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Old 11th November 2012, 07:32 PM   #11
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Quote:
Originally Posted by vitalstates View Post
good thought, I will double check the rectifier wiring.
not just the wiring, if one of the diodes is gone its no longer a bridge and DC flows through the secondary ... may not even have a major impact on voltage/current readings ...
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Old 11th November 2012, 07:36 PM   #12
DF96 is offline DF96  England
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OK, measurements so far seem OK. It might have seemed a daft question, but it eliminates some possible problems.
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Old 11th November 2012, 09:22 PM   #13
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i ended up with a seperate ps for the 3 amp heaters on my gm70 amplifier as the alloy chassis got so hot. i use a 300va tx just for the heaters.
i built a pp sv811-10a amp years ago and still have low milage tubes so nice to see someone using these sv tubes, they look great on paper but are a bugger to use as i'm sure you know!
enzo
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Old 12th November 2012, 06:56 PM   #14
wfmali is offline wfmali  Europe
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Built with SV811-3 years ago as well and still use it. The example of this amp shows pretty good how complex a single ended design can get. But in addition to nice music it can help to stay in shape - if you lift the 50+ pounds from ground to the desk from time to time.

Even though I use the 382X as B+ transformer, the 372FX should be sufficient. If just the 372 would get hot, I would check wiring, rectifier and the transformer itself. An input power supply choke will buzz or rattle if it has any loose parts, such as laminations, and it can also make your chassis sing... But since your ok dimensioned heater transfomer gets hot as well...? Maybe some charts showing both transformer load currents can help...
Marcus
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Old 13th November 2012, 09:45 AM   #15
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thanks for the interest guys.

Current thinking puts the problem in 1 or more of 3 possibilities:

1. Both transformers(B+ and heater) have no insulating washers on the frame bolts...I am waiting for delivery of shoulder washers to see what effect these have.

2. I have 10 transformers in/on a steel chassis....many people have commented on the use of steel chassis and the perils therein.

3. The big mains transformers and one large choke are very close to each other which may give induction osmosis(my phrase, for humour).

I am starting with the transformer washers and will progress through the list if a solution is not found.

Ed
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Old 17th November 2012, 06:23 PM   #16
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I've bumped this up because I'm still scratching my head over this one....

I have taken both transformers off the chassis and run them on the bench with their secondaries in a screew block with nothing attached. i.e absolutely no load. I have a maplin wall meter which measures, among other things, current taken from the wall.

both transformers(ht: 0-600v 200ma spec & heater: 2x9v 12amp spec) consume 250ma at the wall and both get hot after 1 hour running no load. The ht transformer gets very hot.

I have very limited experience with transformers, to date all my Hammonds have worked as per spec, so I really don't know if this is acceptable or not. Certainly I don't feel happy running an amp with transformers that get this hot.

I'd be grateful for any further input. I'm still waiting for delivery of the shoulder washers to see if they have any effect.

Ed
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Old 17th November 2012, 07:15 PM   #17
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Are the primaries wired correctly?
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Old 17th November 2012, 08:52 PM   #18
wfmali is offline wfmali  Europe
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Interwinding fault? But on both at the same time?
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Old 18th November 2012, 04:38 AM   #19
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Hi Ed,

Some transformers do get hot regardless of load. It depends on the specified core-losses, and the rated primary voltage.

For instance, many transformers sold in the UK are rated 230V, (as per the UK supply spec), but the actual street hardware is still the old 240V supply we have had for decades. 240V into a 230V primary is usually OK, but a cheap or badly designed item, that already has high core losses at 230V, may get unpleasantly hot at 240V. Check your supply too - you my have 245V at your location.

My personal solution is to buy trafos from JMS, and specify 240V primaries. If you ask, they will specify the core losses and winding resistance for a given design, so that you can compare. With a 200VA (240V primary) and a 240V supply connected, you can expect core losses below 10W. Why not ask your trafo vendor for the rated losses for your parts, and we can then compare.

example JMS trafo, highly recommended 200VA split-bobbin design:

200 VA

These trafos work very well, despite low cost, but the appearance is somewhat industrial.

I am always willing to recommend a trafo for use with my Filament regulators, please ask at any time.

Last edited by Rod Coleman; 18th November 2012 at 04:48 AM.
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Old 18th November 2012, 05:02 AM   #20
AJT is offline AJT  Philippines
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Quote:
Originally Posted by vitalstates View Post
Is the loud buzzing the result of some interaction between all the transformers and chokes and the steel base. Would an aluminium base cure the problem?. The thing that confuses me is that the last incarnation didnít buzz/vibrate and the only thing thatís changed is one choke that used to be on top is now inside and 1 transformer that used to be inside is now on top.

Ed
i never used steel chassis for this reason....aluminum is easy to work with and does not interact with your traffos....

commercial traffos operate at higher flux densities, they have lesser primary turns and so can really run hot, especially when run at near their maximum ratings.....

that is the reason i design and build my own traffos, i run my traffos at less than 1T, some at even 0.6T, i have no heat issues as a result, i make them bigger than commercial offerings....

you can try to seat your traffos using acrylic....
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