Hammond Transformer Voltage selection- need ideas

[m3moser]

I have an amp that is using one of the Hammond Universal voltage transformers and I want to be able to switch it from 120 volts to 220 volts.  Is this going to be possible with a double pole style switch?
   I don't need to get all the voltage options like with a multiple pole selector switch, just two different voltages.  I attached the diagrams from the Hammond site.  Any thoughts??

[sluckey]

Why do you want to use 220? If you are in the USA, 120/240 is the standard now.

Switching between 120 and 220 would be tough. A standard double pole switch can't do it. However, switching between 120 and 240 is very easy with a DPDT. See pic below...

[m3moser]

Thanks Steve- I will have to check on the voltages.  This amp will also be used in Korea and the voltages seem to be either 220 or 240 there.  If set up for 240 and the voltages are actually 220 at the plug then the risk is having the amp voltages run low which may not sound good.

[sluckey]

If I was unsure of the voltages and/or did not have a need to switch on a daily basis, I'd just terminate all the primary leads to a terminal block using spade lugs and make jumper connections on the block.

[DummyLoad]

agree completely with steve on this point. it's too easy to have a switch bumped/set in the wrong position and then amp leaks magic smoke. as far as i'm concerned something like a guitar amp should be set internally.

if you must have a switch, you can wire a 4PDT toggle to make switchable 120V/220V to accommodate hammond 300 series. schema attached.

i can't see why hammond just won't wind a single primary with taps; there must be a reason relating to optimum transformer design?

--pete

[PRR]

> can't see why hammond just won't wind a single primary with taps

The part above the tap goes un-used; and also "wastes space" which could be used to lower the dead resistance of the part of the winding that is used.

No big deal for 110-120 taps.

Big deal for 120V-240V taps.

Say the total load is 120VA. So we want either a 120V 1A winding or a 240V 0.5A winding. If we do the latter, but only use half of it for 120V, we are asking 1A in a 0.5A winding. Or we could wind the whole thing for 1A, but now we have 240VA worth of copper for a 120VA job. We actually could wind 120V 1A and 120V 0.5A; even so, that's 180VA of copper for a 120VA job.

The 120/240 split winding seems simple.

The 110-120 taps make it harder.

However if they only sold 120V without taps, I wouldn't even think about it.

> the risk is having the amp voltages run low which may not sound good.

I have seen "120V" as high as 128V and as low as 108V.

Small clubs are notorious for power problems.

IMHO, the amp should tolerate a wide range, and not sound any more different than the other side-effects from the change in venue.

[DummyLoad]

Say the total load is 120VA. So we want either a 120V 1A winding or a 240V 0.5A winding. If we do the latter, but only use half of it for 120V, we are asking 1A in a 0.5A winding. Or we could wind the whole thing for 1A, but now we have 240VA worth of copper for a 120VA job. We actually could wind 120V 1A and 120V 0.5A; even so, that's 180VA of copper for a 120VA job.

thanks PRR, i knew there had to be a reason. it seems much more complex from a winding perspective to wind more than one winding. the hammond has two windings so it is more labor intensive to build as in you stop and insulate yet another winding. ok, so the dual winding approach saves bobbin space, and wire cost at the expense of increased build complexity. the new chinse stuff i've seen so far is wound multi-tapped on a single winding.

--pete