Warning! ZETAGI DUMMY LOAD FAULT

Hi All,  

I have just bought a Zetagi dummy load. I tried it on my SS6900 and it set off the high SWR alarm. When I tested it I found it was open circuit. This was caused by the screw holding the circuit board to the case not earthing due to the paint. I cleaned off the paint around the screw head and fitted a star washer. Problem solved. If you have a radio without the SWR alarm you would not know there was a problem and could blow the finals. 

73s, Mick

Zetagi is not all it is made out to be.
30 Years ago it was thought to be the dogs dangly bits but it's not.

I've moved this posting to the 'Information and Guides' section of the forum.
(I'm supposed to do a bit of 'housekeeping' as an admin now and then. )


Don't tell me, would that be the DL-50 by any chance?

The old version had four 200 ohm resistors in them with two chassis screws whereas the new has nine 470 ohm but a single screw.

I've never owned one but I would love to stick one on a NanoVNA out of curiosity to see what the overall frequency response actually was. I built my own dummy load from an RF termination resistor mainly for the fact that I'm a cheap git but also so I know exactly how it behaves.

I think pretty much every transceiver nowadays has a type of fold-back or SWR protection circuitry within them usually to protect from over voltage conditions. Never seen a blown final from high SWR but seen a fair few after someone 'twiddled' the PA biasing or output stage filters in an attempt to gain 'more Watts Igor'.

Tell a lie, I did once see one where not only were the output transistors blown but pretty much most of the semiconductors in it.....I can only presume a static build up charge during a hilltop DX whilst thunderclouds built up around them. That or they hooked the thing up to a well dodgy power supply!
Needless to say it was BER (Beyond Economical Repair) but at least it hadn't 'Failed Under Continuous Testing'. (Used to love that acronym!)


Might simply have been a manufacturing defect Mick. I once had a guy supposed to mask off all the chassis screw mounts on some equipment housings before they went off to the spray booths...he didn't. He did however learn a valuable lesson by retrieving them all and scraping the paint off them(!)


All the best,
Victor

Hi Victor,
Thanks for that. I wasn't sure were to post it. I did think of the information and guides. 

Yes it is a DL-50 with nine 470 ohm resistors. It meters out to about 52 ohm. It was a simple fault to find and correct. I could have made one. I have made a dummy load to replace the speaker in radios for when I am setting the IF and tuning. It's switchable from 8 to 4 ohms using two 25 watt 8 ohm wire wound resistors. That's so I don't have to here the 1K modulation tone. 

Hope to get my callsign tonight if Gary can do it.

All the best, Mick

Mick Lake wrote:

Hi All,  

I have just bought a Zetagi dummy load. I tried it on my SS6900 and it set off the high SWR alarm. When I tested it I found it was open circuit. This was caused by the screw holding the circuit board to the case not earthing due to the paint. I cleaned off the paint around the screw head and fitted a star washer. Problem solved. If you have a radio without the SWR alarm you would not know there was a problem and could blow the finals. 

73s, Mick

I had same problem what was the Swr after repair please