Carlos, a couple of pointers: THe SB-200 is rated for 500 mA plate current with 100 mA of grid current. If you exceed either of these, you are still overdriving the amplifier (and likely damaging the tubes). Voice peaks on the meter during SSB operation should hit 200 mA plate current, no higher. The T-4XC has considerably more power avaailable than that required to drive the SB-200 to full output.
Amplifier ALC by its very nature introduces distortion. ALC really is just there to keep the amplifier from being overdriven & causing tube/power supply damage. Think about it: if you drive the amp hard enough to kick in ALC action, you are essentially clipping the signal waveform, which produces distortion and intermodulation products, which can generate anti-social tendencies in your fellow hams. So be a pal and don't drive the amp hard enough to kick in ALC. The reed relay Icom uses in their transceives is woefully under-rated for switching "legacy" amplifier TR relays, most of which operate at 117 VAC or thereabouts (the SB-200 uses a 110 VAC relay, but the circuit actually runs it off of the grid bias supply, which is approx. -100 VDC). The ICOM manuals rate this relay at 16 VDC 2A, but several have looked up the specs for the actual relay and have found that it's actually rated for considerably less than this. When keyed, the SB-200's relay jack passes not only the relay current, but also all of the amplifier's grid current. To add insult to injury, there is a 2 uF capacitor in the amplifier connected across the keying line, so besides the grid/relay current, you have to dump the transient from this capacitor every time you key the amplifier! There is a 33 ohm resistor in series with the keying line in the amplifier which softens the blow to some degree, but it's still enough to damage the relay in the IC-746. OK, bottom line, you've welded the reeds of the IC-746 relay together and there is no solution for it other than replacing the relay. -- regards, Mahlon - K4OQ > "Carlos Augusto S. Pereira" wrote: > > Hi again guys, > > Well, the ALC is working. When I turn the SB200 on, the T4XC plate > current drops a little, so the amplifier keeps its plate current > around 550ma (600w on 15m). So, this is the good news... The bad news > is that I connected the SB200 to my Icom IC746 and the radio relay or > transistor (whatever) went to the outer space... Now the solid state > transceiver needs to be fixed. The Icom is working but the relay jack > is in short. > > I had the feeling that the the T4XC was overdriving because the gain > control is not much linear, in other words, with the T4XC the linear > tuning needs to be slower... smoother. > > 73 Carlos PY4RO > > Carlos Augusto S. Pereita PY4RO > www.qsl.net/py4ro > E-mail: [EMAIL PROTECTED] ---------------------------------------------------------------------- Submissions: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] - subscribe drakelist in body Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Brought to you courtesy of TLCHost.net http://www.tlchost.net ----------------------------------------------------------------------
