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Author Topic: Peavey Classic VT Blowing Fuses  (Read 10910 times)

Roly

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Re: Peavey Classic VT Blowing Fuses
« Reply #15 on: October 18, 2014, 05:36:50 PM »
Given their position on the OP valve sockets these will be diodes intended to protect the OPT if the amp if fired up without a load, e.g.;



I would therefore give the whole OPT secondary circuit a really good scrute for any possible intermittent opens, lazy OP socket contacts, broken braids on the speaker(s), &c.
If you say theory and practice don't agree you haven't applied enough theory.

ChewyNasalPrize

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Re: Peavey Classic VT Blowing Fuses
« Reply #16 on: October 20, 2014, 04:03:39 PM »
Just ordered two of these from Tube Depot: R3000 .25A / 3000V High Voltage Protection Diode

Checked with Peavey and they did have the original diodes but they had a minimum order $$ plus shipping would have made them too much to justify when I was able to get the R3000's for less than $3 shipped.

Should be here in a few days.  :dbtu:

ChewyNasalPrize

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Re: Peavey Classic VT Blowing Fuses
« Reply #17 on: October 23, 2014, 05:43:52 PM »
I just got the diodes. I want to be sure I only need one per tube socket. They are really small compared to the originals.

Also, which end goes to ground? There's a silver stripe going around one end of the diode.

Thanks!

DrGonz78

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Re: Peavey Classic VT Blowing Fuses
« Reply #18 on: October 24, 2014, 05:54:26 AM »
Think about in terms of just replacing the part in the same orientation that the other part was connected. You have the old diodes and the new diodes with a stripe on one end of both type of parts. The striped end is the cathode and the other side is the anode. Looking at your pictures it is easy to see how to just replace the part in the correct orientation. Also, look back at your schematic and find those diodes(CR16 & CR17) on the power amp, the anode is clearly going to chassis ground. Still we can assume the amp was working great before and the old diodes were original, thereby correctly installed.

Edit: Also the peavey 2873 diode is 2kv rating with 250ma(0.25A) rating. So the R3000 .25A / 3000V rating means that just one will be sufficient. Actually the R3000 is a higher rated part as you can see. I have read some other data sheets on the R3000 that had it at 200ma(0.2A), but that might have been a different manufacturer. If they say that is the rating then it must be accurate, I hope.

Double Edit: All the info is actually stated on the tube depot site where you bought the part. Telling you the cathode goes the plate of the tube and anode to ground. Also, tells you what the part is designed for in the fender amp example.
https://tubedepot.com/products/r3000-25a-3000v-high-voltage-protection-diode

Don't forget to read Roly's post again(reply#15) and check over the items he listed that might have caused this diode to go bad.
« Last Edit: October 24, 2014, 06:16:27 AM by DrGonz78 »
“A person who never made a mistake never tried anything new.” -Albert Einstein

ChewyNasalPrize

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Re: Peavey Classic VT Blowing Fuses
« Reply #19 on: October 24, 2014, 04:44:12 PM »
Replaced the diode and checked for frayed wires and such- couldn't find anything obvious that might cause the diode to fail.

Fired it up and it seems to be working fine again. Played it for about an hour and sounds right to me. Of course I'll keep my eye (or ear) on it. If it fails again anytime soon I'll know to look elsewhere for the cause.

Thanks everyone for the help on this! I really appreciate it. :dbtu:

Chews.

Enzo

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Re: Peavey Classic VT Blowing Fuses
« Reply #20 on: October 24, 2014, 05:52:22 PM »
Frayed wires are not what those diodes care about.   They die when large transient voltages occur and they must deal with them.   The kind that occur when the speaker goes intermittent or the connections to it fail.

loudhouse

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Re: Peavey Classic VT Blowing Fuses
« Reply #21 on: October 28, 2014, 02:12:37 PM »
Hi guys; my first post.  I have here a Classic VT series 100, 2 tube 50 watt.  Was a combo, someone cut it to a head.  I was asked to repair it. I have read many posts about blowing fuses, and checked many components including all diodes.. Can't find the problem. I have less of a legit troubleshooter, more of a 'check for breaks' education.

The preamp board has a couple ugly repairs, a few off-value E caps. C10 350V is leaking and reads 15 microF.

One of the large power board 100 microF Ecaps reads .39 nanofarad. That seems a bit too far out of range.
With tubes out, the input power fuse blows immediately.

I dont want to throw parts at this thing since it isnt mine.
Can someone help?

Enzo

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Re: Peavey Classic VT Blowing Fuses
« Reply #22 on: October 28, 2014, 06:07:16 PM »
Hi, always better to start a new thread for a different amp, instead of hopping on the discussion of someone else's amp.

Pull the tubes.

Isolate your problem.  It is in the circuits or in the power supply.  You have all the fuses in the power supply?  Note where they go and remove them.  Does the amp still blow the main fuse?   If so, then your transformer is suspect.  Rare, but it happens.   If the amp now will hold a fuse, put the secondary fuses back in one at a time to see which one makes the mains fuse go off.

By the way, no point in wasting fuses, look up "light bulb limiter" then make one and use it.

SOMETHING is blowing your fuses.  The transformer itself, or something associated with the secondary supplies.  We need to determine WHAT.   Usually the high voltage circuits are responsible for fuses blowing.    Very often one of the flyback diodes is shorted.  Those are the ones from pin 3 of each power tune to ground.  Rarely but happens, the output transformer itself.  Is there a low resistance to ground from either pin 3?

Filter caps don't usually "short out" but it happens.  be aware that your ohm meter works on just a volt or two, and a cap tested at a volt or two may "check" fine, but leak like a screen door at 200v or more, and since these caps do work at hundreds of volts we ned to keep that in mind.