Hot Rod Transformer Question

Psygoat

Hi.
I have a Fender Hot Rod iii in for repair, with a blown mains 230 V transformer.
The problem is that the replacement I have bought from Hot Rox UK has different colour coding and I'm a bit unclear as to how to wire it up, as the colour coding is different.

I am waiting to hear back from them, but I was wondering whether anyone could shed any light on this in the meantime.

Cheers

This is the info that Hot Rox provide, with my notes  -

Viol Thermo to CP11
Viol Thermo to CP6
0V Black to CP7
230V White to CP25
240V Grey to CP13

Firstly – there are 2 violet wires – one of which goes to 230V and the other joins to the second coil in the transformer.

As I look at the transformer the order of the wires, from one end to the other are – violet – violet – grey – white – black.

How do you tell which of the violet wires is which? Which one goes to the live? Or doesn’t it matter?

Also the black wire is marked 0V on the box and in the listings.
When wiring up transformers which have 2 primary windings connected in series, 0V usually goes to the neutral. On this transformer does the black wire join to the first coil instead?
That’s what the specifications seem to be saying.

If I wanted to use your transformer as a 240V transformer, the grey wire would then go to the neutral, Is this correct?

jpfamps

I expect the violet wires go to an internal thermal fuse.

On the original there is one violet wire and red/black wire to signify the thermal fuse connection and the start of the primary windings, but this transformer seems to have the thermal fuse on two separate connection.

If this is the case then there will not be continuity between the thermal fuse and the primary, which is easy to test.

Transformers don't know which way around they are wired so you can connect the primary in either orientation.

It looks for 240 VAC operation you will connect the black and grey wires to the mains, and leave the white wire disconnected. Either orientation is fine.

When presented with a transformer I'm not 100% certain of I will test it on the bench by applying an AC voltage to either the primary, or 6 VAC to the filament wiring and measure the voltages. This is obviously potentially hazardous.

I would also advise using a current limiter when energizing the amp after fitting the transformer. I use a light bulb in series with the load.

Cocking the mains wiring is not something you really want to do.

 

Psygoat

Hi. Thanks for your repsonse.
The  2 violet wires are for the thermal fuse. I am making the assumption that you can see which end of this coil is which from just looking at it. - ie the violet wire nearest the end is the start of that coil and the one towards the middle is the end of it.
What is confusing is that the black wire which in the spec says 0v doesn't go to the neutral but according to them, joins to one end of the primary coil with the thermal fuse in it.
I know this is hard to visualise... I'm not explaining it very well !!!

ICBM

Curious as to why you didn't get one from Fender...?

Psygoat

Hi ICBM.
We just googled a replacement. I seem to recall having trouble getting Fender spares in the UK without an account. So I had to go to Fender and then to Allparts, I think it was. TBH I didn't check to see if anything had changed.

RiftAmps

ICBM said:

Curious as to why you didn't get one from Fender...?

Even more curious as to why the OP can't hook up a new PT with v.simple Primary and Secondaries. A competent tech would be able to work this out quite easily.

My first port of call would be to obtain both the correct schematic and the TX datasheet, then cross reference each wire.

A few questions:

1. What 'Hot Rod'? - Deville, Deluxe etc?
   
   
2. How did you diagnose a blown PT? What steps did you take to verify this?
   

Psygoat

Hi. It's a Hot Rod Deluxe III.
The amp didn't power up.
If I measure resistance between the violet on the primary and the next tap (black/red) it's open circuit so the thermal fuse has gone.
If it was that simple I would have done it by now.  All it is, is that I'm a bit unsure about the info that I've been given by the supplier and wanted to double check. The colour coding is completely different and it's an expensive mistake to make.

jpfamps

Psygoat said:

Hi ICBM.
We just googled a replacement. I seem to recall having trouble getting Fender spares in the UK without an account. So I had to go to Fender and then to Allparts, I think it was. TBH I didn't check to see if anything had changed.

Or rather Noparts.

Fender spares can be hard to get from Fender too.....

Psygoat

"No parts"

Ha ha ha ha - very good !!!!

ICBM

We call them "Bugger-All Parts" .

Fender have been fine to get transformers from, for me - but the last one was probably a couple of years ago. Fender transformer failures are relatively rare compared to some other companies I can think of...

Psygoat

I'm going to have to talk to Hot Rox first and try and get a diagram, then I might have to go to Fender.
We'll see. Thanks for your time.

jpfamps

ICBM said:

We call them "Bugger-All Parts" .

Fender have been fine to get transformers from, for me - but the last one was probably a couple of years ago. Fender transformer failures are relatively rare compared to some other companies I can think of...

Fender have been a total shower recently, I think ,mainly as a result of relocating their entire European operations to East Grinstead (a friend of mine is convinced there is some link the Scientologists. There new US office is a couple blocks away from the Scientologists too!!).

I think they are getting better, but getting parts has still been a pain.

My main requirement for Fender transformers is from people who have relocated from North America.

ICBM

jpfamps said:

My main requirement for Fender transformers is from people who have relocated from North America.

Strangely enough I can't remember being asked to do a single one like that. Several Mesas though... which is much more of a problem.

Psygoat said:

I'm going to have to talk to Hot Rox first and try and get a diagram, then I might have to go to Fender.
We'll see. Thanks for your time.

It should be very easy, you just need the thermal fuse connections and the full 240 winding. You can connect the two together using the joined terminals that are meant for the 120V connection in the original, and one of the spare unconnected ones for the 230V. There are more than enough on the board.

Have you tested the original transformer with the thermal fuse bypassed?

Psygoat

Hi. i could try running the original transformer up on a variac and seeing if it will go. The thermal fuse is a safety feature so I'm not that happy leaving it out, It will allow me to see if there's any problems anywhere else, so that could be a plan.

Psygoat

I reckon I've worked it out now - thanks for your help.
I've heard that it's better to run these on at 240 V rather than 230 V, Can anyone confirm this?

ICBM

Psygoat said:

I reckon I've worked it out now - thanks for your help.
I've heard that it's better to run these on at 240 V rather than 230 V, Can anyone confirm this?

Yes.

Psygoat

Cheers. Now I've figured out what's happening its really simple. D'oh !!!
It's just one of those days !!!