Kit 34 at it again

[Richard]

Well John's near to you, but that looks like a fair price for a new transformer, do let us know how it goes

[jiten]

Hi, yes he is not far but it would be an imposition just for a technical exercise unless it adds to knowledge. I shall await the new transformer.
If anyone wants the old one, free to play around with, happy to send it on.
Best wishes,
Jiten.

[jiten]

Hi All,
Can I ask a couple of simpleton questions please?
I am waiting for the new transformer which should arrive next week.
We talked about a filter in the circuit but as far as I can see there is none. How would I identify one if there is one? Is it the smoothing applied by the the two 5U4s and the large capacitor C5?
Secondly, there was a query about the bridge rectifier. Should I change that anyway in case it is upsetting the transformer in some way? Is there any way to test it to ensure that it is not faulty?
Thanks.
Jiten.

[John Caswell]

Errr, why would it be an imposition, gaining of knowledge can only help everyone and and may save an expensive mishap.
The filter I guess that you are talking about is across the power line input, and usually consists 3 capacitors "X" and "Y " rated types. I think you will find a circuit in the FAQs by Richard, if not it can soon be drawn out for you, however in most cases it is only required if the power lines are noisy.
I cannot see any reason to change the bridge rectifier unless it is faulty or you require higher efficiency diodes.
Do not get into the disease of "changing things for changes sake"
I see far too many units where people have "changed all the capacitors" because they have read that it is the thing to do, and then find they they have screwed up.
Initially leave well alone, use the "if it ain't broke don't fix it" syndrome. You won't go far wrong.

John

[jiten]

Thank you John.
I am very happy to bring over the transformer and or amp to you if you have time.Postmortems were one of the best ways to learn though the politically correct brigade have virtually put paid to that now.
I usually don't work on Thursdays and Fridays. Alternatively, once I replace the transformer, I can then bring or post the old one to you.
I agree with the philosophy but there is also an element of " I am bored so maybe I could change X...." .
I am glad you help to keep me grounded.
Will be in touch once the new transformer arrives - and will hang on to the rectifier.
Best wishes, Jiten.

[bikerhifinut]

I hope your problems are solved jiten.
John C's words are those of wisdom.
Don't chuck the old transformer out, even if you don't need or want it, the lamination stack can be reused to wind another transformer for a different project.
I say this because I have a pair of Danbury mains transformers that are horribly noisy but could be rewound, and probably will be by a guy I know locally for a Single ended power amp project I have on the back burner.
£135 sounds a very fair price for a new replacement, I doubt you'd get a rewind for much less. And a lot cheaper than a new amp.
Slightly concerned though that it has failed, is this a known weakness with WD/WAD mains transformers? I know that the original supplier for my KT88 is no more I am led to believe? (Morite).

A.

[bob orbell]

Yes, I am with you on this one Andy, just because Jiten left it on for 24 hours, there must be a reason why it packed up, or is it like the SUT's that we have had problems with, a corroded joint?. BOB

[bikerhifinut]

yes bob i'd have been inclined to get the transformer looked at to see if the fault was one that could be rectified so to speak.
I see Amethyst have the info and engineer from Morite i looked at their website.
that's reassuring if we need any attention on our kit.

A.

[jiten]

Hi,
Amethyst. for information, they have all the world audio design transformer specifications.They are very quick and the transformer is already on its way.It might even have arrived but after a particularly hectic morning, I actually forgot to check with the post room to see if it had been delivered. Will look on Monday.
Second, I think after 10 years, the transformer failure could be just age though I am not sure what the normal should be. I am happy to deliver /post the old transformer to John or anyone else who is keen to open it up.
Of course if the new one pops fuses as well, then I really do have an issue......
Thank you all for your help and comments so far. Will try and fit the transformer as soon as I can.
For the biker ( push bike?) Hi-fi nut, thought you might like to know that I have recently cycled the death road in Bolivia. Interesting experience. It isn't often that you find an ambulance parked half way down the route just in case and guides telling you that they have enough rope to rescue you as long as you don't fall more than 500 feet! Beyond that rescue is only a technical exercise but I digress.
Best wishes,
Jiten.

[bob orbell]

Hi J, bikerhifinut is a motorcyclist, it is me that is the cyclist, with regard to your new transformer blowing fuses if there is a fault, be very careful, if you do have a fault on one the secondary's, it will not blow a 5 or even a 2 amp fuse, you will need to check voltages as soon as you switch on, I would start by fitting the new transformer, re-solder all the wires back on, and in the absence of a varyac, remove all the valves and check all secondary voltages with your meter at AC, be careful with the HT, it will be over 500 volts , then switch the meter to DC and see if the voltage is OK to the ECF80 terminals, all voltages will be over the stated because of no load, if all is well, put the valves in and check again. Hope this helps you. BOB