I would rather my amplifiers didn't blow up at all?
Ali Express 'clone' amps...great stuff!!
- Thread starter rontoolsie
- Start date
vacuum_tubes
pfm Member
I bought a LM-518ia direct from China for 1/3 of the UK price and then got a 240v to 220v step down from RS
It was surprising (but not unexpected) how much cooler it ran with the step down.
vacuum_tubes
pfm Member
It was £90 when I bought it in 2018 but looking now it's gone up to £160
Salamander
pfm Member
What do you think will happen? I've purchased 3 valve amps from China, all would be called cheap and never had a problem, I still use two of them.
Zombie
pfm Member
They probably have set up a small sleeping cell feeding you with subliminal propaganda just like the rightwing dictatorships in South Korea and Taiwan did in their time.
Salamander
pfm Member
The LM-518a are no longer easy to find now, guessing they are discontinued but hifi-amplifiers.com still have some in stock. If only I had the money this would be the amp I'd go for.
Is that the exact specification model of step-down transformer you purchased?
Salamander
pfm Member
I purchased my first China amp when living in Cambodia due to cost and availability, the only problem I have is the heat, but I have a fan blowing on it and everything is good.
I know what will happen, at first hand and the experience of my friends. They are designed for 220V, we run ge erally 240 here, so they get hot and the failure rate increases. Early Yaqin MC30s had a tendency to catch fire. Not all of them, but enough for people to notice. Mine never has done, but it fried its transformer and now has one with the correct 240 primary.
Salamander
pfm Member
vacuum_tubes
pfm Member
Yep that's the exact one I bought.
It's rated as 2.5A at 240v in so has power handling of around 600 Watts
The LM-518 has a power consumption of around 350 Watts so chose that one so it has plenty of headroom and won't run too hot in itself.
No, and nor did I. Both were bought SH. My replacement trafo cost £90 delivered, my pal is still running the original and accepts the higher repair frequency. One day his trafo will fry too, then he's into the same as me. The RS 240-220 above costs the same, the benefit is that it won't fry the internals or risk catching fire, and you can use it on other 220V rated stuff.
It's really easy for a repairer to fit a bucking transformer, and inexpensive for parts. They just have to know how to do the sums and wire it in, it's not especially obvious even if you know what's going on.
+1 for bucking transformers. I fit them all the time for clients
Are they inexpensive? ISTR that the bucking transformer can be a smaller one, provided it is able to handle the primary coil current, and so it needn't cost a lot. Do you have to put some sort of load on the bucking transformer secondary to give it something to do, or will it stabilise without that?
I've done the same to my China sourced gear, normally valve based as they're a lot more sensitive to the 253v mains I have here.
If you have the space and understand the wiring, it's quite straightforward and not expensive. I aim for 24v drop as a minimum. You can get custom wound trafos from someone like Tiger Toroids if you want an exact match. He can even put some taps in for you. A step down transformer is also an option.
You don't need a custom transformer. 30v from my mains voltage of 249 gives a nominal 219 so perfect. Valve amps are generally more sensitive because of the multiplier effect of high ht voltage-eg 10% on 400v = 440v which may be getting marginal for many valve circuits. Plus 10% on 6.3v heaters gives 6.93v which is higher than I'd want to run them. A good Toroid from eg RS will cost you around £30 then it's fitting charge or you do it yourself.
Ah, I remember now. So assuming your nominal input voltage is 240, the bucking trafo that you buy is a 240V primary, 30V RMS secondary, and you take the 30V off your measured input voltage which in your case is 249. If you buy a 20V secondary then it will take 20V off, so converting 240V to 220, is that right?
I have measured my voltage, I frequently get 250-253 when the maximum legal is 254, so taking 30 off as you do makes perfet sense.
24V off or 30V is also reasonable. I can live with slightly less than 220V input into a valve amp, I lose some power but my amp is EL34 push pull so at something like 30-35W nominal I can lose a bit of that and not notice.