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#1 2009-01-07 07:37:29

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

transformer measurments for V4

there has been enough interest in transformer measurements by forum members that I thought I would post these for everyone.   these measurements are for the non-distortion models.   if anyone has power transformer measurements for the distortion model, send me a PM or email them to me, and I will post them here. 
thanks!

Output transformer:
primary-   violet to orange - roughly 60ohms
            blue to orange  - roughly 60ohms 
           violet to blue   - roughly 120ohms
secondary -  all taps should read less than one ohm with reference to the grounded tap.   

Power transformer:
secondary voltage: roughly 410V RMS

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#2 2009-01-07 13:15:30

rob
Member
Registered: 2008-10-28
Posts: 171

Re: transformer measurments for V4

Thanks Hangman...good stuff. I measured similar DC resistances on mine. One thing that I noticed was the primaries to center tap were very closely matched on this transformer. I believe Ampeg used a very high quality transformers. It is also a huge chunk of iron.

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#3 2009-01-08 17:31:01

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

Re: transformer measurments for V4

Agreed.    very closely matched primary sections.   in addition to simply sounding great,  it also keeps the hum down.   another reason why these amps are so damn quiet comparatively speaking.

its amazing too, i feel like they used great transformers, but often used kinda lousy capacitors.  go figure.

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#4 2009-01-08 17:37:30

foxfire
Member
Registered: 2008-12-09
Posts: 215

Re: transformer measurments for V4

at least it ain't the other way around...

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#5 2009-01-10 14:48:04

rob
Member
Registered: 2008-10-28
Posts: 171

Re: transformer measurments for V4

The V4 / VT22 chassis layout also contributes to its low hum. The OT is as far away from the supply transformer as possible. This is a good practice that is seldom followed. These amps are amazingly quiet, and without enormous filter caps, or a choke. Yes the signal caps are crummy, and a lot of the resistors are not great either (noisy carbon comp). So I wound up changing a bunch of inexpensive parts. The good news is that those NJ engineers (ME and EE)really got it right and the expensive stuff will last a lifetime. Long live the Peg!

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#6 2011-04-23 23:01:52

chabby
Member
Registered: 2010-06-08
Posts: 37

Re: transformer measurments for V4

good job- i just measured to and found your numbers dead on.

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#7 2012-12-14 19:29:52

simondolanbass
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From: Montréal, Québec, Canada
Registered: 2011-11-28
Posts: 14
Website

Re: transformer measurments for V4

HI,
I think that this post is what I look for. I measure 0.2 ohm from blue to orange... I always thought that a bad transformer would be OL...
60.3 ohm from violet to orange.

So I guess I have to change that xfo?

What cause output xfo to burn?

Is there something in the amp that cause the xfo death?

I don't want to install a new one and burn it!

Thanks
Simon

Last edited by simondolanbass (2012-12-14 19:33:15)

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#8 2012-12-14 20:34:36

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

Re: transformer measurments for V4

Hi Simon,   Transformers can fail in many different ways.

First let me ask you,  did you disconnect the transformer before measuring it?   

Just want to make sure.   

Transformers can fail for many reasons,   But ultimately the technical reason is that the insulation on the windings can breakdown/crack causing shorts between winds

This can be the result of storage conditions (leaving it in a garage through many wet summers andcoldwinters). Or abuse ( putting a 10 amp fuse instead of a 6 amp when the power tubes are failing)
Or sometimes there is no obvious reason.  But it happens, and will eventually happen to all of them.

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#9 2012-12-14 21:51:27

simondolanbass
Member
From: Montréal, Québec, Canada
Registered: 2011-11-28
Posts: 14
Website

Re: transformer measurments for V4

Hi Hangman,

No I didn't disconnected it... So maybe the problem is elsewhere ? The sine wave before the output tube is fine, it get distorted after the power tube...

Also the high voltage is not the same as the schematic. plate is 518V, supp grid is 515V and grid is -62V.

I noticed that on others V4. Why is that?

Thanks


Simon

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#10 2012-12-15 09:25:03

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

Re: transformer measurments for V4

Try disconnecting it first, and then measuring it.   Does your amp have the flyback diodes?

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#11 2012-12-16 15:45:04

simondolanbass
Member
From: Montréal, Québec, Canada
Registered: 2011-11-28
Posts: 14
Website

Re: transformer measurments for V4

Hi,

I disconnected the xfo and it is fine!  I found that a cap is short. I think that this cap was a mod. I was connected from the bridge diode to the blue wire of the transformer.
Check the picture https://www.dropbox.com/sh/w5mu1qfirtm51s5/GjyqT3gM9m

Was I the purpose of those caps?
I removed them both and the amp work great!

Should I put caps (good ones) back?

About the flyback diode: I always saw them on schematic and never found them in three V4 that I opened!

Back to the high voltage: Why are they lower than what it is written in the schematic?

Thanks a lot!

This site is incredible as the V4 are!

Simon

Last edited by simondolanbass (2012-12-16 18:28:03)

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#12 2012-12-16 22:53:33

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

Re: transformer measurments for V4

wow.... those caps have no business being in there.  I can't imagine why anyone would have put them there.   leave them out.


as for the power supply voltages... I would double check your AC from the wall.  is it a full 120?

even if its only 116 or 117  you will see a -10V drop on the B+

this is why people use voltage regulators.  back when I used an SVT I tested it at full power and it put out 230 watts.   which seemed low.    But when I realized that when it was putting out 230watts,  the voltage at the socket would drop 10-15VAC  and the B+ would drop with it.... if I used a voltage regulator I got the full 300 watts.

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#13 2013-03-08 02:55:05

beedoola
Member
Registered: 2009-05-25
Posts: 58

Re: transformer measurments for V4

To test the OT - do I need to disconnect all the wires from both the primary and secondary to accurately measure or can I just remove the primary wires to see if they check out?

And the PT needs to be measure while the amp is On? Do I test both the Red and Green wires? - each respectively to ground.

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#14 2013-03-08 08:10:05

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

Re: transformer measurments for V4

For dc resistance measurements you can leave the secondary wires connected,  there will be some resistance in parallel with the secondary,  but because the resistance is relatively high compared to the dc resistance of the transformer it will not make much difference.
  The primary should be disconnected.

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#15 2013-03-08 20:38:19

beedoola
Member
Registered: 2009-05-25
Posts: 58

Re: transformer measurments for V4

hangman wrote:

For dc resistance measurements you can leave the secondary wires connected,  there will be some resistance in parallel with the secondary,  but because the resistance is relatively high compared to the dc resistance of the transformer it will not make much difference.
  The primary should be disconnected.

I removed all the wires - prior to seeing this, on the OT.

For the Primary I got:

violet to orange - 58.3

blue to orange - 59

violet to blue - 116.4

And the secondary were all under 1ohm.

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#16 2013-03-08 21:54:34

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

Re: transformer measurments for V4

That is good, your measurements agree with mine in the first post.

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#17 2013-03-09 02:26:37

beedoola
Member
Registered: 2009-05-25
Posts: 58

Re: transformer measurments for V4

Do I measure the PT voltages while connected?

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