#1
I switched the ohms to 4 when I switched my Peavey JSX to low power (60 watt) last night. I played for a little while today and my amp died on me. It was making a weird noise so I stopped playing then I started losing power and it just shut down.....Now no noise whatsoever from any channels.

Any ideas on what happened it what it's gonna cost me?...
Jackson DK2
1962 Fender Esquire
PEAVEY JSX 212
PEAVEY 6505+ 112
#2
What's your cabinet imp rating/speakers? iirc I think that's a power transformer issue, among other things possibly

From your NAD:
Quote by trashedlostfdup
if you run at half power, you need to cut the load ohms in half.

half power = half ohms

i run my splawn promod in half ohms sometimes, just flick the half power switch, and dial the load rating to half takes five seconds.
Why is that?
Last edited by Will Lane at May 28, 2015,
#3
Lowering impedance (ohms) usually should not be an issue as the load is put on the speakers.
Did you put it back and test the power amp through fx return? I'm thinking maybe you fried a tube but could be transformer. Did you check fuse?
#4
I don't understand what happened and I'm pissed the guy that sold it to me told me to put it at 4 ohms if I switch to half power someone on this site also told me this. Not blaming anyone I should know my own stuff but I can't see why the previous owner would tell me that unless he wanted me to seriously **** something up.

It's a combo with 2 upgraded 30 watt speakers. Celestian G12H and Scumback H75.
Jackson DK2
1962 Fender Esquire
PEAVEY JSX 212
PEAVEY 6505+ 112
#5
Ok how do I test the power amp through the FX return?
I'm looking at the fuse now too but it's just covered in like a gray covering?
Jackson DK2
1962 Fender Esquire
PEAVEY JSX 212
PEAVEY 6505+ 112
Last edited by UFC on VHS at May 28, 2015,
#7
Quote by UFC on VHS
I don't understand what happened and I'm pissed the guy that sold it to me told me to put it at 4 ohms if I switch to half power someone on this site also told me this. Not blaming anyone I should know my own stuff but I can't see why the previous owner would tell me that unless he wanted me to seriously **** something up.

It's a combo with 2 upgraded 30 watt speakers. Celestian G12H and Scumback H75.
I don't know either. I think there's a misunderstanding somewhere. I wouldn't think that you would need to lower ohms for lower power. IIRC Solid States tolerate ohm mismatches as long as the speaker load is higher than the amp's rating. I don't think tubes are that happy about it.

I think your cab load is 8 ohms. The H75 is 16 ohms I think, so I guess the G12 is 16 as well wired parallel, and you said half ohms so 8-4.
Last edited by Will Lane at May 28, 2015,
#8
Yeah I'm a moron.

I'll Have to take it somewhere for someone who knows what their doing to evaluate the damage that I've done.
Jackson DK2
1962 Fender Esquire
PEAVEY JSX 212
PEAVEY 6505+ 112
#9
Quote by UFC on VHS
Ok how do I test the power amp through the FX return?
I'm looking at the fuse now too but it's just covered in like a gray covering?

Plug your guitar into the FX return and the master volume should work if the power amp is good. If you get no sound, try another set of tubes.
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#10
Quote by Robbgnarly
Plug your guitar into the FX return and the master volume should work if the power amp is good. If you get no sound, try another set of tubes.


Ok I did and absolutely no sound. Is it possible it's just bad tubes and unrelated??
Jackson DK2
1962 Fender Esquire
PEAVEY JSX 212
PEAVEY 6505+ 112
#11
Quote by UFC on VHS
Ok I did and absolutely no sound. Is it possible it's just bad tubes and unrelated??

It could be, pop the other pair in and see what happens.

check the fuse on the outside and the Ht fuses on the inside of the amp also
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#12
+1 Rob

I wouldn't take it to a tech just yet. They will overcharge you for a bunch of things you may not need.

To check the HT fuse you will need to remove the chassis from the amp shell. That can be dangerous if you touch something you are not supposed to. You can find the fuse and look for yourself just don't touch anything else. A blown tube could take a fuse with it.

I believe the JSX tube pairs run like this: XOOX.

Read this thread here. Roger Crimm is a mod on the Peavey forum. He works for Peavey.

http://peavey.com/forum/viewtopic.php?t=26631

He is saying that if you flip the half power switch you don't need to do anything else.

With Splawn amps, what trashedlostfdup and I both have, you also have to manually adjust the ohms in half if you pull two tubes and leave it that way for long periods of time. I don't have a JSX so I can only tell you what Scott Splawn says. If you just want to play on half power for 1 gig or to see what it is like then just use the half power switch and don't change anything else. If you want to run at half power all the time, then pull the two outer tubes, rebias the amp, and drop the the ohms in half in addition.

What happened to you could be related or it could not be related. Generally speaking I'd say doing what you did should not hurt the transfromer or the amp. It could have blown a tube (after reading Roger's explanation on how the JSX works) but like Rob said, try a different pair of tubes and check the fuses. If the mains light on the front of the amp does not come on then it is the mains fuse accessible on the back of amp by the power cord. If that light works but there is still no sound, then it could still be a HT fuse which is inside the amp chassis (so be careful).

Also, download the user manual (even though it won't help with your problem).

good luck,
Last edited by 311ZOSOVHJH at May 28, 2015,
#13
Quote by 311ZOSOVHJH
+1 Rob

I wouldn't take it to a tech just yet. They will overcharge you for a bunch of things you may not need.

To check the HT fuse you will need to remove the chassis from the amp shell. That can be dangerous if you touch something you are not supposed to. You can find the fuse and look for yourself just don't touch anything else. A blown tube could take a fuse with it.

I believe the JSX tube pairs run like this: XOOX.

Read this thread here. Roger Crimm is a mod on the Peavey forum. He works for Peavey.

http://peavey.com/forum/viewtopic.php?t=26631

He is saying that if you flip the half power switch you don't need to do anything else.

With Splawn amps, what trashedlostfdup and I both have, you also have to manually adjust the ohms in half if you pull two tubes and leave it that way for long periods of time. I don't have a JSX so I can only tell you what Scott Splawn says. If you just want to play on half power for 1 gig or to see what it is like then just use the half power switch and don't change anything else. If you want to run at half power all the time, then pull the two outer tubes, rebias the amp, and drop the the ohms in half in addition.

What happened to you could be related or it could not be related. Generally speaking I'd say doing what you did should not hurt the transfromer or the amp. It could have blown a tube (after reading Roger's explanation on how the JSX works) but like Rob said, try a different pair of tubes and check the fuses. If the mains light on the front of the amp does not come on then it is the mains fuse accessible on the back of amp by the power cord. If that light works but there is still no sound, then it could still be a HT fuse which is inside the amp chassis (so be careful).

Also, download the user manual (even though it won't help with your problem).

good luck,


Thanks a ton for taking the time to share all this info as it stands now i'm gonna take it to a tech I just got off the phone im dropping off the amp in an hour. I will definitely take the time to do the research so next time I can maybe handle it. right now though I just don't feel comfortable taking the amp out and touching stuff.

I will let you guys know how I make out hopefully I can get some answers by tonight.
Jackson DK2
1962 Fender Esquire
PEAVEY JSX 212
PEAVEY 6505+ 112
Last edited by UFC on VHS at May 28, 2015,
#14
Since it was asked, the reason you usually halve the impedance when using half power is this (TL;DR at bottom) :

The output transformer, as its name implies, transforms the output impedance of the output (power) tubes to match the impedance of the speaker. The output impedance of the power section works much like it does with speakers in parallel: more tubes means a lower impedance. The transformer simply matches the two numbers, and though you might not know it, the settings on the transformer are not actually "set amp for 8 ohms" but "transform this impedance into that impedance" settings, or "taps" that select different amounts of windings. The more windings on one side, the larger the difference in impedance. A transformer that didn't transform at all would have the same number of windings on both sides. The ohm settings on your amp simply access different amounts of windings to let you 'transform' your output impedance for different numbers.

So, for example:
  • With four power tubes, the output section impedance is 4000 ohms. Your speaker is 8 ohms, so you set the impedance selector to 8, which is actually a 500:1 setting on the transformer (4000/500=8). It's labeled 8 because there's usually no reason to make you do this math.
  • Now, you pull two power tubes (or use the half-power switch, if it is wired to simply disconnect two tubes). Your output section impedance is now 8000 ohms. So, naturally, you need the transformer to 'transform twice as much' or 1000:1. Not surprisingly, this is the setting labeled 4 ohms.
  • You can see then that the "ohm settings" are actually transformer winding taps, and if you mess with the output tubes the ohms listed on the knob are not actually the output impedance. You just need to match each side, and with a bit of math it's a trivial fix.
  • As 311 mentioned, is is not the only way that half power switches are wired.
  • Note that this is only for going from 4 tubes to 2. Tubes typically work in pairs so usually you only pull or disconnect tubes in pairs from amps with four power tubes. Half-power options on 1 or 2 tube amps are usually triode mode or something similar.


TL;DR: Output transformer changes power tube impedance into speaker impedance; mess with power tubes and you need to adjust the transformer settings because it's not smart.
#15
Quote by diabolical
Usually lowering impedance hurts the speakers, not the amp.
Test power amp through fx loop, test fuse.
I think those low power modes are putting strain on the transformer so it might've blown or its protection.


Not in my Mesa Boogies. The manual states that you can increase the impedance without causing any problems, but too low of a resistance will likely cause problems. When those problems do occur, it's usually the output transformer that sacrifices its life for the tubes and speaker. Depending on the amp, this can be $$$$.
#16
Quote by Roc8995
TL;DR: Output transformer changes power tube impedance into speaker impedance; mess with power tubes and you need to adjust the transformer settings because it's not smart.
So the case with this JSX is that it didn't disconnect half the quad?
#18
In other words, I think, with the TS and the JSX he just needs to turn the switch to half power and...."it adjusts the transformer setting at the same time" (as Roc said).

So if he also dropped the amps impedance in half he is now actually mismatched by 1 step. 4 to 8.

Again, I wouldn't think that would be a big deal but maybe over time (if the seller has been doing it that way for a long time) it just took its toll on the tubes. I hope it is not the OT.

Yes, the Splawns are pentode/triode Roc so we have to manually make the adjustment.

Best advice I give people - check with the manufacturer.


Edit: Also it should probably be verified exactly what the combined speaker impedance is. 2 - 16s wired in parallel for 8 total (as Will is speculating) is probably correct.
Last edited by 311ZOSOVHJH at May 28, 2015,
#19
Just got back from the dropping it off had a long talk with the guy. He feels pretty confident that I didn't do any severe damage to the amp but he won't be able to look at it until monday though so im just gonna have to wait and wonder unfortunately.

I guess better this happened now then during a gig but that's about the only positive thing I can think of at the moment.
Jackson DK2
1962 Fender Esquire
PEAVEY JSX 212
PEAVEY 6505+ 112
#20
I'm hoping it is a $2 fuse and maybe $40 in a pair of tubes.

And yeah - better to just get this figured out now vs something like this happening at a gig. Do you have a backup? Get spare tubes too if you can afford it.
#21
Quote by UFC on VHS
I don't understand what happened and I'm pissed the guy that sold it to me told me to put it at 4 ohms if I switch to half power someone on this site also told me this. Not blaming anyone I should know my own stuff but I can't see why the previous owner would tell me that unless he wanted me to seriously **** something up.

It's a combo with 2 upgraded 30 watt speakers. Celestian G12H and Scumback H75.


Wait a minute. This is a combo amp. And are you saying that there's a switch on the amp to cut to half power? Like most Orange amps have, among others? Or are you trying to achieve a cut in power BY adjusting the impedance?
Guitars
Schecter Hellraiser C-1FR, C-1 Classic, Hellraiser Hybrid Solo-II, Special Edition E-1FR-S
Orange Rockerverb 50 212
Basses
Yamaha RBX374 and Washburn MB-6
#22
Quote by 311ZOSOVHJH
+1 Rob

I wouldn't take it to a tech just yet. They will overcharge you for a bunch of things you may not need.

To check the HT fuse you will need to remove the chassis from the amp shell. That can be dangerous if you touch something you are not supposed to. You can find the fuse and look for yourself just don't touch anything else. A blown tube could take a fuse with it.

I believe the JSX tube pairs run like this: XOOX.

Read this thread here. Roger Crimm is a mod on the Peavey forum. He works for Peavey.

http://peavey.com/forum/viewtopic.php?t=26631

He is saying that if you flip the half power switch you don't need to do anything else.

With Splawn amps, what trashedlostfdup and I both have, you also have to manually adjust the ohms in half if you pull two tubes and leave it that way for long periods of time. I don't have a JSX so I can only tell you what Scott Splawn says. If you just want to play on half power for 1 gig or to see what it is like then just use the half power switch and don't change anything else. If you want to run at half power all the time, then pull the two outer tubes, rebias the amp, and drop the the ohms in half in addition.

What happened to you could be related or it could not be related. Generally speaking I'd say doing what you did should not hurt the transfromer or the amp. It could have blown a tube (after reading Roger's explanation on how the JSX works) but like Rob said, try a different pair of tubes and check the fuses. If the mains light on the front of the amp does not come on then it is the mains fuse accessible on the back of amp by the power cord. If that light works but there is still no sound, then it could still be a HT fuse which is inside the amp chassis (so be careful).

Also, download the user manual (even though it won't help with your problem).

good luck,


+1 i am referring to my splawns. i am sorry if i generalized, but i should have said to check with the manufacturer. also some amps you pull different pairs (RR or LL) or (inner pair or outer pair). i know that splawn and other amps are different as far as pairs of tubes. and as far as splawn goes, i called Scott Splawn and asked hime over the phone and he explained it to me.

+1 to roc's post as well. that is what i spoke based on.

every amp i have ran in half power was the same as the splawn, and i have looked it up every time, and it has been the same. i haven't bothered to do it with a peavey amp, and i haven't owned a peavey amp for five or six years.

i am sorry if there was a misunderstanding, i genuinely feel terrible.
WTLT 2014 GG&A

Quote by andersondb7
alright "king of the guitar forum"


Quote by trashedlostfdup
nope i am "GOD of the guitar forum" i think that fits me better.


Quote by andersondb7
youre just being a jerk man.



****** NEW NEW NEW!
2017-07-07 2017-07-07 Update and a Chat On Noise Constraints *** NEW FRIDAY 7/7
2017-04-13 RUN AWAY from COMPUTERS!!! TCE? RANT ALERT!!!
2017-03-02 - Guitar Philosophy 1001- Be Prepared For the Situation (Thursday 2017-03-02)
2017-02-21 How to Hot-Rod the Hell of your Stratocaster for $50! (Tuesday 2017-2-21)
Resentments and Rambling from a Guitar Junkie
---> http://trashedengineering.blogspot.com/
#23
Quote by Roc8995

  • With four power tubes, the output section impedance is 4000 ohms. Your speaker is 8 ohms, so you set the impedance selector to 8, which is actually a 500:1 setting on the transformer (4000/500=8). It's labeled 8 because there's usually no reason to make you do this math.
  • Now, you pull two power tubes (or use the half-power switch, if it is wired to simply disconnect two tubes). Your output section impedance is now 2000 ohms. So, naturally, you need the transformer to 'transform half as much' or 250:1. Not surprisingly, this is the setting labeled 4 ohms.

Just a quick Question because i want to understand this: You said the 8 Ohm setting is actually a 500:1 because 4000/500=8.
So shouldn't the 4 Ohm setting be 1000:1 since 4000/1000=4, and the 16 Ohm setting a 250:1 since 4000/250=16? But that would mean you have to use the 16 Ohm setting since (with two power tubes pulled) 2000/250=8, which would contradict every advice given here?

EDIT: Ok, a bit of googling solved this: Pulling two powertubes doubles the impedance of your output section, so in Rocs example we would now have 8000 Ohms. That means to get our desired 8 Ohms we need the 1000:1 setting, and this is the 4 Ohm setting because 4000/1000=4.
Last edited by ~Luke~ at May 29, 2015,
#24
Yes, thanks for the correction. I went the wrong way with the ohms and instead of noticing it, made the math line up. I fixed the first post.
#25
Quote by the_bi99man
Wait a minute. This is a combo amp. And are you saying that there's a switch on the amp to cut to half power? Like most Orange amps have, among others? Or are you trying to achieve a cut in power BY adjusting the impedance?

yes, there is a half power switch on the amp

with this amp, if you want to run at half power you just flip the switch - you don't need to pull tubes or adjust the impedance.
#26
Great news guys the tech checked it out last night (curiosity must have got him) and al the tubes and everything else is fine it was just a fuse inside that blew. He went over everything cleaned stuff out tested everything and he thinks everything should be ok but the ohm setting should be left at 8 from now on.

I will be able to pick it up tonight, what a relief.
Jackson DK2
1962 Fender Esquire
PEAVEY JSX 212
PEAVEY 6505+ 112
#27
Great news and now you know your used amp is 100%. Look at the positive!
Guitars:
Ibanez RG1570 Prestige
Jackson Kelly KE3 - MIJ (Distortion/Jazz)
Jackson DKMGT Dinky (EMG 81/85)
ESP E-II Eclipse Custom (JB/'59)
ESP LTD EC-1001FR (EMG 81/60)
Fender MIM Strat

Amps:
Mesa/Boogie Dual Rectifier Roadster 212
Laney IronHeart IRT-Studio
Peavey Vypyr 30
Peavey ReValver Amp Sims
TOOOO many T.C. Electronic Pedals. . .
#28
great news
I'm an idiot and I accidentally clicked the "Remove all subscriptions" button. If it seems like I'm ignoring you, I'm not, I'm just no longer subscribed to the thread. If you quote me or do the @user thing at me, hopefully it'll notify me through my notifications and I'll get back to you.
Quote by K33nbl4d3
I'll have to put the Classic T models on my to-try list. Shame the finish options there are Anachronism Gold, Nuclear Waste and Aged Clown, because in principle the plaintop is right up my alley.

Quote by K33nbl4d3
Presumably because the CCF (Combined Corksniffing Forces) of MLP and Gibson forums would rise up against them, plunging the land into war.

Quote by T00DEEPBLUE
Et tu, br00tz?
#30

2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#31
Quote by 311ZOSOVHJH
Good to hear


Can I ask how much he charged?


He's charging me $70 Canadian so he's making his money but whatever I was prepared to pay a lot more lol and it's nice to know everything is all good.

Allllright....These amps sound good, yes they do yes they do.
Jackson DK2
1962 Fender Esquire
PEAVEY JSX 212
PEAVEY 6505+ 112
#32
Quote by 311ZOSOVHJH
yes, there is a half power switch on the amp

with this amp, if you want to run at half power you just flip the switch - you don't need to pull tubes or adjust the impedance.


That's what I was thinking.

So TC, good to hear that it was just a fuse, and it's better now. But yeah, with a half power switch like that, that's all you change for cutting power. impedance should match the cab, no matter what the other switches are set to.
Guitars
Schecter Hellraiser C-1FR, C-1 Classic, Hellraiser Hybrid Solo-II, Special Edition E-1FR-S
Orange Rockerverb 50 212
Basses
Yamaha RBX374 and Washburn MB-6
#33
Quote by UFC on VHS
He's charging me $70 Canadian so he's making his money but whatever I was prepared to pay a lot more lol and it's nice to know everything is all good.

Allllright....These amps sound good, yes they do yes they do.


Peace of mind.

Honestly, if you are not comfortable around high voltages like that it's best to let someone else handle it.

For future though:
*feel free to grab the outside of the transformers to physically pull the chassis out
*don't touch anything on the inside while doing this
*have a safe place to lay the chassis upside down or against a wall
*put one hand in your pocket
*use the other hand to find a fuse or knock on something with a chop stick or wooden spoon
*live and profit


Again - I'm happy it worked out.

311
Last edited by 311ZOSOVHJH at May 29, 2015,