glowing like the 4th of july...basically to my mind, it's finally giving me evidence what the issue was.

....Or so I think (/hope!). I'll see in a few days when tubes arrive.
#14
did you see redplating on the tube?

its a long shot, the 5150/etc. maybe for some reason the fixed basis was stupidly ****ed. can you check the bias now? or maybe do the adj bias mod.'

really the only option that hasn't come up
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#15
as promised, update. Nice new set of tubes arrived one day after I ordered them!
Push new tung sols (6L6 GC STRs) nice and firmly into place, power amp up..NO NOTHING. Not f***ing happy.

Pretty sure I saw redplating the with old tubes.
Also, Trashed, surely the bias wouldn't affect it like this, would only make a difference to tube life/tube sound? How would I go about checking the Bias?
#16
red-plating is bad

my guess is that grid resistor is blown

check the high-tension fuse and the mains fuse (buy a bunch more)

you can get a bias probe on-line starting at around $25 that you can then read the amp's bias with a voltmeter/multimeter

the bias range is very limited on these amps which is why people do 'The Bias Mod' on them

i doubt the bias was the issue anyway...more likely a crappy Chinese tube or solder joint
#17
A hard question I know, but from what you've heard so far, does this sound like an easy fix? Because i'm getting pretty fed up of sorting a problem out, for another to pop up (thinking of storing amp & going to a pure modeller setup).
#18
Honestly I would take it back to your tech, explain the situation, and see what he says. Trying to diagnose an amp with a problem like this is kind of tough over the web.
I'm just a kickin' and a gougin' in the mud and the blood and the beer.
#19
Sorry for the revive of this thread, after seeing Kaim manage to get his amp to work again, i've been tempted to do it myself.

So far, after booting it up, i've found V1-4 work, however both PI and power tubes do not light up.
I've looked at fuses, and from what it seems, F2 could be blown. It's blackened, and yet at closer inspection..the wire is still unbroken by the looks of it.

Also could anyone clarify what 331 means by grid resistor? Looked around on the schematic, nothing seems to note itself as a grid res.

So, judging by the issues, could anyone give a suggestion as to what parts may be causing the issue? Seems to be all past the preamp stage, looking at the schematic.

Here is the schematic: http://www.prowessamplifiers.com/schematics/images/6505112.pdf

Thanks.
#20
If it's the power tube heater it's just the PACH1 and PACH2 section. As you can see there isn't a lot to it. The heaters are AC to the power tubes so no rectifier, just wiring. You have to follow the path from that PT winding to the heater connections on the tube sockets. Chances are very high that it's simply a bad solder joint.
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Last edited by Cathbard at Feb 16, 2015,
#21
Actually, from a second look, F2 fuse looks like it's blown..I'll try replacing that.

Any tips on how best to drain the caps? I found one person on youtube used a set of croc clips, connected one to the earth and one to the start of the circuit, so it drains slowly as it goes through all the resistors in the circuit.
#23
F2 is the HT supply. You didn't check that first?

I discharge the filter caps with an old multimeter probe - but it takes a knack to do it without welding it into place. For beginners, use a 1k to 10k resistor. Wear a glove to hold onto it.
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#24
A grid resistor was shot in my 6505+ head. It's an easy fix if you have some electrical knowledge but I'd need a full update on what's not working to advise you further.

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#25
I did, but from one angle it looked ok, another look at it showed it was bust.

And you literally mean get the end of a 10k res and hold it against the caps? I could potentially rig up a croc clip rig, put the res in between and just leave it to drain the whole circuit over time.

Tremolo, i'll give the fuse a shot first, then come back if it ain't sorted.
#26
When I was working on mine, I took a wire with a crocodile clip soldered to one end, stripped the other end, clipped it with another crocodile clip, and stuck the tube of a bic pen onto the other end of the crocodile clip and touched it to the capacitors. It seemed like a good idea to put some distance, through a plastic tube, between my hand and the capacitors; don't know if it would really help or not. (I didn't use a resistor -- I'll get around to putting one of those on my wire eventually). I never experienced any arcing or sudden discharge of voltage -- because at least on my 6505+, when I let the amp warm up (so the power tubes are pretty warm), then unplug it, the voltage drains out of the caps in just a minute or two. I watched it happen several times using my multimeter in between my fix attempts.

***But, that is on an amp in which the power section is still working. The power tubes, when warm, help "suck" the residual voltage out of the components.
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Last edited by KailM at Feb 17, 2015,
#27
Draining Filter Caps: https://www.youtube.com/watch?v=Rg3-dZC5Fww

I'm sure the experienced techs on this forum will tell you to always check the caps with a multimeter before working on an amp, as well as working with "one hand in the pocket". Never presume the caps drain. I watched a vidya where a Blues Jr. drained effectively, but not all amps do that. I also saw another video where the resistor was soldered on the end of one of the alligator clips, instead of soldered in the middle. Your clips should also be insulated.
Last edited by Will Lane at Feb 17, 2015,