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Old 2nd September 2010, 01:57 PM   #1
divad68 is offline divad68  United Kingdom
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Default 240v to 220v

Guys, I've got a Yaqin MC-100B and after having read through a few threads on here I started becoming concerned as I believe my unit is designed to run on 220v, but in the UK our mains supply tends to fall somewhere between 230 & 240v. Mine usually measures around 235v. If it helps, I also tested the voltage across pins 4 and 9 of one of the 12AX7 sockets (with the amp plugged straight into the mains) and it read 6.6v and I think it's supposed to be at 6.3v? Don't for one minute assume I know what I'm on about...because in reality I'm new to it all and just read somewhere that this was a useful measurement to take (I didn't even know how the pins were numbered)!!

With this in mind I bought an APC Line-R 1200 Voltage Regulator, as that can be set to 220, 230 or 240v and the idea (I thought) was if I set it to 220v it will output that level. In reality what seems to happen is that it senses what the incoming voltage is and only if it goes above (or I assume below) a certain level will it actually regulate the output. So, with mine set at 220v it will spend half it's time indicating that the input voltage is 'normal' and won't adjust it at all, but when I test the output it's around 234v. Then I might hear it click and the indicator light on the panel will show the input voltage is' high'. In this circumstance I'd expect the output voltage to measure 220v, but it tends to measure around 205v!

So, to sum up, I don't think that the Line-R 1200 is actually doing what I want it to do because it doesn't continually regulate down to 220v, but only when a threshold level is exceeded and even when it does regulate down, the measured output is significantly lower than it ought to be.

Please can anyone advise what else I can buy that will be able to give me a reliable and (fairly) constant 220v? I've heard mention of 'buck transformers', but I'm not sure what they are and couldn't see any to buy when I put that term into Google.

As a side point, how can I be sure that my particular amp is actually designed to run at 220v? I'm pretty sure it is as they seem to be either 110v or 220v, but would prefer to be certain.
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Old 2nd September 2010, 02:45 PM   #2
Arnulf is offline Arnulf  Europe
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Old 2nd September 2010, 02:49 PM   #3
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It will work fine on that voltage. A buck booster is just a transformer that will make small voltage adjustments depending on how the windings are configured. It will fluctuate with incoming voltage. It is not a regulator. If your incoming voltage is pretty steady at 235 and you want to reduce the voltage with a buck booster then that would work. Common versions will adjust the voltage up or down 12/24 volts or 16/32 volts or 24/48 volts depending on the version and how the booster is wired. The windings are user configurable. You either wire it in series or parallel to get the low or high voltage and feed it in forward or reverse for boost or cut.

The amp should still run fine on that voltage anyway. Electrical appliances are designed to operate within a range without the need for stiff regulation.
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Old 2nd September 2010, 03:02 PM   #4
divad68 is offline divad68  United Kingdom
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Okay thanks for the responses. Maybe I am worrying too much, but I just want to be sure I'm not stressing-out the internal components (and possibly degrading the sound) when there's something I could do fairly easily to remedy the situation.

NB: Just checked again and the figures are now a little higher - voltage across pins 4 & 9 measures 6.68v and mains input voltage is reading 238v. Still okay?
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Old 2nd September 2010, 03:57 PM   #5
Arnulf is offline Arnulf  Europe
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Line voltage should be 230V +/- certain percentage of this value (+/- 5% minimum) according to EU regulations. Your reading is well within these limits. There is far larger variation among parts in your amplifier than there is in the line voltage. If your amplifier fails at 235V it would just as likely fail at 230V.
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Old 2nd September 2010, 04:16 PM   #6
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Living in another 240V country I can tell you that loads of 220V equipment blows up and tube equipment is worse off because of the higher secondary voltages.

Look at Rod Elliotts ESP site which has some good info on making a buck transformer.

sp
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Old 2nd September 2010, 04:33 PM   #7
kevinkr is offline kevinkr  United States
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Your filament voltage is about 5% high which is a fair indication that your amplifier was designed for something approaching 220V based on your measured line voltage.

I completely agree with stoolpigeon and suggest you make and use a buck transformer based on stories of overheating and melted power transformers in some Chinese made tube amps here and at other forums.

In this case I'd recommend a 12V/4A transformer installed in a small box with the appropriate mains input and output sockets - I'm thinking IEC 10A types..

The primary of this transformer will be wired in parallel with the incoming mains, the secondary will be wired in series with the hot side of mains between the input and output sockets. The neutral and ground will go straight from one socket to the other. If you use a metal box also connect the ground securely to the box.

Once completed check the output voltage, you have a 50% chance of having wired it correctly, if not just reverse the secondary connections and voila..

Please use a fused mains plug based IEC cordset as is standard in the UK to power the box, use a 4A fuse in the plug. Get one of those IEC cordsets with an IEC male on one end and IEC female on the other to power the amp - make sure it is rated for 240V mains.

You can find all of the parts very cheaply on eBay for this project including the box. For the transformer you can use either a toroid or an EI type which you might want to purchase from RS or Maplins.

I'm assuming you can solder..
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Last edited by kevinkr; 2nd September 2010 at 04:49 PM.
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Old 2nd September 2010, 04:49 PM   #8
divad68 is offline divad68  United Kingdom
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Quote:
Originally Posted by kevinkr View Post
Your filament voltage is about 5% high which is a fair indication that your amplifier was designed for something approaching 220V based on your measured line voltage.

I completely agree with stoolpigeon and suggest you make and use a buck transformer based on stories of overheating and melted power transformers in some Chinese made tube amps here and at other forums.

In this case I'd recommend a 12V/4A transformer installed in a small box with the appropriate mains input and output sockets - I'm thinking IEC 10A types..

The primary of this transformer will be wired in parallel with the incoming mains, the secondary will be wired in series with the hot side of mains between the input and output sockets. The neutral and ground will go straight from one socket to the other. If you use a metal box also connect the ground securely to the box.

Once completed check the output voltage, you have a 50% chance of having wired it correctly, if not just reverse the secondary connections and voila..

Please use a fused mains plug based IEC cordset as is standard in the UK to power the box, use a 4A fuse in the plug. Get one of those IEC cordsets with an IEC male on one end and IEC female on the other to power the amp - make sure it is rated for 240V mains.

You can find all of the parts very cheaply on eBay for this project including the box. For the transformer you can use either a toroid or an EI type which you might want to purchase from RS.

I'm assuming you can solder..
Thank you very much for that advice and those instructions. I'm okay at soldering, but I'll get a mate of mine who is much better to do that for me.
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Old 2nd September 2010, 09:49 PM   #9
piano3 is offline piano3  United Kingdom
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If you have any steady voltage off the wall in the UK you are very lucky! Mine varies from less than 200 to about 240 on a daily basis! And I am in London.........
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Old 2nd September 2010, 10:23 PM   #10
divad68 is offline divad68  United Kingdom
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Quote:
Originally Posted by piano3 View Post
If you have any steady voltage off the wall in the UK you are very lucky! Mine varies from less than 200 to about 240 on a daily basis! And I am in London.........
Less than 200, that's crazy and I'm sure it must be out of any acceptable limits that may have been set. I'm in London too and the highest I've measured so far is 239 and the lowest about 230, but it's usually around the 235 mark.
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