|
Post by instigator on Sept 19, 2010 21:36:20 GMT -5
I have a Mark IV that develops a hum in the transmit audio after the radio has been on for am hour or so. Any quick things for me to check before it goes to barketts? Thanks.
|
|
|
Post by Tombstone (R.I.P.) on Sept 20, 2010 14:04:39 GMT -5
Right off the wall I'd say bad filter caps or something else screwy like the rectifier in the transmitter's power supply. If the caps are original they're overdue to fail anyway. Replacing all of the caps in the entire radio would be a good idea, they just weren't made to last this long. If Fixr or 2600 reply to your post, they're the experts. I don't know if bad filter caps in the receiver would effect the transmit audio, probably not.
Tombstone
|
|
|
Post by FIXR on Sept 20, 2010 15:21:26 GMT -5
Is the hum on both AM and SSB transmit?
Fixr
|
|
|
Post by instigator on Sept 20, 2010 15:48:15 GMT -5
Not sure about sideband but AM for sure. I will have to check SSB. Seems to be heat related or lenght of time the radio is on.
|
|
|
Post by FIXR on Sept 20, 2010 16:10:53 GMT -5
It could be one of the tubes in the audio or the MKIV's can have a problem where the socket solders to the printed board. The MKIV's transmitter shares the same power supply with the receiver. Usually if it is a filter problem you will have a hum in the receive audio also.
Fixr
|
|
|
Post by Tombstone (R.I.P.) on Sept 20, 2010 16:44:07 GMT -5
My mistake. I'm not familiar with any of the Browning radios after the Mark III.
Tombstone
|
|
|
Post by instigator on Sept 20, 2010 16:45:22 GMT -5
Do you know which tubes control the audio?
|
|
|
Post by instigator on Sept 22, 2010 6:16:07 GMT -5
After some more investigation im finding that the D-104 is causing the hum. When im touching the mic i can touch the radio and the hum goes away. So im back at chasing a ground problem i guess.
|
|
|
Post by cbrown on Sept 22, 2010 8:55:39 GMT -5
Try moving the microphone cord next time the hum appears to see if the cord is bad.
|
|
|
Post by instigator on Sept 22, 2010 9:09:27 GMT -5
Touching the cord seems to have an effect on it. But its almost like ive got RF feed back. I have my other radio on to monitor the hum and when i touch certian parts i see different S-meter movements on the other radio. Im going to try i different mic tonight.
|
|
|
Post by cbrown on Sept 23, 2010 9:10:54 GMT -5
I'm wondering why it takes an hour before the hum appears. You may have a capacitor that might be starting to fail.
|
|
|
Post by instigator on Sept 23, 2010 11:56:00 GMT -5
Well i wired a astatic 575-m6 to the radio and on air reports say that my hum is gone. When i key up and listen in my other radio is still here it a little. I may go after the power supply caps when i get a chance. Im doing my comparison with my MK III which has no hum at all when keyed hot or cold.
|
|
|
Post by cbrown on Sept 24, 2010 9:12:42 GMT -5
Well i wired a astatic 575-m6 to the radio and on air reports say that my hum is gone. Even after having the radio on for an hour or more?
|
|