Surplus NEC UHF amplifier modules.

[VK3WRE]

For those who have obtained a surplus UHF TV module at Gippstech there is an artical on the VK3BEZ web site

http://www.vk3bez.org/Files/Surplus%20N ... odules.pdf

It is aimed at helping people get the amps going.

cheers
Ralph VK3WRE.

[VK1JA]

Thanks Ralph, this will help a lot as I didn't manage to write down any details while you were talking.

It'll be a good project

[VK2JDS]

Thanks for the info Ralph,
For the benefit of people who may be reading this and didn't attend GippsTech, do you have any more of the modules and combiners you had there available for sale ?
Its such a cheap and easy way to make big power on 432
73 Dave

[VK1JA]

Hi Ralph,

One last thing, I seem to recall you saying that changing the capacitors after the final PA's (see pic) would increase the efficiency. What value capacitors would you recommend.

Thanks again!

Jayson

VK1JA

Edit - attachement deleted as it showed the caps on the input rather than the output!!

[VK3WRE]

Hi Jayson, the original caps were 4 pf so 10pf sounds about right.

Regards Ralph

[VK3XL]

Hi Ralph, I have one of the 1KW uhf amps which contains 3 of these modules. (http://members.rennlist.org/warren/nec.html) I have not done anything with it yet. I heard that the things will take off if you try to operate them without the cover in place (i presume this is for the 1KW configuration. The circulators will not work effectively at 432Mhz. So to my question. If I was to remove the 3 modules and then cut the hearsink carefully into the 3 (1 for each module) remove the circulators and do the other mods you have outlined, would I have the same as you have or is the heat sink significantly different.
I believe that there are cavities etc machined into the heatsink of the amp that I have that effect the tuned circuits etc, thus my question about cutting it up.
ps I have the 3 phase power supply as well.
Regards
Mike VK3XL

[VK3WRE]

Hi Mike, The heat sink is just a flat surface and the PCB is mounted on a spreader plate so not to short out the hybrid sections.
What I have done is exactly what you said. remove the PCBs and cut up the heat sink into 3 bits.
The spreader plate will let you put the module down on a larger heat sink if you have one.
you shouldn't have any trouble if the pots are replaced and the bias setup again.

Cheers Ralph.

[VK3XL]

Thanks Ralph. I knew if I held onto this thing long enough someone would work out how to get it working on 432, now I have another project

[VK2XSO]

I wasn't able to make it to Gippstech this year. I would have liked to get hold of one to play with.

[VK3XL]

Try getting in contact with Ross VK3CE, He may have some left for sale.
<ross.vk3ce@gmail.com>

[VK3KG]

Hi Ralph etc all. Have modes the power supply by installing an IEC connector in place of round 3phase unit and made the bridge on the centronics socket. Powers up well although still to do a load on test. Over pleased. Hope to get pots changed shortly and mount the PA in a box with the power divider a and a signal into dummy load and radiate before Christmas.

Great project and enjoyed the presentation at Gippstek.
73. Craig
VK3KG

[VK3ZAZ]

There are still 8 or 10 under floor at Mt Dundas CH28
plus power supplies
I can take them to Mt Gambier or Ballarat some time but not doing it for free.

[VK1JA]

Hi Ralph etc all. Have modes the power supply by installing an IEC connector in place of round 3phase unit and made the bridge on the centronics socket. Powers up well although still to do a load on test. Over pleased. Hope to get pots changed shortly and mount the PA in a box with the power divider a and a signal into dummy load and radiate before Christmas.

G'day Craig,

It'd be great to see a picture of the IEC mod you've done, a picture paints a thousand words

Just on replacing the trimmers, I found that Jaycar sells the 10 turn 10k pots, so I picked up a few while I was there. Yet to replace them, but it doesn't look like a hard job.

[VK1JA]

For those that bought one of these amp pallets form GippsTech this year, I've posted my progress in the 'Whats on your workbench' thread.

http://www.vklogger.com/forum/viewtopic ... &start=320

Cheers

Jayson

[VK1JA]

For those that have experience or are currently building up one of these amps, what can I expect the bias current to be when setting the bias voltage at 2.8v with a supply voltage of 28v?

I'll be switching the bias voltage between rx/tx and was wondering if I can run the bias voltage straight from the sequencer?

Thanks