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  #1  
Old 29th April 2022, 01:53 PM
Audiophill Audiophill is offline
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Location: Benfleet
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Default KEL 84 power transformer replacement

Hi all, my power transformer is really noisy and notice it more since I got got rid of the source hum, I have tried tightening the lamination bolts but noting changes, also tried some small rubber grommets under it but still noisy, I think I have found a replacement transformer but the heater supply is only 3 amp and it shows 5 amp on the schematic, would 3 amp be enough?
Many thanks
Phill
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  #2  
Old 29th April 2022, 02:31 PM
snowman_al snowman_al is offline
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Default Re: KEL 84 power transformer replacement

No 3 Amps is not enough. Looked at the valve spec sheets?
EL84 draws 0.76A each and the ECF80 0.43A each, so a total of 3.9A minimum.

With the existing transformer, is it quiet(er) if you remove the mounting bolts and rest it on rubber pads? Are the insulating washers present on the mounting bolts? Is it the end bell vibration, remove it and see if it is quieter? Is it still noisy with the valves removed?

I had to put plastic shims between the core and end bell and rubber mount the transformer to get my transformer quiet. See here
Quote:
Originally Posted by snowman_al View Post
Well the humming transformer is fixed.

As mentioned previously, I made a thin plastic gasket to go between the core and the top cap. I bought 4 longer bolts, 55mm, and some half (or locking) nuts. These I fitted under the transformer and nipped the bolts up just tight enough to stop the cap 'buzzing.

The remaining hum is when the bolt(s) touch the chassis. The mounting holes in my chassis were only just large enough for the bolt to go through. It was all but impossible to position the transformer without a bolt touching the chassis, so:

First I opened the holes up to 6mm so I could fit the hard plastic spacers to the chassis. I tried this configuration and it is very quiet, but still needed the under chassis nuts to be 'critically' tightened to get to a low level.

Next I tried four soft grommets in the holes. I had to open them up to 7mm this time. This needs the under chassis nuts to be changed for 'nylock' types as you only need to pinch the grommets a little. And its silent...

To ensure the transformer is earthed, I fitted a star washer on one of the clamp bolts and an earth lead under the chassis to the mains input socket earth.

I have included a few pictures here: https://goo.gl/photos/d6PHZjjv3C6PDCm67

Alan
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  #3  
Old 29th April 2022, 04:31 PM
Audiophill Audiophill is offline
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Default Re: KEL 84 power transformer replacement

Thanks Alan, will give it a try.
Cheers
Phill
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  #4  
Old 29th April 2022, 06:05 PM
A Stuart A Stuart is offline
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Default Re: KEL 84 power transformer replacement

Elsewhere on the forum (also, I think in the FAQ) there is mention of blocking mains DC for noisy transformers.
No idea if this applies to a particularly recognizable type of noise, and never had enough problem to get round to trying it myself.
Also high mains input voltage has been mentioned.

In both cases, I can do no more than pass on what I have seen others write.

Alastair
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  #5  
Old 30th April 2022, 10:50 AM
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Paul Barker Paul Barker is offline
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Default Re: KEL 84 power transformer replacement

Quote:
Originally Posted by snowman_al View Post
No 3 Amps is not enough. Looked at the valve spec sheets?
EL84 draws 0.76A each and the ECF80 0.43A each, so a total of 3.9A minimum.

With the existing transformer, is it quiet(er) if you remove the mounting bolts and rest it on rubber pads? Are the insulating washers present on the mounting bolts? Is it the end bell vibration, remove it and see if it is quieter? Is it still noisy with the valves removed?

I had to put plastic shims between the core and end bell and rubber mount the transformer to get my transformer quiet. See here
Nice photo record of a good job done.
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