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FDP Forum / Amp Mods, Repairs, and Projects / Peavey Valve King is just humming....

Cal-Woody

USA/California

Why do I keep fixing things that work?
Sep 8th, 2017 09:02 PM   Edit   Profile   Print Topic   Search Topic

So, I went to band practice and turned on my amp and all it did was a constant loud hum. I immediately turned it off and did a tube swap. No change. All tubes light up and tried plugging my cord into every jack hole to see if anything would change, but no difference, the hum persists.
Got it home and pulled out the chassis and saw no physical damage, so, I was thinking that maybe it could be the output transformer. I called Peavey tech support and spoke with a technician and he said that if it was the output transformer, it would have blown the fuse. All fuses are good, no burnt traces o try bulging/burnt components. Next, I'll have to check and see if all components are physically solid and reflow the soldertraces but aside from this, anybody care to venture a guess?
I've tried plugging into the effects loop, and all other inputs andI get little sound at full volume, but it is very faint and disdistorted. Tried a different speaker, nope! Same-O!
So, not being a real tech and hoping for something simple, as it never has happened before or given any hint at failure, I'm not sure what it is and does anyone think that my guess on a failed output transformer a wrong guess?
Thanks guys, your thoughts and experience are always welcome. Woody

j!mi
Contributing Member
***

NNJ

and meanwhile, I'm still thinkin' . . .
Sep 8th, 2017 09:15 PM   Edit   Profile   Print Topic   Search Topic

My guess would be the input jacks. Check for loose fittings of loose wires.

stratcowboy
Contributing Member
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USA/Taos, NM

Sep 8th, 2017 10:14 PM   Edit   Profile   Print Topic   Search Topic

Other guitars? Other guitar cables? When stuff isn't plugged in? Or just when guitar is plugged in?

Cal-Woody

USA/California

Why do I keep fixing things that work?
Sep 9th, 2017 12:14 AM   Edit   Profile   Print Topic   Search Topic

Thanks, I will be checking all jacks and their integrity plus the solder traces and the amp is humming either with or without a cord/guitar connected. As I mentioned earlier, the amp was /buzzing by itself, then I went and started trying all the input jacks to see if I could cause the hum to stop. Also checked to see if maybe the footswitch was the culprit, but nothing stopped it nor made it better or even less. It was a real head scracher for me and after experimenting for a while, I tried tube changes. All appeared normal except for the continuous buzz/hum.
I tried numerous guitars and checked all cables, nada!
Thanks for posting, still looking.
Woody

SonicBlue

Sunbury-on-Thames

Sep 9th, 2017 03:45 AM   Edit   Profile   Print Topic   Search Topic

If the hum (how loud? affected by controls?) is coming from the speaker the OT is very likely OK.

It sounds like a signal path fault, a useful little ruse for quickly checking it is to tap the valves in turn, listening for a microphonic rattle from the speaker. If you have a spare 12AX7 previously rejected for microphony even better. Put it in V2 position and tap it with an insulated tapping stick. If it makes it out of the speaker there's a reasonable chance the amp is OK from there forward. If you don't hear it when in V1 you know where to look. If you do hear it in V1 the problem may well be the input jack or associated wiring.

As always, valve amps can bite and bite hard. Do be careful and always keep one hand behind your back or in your pocket when poking around live kit.

Cal-Woody

USA/California

Why do I keep fixing things that work?
Sep 9th, 2017 06:12 AM   Edit   Profile   Print Topic   Search Topic

The hum is not affected by controls. I do have a m icrophonic tube to try and that would be an interesting thought!
The Peavey tech emailed me a schematic also. Hopefully something will make sense.
Thanks for posting.
Woody

willie
Contributing Member
********

Too Near Atlanta GA

Amp Tech Emeritus
Sep 9th, 2017 07:56 AM   Edit   Profile   Print Topic   Search Topic

Generally speaking, when you get a hum (60 or 120 Hz?) that doesn't respond to any controls we suspect a power supply filter cap. It can also be a phase inverter issue, or a rectifier failure...that just narrows it a bit as there are several other options that could prove to be the culprit as well.

w

Peegoo
Contributing Member
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Creed

Clearwaterrrrr Revival
Sep 9th, 2017 08:23 AM   Edit   Profile   Print Topic   Search Topic

If all the above checks out, it might be an open signal path to V1. Some amps hum loudly when this happens.

Check for a good path between the input jacks and pin 2 of V1.

Per the linked schematic...see top left corner of page 9.

PV VK50112 Schematic

j!mi
Contributing Member
***

NNJ

and meanwhile, I'm still thinkin' . . .
Sep 9th, 2017 08:57 AM   Edit   Profile   Print Topic   Search Topic

Try pulling V1. Still hum?

Cal-Woody

USA/California

Why do I keep fixing things that work?
Sep 9th, 2017 02:36 PM   Edit   Profile   Print Topic   Search Topic

So, pulled valve #1and it hums with no change in intensity, put #1 back in and pulled #2, same hum and no change in intensity of the hum. Pulled both preamp tubes and it is quiet.
I reflowed all solder traces and did notice that a fuse, attached to the PC board was slightly discolored but not blown. There are 3 fuses on the PC board, soldered in place and are all good.
Kinda sucks that you would have to get axial style fuses that mount on PC board and not the regular clip in ones.
Ok, so in measuring pin 2 to the input jack, what should I set my meter to? AC voltage? Or DC? And where would I put my leads at?
I think you are on the right track that something is wrong with the components connected to the first tube. It has a lot of small components and I don't have any of that form factor. Just old composite resistors, you know, the brown colored ones.
Thanks, I think we are narrowing it down!

willie
Contributing Member
********

Too Near Atlanta GA

Amp Tech Emeritus
Sep 9th, 2017 05:03 PM   Edit   Profile   Print Topic   Search Topic

Pulling both preamps (V1 and V2) would leave you with no audio amplification at all so it's not surprising you would hear no hum. V3 is a cathodyne style phase inverter that balances the output tubes.

w

Cal-Woody

USA/California

Why do I keep fixing things that work?
Sep 9th, 2017 05:50 PM   Edit   Profile   Print Topic   Search Topic

Thanks Willie, understood. I was just trying to see if I could eliminate the noise, which it did.
Now I need to figure out how to repair/rebuild the preamp section and get my amp running. I'm booked starting the end of the month through the New Year and need to have a reliable amp. I'm so used to this sound and need to get it done.
Wish all you folks lived close by to help with my problem.
If I could, I would order the preamp board instead of repairing it and be ready to go. Might have to call Peavey and see if they do this. SLM music sold me the complete preamp section for my VL1002 and that worked like a charm! Hummm, will have to call and see if I can.
Meanwhile, I'm stuck like Chuck! Lol
Thanks for posting and hope to learn where my issue is and repair.

SonicBlue

Sunbury-on-Thames

Sep 10th, 2017 06:45 AM   Edit   Profile   Print Topic   Search Topic

Does the Valve King have Peavey's horrible jumper wires between boards, like in the Classic 20/30/50?

They're famous for fracturing and causing all kinds of problems. Last time had my C20 apart I found several had died and ended up replacing the whole lot with solid copper wire.

Cal-Woody

USA/California

Why do I keep fixing things that work?
Sep 10th, 2017 07:26 AM   Edit   Profile   Print Topic   Search Topic

Yes it has wired jumper from the power supply to the preamp section. I'm assuming that it is modulated by the transformer. It is not stiff like the ones on my HotRod Deluxe and are secured with hot glue on both ends. It also has a bunch of wires running between the preamp section to the phase inveerter/power tube board. These are not a ribbon style connector like the small 4 strand one from the power supply.
I tried moving them slightly and no change to the noise.
It's looking more likely to be something preamp related.

Peegoo
Contributing Member
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Creed

Clearwaterrrrr Revival
Sep 10th, 2017 07:35 AM   Edit   Profile   Print Topic   Search Topic

Probably a filter cap like Willie suggested.

He's da man.

willie
Contributing Member
********

Too Near Atlanta GA

Amp Tech Emeritus
Sep 10th, 2017 11:24 AM   Edit   Profile   Print Topic   Search Topic

Kind words from a kind man... :-)

Wondering just what test equipment you have Woody and what level of experience/training you have to do electronic service work? I ask so I can perhaps give you the best advice and ensure a modicum of safety in the process.

The basic process is to first consider the symptoms and what are the most obvious causes of those symptoms (cables, jacks, fuses, tubes, etc). After the obvious cursory exam you need to employ the proper test equipment such as volt meters/ohm meters (usually a multi purpose digital one these days), Oscilloscope, signal generator, cap meter, ESR meter, "Variac",just to name a few basic ones.

Make sure the power supply is providing the proper voltages and the caps are filtering the ripple to spec. Check for proper voltages at key points (plate voltage of all tubes, cathode voltages of preamp and phase inverter). If all the vital voltages are within spec then you need to start working with the signal gen and O'scope to analyze the hum or other issues.

Often a very close examination of all components and their solder joints using a strong lighted magnifier as well as a wooden chopstick or similar insulated tool to move the components can identify a problem that stumps you after doing all the initial tests.

There are many more things we do in the process of troubleshooting an amp but they go a bit too deeply to describe here.

Always be safe with high voltages...and generally I don't recommend working with them if you are not trained or experienced doing this type of work...but I know people do it on a large scale..it just bares repeating the warning that high voltages and currents can kill you.

willie



Cal-Woody

USA/California

Why do I keep fixing things that work?
Sep 10th, 2017 11:58 AM   Edit   Profile   Print Topic   Search Topic

Thanks Willie for responding again, but I will say that I do not have any real skills as to electronics. Just from experience I can kinda figure some things out, but to be totally honest, I am not tech savvy and have some basic equipment to test circuits with. I have 2 VOM's, one digital and the other analog. I use the analog most because of familiarity.
All the other equipment I have is not for testing circuits. I have 2 tube testers and acquired an O-scope, might be an old Radio Shack or a Singer branded one from a gentleman whom did radio and ham radio repairs. So, old radio tubes, yeah, I've got those.
I have decent solder skills and have been doing so for a lot of years. Mostly home and guitar related. Amplifier repairs, not much of anything to mention.
I guess I need to visit the local repair shop but if I could effect repairs at home, because of shops backlog, that would be great! Basically, I can remove and replace components, if I know what they are, but parts availability is the hard part. Hardly any, if at all electronic stores in my area.
So, I guess until I can get it done, it might be acquiring a backup amp for all the shows we have coming up.
I have large amps but most places we play don't have the realestate needed for these monsters! Lol
The smallest working amp I have is my Mesa Nomad. It's like aTwin on steroids, but 3 channels. Everything else is too big. Mesa Tri-Rec, a couple of Marshall stacks, Ampeg VL1002 and others. .... So, if I know the components to replace, I can do it with great confidence.
The wife thinks I need to have a yard sale. Nope, ain't happening! I like what I have. Not unless a decent trade came along, then we might have a good 'maybe'!
Alright, I have carried on for quite some time and should have kept my answer more concise.
I most certainly Do appreciate your help and support and would be remiss not to acknowledge so! Thank you, Woody

(This message was last edited by Cal-Woody at 02:00 PM, Sep 10th, 2017)

Cal-Woody

USA/California

Why do I keep fixing things that work?
Sep 19th, 2017 04:27 PM   Edit   Profile   Print Topic   Search Topic

If I were to replace the capacitors and accompanying resistors for the preamp section, could someone help me in identifying those parts and the values of each needed for their replacement? Like I had said earlier, I can solder efficiently andrremove parts from the PC board, but to actually know what they are and how to test them is beyond my scope of ability.
So, if I may solicit your help on this matter, it would be the utmost importance and desire to bring this amp back to life and have it back in service.
We don't have a good electronics store locally and all parts would have to be sourced from either the web or directly from Peavey.
All of the components I have are older carbon comp. resistors and their size is much larger than the metal oxide equivalents.
But I have quite a few of these parts and thought I had some weird looking resistors just to find out that they were bumblebees bee capacitors. A friend of mine got super excited about these and for other reasons of horse trading in the past, they are now resting comfortably in the cavity of his Les Paul Historic and are giving him great pleasure to have them installed. Personally, I didn't hear any appreciable difference between these and the Orange drops, but he is stoked and made his year for him.
Sorry to have got off topic, but I really need the help and time is of the essence. I don't want to haul around an 100lbs to just play our shows, but until I can get my little amp back in service I have to do this, for just now, I hope!
Thank you everyone. ......
Signed, Stuck in South Fresno. ......

FDP Forum / Amp Mods, Repairs, and Projects / Peavey Valve King is just humming....




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