Page 1 of 2
#1
Hey guys -- after a grueling day on the job I came home to get a little stress relief; fired up my 6505+ 112 (converted to a head), flipped the standby off and got......nothing. Just a hum from the amp, not necessarily from the speaker.

So I thought, ok -- it's probably just a tube. I pulled the grill off and noticed immediately that none of the preamp tubes were lit up. The power tubes and PI tube were lit up and warm as normal. But V1-V4 were cold and dark.

What I've tried so far:

1. Plugged directly into the front of the amp to eliminate pedals/effects loop from the equation. Nothing.

2. Plugged directly into the effects loop send and got clean sound with plenty of volume. But no distortion, obviously. So at least the power amp is fine. (I think).

3. Took a known good preamp tube and swapped it through all of the preamp tubes. None of them ever lit up. No sound.

4. I checked the main fuse. I've never really looked at one before, but there is a very thin wire running from one end to another -- seems to be fine, if I'm not mistaken. Plus, the Peavey logo still lights up, and the power amp works... so.

So now I don't know what else to try. I'm assuming it's something major inside the amp. I'm planning to pull the chassis out and have a look, but honestly, I don't know what I'm looking for and I sure wouldn't be comfortable soldering on a circuit board. And I'm not too excited to get zapped either.

Is there anything else basic that I might have missed? Thanks!
#2
There are possibly some internal fuses you need to check out at least the big boys have them 6505/6505+.
Mesa Boogie Single Rectoverb 50 series 2 combo
Randall RM100
Peavey 5150 4x12
Peavey XXX 2x12 combo
Pedals
#4
The 6505 uses bus connectors between a few circuit boards. The preamp has its own board, I'd bet that the bus connector for the preamp board has become damaged or dislodged.

There are more fuses on the board, check those too if you're comfortable opening the chassis.
#5
Happened to me and a couple others on here, your preamp heater circuit is probably gone. I can't remember what component it is that is normally to blame but Google around a bit and you may see it, this is a reasonably common problem on these. If you don't feel comfortable digging around inside it may be worth it to take it to a tech.
I'm just a kickin' and a gougin' in the mud and the blood and the beer.
#6
Thanks for the responses guys. I'll take it apart tomorrow and have a look. I would be comfortable rplacing a fuse if i saw that one was bad. I just dont want to get shocked.

Weird thing is i played it this morning and there was nothing amiss.
#7
That's how mine was, I played it fine and then the next time poof it shat the bed
I'm just a kickin' and a gougin' in the mud and the blood and the beer.
#8
Quote by KailM
Thanks for the responses guys. I'll take it apart tomorrow and have a look. I would be comfortable rplacing a fuse if i saw that one was bad. I just dont want to get shocked.

Weird thing is i played it this morning and there was nothing amiss.



careful, they can kill you long after they're unplugged
#9
Quote by Tempoe
careful, they can kill you long after they're unplugged

To clarify - the fuse won't shock and potentially kill you. A filter capacitor or any lead to it may and that's what you need to steer clear of. To be safe there are ways to discharge an amp but if you are not familiar with how to do it or not sure of yourself - take it to a tech. If you do replace a fuse inside the chassis the best advice is put one hand behind your back.
#10
+1 zapped myself one two many times before I learned this lesson.
Mesa Boogie Single Rectoverb 50 series 2 combo
Randall RM100
Peavey 5150 4x12
Peavey XXX 2x12 combo
Pedals
#11
Most tube amps can be drained by simply turning it on to full operating mode (not in standby), leaving it on until power tubes or hot and then simply flicking it off but leaving standby switch to operating mode. This will allow the hot power tubes to drain the caps.

ESP LTD F-50 + Tonezone
Cort EVL-Z4 + X2N
Cort EVL-K47B

Marshall Valvestate 8100
Randall RG1503
Bugera 333
Peavey Rockmaster preamp

Line6 Pod X3
#12
I've had something very similar happen to mine. Most of the preamp tubes weren't lit and I wasn't getting any output from the preamp section, but got output from the power section. Turned out the diodes of one of the bridge rectifiers overheated and burned out. I think it was D6-D9 of this schematic (the first bridge rectifier to the left of the drawing). But I could be wrong, I don't remember which one of the 3 it was all that well.

http://www.prowessamplifiers.com/schematics/images/6505112.pdf

There were minor burn marks surrounding the trace so the issue was easy to spot. We checked for continuity but the circuit was open. So we replaced the diodes and everything worked fine again. It was a simple fix.

I was fortunate since my dad is an electrical engineer and he has all the right tools for these sorts of jobs.
Roses are red
Violets are blue
Omae wa mou
Shindeiru



Quote by Axelfox
Reeeeeeeeeeeeeeee
Last edited by T00DEEPBLUE at Feb 5, 2015,
#13
had the same sort of issue that you have by the sounds of it, a sad moment.

With mine, I had a look at the internal fuses etc., the tech I took it to multiple times had no clue what was up (after a fairly brief search).
I found after a while I was running it and suddenly it worked again..then a little later, by the looks of it the power tubes suddenly red plated..which was worrying.

Been left in my room for the last 6 months, tempted to see if I can throw a bit of cash at it to get it up and running again, especially considering I brought a new 6L6 pair a bit back as I thought the power tubes died/were dying
#14
Quote by KailM
Weird thing is i played it this morning and there was nothing amiss.


This isn't helpful at all, but I'm always amused when people say things like this. Would you apply it to anything else?

"I can't believe that tire is flat, it was fine when I drove the car yesterday!"

"I can't believe that light is burned out, it was fine last night when I used it!"

"I can't believe I'm out of gas, I had some last week!!"



“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin
#15
Quote by Arby911
This isn't helpful at all, but I'm always amused when people say things like this. Would you apply it to anything else?

"I can't believe that tire is flat, it was fine when I drove the car yesterday!"

"I can't believe that light is burned out, it was fine last night when I used it!"

"I can't believe I'm out of gas, I had some last week!!"





Indeed. Something must be working before it can break.

ESP LTD F-50 + Tonezone
Cort EVL-Z4 + X2N
Cort EVL-K47B

Marshall Valvestate 8100
Randall RG1503
Bugera 333
Peavey Rockmaster preamp

Line6 Pod X3
#16
Hey, I had the exact issue with my 6505+.

I ended up sending it to peavey. I don't believe it was an issue with any tubes as my 6month warranty was over. I still was under warranty for everything else though and they sent it back fixed. I was not charged and they did not say exactly what was wrong. But if you aren't experienced in tube amps like myself maybe take it to someone.
Just another Sheep in the design of the Almighty Machine.


-GEAR-
Gibson 60s Les Paul Tribute (Sunburst)
1999 Ibanez RG470 (TitaniumIce-MIJ)
Jackson RR3 (Trans-Red)
Peavey 6505+
Podx3
#18
Quote by Arby911
This isn't helpful at all, but I'm always amused when people say things like this. Would you apply it to anything else?

"I can't believe that tire is flat, it was fine when I drove the car yesterday!"

"I can't believe that light is burned out, it was fine last night when I used it!"

"I can't believe I'm out of gas, I had some last week!!"





Haha. What I meant was it didn't make a sound or do anything to indicate that it was about to fail. It simply worked in the morning perfectly and then did not even make a sound when I tried it that evening. An empty gas tank is the result of looking at your gas gauge and continuing to drive even when it says "E." But I get what you're saying.
#19
Just stopped in to say that your initial diagnostic skills and ability to relate them here were excellent. At this point I'd have to break out the meter and schematic.
#21
Update: I took it in to the local tech and he couldn't fix it. Basically, I paid him $60 to tell me what I already know -- the preamp isn't getting any juice. He did check all the tubes and internal fuses and those were all good. He said he can normally fix anything on a traditional tube amp, but this one has a lot of "solid state" stuff inside. He also said it looked like someone had changed the capacitors before and did a shoddy job. I told him that I bought it brand new, and haven't touched any of that stuff. Could be the "made in China" bit. So I don't know what to do now.

I found a thread on the Peavey forum that really seems to pertain to my problem, but honestly, the stuff they're talking about is way over my head/knowledge of electronics. I pride myself in my ability to troubleshoot and fix certain things, but this is just way above my skillset.

So I guess my next step is to email Peavey and send it in. Thing is, I'm not sure if I want to dump potentially $200+ into this amp when it could fail again. I'd just as soon pay a few hundred more for an AMERICAN MADE 6505 or 5150. Plus, I'd be without an amp for who knows how long. The shop gave me the number of a tech in a town 2.5 hours away that can usually work on stuff like this -- but I'm thinking I should just send it to Peavey?

This shit fricken' sucks -- I don't have another amp to play and I'm going into withdrawals...
Last edited by KailM at Feb 7, 2015,
#22
Personally, I'd tell the tech he's full of shit. He probably told you the stuff about capacitors hoping it would go over your head.

My guess is the same as someone already posted. I bet one of the ribbon connectors is fried. Are you comfortable opening up the chassis and taking close up pics?

Jackson RR3 Rhoads and DK2M Dinky
Peavey 6505+ w/ Avatar 212 cab
Ibanez TS9, ISP Decimator, MXR 10 Band EQ
-Digitech RP1000
#23
Yeah man I garauntee it's something simple that you could do, that burnt out diode someone mentioned earlier I've heard before, I'd start there. Your tech blows, mine fixed it in 30 min for $25
I'm just a kickin' and a gougin' in the mud and the blood and the beer.
#24
Ok -- you guys have persuaded me to look. I just dont know how to tell if anything im looking at is the culprit. I fired it up earlier and let the power tubes warm up, the just pulled the power cord in hopes that it would drain the caps. I guess i'll see what i see.
#25
Quote by KailM
Ok -- you guys have persuaded me to look. I just dont know how to tell if anything im looking at is the culprit. I fired it up earlier and let the power tubes warm up, the just pulled the power cord in hopes that it would drain the caps. I guess i'll see what i see.

I'm sure you know this if you have researched the dangers of caps, as this is a common piece of advice (standby or power cord tricks), but it's never safe to assume the caps are drained because of these techniques. Drain them with a resistor and check them with a multimeter or just stay away from them. You can find info online on how to do this.

Generally speaking, as long as you do a bit of research and follow safe electrical practices, you will be fine. But since capacitors literally can kill you, no one wants to be "that guy" on the forums that gave advice that got someone killed.

My local amp tech actually helped me learn how to properly bias my amp after I did the 6505 bias mod. If you take it slow, as much of a pain in the ass as it is, you can really learn some good electronic practices.

-Edit-
I zapped myself repairing a valveking 100 after stupidly putting both hands inside the chassis to get a tube seated

Jackson RR3 Rhoads and DK2M Dinky
Peavey 6505+ w/ Avatar 212 cab
Ibanez TS9, ISP Decimator, MXR 10 Band EQ
-Digitech RP1000
Last edited by Tremolo Bum at Feb 7, 2015,
#26
^^Thanks. I will do my research first and also buy a multimeter. I guess I'd rather just learn this so that I can fix things in the future. I don't really have the money for a huge repair bill nor a new high-gain head. I do know how to solder, as I've changed pickups several times. I'm a bit leery of soldering on a circuit board, however, because the chance to ruin something is much greater.

As for your earlier comment about my tech, I think you're right. He was kind of a weird guy. Based on his comments, he's a "vintage amp" guy that only likes those kind of amps. I got the sense that when he sees a PCB board, he runs. He kept saying there was all of this "solid state" stuff in my amp -- and to my knowledge, even the 112 version of the 6505+ is still all-tube. I don't think he's accurate on that.
#27
Yeah I think he was full of shit dude.
I'm just a kickin' and a gougin' in the mud and the blood and the beer.
#28
Honestly its worth checking the bridge rectifiers. They receive a lot of current and get quite hot under normal operation. It could just be that it got a little too hot and damaged the rectifier. Replace the diodes and its all fixed.

That tech you've got sounds like a cowboy who doesn't know what he's talking about.
Roses are red
Violets are blue
Omae wa mou
Shindeiru



Quote by Axelfox
Reeeeeeeeeeeeeeee
#29
Quote by KailM
Update: I took it in to the local tech and he couldn't fix it. Basically, I paid him $60 to tell me what I already know -- the preamp isn't getting any juice. He did check all the tubes and internal fuses and those were all good. He said he can normally fix anything on a traditional tube amp, but this one has a lot of "solid state" stuff inside. He also said it looked like someone had changed the capacitors before and did a shoddy job. I told him that I bought it brand new, and haven't touched any of that stuff. Could be the "made in China" bit. So I don't know what to do now.


So I guess my next step is to email Peavey and send it in. Thing is, I'm not sure if I want to dump potentially $200+ into this amp when it could fail again. I'd just as soon pay a few hundred more for an AMERICAN MADE 6505 or 5150. Plus, I'd be without an amp for who knows how long. The shop gave me the number of a tech in a town 2.5 hours away that can usually work on stuff like this -- but I'm thinking I should just send it to Peavey?

(


Nothing to do with made in China, sounds like that tech didn't know jack s..t. Locally when they don't do anything on your amp, like this guy didn't do anything they charge $25 diagnostic fee. You went to a moron and he ripped you off...

I'll look at Peavey "certified" repair, at least there are two guys here that are. They're slow in getting parts and backed up with a lot of work, but so far solid.
#30
^^I concur. I opened it up today to have a look, and while I'm not an expert, I saw NOTHING that looked dodgy or unprofessional. Everything seemed well put-together and there's no indication of any failures anywhere.

I've been reading a thread on the Peavey forum in which a guy had exactly the same problem as me. After going through a bunch of things, he was recommended to check diodes D18, 19, 23, and 24. (They are for the rectifier section) After replacing them, the amp was fixed.

So I went out and bought some replacement diodes today as well as a multimeter and some soldering supplies. I was thinking of just replacing them and hope for the best. If anything, it won't hurt the amp any (*as long as I install them correctly -- those bastards are tiny.) Any tips for de-soldering and soldering diodes that are 1/8" long? In a PCB board?

I might wait to see if Peavey answers my email tomorrow. If I can fix it, it will have cost about $2, minus the multimeter, of course. Also, how do I use that multimeter to check those diodes first? What value should I look for? Sorry I'm such a noob at this.

Here's a link to the schematic:

6505+ 112 schematic

Let me know what you guys think, even if it's to say I'm crazy for trying this.
Last edited by KailM at Feb 8, 2015,
#31
Diodes have polarity, don't put them in backwards.
Those particular diodes are just for the heater current. Don't the tubes light up at all? If they do then that isn't the problem. The HT supply is from D6, 7, 8 and 9.

To test a diode just use resistance. It should be short circuit in one direction and open circuit when reversed, more or less.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#33
Quote by Cathbard
Diodes have polarity, don't put them in backwards.
Those particular diodes are just for the heater current. Don't the tubes light up at all? If they do then that isn't the problem. The HT supply is from D6, 7, 8 and 9.

To test a diode just use resistance. It should be short circuit in one direction and open circuit when reversed, more or less.


Nope, they don't light up nor do they even get warm. PI and power tubes light up though, and even provide sound if I plug the guitar into the effects loop. But obviously no control over that sound nor distortion.
#34
Quote by diabolical
Might want to practice soldering on something first if you haven't done it, some old electronics if you have them, like broken radio, etc.


I installed a new pickup in a guitar a couple weeks ago, does that count?

I do have over 20 years of experience welding though; I've got a pretty steady hand. The only thing I'm really worried about is overheating the PCB or getting too much solder in the joint.
#35
The PI isn't heated from that circuit so the fault is definitely in that block then. Could be any part of it almost. If it was the caps going short circuit it would blow the main fuse of even maybe the PT heater winding itself.
How I'd find it would be to chase voltages across that circuit. I'd start by measuring the voltage (DC) on both sides of R82. If you get no voltage on the LHS of R82, move onto the diodes. Before removing diodes, measure the AC voltage across C67. If there is no voltage there then the PT is blown; if you do, then the diodes are ****ed.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Feb 8, 2015,
#36
Quote by Cathbard
The PI isn't heated from that circuit so the fault is definitely in that block then. Could be any part of it almost. If it was the caps going short circuit it would blow the main fuse of even maybe the PT heater winding itself.
How I'd find it would be to chase voltages across that circuit. I'd start by measuring the voltage (DC) on both sides of R82. If you get no voltage on the LHS of R82, move onto the diodes. Before removing diodes, measure the AC voltage across C67. If there is no voltage there then the PT is blown; if you do, then the diodes are ****ed.


Thanks Cath! A few more questions: what/where is R82? I saw references to it in that Peavey.com thread as well -- but i cant find it anywhere on my circuit board. And by PT do you mean power transformer? I hope it's not that.
#37
It's up near the diodes. It's a 5W'er so it will be pretty big.
Yeah, PT = power transformer. It wouldn't be as bad as you think, you can add a little tranny for that heater circuit. No need to replace the whole thing. It's not likely anyway.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#38
I just did some testing. Forgive my ignorance, but I have to get clarification on these things -- I've been learning a TON lately. I did my tests with the amp powered up and flipped it off standby (made sure to plug it into my cab too).

First I tested the DC voltage on R82 --- nothing. I've been holding the negative probe to the metal on the chassis and testing with the red probe. I flipped my multimeter over to AC and tested C 67 -- didn't get any voltage there.

But then I tested those diodes and got 6 volts on the left side of both D 24 and D 23.

Nothing on D 18 or 19 -- and I made damn sure I had a solid connection before finally giving up. Just no voltage there at all. So I think I may have found my culprits. But I'm still not sure why I couldn't get a reading on C 67 if D23 and 24 are after it. Weird.

On a whim, I put the red probe on C66 and there was definitely some voltage there! It jumped between 350-1000+ volts.

So my feeling is that I definitely need to try changing out those two diodes. Any tips on de-soldering/soldering those? I can't even see the solder on them -- but I assume there isn't much there.

Also, just to be sure I'm doing this right -- I can check for residual voltage by simply touching the chassis with my negative probe and then touching the caps with the red one? It seems that the amp does indeed drain the caps mostly by just unplugging it when the power tubes are warm. Thanks for you help and advice!
Last edited by KailM at Feb 9, 2015,
#39
The best way to remove the diodes, for a novice, is to lift out the board and do it from underneath. A solder sucker will help. Just the old fashioned spring loaded ones will do the job. They're pretty cheap. That's what I use.
Grab the diode lead with a pair of needle nose pliers from component side and heat up the solder from the other side, gently pulling all the while. After it comes out remelt the solder and hit it with the sucker to clean out the hole.

And yes, black to chassis, red to test point.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Page 1 of 2