transformer noise

[vitalstates]

I have just made some mods to son of rocky and my mains transformer has started to buzz/hum, loud enough to hear across a quiet room. The question is ....is this coincidence or the result of my mods.

After some advice I upped the first cap on the pi filter from 8 to 16 uf. Somebody at EF3 suggested that my parallel GZ32s were not in fact GZ32 at all but some direct heated valves badged as GZ32. I havnt a clue what they are but a number of people have suggested that 16 is a better value all round.

Can anybody suggest whether this change would cause a transformer to start humming.

I have been searching for references but all the obvious books seem a bit shy on valve rectification and would rather talk chapter and verse about solid state.

Regards

Ed

[NickG]

Morgan Jones and RDH4 are the places to read about this. There are a number of things that could be going on, my guess is the extra cap could be asking for bigger peak current from the TX, this could be inducing ringing in the windings. You may need to add some series resistance to damp the current spikes.

PSUDII is a good thing to use to play with this. What were you hoping to gain from the larger caps?

[pre65]

Hi Ed-when i was thinking of changing my Quad rectifiers i made a chart of the differences between GZ32/34/37.
according to the "chart" i have noted the max capacitance for GZ32 as-

16uf min 150 ohm
32uf min 100 ohm
60uf min 50 ohm

cant remember exactly where i got these values from but it was on the internet somewhere.

the GZ32 i got from Jibbles were russian equivilants but mine dont heat up for a few seconds after switch on so must (should) be indirectly heated.


Philip

[James D]

Youhave donetwo things that lead to bigger current spikes drawn from the transformer for shorter periods of time - this is causing magnetostriction in the transformer whichis making it buzz.

1)By parallel two rectifiers you have halved the series resistance between the transformer and first capacitor so the charge current is doubled and the rectifiers only switch on for half the time.

2) By doubling the first cap you have doubled again the current needed to charge the first capacitoragain extending the current spike in size and a bit in time

Magnetostriction is the effect of magnetic materials changing there size under an intense magnetic field - this new big curent spike required to charge the capacitor is causing this to happen every 1/100th of second in your transformer. This causes heating of the transformer so it needs dealing with.

I would go back to 8uF first cap.

James

[dave dove]

james

you are right of course
but
your cap across +ves idea
works a treat on buzzy txs

has to be a meaty cap though

dave

[vitalstates]

Many thanks for the info chaps....

Hi Nick

I wasn't trying to achieve anything specific but was just following general advice due to my ignorance in this field. I was drawn by the fact that the spec sheets for the rectifiers do specifiy a min capacitance which aligned with what I was told. btw I'm still finding MJ a bit of a struggle in places but I'm creeping up on him.

Hi James

I will go back to the 8uf as you suggest. I havnt heard any discernable change in sound with this mod. I am still at the stage of learning whereby if it works and/or sounds good it must be somewhere nearly right, but I'm still not on top of the mechanics of exactly whats happening so I'm a bit wary of stressing certain parts.

Regards

Ed

[dave dove]

ed

you're doing fine
there will always be
some dead techy
who can help us out
but you still have to listen

dave

[James D]

Spot on Dave.!

Keep on trucking Ed!

We can always give you five different flavours of explaination and tweaks

[Greg.]

Hi Ed,

I've followed up with Rob about your GZ32's. He is adament that your rectifiers are infact 5Y3G's.

I hope that helps.

Best wishes,

Greg

[steve s]

Originally Posted by Greg.

Hi Ed,

I've followed up with Rob about your GZ32's. He is adament that your rectifiers are infact 5Y3G's.

I hope that helps.

Best wishes,

Greg

Greg , Ed brought them around to my house and they looked exactly like 5y3's

..350 volt jobs..?


how the gz32's Ed...

steve