Source of high voltage transformers

[VK5TX]

Looking for a source of transformers to build an hf amplifier around 400-500watts

[VK4TI]

Looking for a source of transformers to build an hf amplifier around 400-500watts

microwave maybe , what voltage out ?

[ZL2ADU]

Have a look at http://www.antekinc.com/800va/
I have just obtained a AN8T800 this has 2 windings of 800v at 500ma and 2 x 6v windings..
I have the 2 windings in series and I am getting 2200 no load and 1900 at a load of
600+ ma. At this level the transformer only gets warm with a small fan cooling it.
At a price of US$105 and about US$65 for freight, its a great deal..

[ZL1RS]

Yep, Antek 800VA toroids ... excellent transformers for small valve PAs! The ANTEK "800VA" appears to be a continuous rating, they will comfortably do more in ICAS. I have two of them that are used in my old 2m and 6m 'portable' 8877 amplifiers. http://www.qsl.net/zl1rs/amp.html

The toroid in the 2m amplifier is the same 800 + 800 = 1600V and 6.3 + 6.3V 5A AC windings version that Harry described, and doing more or less the same job. The 8877 is producing 800W RF output and it can run like that in JT65b mode for hours on end while operating 2m EME (the blower air flow is arranged to cool the transformer as well as the tube).

The other transformer in the 6m amplifier is the 650 + 650 = 1300V AC secondary version toroid (also with the same 6.3 + 6.3 V 5A filament windings). The 1300V AC is going into a voltage doubler HT power supply and delivering 3600V DC under no load. This HT sags quite dramatically to about 2800V under a single tone load, but is better than that when the amp is used in a 'dynamic' mode like SSB or CW with a decent value of filter capacitor bank in the HT power supply. That amplifier does 1kW RF output in CW or SSB "all day". It will also do 1kW output in JT65a for 6m EME but starts to 'smell warm' after 1.5 hours of continuous use in that mode at that power level. It is 'quite happy' for much longer when the PA only driven to 800W output in JT65.

The two 6.3V 5A windings are connected in parallel to supply 5V at 10A for the 8877 filament via a bank of resistors in parallel to give 0.1 ohm which drops 1V (the other 0.3V is 'lost' in the filament wiring and filament choke resistance). This 0.1 ohm series resistance forms an effective soft start for the 8877 filament ... but a soft start circuit is still required in the toroid primary anyway to limit the mains in-rush current when the HT capacitor bank initially charges at start up.

FWIW, the ANTEK toroidal transformers have 115 + 115 AC primary windings and thus can be configured for either of the nominal 110V and 230V mains electricity supply systems used in most parts of the world.

Being compact toroidal transformers it is possible to build fairly small 'desktop' style amplifiers. Mine are housed in 300mm x 300mm x 175mm and 320 x 300 x 160mm cases respectively ... that is the whole amplifier including blower and HT supply inside the box.

These 'portable' valve amplifiers are in the process of being replaced by home made solid state amplifiers using a BLF188XR LDMOS device in a W6PQL circuit. These SS PAs are powered by a light weight switch mode power supply and produce 800 to 1200W RF output depending on the supply voltage (800W RF output with the supply set at 40V, and 1200W at 50V). Each SS amplifier weighs about 8kg which is about half that of the equivalent valve PA ... this is a big advantage while traveling.

73,

[VK4GHZ]

Bob VK3ZL (SK) was a fan of toroidal transformers too.

Perusing the VK3ZL Amp topics (now found in the SK section) here may also provide some useful background information with building PAs.

Start here:
http://www.vklogger.com/forum/viewtopic ... 76&t=11822