Ampeg V4.com

forum

You are not logged in.

#1 2008-01-24 16:26:15

JasonG
New member
Registered: 2007-12-18
Posts: 8

Humm when nothing with volume all the way down

I suspect the transformer is bad but one of the tubes is not glowing so It may be a tube.
I am new to tube amps. Is that posable ?
If it is the transformer can I pot it or do I need a new one?

Offline

 

#2 2008-01-24 19:19:48

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

Re: Humm when nothing with volume all the way down

hi jason,  moved your topic to the workshop.

if you could give us some more info that might help alot. 
how loud is the hum?   does it get louder when you turn the volume up?   do you get any sound from a guitar? 
did the amp do anything before it started crapping out?

Offline

 

#3 2008-01-27 16:46:51

JasonG
New member
Registered: 2007-12-18
Posts: 8

Re: Humm when nothing with volume all the way down

Ok well I took some measurements of the unlite tube. V 203 only has voltages on pin 1 ( 130.4 v) and 3 (.7v). all of the other tubes on that board seem off too.
It looks like a tube shorted out and fried some of the poly caps. They have cracks on the tops of them.
At this point I am trying to decide if I should recap it.
  I took the voltages on the power transformer the heater voltage was 5.7 and the main ( red) was 407v.  The voltage at the rectifier is 533v the schematic says it should be 545v.
What gets me is that the things sounds pretty good even with the strange voltages and with one tube out.

Last edited by JasonG (2008-01-27 18:49:18)

Offline

 

#4 2008-01-27 21:03:46

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

Re: Humm when nothing with volume all the way down

hey Jason.  I wouldn't worry about the  voltage at the rectifier being 533.  that is pretty close.  I think mine measures similar if I recall correctly.    thats within spec.
the 5.7 heater voltage Is strange.  I wonder if perhaps your hum balance pot is malfunctioning.  that would cause a big hum. you might

as for the tubes... maybe be more specific as to which board you are referencing.    when does your v-4 date to,  is it pre master volume... etc... ?

Offline

 

#5 2008-01-27 22:38:15

JasonG
New member
Registered: 2007-12-18
Posts: 8

Re: Humm when nothing with volume all the way down

Well the heaters on the small board ( the reverb buffer and recovery stage) are getting 5.4 V.
I have an early 70's modal without the master volume.
I put another 12ax7 in the V203 slot and its still not glowing.  My guess is that its humming because of V203.
I adjusted the humm balancer and that got rid of the real low humm but which is good but it didn't take care of the more mid range humm.
What is funny is that the reverb still works. even though the recovery tube is not up.

Last edited by JasonG (2008-01-27 22:57:17)

Offline

 

#6 2008-01-28 00:35:20

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

Re: Humm when nothing with volume all the way down

the reverb still works even though the recovery tube is not up?

if the reverb is working... then the tube is working.   I've had issues with bad caps in my reverb circuit,  but the hum would go away if I turned the reverb knob down.   

are you saying that ONLY the heaters on the echo PC board are measuring 5.4 Volts?    and that the rest of the heaters are measuring normal? 

does the eq effect this midrange hum?

Offline

 

#7 2008-01-28 01:52:59

JasonG
New member
Registered: 2007-12-18
Posts: 8

Re: Humm when nothing with volume all the way down

Ok so I stuck the original tube in there and now it lights up. It seems a bit dim but its better than it was.
Tubes can operate in a starved mode so I am guessing that it was doing that. It have just enough current to work but not enough to glow. It is the last tube on the heater circuit.
Part of the humm was from the heaters. It was a pretty low frequency. The remaining humm isn't as low maby not in the mid range but not as low as the other humm.
The heater voltage is 5.4  from the transformer.
I just played my guitar through it there is a rustling sound like one of the tubes is going out. So my guess is its the magnavox I put back in there.
The amp shakes a bit. I know that the windings in a transformer can work loose and vibrate. Causing the tubes to resonate at that frequency.

Offline

 

#8 2008-01-28 04:37:34

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

Re: Humm when nothing with volume all the way down

you disconnected the heaters from the circuit and it only measured 5.4 volts?     thats more than 10% off,  which is no good.  have you measured the voltage coming out of your wall? 

the heater hum would be 60hz.  there could be hum from the B+ that would be 120hz.   
once again, if there was a rustling sound from that magnavox it would only appear when the reverb knob was up.   keep that in mind.   

does your ampeg have the 3 prong plug? and have you removed the death cap?

Offline

 

#9 2008-01-28 05:41:18

JasonG
New member
Registered: 2007-12-18
Posts: 8

Re: Humm when nothing with volume all the way down

Yeah, it has a grounded plug.
The death cap?
  My home was rewired a few months ago if there was a problem with the line voltage I would have heard about it.
Am I right in assuming that the transformer is why the amp vibrates a bit?

Offline

 

#10 2008-01-28 08:12:44

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

Re: Humm when nothing with volume all the way down

I think maybe the best idea is to take your amp to someone who knows what they're doing. 
I'm sure the problem could be easily located with the aid of an oscilloscope,  by an experienced tech.

Offline

 

#11 2012-08-29 07:33:21

Zappeddrumer
New member
Registered: 2012-02-11
Posts: 1

Re: Humm when nothing with volume all the way down

Hi folks ! Just got my v4 and as I was checking some caps I found  c207 w the 330/2w resistor from r216 in its place and the 10/25v cap in r216 ! Could that account for a hum that I hear, also a rustling sound? The amp is loud. I have replaced all tubes. I checked and replaced all bad resistors.Also changed c3,c6,c7,c8,c10,c202,and c201. Replaced all the pots and when I removed all the other caps was when I found that mixup between r216 and c207 and was wondering now if recaping is needed? I havnt done the big filter caps yet and like to know if I could replace those with single caps like 40/500 + 40/500 + 40/500 and 40/450 + 100/450 + 40/450 + 100/450 for a total off 7 caps?Volume was low before I replaced the resistors.Thanks for any comments or ideas.Larry.

Last edited by Zappeddrumer (2012-08-29 07:41:00)

Offline

 

Board footer

Powered by PunBB
© Copyright 2002–2005 Rickard Andersson