Ampeg Vh140c power transformer replacement

[Ratsapprentice]

Hi guys,

I’ve had a Vh140c running through an external step down transformer for years (I’m in the UK, and the amp is a US model)and would really like to be rid of it. But I’m having a very hard time finding a suitable 230v PT.

Any help would be massively appreciated.

[joecool85]

Hi guys,

I’ve had a Vh140c running through an external step down transformer for years (I’m in the UK, and the amp is a US model)and would really like to be rid of it. But I’m having a very hard time finding a suitable 230v PT.

Any help would be massively appreciated.

Any reason you want to get rid of the step down transformer?  If it is just to make it all simple and plug straight to wall, I would consider installing the step down transformer permanently in the amp rather than replacing the original transformer.  The reason being, unless you have the specs for the stock transformer, finding a replacement will be difficult.

[Ratsapprentice]

There are a couple of reasons:

1) I'd rather not have to use two switches to turn the amp on/off
2) Size - the S/D is quite bulky
3) Heat

I've not been able to find a step-down transformer small enough to reasonably fit into the cabinet.

What specs do I need? - luckily Ampeg have made both the manual and the schematics available for free.

I need a 3a 240VAC 50hz transformer.

Manual: https://ampeg.com/pdf/VH140C.pdf
Schematic: https://ampeg.com/support/files/Schematics/V%20Series/VH-140C/VH-140C%20Schematics.pdf

The transformer wiring is found on the bottom left hand side of page 7 of the schematic.

[phatt]

Hi,
   If the schematic is correct for your amp then it is already able to run on 120/240V.
You will need to change over the input wiring which is circled showing which taps.

WARNING;
If you do not have experience with this then don't try to swap it over yourself.
Doing so could destroy the whole transformer and blow the amp as well. i.e. smoke and flames.
Get a teck to do the change over.
Cheers, Phil.

[Jazz P Bass]

The transformer in the schematic specifically states "Export Model".
That is not what the OP has.

[phatt]

The transformer in the schematic specifically states "Export Model".
That is not what the OP has.

HUM
Yeah maybe you are right JazzP but the OP would be wise to check before spending money only to find it was a simple wiring swap.

That schematic shows both Local and Export Tx's wound with 2 winding's.
Local TX is tapped in Parallel delivering 120v while Export is the same TX but tapped in series giving 240V. (well that's how I read it?)
The note under Export Model implies the Tx is the same you just have to reconfigure the wire taps.
I'm not familiar with that particular amp but I do know that a lot of gear was wound for both 120/240.
Some older gear came with a rear panel mechanical switch usually next to the power cord and fuse.
But some gear had to be opened to access the taps.
Maybe *Ratsapprentice* could lift the lid and take a picture of the Tx.
Phil.

[Ratsapprentice]

Had a look inside it - it's all sealed underneath the two outside plates - no obvious way to switch it.

[phatt]

Wire taps won't be inside the Tx.

With power cord removed from wall, Follow the incoming Mains wiring.
the sequence will be something like this;
Fuse> switch> THEN look for a tag board or block connector with mains wires that also go to the Tx.

If the Tx primary has dual winding's then there will be at least 4 mains wires between the block con and the Tx. (not to be confused with the secondary wires)
You may even find the numbers on the schematic are also printed on the tags.

Like I said; Take a picture of that section of the amp and post it, that will speed up the answer much faster than us trying to guess it all. hint. 
Phil.

[g1]

Does the power transformer have 7 wires coming out of it?
4 of them should go to a board with a fuse on it (07-315-01).
Like Phatt said, take a close up picture of that board and post it.

[Enzo]

I read it this way.  The schematic doesn't say export model transformer, it points out the export model WIRING.

It does appear to be a wiring change.

[Ratsapprentice]

There you go.

[g1]

Looks like there is only 4 wires coming out of the transformer, 2 red (secondary) and white & black (primary).
So it's not the export version of the transformer and can't be changed by wiring.

[phatt]

Take it to a teck shop, they will know where to source a new Tx. while you are there it looks like you have NO MAINS EARTH. ouch!!!
The tecks can install a new power cord with Chassis EARTH.
These things can be a Death trap without an earth. 
Phil.

[Ratsapprentice]

Don't Worry - It's grounded!

Cheers for the help.

[phatt]

OK,,, if you say so but as there are only two wires exiting the mains cord (Brown & Blue) then it's highly unlikely that it is earthed.
Normally the Earth wire (Green and Yellow in my country) goes direct to chassis and bolted with a lock washer.
Another thing that may not be obvious is the use of Step down Tx's.
Although the 240v side is Earthed some units don't carry the Earth through to the 120v output and that can go unnoticed until someone gets zapped.

If it were my amp I'd be checking there was continuity between Earth pin on cord and Chassis. Only takes a quick check which could save your life.

The Earth pin/Chassis continuity is the first thing I check when I open an Amplifier.
Stay safe, Phil.
(Never rely on visual inspections)