Firefly amp build VAC question

[Shooley]

Hello,

I plan to build a firefly amp using the PCB you can purchase here http://ronsound.com/index.php?main_page=product_info&cPath=129&products_id=882 and the instructions. I live in Israel and to my knowledge it's 230V here from the wall.

My question is whether or not the fuse listed in the BOM is suitable? my knowledge of electronics is limited hence why I chose to build an amp with a pcb and detailed instructions for my first amp build.

thanks,

Amir

[WRGKMC]

First off you cant use the Hammond 269EX transformer they list because its a 115V transformer, not 230.

 

As far as the fuses go, you'd use half the value primary fuses but you need the correct transformer.

 

You see the power companies generate electricity that has Voltage and Current. Current is what does the work, it makes electronics operate, turns on lights, it makes motors run etc.

 

The problem with high amounts of current is the wires that bring the power from the power station to your house resists current flow. They use a trick to get around this. They step the voltage way up to thousands of volts using huge transformers. In the process there is a sea saw effect on the current. When you step voltage up with a transformer, the inverse occurs with current, you step current down as you step the voltage up.

 

What winds up happening is they step the voltage way up but it has very low current. This reduces the issue with wire resistance getting the power from the power station to your home. Then they use step down transformers in your neighborhood to convert the high voltage down to a usable level and the current that does all the hard work back up before it comes in your home.

 

Here in the US, we have 120 and 240 volts. We use 240 for big items like Air conditioning systems. We use the lower voltage for lighting and most other appliances.

 

The Current on our 120V portion is twice as much as the 240V line. We can also obtain 208V from many industrial lines by using various phase wiring. The decision to use the power system we have goes way back to the days of Edison and other industrialists so our power grid is much older then the systems used in Europe.

 

In Europe they deemed it to be unneeded, likely because of the additional costs involved so they simply went with a 220V.

 

I mention all of this so you understand why the transformer listed wont work. Europe uses 220V primary transformers on everything. The voltage that comes off the secondary that feeds all the components is the same as we get off the secondary's of our 120V transformers. The voltage/current used in the circuits are the same, its just the conversion from the lines coming in the house need to be different.

 

Therefore you need a transformer with a 230V primary that has the same secondary outputs as that Hammond 269EX because you'll fry that transformer when its connected to a 230V line. Some transformers have dual primaries which let you operate it at 230V or 115V. You'll have to dig around and find the right one for your project.

 

In any case, using a 230V transformer, the current will be half as much as the 115V transformer, so to protect it you need fuses that are half the value. I don't work with 230V circuits much as a technician but I believe they use two fuses, one on each line because its a balanced system. In the US we have a hot and ground and we only put a fuse on the Hot line because an open ground isn't going to hurt anyone.

 

Anyway, here's the specs on that Transformer. As you can see all of these have a 115V primary. http://www.hammondmfg.com/263.htm

You need to find a 220/230 primary transformer as a substitute.

 

I do know they make 230 to 115V converters so you can run Western devices on European lines. These may be a cheaper alternative for converting a 115V circuit to run on your lines if you have to use the 115V transformer, but You have to take the current draw into account. Most of those converters are for low current devices. Tube amps of any kind have allot of current draw for the heaters and producing the higher B+ voltages. This is why I suggest trying to find a 230V primary transformer first. Its a better solution all around and you wont be dealing with the additional step down unit which is an unnecessary expense at this point.

[Shooley]

thanks for the reply, I should have mentioned I ordered a 369ex instead of the 269

[WRGKMC]

Cool.

 

You should be good then. Use half the value used for a 115V primary and you should be good. If there are fuses in the secondary (which I doubt) they should remain the same as the schematic.

[Shooley]

I have another question, I ordered this lamp assembly

http://www.mouser.co.il/Search/ProductDetail.aspx?R=1030D3virtualkey60600000virtualkey607-1030D3

and now I see it says 105-125 VAC, should I order a different one like this one

http://www.mouser.co.il/ProductDetail/VCC/1031QD1/?qs=sGAEpiMZZMt3jJ7qdVqbk6ZIhBd3NNhuCwBmvXGmMXw%3d

or will the one I ordered be ok?

[WRGKMC]

Well, you're running 240 V and the lamp would be connected to the on off switch parallel to the transformer. It will only draw what it needs in current to operate. The second 240V lamp you listed would be the one to use.

 

You want to be sure the switch is rated 240V with at least double the transformers current rating too.

 

Allot of tube amps run low voltage lamps off the secondary heater voltage. This does add some load to the secondary of the transformer so it would need to be factored in if you were using a 6 or 12V lamp. Since you're using a primary voltage lamp, it simply needs to be able to run off your wall outlet.

 

What I would have suggested is a 240 power switch with the pilot light built into the switch, something like this.

 

 

 

Or this...

 

[Shooley]

Thanks

[Shooley]

the switch that is for the ON-OFF is rated up to 250V, this is it http://www.mouser.com/ds/2/209/MS-101085-200162.pdf

the switches for the boost and standby are rated for 120v, do I need to replace those or will it work?

spdt http://www.mouser.com/ds/2/209/MS-100881-199797.pdf

dpdt http://www.mouser.com/ds/2/209/MS-100882-199930.pdf

[WRGKMC]

When they are before the transformer primary yes, since are after the secondary no.

 

My guess is both are after the transformer so you wont need to change them. A standby switch removes the B+ which is definitely after the transformer and the boost probably changes the B+ level (or changes the speaker output current) so again its after the power transformer so just use whatever the parts list suggests.