Fender 68 custom vibro champ reverb - voltage

Modulus_Amps

Ok, then you have to find the push on terminal that corresponds to the 240v tap if it has one, it will most likely be on the same winding as the 230v tap so you will be able to measure a resistance between the two.

First thing is to measure all the push ons and determine which has a connection to the primary side of the transformer. Then you have to work out which one is which. The neutral connection will be common to them all. Some photo's of your amp may help.

ICBM

I’ve seen some photos online, but it’s difficult to see - it’s quite densely packed.

The standard Fender colour coding is a white with a black stripe wire for 230V and a plain black for 240V, so if you can see those you can check the voltages on them - the 230 will show the supply voltage and the 240 will be about 10V higher - but there are exceptions, so don’t just go swapping those two unless you’re sure.

godders

Thanks both, like you say ICBM it’s all a bit bunched up but a couple of pics here: https://imgur.com/a/xAEj6ff

I’ll break the dmm out tomorrow and check voltages on those taps.

Modulus_Amps

Check resistances first, no power. its safer

idiotwindow

godders said:

Thanks both, like you say ICBM it’s all a bit bunched up but a couple of pics here: https://imgur.com/a/xAEj6ff

I’ll break the dmm out tomorrow and check voltages on those taps.

I have this amp. I'll be interested in what you find out. Thanks.

godders

idiotwindow said:

godders said:

Thanks both, like you say ICBM it’s all a bit bunched up but a couple of pics here: https://imgur.com/a/xAEj6ff

I’ll break the dmm out tomorrow and check voltages on those taps.

I have this amp. I'll be interested in what you find out. Thanks.

I’ll update later. 

godders

Resistance:

Black - black/white - 2 ohms

White - black/white - 2 ohms

Black - White - 4 ohms

https://imgur.com/a/FXQe7xB

I (carefully) measured voltage as well and it's exactly the same on all 3 connectors (239v)?

https://imgur.com/a/NMg4uRS

Does this mean it could be a different coloured terminal on this amp?

BTW when I contacted Fender although they wouldn't give a me a schematic they did confirm it's possible to convert this amp to 240v (thank goodness for the Aussies eh?).

ICBM

Measure the resistances from the purple to the white/black and the black. If it's the standard colour scheme the white is the 220V tap, not the neutral.

You need to have the connectors on the PCB to get the voltage readings - you'll need to poke the tip of the probe sideways against the metal - otherwise the transformer isn't in circuit and all the voltages will read the same as the input.

The white/black is definitely the 230V tap, if it's on the terminal connected to the inrush limiter (the round black thing).

godders

Ok so resistance from purple terminal as follows:

to Black - 35R

to Black/white - 34R

to White - 32R

So presumably that means white = 220v tap, Black/white = 230v tap and Black = 240v?

I'm a bit confused by the voltage readings but probably just my ignorance:

Black/white - 1.3v(?!)

Black - 7.6v

White - 11v

godders

Any thoughts on the above?

ICBM

I don’t know what you’ve measured to get those voltages, but the resistances look right. It looks like the standard Fender colour coding.

godders

ICBM said:

I don’t know what you’ve measured to get those voltages, but the resistances look right. It looks like the standard Fender colour coding.

Thanks a lot for your help, much appreciated.

godders

Measuring voltage on taps:

Modulus_Amps

Move your voltage dial to 600v setting not 200v

if you have 240v going into the 230v tap, you should measure a lower voltage on the 220v tap (white)

godders

Modulus_Amps said:

Move your voltage dial to 600v setting not 200v

That just moves the decimal point to the right (so I get 001, 007 & 011).

Modulus_Amps

What are you measuring between? those values don't make sense

godders

Modulus_Amps said:

What are you measuring between? those values don't make sense

Sorry, I was having a moment and had the black probe grounded to the case. Correct measurements are:

Black/white - 236

Black - 246

White - 226

So presumably ICBM is right and the 240v tap is black? So swap black/white and black (entirely at my own risk, obviously)?

ICBM

Don’t use the chassis for mains voltage measurements - at best you’re measuring to earth not neutral (not necessarily the same potential) and at worst there may be ‘partial ground lift’ diodes in between the two which will give completely spurious results.

But yes, white/black is 230 and black is 240, so swap those.

godders

ICBM said:

Don’t use the chassis for mains voltage measurements - at best you’re measuring to earth not neutral (not necessarily the same potential) and at worst there may be ‘partial ground lift’ diodes in between the two which will give completely spurious results.

But yes, white/black is 230 and black is 240, so swap those.

Thanks again to you and @Modulus_Amps .

godders

Mod done and had a good play this morning. I won't pretend there's a huge differnence in sound (wasn't expecting one) but good to know my valves aren't being cooked!

Pretty sure the top of the amp doesn't feel as hot having been on for a couple of hours.