Hot transformers on valve amps

[bumpy]

I have owned valve amps where mains and output tranny get very hot and others where they run cool. What is it about the design that makes this happen?

[Firebottle]

With the hot ones it could be that they are being used close to their loading limits. The design of a transformer usually allows for a 60 degree rise in temperature above ambient.
It is also dependent on the quality of the steel used for the laminations, better steel result in lower eddy current losses, and reduced temperature rise.

:)

[struth]

Never had any get that hot. warm maybe but not hot

[RothwellAudio]

A perfect transformer wouldn't dissipate any power and wouldn't get hot at all, but in the real world copper windings have resistance that does dissipate power and current flows within the core and dissipates power. The more current that is being drawn from the secondary windings, the more power is dissipated by the non-ideal transformer elements. The valve heaters take a lot of current, so the more vales there are the more heat is dissipated in the transformers. Also, of course, the valve heaters are getting hot (the clue is in the name :) ) and that heat often travels through the chassis and into the transformers by conduction.
Having huge transformers with thick wire helps a lot to keep them cool.

[martian sunrise]

Can I hijack this thread, please?

I have been listening to music all day (DAC > Croft Vitale > firebottle air > tannoy eaton) and the power has just gone and the CB has tripped. I switched it back on and the Croft is dead. No power light, the transformer is roasting and it smells bad.

Could the amp have cause the power to go, or has the power cut caused he amp to die?

Can someone help? I have no idea about electrics!

[Arkless Electronics]

Can I hijack this thread, please?

I have been listening to music all day (DAC > Croft Vitale > firebottle air > tannoy eaton) and the power has just gone and the CB has tripped. I switched it back on and the Croft is dead. No power light, the transformer is roasting and it smells bad.

Could the amp have cause the power to go, or has the power cut caused he amp to die?

Can someone help? I have no idea about electrics!

If the transformer has failed or a failure elsewhere has caused the transformer to fail then yes it can get very hot indeed and eventually go short circuit and blow the fuse and/or breaker. We're talking well over 100C hot here.... It was common problem with MF MA50 monoblocks and to a lesser extent with the A1 but they not only ran very hot anyway but also ran the transformer at the limit (or a bit more) of it's ratings.... Molten plastic where the plastic insulating tape was wound around the toroid was the norm.

Replace the fuse/s remembering probably a 20mm one in IEC inlet and switch it on. If the fuse and/or breaker immediately trips then it is very likely the transformer if it was getting smelly hot... I would not expect something like your Croft to tax the transformer anywhere near that extent so if it is the transformer then it's probably a random failure or a failure of another part which has put an overload on it.

[martian sunrise]

Great - thanks Jez.

[martian sunrise]

Ive checked the fuse in the amp and it does not look blown. However, with only the kettle lead in the amp (nothing else!) when I turn it on/off, there's a clicking in the speakers. What the dickens is this sorcery?

[anthonyTD]

What about the fuse in the plug itself, have you checked to see if that one has failed ?
Ive checked the fuse in the amp and it does not look blown. However, with only the kettle lead in the amp (nothing else!) when I turn it on/off, there's a clicking in the speakers. What the dickens is this sorcery?

[martian sunrise]

that is next on the list! it is difficult to get to, so I will need to do when I have the patience this evening.

[martian sunrise]

I swapped the fuse for no charge at all. Oh well, it off to the workshop.

[Lawrence001]

Could have been the valves?

Sent from my NEM-L51 using Tapatalk

[Arkless Electronics]

No. Not in a pre-amp.