230V - 120V step down converter

[funkyjazz]

Hi all,

I am in the process of buying a vintage amp from the US which runs on 120V and it is a 55W all tube amp.

I live in europe and so need to step down from 230V to 120V at which the amps runs to.
I found this: link

It is 800W so it is very conservative but I might buy later other amps from the US which need higher power.

Is it ok? Is there anything else I need to look at?

Edited February 1, 2022 by funkyjazz

[itu]

As you have done exactly right, it is wise to buy some headroom. A 55 W tube amp may consume quite a lot more power than the mentioned amount. I checked a 50 W MESA tube amp, and its power consumption is around 200 W according to its specs.

[RhythmJunky]

Another option might be to get somebody to change the input transformer for you to a 240v.

 

I've only ever done it on a solid state amp, which was pretty simple, but it might be a bit more complex on a valve amp with the heaters etc.

 

BTW the power reading on the back of the amp is possibly the consumption rather than the output, which is typically about 1/2 the consumption (roughly).

 

Finally, you might be able to run it off a big yellow transformer like the ones builder's use. These are fairly cheap and powerful, but don't leave it plugged i when you're not using it or your electricity bill will rocket 😉 

 

[BillyBass]

1 hour ago, RhythmJunky said:

.

Finally, you might be able to run it off a big yellow transformer like the ones builder's use. These are fairly cheap and powerful, but don't leave it plugged i when you're not using it or your electricity bill will rocket 😉 

 

Those big yellow trannies weigh a ton. They are also 110V not 120V though that might not be a problem, I'm guessing American kit is designed to accept a fluctuating voltage and that 110V would be fine.

[nekomatic]

The transformer @funkyjazz linked to looks professional, but I’m pretty sure it’s an autotransformer not an isolating transformer. That means it’s possible that up to 240 V AC relative to earth could appear on one side of the 120 V output under certain fault conditions e.g. live and neutral swapped in the socket, or neutral gets disconnected. That won’t blow up the vintage amp by itself but it might be a hazard if you touch something that’s not adequately insulated for the higher voltage. 
 

I was also wondering whether a ‘site transformer’ as @RhythmJunky suggested would be a good alternative, as they isolate the output from mains and (as I understand it) tie it to earth via a centre tap instead so that the maximum line or neutral voltage on the output is only 55 V relative to earth. But when I looked one up I found a comment that they aren’t suitable for powering US kit because it might short out one of the 55 V windings. So in summary I don’t know and would wait for someone with actual experience of vintage US amps to comment 😁

 

I’m sure this subject has been covered on coughTalkbasscough though, it might be worth searching or asking there. Also re the safety of the vintage amp itself, apparently there is something known as a ‘death capacitor’ that you need to make sure is removed - again I’m sure a forum or web search will tell you more. 

[funkyjazz]

Thanks!
I am trying to find out about the "death capacitor"
Found out that thomann sells this which is purposedly built for tube amps.

Anyone?

[ossyrocks]

I’ve run vintage USA amps in the UK on a transformer like the one from TAD for 30 years without issues. Just get that one.

 

More importantly, you need to make sure the amp has a modern grounded “three prong” US plug on it, wired correctly, and the death cap removed. This bit is important.

 

After that, if the electrolytic capacitors are original, consider changing those at the earliest opportunity. They have a finite lifespan and could fail at any time.

 

Rob

[funkyjazz]

and I guess the death cap should be removed by a technician since it is dangerous to do by inexperienced folk like me?

[ossyrocks]

1 minute ago, funkyjazz said:

and I guess the death cap should be removed by a technician since it is dangerous to do by inexperienced folk like me?

If you are at all uncertain how to do it, then yes, get it done by a tech.

 

However, I did buy an amp last year, which had purportedly been serviced by a tech. He had replaced the mains lead with a three prong, but he’d wired it as original, keeping the ground switch and death cap. I found this quite amazing really. But I found this before ever even switching it on, and was able to wire it correctly myself.

[funkyjazz]

Actually since I read in the description:
"This amp was recently serviced and received new power tubes, preamp tubes, new filtercaps, 3-prong cord and any caps/resistors that were out of specs."

There is a fair chance that the death cap has been removed already, isn't it?

Edited February 2, 2022 by funkyjazz

[ossyrocks]

13 minutes ago, funkyjazz said:

Acatually since I read in the description:
"This amp was recently serviced and received new power tubes, preamp tubes, new filtercaps, 3-prong cord and any caps/resistors that were out of specs."

There is a fair chance that the death cap has been removed already, isn't it?

Perhaps, but it’s worth checking. Just look at the ground switch, the cap will be visible if present. Often the ground switch is left there, with the cap removed, and the mains leads are hung off the lugs as it’s convenient to use it for this purpose. Post a pic here when you have it in hand.

[funkyjazz]

unfortunately the offer I have expires in a few hours. I guess I have to trust the seller if he answers or anyway do it once it arrives. I guess I can find instructions online.

If I understood it is removing the cap and soldering the ground of the power cord to the chassis. Maybe little bit more but doable with some care

[ossyrocks]

I wouldn’t hesitate to buy it over this one minor thing. It’s very straightforward to put right 

[ossyrocks]

Ok, so the polarity switch on the front of vintage Ampegs IS the equivalent of Fenders ground switch, so if there's a cap in there, that's what it will be connected to. I'm back home now, so will have a look for a schematic.

 

Rob

[ossyrocks]

Here's the schematic. There's a .047 600v cap to ground off the Polarity switch (look bottom right of the schematic), this needs to be removed. Simply clipping it off is good enough. Then you need to make sure that the LIVE goes straight to the fuses, on to the mains switch, and on to the mains transformer. You can hang the wires off a single lug of the switch, just using it like a tag strip. The neutral needs to go straight to the mains transformer too and can be also hung off another single lug of the switch. Wired correctly, the switch will have no function at all except to be a convenient placeholder for the wiring, and it won't matter what position the switch is in, as it will not function as a switch. A simple visual inspection will confirm if this has been done, and if not, it's a ten minute job for anyone who knows what they are doing.

 

Rob

 

 

[funkyjazz]

great thanks!

[Downunderwonder]

6 hours ago, ossyrocks said:

for anyone who knows what they are doing.

I don't reckon that should include the OP figuring he can follow instructions!!!!

[Woodinblack]

Cant you just get the uk transformer to replace the US transformer for it? they are commonly available - generally not the cheapest things, but a lot less hassle than dragging a transformer around waiting for someone to plug it in the wrong place.

[BassmanPaul]

Here in the far north of America, Canada, we run nominally at 120V.  In the US I've seen anything from 110V, 115V 117V and 120V I think maybe dependant possibly on what State the location is.

 

I had the opposite need, a 240V out from a 120V in. This is what I came up with - it outputs 240V @ 5A:

 

 

[BassmanPaul]

2 hours ago, Woodinblack said:

Cant you just get the uk transformer to replace the US transformer for it? they are commonly available - generally not the cheapest things, but a lot less hassle than dragging a transformer around waiting for someone to plug it in the wrong place.

That would destroy the amp's value as a vintage piece.

[Woodinblack]

2 hours ago, BassmanPaul said:

That would destroy the amp's value as a vintage piece.

 

OK, I missed that, I thought it was an amp for use.

 

Obviously if you kept the old one you could swap it back.

[agedhorse]

The good news is that it's a 120V, 50/60Hz transformer so a step-down transformer will work just fine.

 

That replacement power transformer in 230V is going to be an expensive part, and in a vintage amp will probably reduce its value to a collector.

 

[Downunderwonder]

If I was a collector I would still want to play it once in awhile and having the local market transformer would make it more valuable. I would think of it as converted to the export model same as the rest in Europe that weren't private imports, fully reversible for anyone that only wants to look at an amp and admire it.

[funkyjazz]

Someone told me it is maybe possible to rewire the transformer to accept 230V instead of 120V. Anyone knows whether this could be done on an Ampeg B25?

[ossyrocks]

22 minutes ago, funkyjazz said:

Someone told me it is maybe possible to rewire the transformer to accept 230V instead of 120V. Anyone knows whether this could be done on an Ampeg B25?

I know Fenders of that era can’t be done. 
Again, you’ll be able to find out when you look at it. There may be multiple unused primary taps and if there are, then you just need to find out which one is 240.