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#1 2012-03-23 01:58:21

Henry
New member
Registered: 2012-03-13
Posts: 4

V4 Losing Clarity and Volume

Hello Ampeg Forum,

After lurking here for a few years, the time has come for action - what kind I don't know.  I've used this amp since the 70's without any issues whatsoever (unless you count my aching back).  Recently it blew the fuse on two occasions.  I carry spares and that was the fix for both of those evenings.  Soon thereafter it went from beautifully severe clear to sounding distorted - almost as if overdriven in a nice sort of way, what you might go for on purpose with an external effect.  It's also seems to have lost volume - half way up isn't what it used to be (though that could just be my hearing).  It just isn't right and I want my old amp back.  Any pointers for where I can look to find it again will be appreciated.

Here are the clues so far:

One pre-amp tube does voice thru the speakers when tapped with a pencil.  The other tubes don't have any effect when tapped.  None of them glow the plates unusually.

At times a high-pitched ringing will come and go, but I can't figure out how to make it do it on purpose.  It's there sometimes when turning the amp on, other times it isn't.

I've run the head thru a different cabinet and get the same problems.

The guitar and cable are good thru other amps.

Channel 2 hums as the volume is increased, channel 1 doesn't.

Reverb works fine.  Tone controls seem to work correctly.

I've done some electronic component repairs and respect the dangers (including capacitors).  I decided to open it up and take a peek.  Thus far I've taken the top cover off and I was really surprised at how clean it all looked.  No dust or other stuff - it was as clean inside as the sound it used to have.  Here's another oddity:  I can't see that it has ever been serviced.  I got it second hand from the original owner a long time ago so I can't be sure about this, but it doesn't appear to have been opened.  This peg has been going for decades without as much as a sniffle.

Before I dig into it further I figured somebody here might have some ideas for where I should look first.  I thank you all ahead of time.  If anybody is interested in pictures I'll be glad to send them - just tell me how.

Henry

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#2 2012-03-23 07:58:10

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

Re: V4 Losing Clarity and Volume

Hi Henry.

before give any advice,  can you tell me which version of the V4 you have?   (does it have distortion?   does it have a master volume?  what color is the script on the face plate? etc... ) 

just wanna get an idea of which version of the amp we're talking about

-steve

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#3 2012-03-23 22:51:04

Henry
New member
Registered: 2012-03-13
Posts: 4

Re: V4 Losing Clarity and Volume

Thank you, Steve.

No distortion, no master volume.  The graphics on the face plate are black.  Metal toggles for power, polarity and stand-by.  The schematic was dated 6-70, I suppose it wouldn't have been built before then.  I believe the knobs are metal, they're silver aluminum-looking.

Henry

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#4 2012-03-25 19:23:14

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

Re: V4 Losing Clarity and Volume

if you run a cable from the ext amp out.   to a mixer or the power amp in of another amp.   does it sound alright?

(make sure you use the ext amp out,   not the ext cab jack)

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#5 2012-04-08 15:54:53

Henry
New member
Registered: 2012-03-13
Posts: 4

Re: V4 Losing Clarity and Volume

There's no difference in the sound.  It's grimy and grungy out of the ext amp jack.

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#6 2012-04-08 16:02:54

athena
Member
From: USA, CA, Solano County
Registered: 2007-12-02
Posts: 56

Re: V4 Losing Clarity and Volume

Tubes is always the first thing you need to try.
An amp that age, and it seems to not have been disturbed/serviced.?
You need to look hard at the power supply, bias, rectifier, screen resistors etc. etc.
I would just replace the filter caps without hesitation. Take a peek at the screens. If they are less than 1k I would really consider changing them.
Put up some pictures so these guys can have a look, they have worked with these V4's for a Long Time.
Best

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#7 2012-04-08 18:17:12

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

Re: V4 Losing Clarity and Volume

If it sound bad from the ext amp out,  i would check the preamp tubes first....

second,  I would check the DC voltage at the power supply points.

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#8 2012-04-09 21:47:22

Henry
New member
Registered: 2012-03-13
Posts: 4

Re: V4 Losing Clarity and Volume

I appreciate the guidance and understand that the amp is long overdue for service.  I've been very lucky with this amp.  Having some help with getting first things first is going to be a major asset and will help me understand the workings of the amp a little better.

If I knew how to post pictures on this forum I would gladly do so.  Is this difficult to do?  Please advise as to how to post them, along with what parts of the amp would you like to see first.

If the first thing is to replace all of the pre-amp tubes and caps, can you recommend a source and part numbers? 

Henry

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#9 2012-04-10 00:01:29

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

Re: V4 Losing Clarity and Volume

posting pics is not difficult,  if you have a site to host your photos,  you can link to them.   click on the [img] tag:  link below the message box.   it will take you to a list of options for posting pics.   

the big thing is that we don't host photos here.   

anyhoo... if you're not even sure which tubes you need,  it might be best if you took it to a tech.

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