suggestions for simple amp wanted

[x9moto]

hi, there everyone. after looking through some of your pictures of your amplifiers i must say there is some beautifull craftsmanship there, makes my tin case look rather industrial, i wouldnt know where to start with some of those wooden based amps.

well it seems you have given me the bug again after building my kit amp last year and gradually modifying it i think i have reached its best and would like to buitd something from scratch using pp wiring.

due to a lack of funds i would like to go for a line powered design so 240v (uk) and keep it as cheap with common parts as possible.

would like between 8 and 30w. i dont know if its even possible but are there any designs that avoid using an opt of is that essentual? , if so can i use another type of transformer in the meantime whilst ib save up for an edcore or something?

thanks in advance, looking at some of your work i know im in good hands

[Joshua_G]

A simple tube amplifier without a power transformer is not possible, or not practical, since the heaters of the tubes usually require about 6.3 Volt.

Also, using the mains power for the amplifier's high voltage directly, without a transformer, poses a mortal danger. DO NOT DO IT if wish to stay alive.

[Globulator]

Norfolk - near me
Bluebell do some OPTs, but I do miss having an Edcor in the country

That is why my route is to buy a cheap chassis + transformers in the shape of a chinese cheapy. I would like to buy better stuff, but I live in the UK and am therefore poor!

All you really need to build a wooden amp chassis is some wood in a square and a flat sheet of steel or aluminium for the top - how difficult could it be?

BTW (as noted above) - always use a mains transformer. You need one anyway for the filaments - just buy two cheap 6-0-6v toroids and connect them back to back, and you have 6 and 12V for filaments.

[Frank Berry]

There are designs which do not use OPTs but they are expensive and complex.
Why not try to find an old tube amplifier and use the OPT for your project.
You might even be able to use the power transformer.
If you can find an old tube amplifier, you could get some experience by rebuilding the amplifier and, perhaps, changing the design slightly so as to improve the performance.

[x9moto]

so whats the cronic danger with using line voltage, most switch modes do it all the time?

i was thinking of using a small tranny for the heaters and running line into a valve/solid state rectifier for the power supply, we have earth wire in the uk any shorts to case or ground would blow the fuse so where is the danger?

i have an old ecko radio here that runs line and has only an opt, how does that work then?

thanks for replies, oh and its nice to know someone local Globulator

[flatheadmurre]

Find some free transformers at the local recycling and use them back to back for HV any low voltage medium size transformer and and a 1083 will supply for heaters.

DON`T even think about using the mains net directly for HV that´s a fast track to a shorter life !!!

[x9moto]

of course another method i have been toying with is a technology introduced to me from radio control hobby, and that is the lithium polymer battery available in high voltage configurations and can hold over 5000mah for extended periods ie 2-3 hours and could be charged in 25mins with my equipment.

[mashaffer]

Can you scrounge a console (I think they called them phonograms or something like that on your shores)? Here it is sometimes possible to get a nice single ended EL84 type amp in one of those for nothing or next to it. You might also be able to get a matched set of television vertical output transformers from eBay or a salvage outlet. These are essentially moderate power SE OPTs. The trick is finding a matched set as a TV had only one.

[DF96]

Running equipment directly from live mains is DANGEROUS and therefore discussion of this is discouraged here. It was done commercially in the past, but such items (radios, TVs) would not pass modern safety standards. Some are potentially lethal. If it is difficult for a manufacturer to do it reasonably safely, it is virtually impossible for a DIYer. Experienced DIYers would not attempt it. Less experienced ones may be less aware of the dangers. Don't even think about it!

[Globulator]

Originally Posted by x9moto

so whats the cronic danger with using line voltage, most switch modes do it all the time?

No they do not!

The bridge, caps, current sense and switch transistor are on the line side, but the application circuit is isolated via the transformer (and an opto-isolator if using secondary sensing).

You MUST isolate from the mains - it's that simple. Not doing so endangers everyone who comes near to your creation.