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Author Topic: Peavey Heritage VTX ..uh oh..  (Read 29194 times)

ohmy!!

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Re: Peavey Heritage VTX ..uh oh..
« Reply #30 on: July 20, 2010, 02:49:19 PM »
Well I got the tubes in.  What I thought was noise from bad tubes apparently isn't  :-\.  The transistors fixed the tube red lighting problem, but I'm wondering if maybe the filter caps were killed off too when everything happened  ???.  I had swapped them out a year and a half ago so it's kind of a bummer.



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ohmy!!

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Re: Peavey Heritage VTX ..uh oh..
« Reply #31 on: July 20, 2010, 07:58:22 PM »
I got lucky, only one of the smaller caps actually needed replaced and I was able to get it at radioshack for $1.60  :tu:.

ohmy!!

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Re: Peavey Heritage VTX ..uh oh..
« Reply #32 on: August 30, 2010, 09:41:53 PM »
Hate to bring this thread back, but.. Q6 and Q8 transistors keep dying.  I'll replace them and after a good 3-4 hours of playing the amp will just start to sound like some kind of awful fuzz monster with volume jumping up and down.  I've replaced them like 3 times now.  Any suggestions as to why this is happening?


bry melvin

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Re: Peavey Heritage VTX ..uh oh..
« Reply #33 on: August 30, 2010, 10:12:35 PM »
check your data sheets: make sure you are putting them in correctly

The last ones I bought had a different pin out from the original peavey transistors

ohmy!!

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Re: Peavey Heritage VTX ..uh oh..
« Reply #34 on: August 30, 2010, 10:51:12 PM »
Do you know the pin out of the originals? I can't seem to find the info.

ohmy!!

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Re: Peavey Heritage VTX ..uh oh..
« Reply #35 on: August 30, 2010, 11:24:57 PM »
Here's what I have.  Still can't find the original's pin out.

http://www.fairchildsemi.com/ds/MP%2FMPS6531.pdf

bry melvin

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Re: Peavey Heritage VTX ..uh oh..
« Reply #36 on: August 31, 2010, 12:18:12 AM »
http://www.datasheetcatalog.com/datasheets_pdf/M/P/S/6/MPS6530.shtml

looks the same...flat should be as in the layout linked earlier on this thread

looking at notes: I used 2n3642 per peavey cross reference list.

ohmy!!

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Re: Peavey Heritage VTX ..uh oh..
« Reply #37 on: August 31, 2010, 01:27:29 AM »
Maybe that's not the problem then?  Seemed like when I'd replace it, the amp would go back to sounding right.

I just switched the amp back on a bit ago and it all of a sudden sounded normal, then after about 15 minutes went back to sounding all fuzzy and the volume dropping and raising.  ???

Enzo

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Re: Peavey Heritage VTX ..uh oh..
« Reply #38 on: August 31, 2010, 01:50:54 AM »
Stick with the stock MPS6530/6531.  It is what the amp is designed around, all MPS6531 will have the same EBC pinout. Mounted flat side away from the drivers. I can't speak for the 2N3642, I don't know what package they are in.

Those are limiters, the amp should work fine if you simply remove them.  Of course that would also remove some of the amp's own protection.

Like any limiter, they turn on when their base is energized.  Look at the circuit.  When the voltage across resistors R155, R159 gets large enough, the transistors turn on and ground off the signal at the base of the drive transistors.   And what causes that voltage in R155, R159?  Current through them, the same current flowing through the tubes.

SO the question arises, have you put different tubes in it?

And for that matter we could have a failing drive transistor, or two.

And look at those resistors, they are the two 5 watt resistors next to the drive transistors.  DO both measure 3 ohms?  And is the solder to each in good shape?

Measure the voltage across each resistor, does it meet the spec on the schematic?  20-40mv each?  And when it fuzzes out, do those voltages change?

ohmy!!

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Re: Peavey Heritage VTX ..uh oh..
« Reply #39 on: August 31, 2010, 02:50:22 AM »
Well I had Sovtek 6L6 WXT+ tubes in there before and now I have the Ruby Tubes 6L6 since replacing the transistors Q6,Q7,Q8,Q9.  The tubes appear to be fine visually, but that doesn't really mean anything I guess. I'll have to take it apart and check those voltages later.  For the last hour or so I've been playing it and the amp has been fine. 

Thanks
« Last Edit: August 31, 2010, 02:51:23 AM by ohmy!! »

ohmy!!

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Re: Peavey Heritage VTX ..uh oh..
« Reply #40 on: August 31, 2010, 07:56:31 PM »
When I measure the ohms of those resistors, the meter's needle just drops down below zero.

Enzo

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Re: Peavey Heritage VTX ..uh oh..
« Reply #41 on: August 31, 2010, 08:33:54 PM »
You are not measuring them with the amp on are you?   If your ohm meter goes backwards, that means there is voltage in the circuit.  Flip it to volts and see.   At worst, unsolder one end of each resistor and lift it up to measure it.

ohmy!!

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Re: Peavey Heritage VTX ..uh oh..
« Reply #42 on: August 31, 2010, 08:56:09 PM »
I have the amp unplugged.  It's measuring other resistors in there, but it's off by a bit (the 100ohm is measuring at 80 and the 150ohm measuring at 130-140). The meter could be off by a bit.  If I flip it to volts the needle doesn't move at all.  Then again I couldn't measure the voltage on these if they're supposed to be 20-40mv, my meter's selection for volts starts at 10.

ohmy!!

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Re: Peavey Heritage VTX ..uh oh..
« Reply #43 on: August 31, 2010, 09:09:31 PM »
Pulled the resistor out completely, same issue. Reads below the zero, just as if I put the two probes together.  I need to find my digital meter.

ohmy!!

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Re: Peavey Heritage VTX ..uh oh..
« Reply #44 on: August 31, 2010, 11:26:29 PM »
Can't find my digital meter. I did notice though, that one of the tubes has bit of a blue glow to it and when it starts getting fuzzy and lowering volume that the blue glow dies down.  I tapped on a couple of the tubes a little bit and the sound returned to normal, the blue glow on the one tube returning as well.  Maybe bad tube and/or bad driver transistor?   :-\