Why did my TX Burn out Help

[colin.hepburn]

Why did my TX Burn out Help
OK as most of you will now known my ASK JAN TX burned out on my JE EL34 Amp Build this was discussed in a earlier thread so will cut and paste only what I think is relevant to this so to try and not repeat old ground to much
Ask JAN TX TRA 400 SPEC
Multipurpose 200 VA transformer
Secondaries:
2*270 V 0,2 A
2* 50 V 0,2 A
6,3 V 2 A
5 V 2.5 A
6,3 V 7 A

B+ secondaries can also be connected in parallel for use with a rectifier bridge. The 50 V secondaries can be used for biasing or in series wit hthe 270 V secondaries to get a 320 V plate supply.
Ok so this TX can be used in three different configurations
270-0-270@200mA
320-0-320@200mA
640 Bridge rec@200mA
For the JE Amp used 320-0-320v using the following wiring see image

So we are requiring 640CT @200mA using full wave Rec
However if wired in this way in series doesn't this half the current to 100mA and what about correct phasing
Copyed from old thread
Paul wrote

it is a 540vct not 270.

You can bridge rectify the whole 540v winding but it is only rated at 100mA in that case. When a transformer secondary is centre tapped the designer knows that only one leg is to pass current at a time so the expected power demand is 54 watts. You would design your core size and your primary winding wire diameter to cope with that and you would also determine your underwind of the primary for regulation based on 54 watts.

So if you then take constant current from the full winding you can only expect the core, primary and underwind for regulation to cope with 100mA to maintain the 54watts.

As you go over noise, heat, and voltage drop ensue, excessive overdemand leads to fire


And Nick Wrote
You have loads of options there, In fact in real terms, you can describe the TX as a 540v CT @ 400ma, because each winding is rated at 200ma. And with the extra windings it could be used as a 640v CT @200ma

Paul was describing what you would get if you went to a winder and asked for a 540v CT @200ma secondary.

So you have more than enough options there to give you a supply for a 2a3 amp.

You could use SS diodes, or the 2.5A 5V for a GZ34 rect, or the 7A 6.3v for a pair of damper diodes.

[pre65]

Colin, you are flogging a dead horse.

The answer may lie in doing the tests Paul suggested using the 1R resistor.

IF those tests don't unearth a problem then perhaps the Ask Jan transformer just died and was "one of those things" ?

[colin.hepburn]

No I don't see the problem the answer I am looking for is what is the current when the ask Jan is wired as per the image in the post
Here is a email from Jan I got today doesn't seem to help
Colin,

please refer to the numbering on the transformer, it is really not
difficult to understand.

The numbering gives the windings in the order of beginning and end so
for example (JUST an EXAMPLE)

4-5 :270V means Pin 4 is the beginning, Pin5 the end of a 270V
winding.

The current rating of the transformer (200mA) is for ohmic load ac
given, this is how its done in Germany.

I know that the Amercians rate the transformers as DC after the
rectifier. Which means that 200mA AC result in about 120mA DC rating.

Please take care of this.


But a burnt TRA400 with a SE KT66 which I assume to run at about 60-
80mA is more than strange, I assume you made something wrong.

I suggest you search for possible counter-phase series connected
windings, those will heat up the transformer. You will find this out
by measuring voltages in idle.

properly series connected results in addes, counterphase connected
results in substraction of voltages.

Let me know if this works out.

[pre65]

So, has Ask Jan given you the answer ?

[colin.hepburn]

ok you explan it them

[pre65]

ok you explan it them

Well Colin, as the transformer is dead you can't measure the voltages on each winding.

Are you absolutely 100% sure each winding was wired up correctly ?

[Paul Barker]

From the above spec Collin the 270v windings are each rated at 200mA and so are the 50v windings so if you full wave rectify the four all joined together in series that is also 200mA rated according to what they have said.

However when he talks about windins bucking what he means is if you connect one of the windings back to front. This will give you the wrong voltage, it will actually subtract rather than add it's voltage, so you should soon discover such a mistake. they are saying this would be a possible cause of the failure.

I think it is more likely that the failure was elsewhere and the transformer was the casualty.

Thank you for finding and printing faithfully the British way of designing a power transformer which I wrote about. this is different to what the spec's above imply. If you look at any British centre tapped transformer you will see that the entire winding has a current spec. that is a spec as I described above. whereas the transformer you had is given a number of stand alone windings which are each spec'd as if they might all be used independently of each other. This transformer would have a suitably sized core and primary guage wire to provide for such use.

This was probably a very good transformer which broke.

Because of size and weight constraints and now that we have a so called harmonised 230v nominal voltage (which is a lie we have higher voltages) most power transformers are operating very near saturation. So for audio quality we need to over spec, and in my opinion we always should ask for overwinding of the primary so that the transformer is quiet at your actual voltage which can be anything from 240 to 270v. So you specify a +5% and a +10% primary tap, and always use it. you can take one of the secondaries and add it into the primary (careful of phase) to do the same job (although it will bride your screen, if you have one). Your secondary voltages will drop but you will have a quieter transformer and better quality as the core is kept from saturation.

You would be amaised how much difference it makes to the quality of an amp to ensure the power transformer core is well away from saturation, and when using valve rectification windings of equal length and resistance sound very much better especially in bass (on a single ended amp). all of these things I have experimented with and heard when I wound my own transformers.

[colin.hepburn]

Paul Wrote
From the above spec Collin the 270v windings are each rated at 200mA and so are the 50v windings so if you full wave rectify the four all joined together in series that is also 200mA rated according to what they have said.

Thank you Paul
This TX has caused me and other s so much confusion over the wiring configuration I kept thinks I was halving the current to 100mA with this wiring diagram wiring it this way gave me from memory a no load of 744volts AC on my steady 241 main

I wanted to make sure I had it wired up correct for the 200mA as I a going the get another one from Jan at a price of £62.00 including shipping from Germany seems like a good deal

if it don't burn out
PS I did ask him if he would email me a schematic of all the wiring configuration but he doesn't seem too keen to do this It would save me a lot on stress to

[pre65]

Colin, can you draw out EXACTLY how you had the windings connected ?

[colin.hepburn]

Colin, can you draw out EXACTLY how you had the windings connected ?

Philip
The two images at the top of this thread show you just add the full wave rec

[pre65]

I know from experience that sometimes errors are made when wiring things up.

We can check, recheck and recheck again and it can take ages to spot a simple wiring error.

So, I did't ask how it should be wired up, but how you actually wired it up.

[colin.hepburn]

I know from experience that sometimes errors are made when wiring things up.

We can check, recheck and recheck again and it can take ages to spot a simple wiring error.

So, I didn't ask how it should be wired up, but how you actually wired it up.

yep thats what i meant Philip i wired it that way thats my wiring the images is showing my wiring not how it was wired

[Paul Barker]

Colin your no current secondary voltage shows two things. That you hadn't bucked the phase, and secondly that the primary is underwound for your mains. this is a problem. I would add a low voltage secondary to the primary, in phase to get the correct secondary voltages, because this will ensure that the core doesn't saturate.

My voltage is 240 aswell, as is most of Britain but I meet people who report 270 volts consistently. that would kill a lot of components.

[colin.hepburn]

I know from experience that sometimes errors are made when wiring things up.

We can check, recheck and recheck again and it can take ages to spot a simple wiring error.

So, I didn't ask how it should be wired up, but how you actually wired it up.

yep thats what i meant Philip i wired it that way thats my wiring the images is showing my wiring not how it was wired

OOPs wrong image should be this one and this one

[colin.hepburn]

Colin your no current secondary voltage shows two things. That you hadn't bucked the phase, and secondly that the primary is underwound for your mains. this is a problem. I would add a low voltage secondary to the primary, in phase to get the correct secondary voltages, because this will ensure that the core doesn't saturate.

My voltage is 240 aswell, as is most of Britain but I meet people who report 270 volts consistently. that would kill a lot of components.

Hi Paul
Thank for this info i think i will email Ask Jan and see if he will beef up the primary before i order a new one from him
Paul could you confirm if i have the wiring for bridge rectifier use ov to 640v
Hi All
Ok then thanks to Paul
The wiring misunderstanding for 640CT@200mA all windings are connected in series
Same for 540CT @200mAsame but leave the two 50v winding out
Ok good that's two out of the three ways then
Now we want 640@400mA Bridge rectifiers
Right to get this we wire up the winding in parallel correct
See posted image pleas to confirm if I have this right
Thank you