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#1 2006-09-20 22:27:47

trojansloth
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Registered: 2006-09-20
Posts: 1

vt-22 blowing fuses

I'm trying to fix a vt-22 that has been blowing fuses. 

The amp is Magnavox era, pre distortion knob.  As advised on the Budda amp website, I pulled all the tubes and tried to turn the amp on with a new fuse.  The amp turned on for a moment, making a loud sound not unlike 60 cycle hum and  then blew the fuse.  Does anyone have any smart ideas about what may be wrong?

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#2 2008-01-10 20:57:36

Natron
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Registered: 2008-01-10
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Re: vt-22 blowing fuses

I'm bumping this up just because I have a V-4 head doing the exact same thing right now and am trying to find an answer.  Thanks.

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#3 2008-01-10 21:10:05

hangman
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Registered: 2006-09-04
Posts: 1848

Re: vt-22 blowing fuses

there are a number of things it could be.  and unless you're tech savy,  I would say take it in.

some potential problems:
1.blown filter cap
2.blown output transformer
3.bad d7-d10 (if yours has them, some of them don't)

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#4 2008-01-14 21:05:10

Natron
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Re: vt-22 blowing fuses

Well, I fixed mine yesterday.  A friend came over and we started testing components.  It turned out two of the rectifier diodes were shorted.  Replaced them with two identical new ones and the thing lives once again!

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#5 2008-01-15 02:49:36

hangman
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Registered: 2006-09-04
Posts: 1848

Re: vt-22 blowing fuses

good work!  its amazing how a couple of sub-dollar parts can make so much difference isnt it?

Glad you got it working Natron.  did you just get your V-4 or have you had it a while?

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#6 2008-01-15 04:02:37

snowblinder
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Registered: 2007-12-12
Posts: 50

Re: vt-22 blowing fuses

My VT-22 is doing the same thing, all of a sudden. It has been working fine...I just took it to my local tech this afternoon to have a brand new matched quad of Svetlana 6L6-GC's installed (I wasn't sure how old the Sovtek 7027A's that came in it were) and to have the amp biased accordingly. He also cleaned the tube sockets, checked the amp over fully, fixed the wiring of the speakers (it was a mess). Took it to practice, played it loud for about an hour and a half. Sounded great. And then.....the amp just died. The whole thing shut down. Power went off, everything.

I pulled the fuse out. Sure enough it was blown. The amp takes 6 amp, 250v fuses. I examined the one that I pulled and it was a 5 amp, 250v. I'm hoping that when i pop in a 6 amp fuse tomorrow, all will be well again. Still....does this sound like a potentially larger issue than simply a case of the wrong fuse being installed? I'm really afraid of it being a blown transformer...can't afford that magnitude of a repair right now.

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#7 2008-01-15 09:33:00

hangman
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Registered: 2006-09-04
Posts: 1848

Re: vt-22 blowing fuses

try the 6amp fuse before you get too worried.  if it does it again we can assume there is still an issue.

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#8 2008-01-15 20:35:35

Natron
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Re: vt-22 blowing fuses

1. The fuses are there to blow up before more expensive components do.  Be happy they DO blow instead of withstanding a malfunction and making a tube, transformer, or other part blow up. smile  But yeah.. try the 6A fuses first.  May be a non-issue.

Now the story of MY head.. A local guy posted an ad for a broken V-4 for sale (he said it had a blown transformer) with no power tubes for $200.  I said I'd take it as a project amp and he dropped it off. The filter caps were new so I doubted it was those.  Those transformers are massive so I doubted it was those... but didn't rule it out since he said he thought one was shorted.  After some digging, we came up with those two blown $0.05 diodes, replaced them and it works.  Just cost me the $200, dinner and a beer for my friend who helped me, and $76 for a new quad of 7027A tubes.  It's the early pre-Magnavox non-master volume version with the old metal switches instead of the plastic rocker switches.

Good deal, no?

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#9 2008-01-16 00:05:39

snowblinder
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Registered: 2007-12-12
Posts: 50

Re: vt-22 blowing fuses

Okay, popped a 6 amp fuse in today and it started up, no problem. Sounds great too. Yet, something just tells me it isn't operating at full capacity. I have the pre at 10:00 and the master nearly cranked. It's loud enough, but heavily saturated. Everybody always talks about the incredible clean headroom these amps offer. Where is it?

(Playing through a '75 Gibson Les Paul with a Gibson '57 Classic in the bridge, which isn't supposed to be a very hot pickup.)

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#10 2008-01-16 05:32:03

hangman
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From: Seattle Washington
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Posts: 1848

Re: vt-22 blowing fuses

hard to say without seeing it,  or knowing your setup. 

if you want to keep it a little cleaner... turn the master all the way up, and use your pre as the volume. 

have the filter caps been replaced? 

what cab are you running?  are you sure IT is functioning correctly.. or are you sure that your impedances are matched?

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#11 2008-01-16 15:46:08

snowblinder
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Registered: 2007-12-12
Posts: 50

Re: vt-22 blowing fuses

I'm not running a cab, just the combo itself. Speakers are unlabeled square magnet 12's (Eminence 67 or CTS I believe, from what I've been told). Impedance is definitely matched...I checked (8 ohms). I have been using it with the master turned close to or sometimes all the way up and adjusting the pre for volume.

The tech who checked it out when I first bought it supposedly went through everything. I'll double check with him to see if the filter caps were indeed looked at. The power tubes, as I said, were switched over to Svetlana 6L6-GC from Sovtek 7027A and the amp was biased accordingly. I know all of the preamp tubes were left as is.

This is turning into a whole other thread in and of itself now. What are good replacement speakers for these amps? I really love the sound that the current ones produce, but if they are in fact original, maybe replacing them would be wise at some point soon.

Basically, I'll do whatever it takes to make this amp as great as I can. It's pretty damn close as it is now.

Last edited by snowblinder (2008-01-16 15:48:02)

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#12 2008-01-16 18:49:56

hangman
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From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: vt-22 blowing fuses

are you sure that the impedance is 8ohms?  my vt-22 runs two 8ohm speakers in parallel (making the total load 4ohms).   double check that.

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#13 2008-01-16 21:03:40

snowblinder
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Registered: 2007-12-12
Posts: 50

Re: vt-22 blowing fuses

Yes. My tech checked it yesterday with his meter (I'm sorry, I'm completely clueless as to what the device is actually called), as I stood there watching. It was actually something like 7.6 ohms total. So, basically 8.

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#14 2008-01-16 23:40:26

hangman
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From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: vt-22 blowing fuses

make sure both speakers are working. 
aside from that I'm not sure what to tell you short of suggesting that your tech take another look at it.
It is a loud amp.  mine is pre master volume,  and I never turn it up past 3 or 4.  i often consider getting a vt-40,  because it is so loud.

but I suppose it depends on what you're competing with.

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#15 2008-01-17 03:13:09

snowblinder
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Registered: 2007-12-12
Posts: 50

Re: vt-22 blowing fuses

It holds its own with an SVT Classic plus 8x10 cab setup, 100 watt Fender Twin 2x12/50 watt Marshall JMP plus Marshall 4x12 setup, and a very powerful drummer. I guess I can't really ask for more. All I was noting originally is that with the master anywhere past 12:00 and the preamp at about 10:00, the amp is already into pretty heavy overdrive, which conflicted with a lot of reviews I've read that raved about the clean headroom these amps have at insanely high volume levels.

Not complaining really though. It is a beautiful sound.

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#16 2008-01-17 07:43:34

hangman
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From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: vt-22 blowing fuses

I can tell you that Electronically.  a v-4 puts out 100-105 watts CLEAN.   which is pretty nice.  a twin reverb will put out 75-80 as will most "100 watt" marshalls.

I would suggest cranking the master up all the way and just using the gain knob.  you shouldn't have to get dirty to be really loud.

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