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Title: Need Help with RCA BTA 500 BTX Post by: KR4WI on November 15, 2009, 10:29:02 AM Hello, My friend WI4M is working on getting this TX on the 160 mtr band. Has anyone put this TX on the air? He is having problems with tubes glowing red, when in tx mode for only a few seconds. Thank You for any help. Matthew KR4WI
Title: Re: Need Help with RCA BTA 500 BTX Post by: DMOD on November 15, 2009, 10:47:31 AM I haven't had any experience wih this rig, but have you and your friend checked
the HV and especially the bias voltages. Which tubes are glowing red, the finals or modulator tubes? Phil - AC0OB Title: Re: Need Help with RCA BTA 500 BTX Post by: W3SLK on November 15, 2009, 11:01:05 AM First things first. Get your dummy load and and see if you get output at the frequency it was set at whilst in service, (the BC freq). Then tune from there. This will tell you whether you have a coil-tap issue or not. I wouldn't dive into anything until you get it working at that freq. Then proceed with the shift up band. By the sounds of it, like you don't have your final tuned properly.
Incidentally, (not to hijack the thread), I just looked at the schematic and it show a tertiary winding/tap off of the mod transformer. When I first saw it I thought it was negative feed back for the speech amp but see that it goes to the RF driver section. What's up with that? ??? BTW I have the manual on PDF if you need it. Title: Re: Need Help with RCA BTA 500 BTX Post by: W7TFO on November 15, 2009, 11:49:25 AM About 10% mod to the RF driver stage is very common in broadcast rigs, really helps keep the distortion and noise levels down.
Title: Re: Need Help with RCA BTA 500 BTX Post by: K6IC on November 15, 2009, 01:29:35 PM Incidentally, (not to hijack the thread), I just looked at the schematic and it show a tertiary winding/tap off of the mod transformer. When I first saw it I thought it was negative feed back for the speech amp but see that it goes to the RF driver section. What's up with that? ??? Many of the Gates rigs, especially those with Triode finals used this technique to increase the grid drive under modulation peaks. This allowed lower resting drive to the finals and quite a bit more on mod peaks. Am not familiar with this RCA rig, but assume this is used for the same purpose. 73 and Good Luck to your friend, Vic BTW I have the manual on PDF if you need it. |