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Old 10-30-2012, 06:29 PM   #1
TJHague
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Channel Switching Issue on Peavey Valveking 112

Hello all,

I have a Peavey Valveking 112 combo that has developed a channel switching issue. I am looking to fix this myself for 2 reasons:
1. I intend to sell the amp soon when it is working properly; I recently acquired a Carvin V3 that I like much better. I have contacted all of the Peavey service centers in my area and I have to pay a decent chunk of money just for a quote. Over the phone what they were able to tell me sounds like the cost of having it fixed will be roughly how much I can sell it for.
2. I have electronics experience (experimental physics graduate student) and would like to learn about how tube amps work. So, this seems like a good opportunity to do so.

Anyway, description of the problem: When I am on the clean channel, the amp will not switch to the lead channel unless I push the 'Gain Boost' button on the front of the amp. Conversely, when I am on the lead channel, I cannot switch back to the clean channel without unpushing the 'Gain Boost' button. This only applies to the button on the front of the amp, pressing the boost button on the footswitch does not allow me to switch channels.
Also, it seems that the gain boost is stuck to permanently on when on the lead channel, there is not an audible difference when I shut it off.

I have been studying the schematic from the valveking wiki and suspect that it may be one of the relays that has gone bad. I have the amp open (with the capacitors properly drained so as not to kill myself) and there does not appear to be anything wrong from a visual inspection.

So, before I remove any parts and test them to try to find the culprit, I thought I would post here to see if anyone has any guidance/tips to offer.

I am also attempting to get some guidance from contacting Peavey, but based off of their initial responses, I don't think they are going to be able to say anything other than go to an authorized service center.

If something here wasn't clear or you need more information, let me know and I'll do my best to provide.

So... any suggestions on where to start? (ie. do you think my suspicions are reasonable or do you possibly have a better idea of what it could be or how to track down the problem?)

tl;dr
Peavey Valveking won't switch channels with out messing with the gain boost switch. Want to fix it myself and suspect it might be a relay. Suggestions/guidance/tips appreciated.

Last edited by TJHague : 10-30-2012 at 06:41 PM.
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Old 10-31-2012, 10:23 AM   #2
CECamps
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The first thing I would do is test the switches themselves. Use continuity check on a DMM to test the channel switch and the gain boost switch to ensure that you get appropriate continuity from pole to pole in both switch positions. If one or the other switch has a contact issue in one position or another, this could be the problem.

I'd do this before starting to R&R parts.
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Old 10-31-2012, 10:27 AM   #3
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Oh, and be sure that you look at the PCB traces on the layout diagram because some of the poles are connected to one another and therefore you'll get continuity regardless of switch position. Here's the schem I'm looking at:

http://web.archive.org/web/20090305...king_50_112.pdf
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Old 10-31-2012, 10:37 AM   #4
TJHague
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Ok. That makes sense, I'll definitely do that. That is the schematic I've been looking at as well. I'll post back once I get a chance to check that out, might be a day or two. Have a lot of homework to get done tonight.
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Old 11-01-2012, 11:32 AM   #5
TJHague
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Peavey responded to me today and gave me very similar advice to what you suggested CECamps. They said it's most likely either the switch has a broken solder joint or that the footswitch is not getting to ground since that is interconnected with the switch. I'll be checking that tonight after classes and will post back with results.
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Old 11-01-2012, 09:47 PM   #6
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Cool, hope you get it worked out!
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Old 11-01-2012, 10:10 PM   #7
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The switches do go bad and should be checked as Craig described.

I couldn't quite understand if the problem was limited to the switch on the head and foot switch ok?

Sometimes the a switchcraft style jacks don't make contact when you pull the foot switch out. It can be checked with a multimeter as well. Basically it thinks a foot switch is plugged in. Could effect just one switch or both.
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Old 11-02-2012, 01:11 AM   #8
TJHague
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Well, I checked the switches and they seem to be switching properly and are properly connected to the board (checked a couple different points and switching the switch to make sure).
It might be the footswitch jack. The ring and tip are supposed to connect to the sleeve when nothing is plugged in. This happens and the sleeve does connect to ground as it should, but I measured a bit more resistance between the sleeve and ground than I thought there should be based on the schematic. It might just be that I'm misreading or that my circuit analysis skills are rusty though. I emailed what I measured to the guy at Peavey to see what he says.

@R45VT
Essentially the footswitch doesn't do anything anymore. When on the lead channel, the gain boost will not turn off with either button (head or foot).
To be able to switch to the clean channel, I have to first switch off the gain boost button on the head (foot does not matter). And to switch back to the lead channel I have to switch on the gain boost button on the head (again, foot does not matter).

No matter which channel I am on, turning on the gain boost on the head automatically switches me to the lead channel. If I have the channel select button (on the head) set to lead while the gain boost button (head) is on, I am stuck on lead + gain boost until both buttons are switched off.

Kinda convoluted, but I do know how to switch channels finally. But as it stands the footswitch is completely useless.
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Old 01-30-2013, 10:22 PM   #9
TJHague
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Well, I'm reviving my old thread with some good news and some bad news. The person at Peavey was little to no help; he also stopped responding to my email after I had to take a week and a half to study for finals. Oh well. Anyway, before I removed the relay that I suspected to be the offending component, I was doing a google search for where I could get a replacement for it and happened upon a thread on another website where a person described a similar problem. I had done google searches before, but it didn't show up then. I think what brought it up this time was that person suspected a relay as well. This person discovered that it was actually Q103, a JFET, to be what had failed. I tested that, and it turned out to be my problem. I received the replacements in the mail yesterday, installed it tonight, and it fixed my problem!

Now, I just want to look into the circuit and try to understand why that would cause the problems. (I know transistors are often used for switching, I just want to understand better what is going on)

Unfortunately in what I thought was going to be the last time putting this back together, I managed to somehow damage the treble pot on the clean channel. I'm guessing that I must have not been paying attention and used too much force putting the knob back on. So, now I have to find a replacement for that. It is my preference to get the exact replacement piece. I saw that I can call Peavey and order a replacement, but I am wondering if they might have a high price. Do any of you have any ideas where I could find it? The only online stores that I found having it are located in Europe and have very high shipping prices to the USA.

The part is Peavey Part Number 71190908 and is a 250K pot with a 12mm shaft. I'm sure there are off-brand ones that would work, but I would like to get the Peavey genuine replacement. If you guys think that I would just be best off calling Peavey, I'll do that.

I'm feeling kinda silly for this mishap after I thought I had it fixed... Thanks for any help everyone
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