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View Full Version : Base Radios 546 Omni C Buzzing in CW Mode



KB3ZHX
Fri 21st Dec 2012, 01:28
Recently I purchased an older Ten-Tec Omni C and everything seems fine (great signal reports) but on my end I have an intermittent buzzing or humming in the audio. But it's only present when I key down in CW or Lock mode at full- or near full power. (it begins just before the ALC light comes on -about 80watts output to full power)

Sometimes, if I power up/down the power supply (Ten-Tec PS 280) the noise will go away completely.. then if I either power down, switch bands, or change antennas, the noise will re-occur.

The noise comes through the speaker or headphones if attached.

To describe the noise; it's like a build up of energy on each key dah or dit... It could be described as a humming or buzzing, but either way it's very annoying.. another note is that once it begins, I will hear an audible hum on receive as well... This noise goes away immediately after I power down and power up the power supply..

Could it be that the power supply is causing it?? or something inside the rig itself??

Any input is appreciated...

K7KBN
Fri 21st Dec 2012, 15:30
Have any of your contacts made with this radio mentioned that they hear the hum/buzz? If so, I'd look at the power supply filter capacitors.
If it's purely a MECHANICAL vibration, try taking a heavy screwdriver and tightening all of the screw fasteners that hold the laminations together. It's not exactly a rarity that these sometimes work loose. In the worst cases you might have to remove the transformer, loosen these fasteners just a bit, and apply insulating varnish to all sides where the laminations are visibly stacked. This will seal up the gaps - most of them, anyway - and quiet things down.

We had to do that with ALL of the 400Hz transformers on one of the USNs finer ships. That 400Hz note gets stuck in your head, and it reduces the efficiency of the transformers.

G4FUT
Fri 21st Dec 2012, 15:35
A way to cure buz in the headphones is to connect a 1000pf capacitor across the connections in each phone.

KB3ZHX
Sun 23rd Dec 2012, 20:08
Thanks for the suggestions guys. After opening the power supply, I discovered a loose grounding nut on the regulator board. I tightened it up (and everything else) and the buzzing is completely gone.

2nd problem - this started just the other day (before I opened anything up).. When going from TX to RX, the rig somehow goes into attenuation. I can still hear signals, but it is seriously degraded and surrounding signals and static are gone! This is great for strong sigs, but mutes out the weak ones!!!

Sometimes I can restore the audio by clicking the ptt with the mic in SSB or by fast keying in cw. It doesn't require any power out, just the keying action and ptt that "un-sticks" the attenuation.

Any ideas??

Thanks again! Brian KB3ZHX

G4FUT
Mon 24th Dec 2012, 16:54
2nd problem = Definitely a relay problem.

KB3ZHX
Mon 24th Dec 2012, 22:32
Thanks G4FUT... I will try that first... Appreciate your help!

KB3ZHX
Wed 9th Jan 2013, 03:14
Update: Called Ten-Tec's service dept and spoke with Jim... He also recommended the TX/RX relay and said that the old relay was no longer available, but a new design replaced the old one. I couldn't believe my ears when he told me that they actually had one in stock! $35 plus shipping and my rig runs like new. Excellent product support for a 30 yr old rig!