You need a crystal or ceramic mike.  If you try to use a high impedance dynamic mike, you will have very low modulation.  The Piezo-electric mikes (crystal or ceramic) had much higher (voltage) output than the dynamic mics.  You will need a pre-amp if you use a dynamic mike.

Hi,

    To answer Mike's question, I operate at W6RO, aboard the Queen Mary in Long Beach CA.  And yes, the pileups CAN get quite extensive, especially on 10 Meters. (My record is 3 1/2 hours...)  But sometimes it's just not possible to continue, so I'll take the advice given here, and just make the announcement that I have to go QRT.  
    I hate to disappoint those that didn't make contact, especially if they have been trying for a while, but I'll probably be back around the same place a week later!  So there will always be another chance.  

For one thing, pull the tubes first, and then after re-forming the caps (even relatively new caps can fail for unknown reasons...)  proceed cautiously.

    I don't know if you meant thea the HV is dead completely, or if it's back to normal.  If the VV is NOT at normal, but not completely dead, turn odff the amp, pull the plug, move the plug AWAY from the A.C. socket (these things sometimes have a mind of their own)  and wait about a half hour.  (I'm being conservative, but safe.)
  Then, dig into the amplifier, and carefully short out all of the electrolytic capacitors (not just those in the HV supply; even the bias supply could have quite a kick, and if the bleeder resistors have gone bad, there could still be a hefty charge!)
    Then check across each HV cap for a high resistance; anywhere from about 47K and about 100 K, (I'm not familiar with the actual circuit) these readings should be the same in either direction.  If not, the cap is probably bad.  If you get infinite resistance, then that bleeder resistor is gone, and needs to be replaced.  Also, if any of the resistances across any one capacitor is much different than the other resistor values, that resistor also needs to be replaced; it might be prudent to replace the whole bleeder string.

    Finally, check the rectifiers; there should be conduction in one direction only; reversing the ohm meter leads should have a very high resistance.  Since this design probably had equalizing resistors across the diodes, these should have a high resistance corresponding to  their marked value in the reverse direction of the diode conductance.
    Also, do not try to replace a string of resistors with a single unit.  Resistors have a voltage rating, as well as power and resistance ratings. Only replace single resistors with single resistors.  (I.e., if a capacitor rated say, 450 volts is bridged by two 100K resistors, don't try to replace the two resistors with a single 200K resistor!  That's because the original's had a voltage rating of only 250 volts, and you'd like have failure if you replaced it with a single resistor.
    Good luck, and keep us posted as to your progress!

Is there a polite or acceptable way to shutdown a pileup?
    I occasionally work at a club station, and after responding to an occasional CQ, I've found a pileup ensues that gets entire unmanagable.  (Sometimes it seems the pileup could go on for "daze" at a time.)
    After three hours or so of handling calls, what is a reasonable to say, in essence, "I'm hoarse; I'm hungry and need to get lunch, etc." and end the pileup when there are still many operators still trying to make contact?
    I hate to be rude, and just say "going QRT" and disappoint a number of operators.  Is there an acceptable way to end things, or am I just being thin-skinned.  (I know if I were on the other end, I'd just shrug it off, and try again some other time, but some other operators aren't as forgiving.)
    My biggest concern is not to leave a poor image for the club station, but sometimes enough is just too much, and operating any longer just isn't an option.

For starters, disconnect the ext. modem temporarily and see if you can set up the TNC on COMM Port 2.  That will tell you if it's a COMM Port problem or not.  THEN, if it still doesn't work, look at a serial interface cable problem.  There are all kinds of wiring variations for serial cables, and that could be a problem.  Of course, there COULD be a problem with the radio, but I think that's the least likely scenario.  If you can substitute a different cable, I'd try that first, or use the modem cable from COMM Port 2 to connect to the radio and see if that works.
    Does the radio manual describe the type of serial cable needed, or better yet, give a wiring diagram?
    Lastly, you can ask these questions of the Customer Service Dept. for the radio.  Good luck!

Shannon,

    Since no one else has mentioned it yet, please accept our condolences on behalf of the Amateur Radio Community.

Try Jameco Electronics.  They list the 8251A for $3.99.  The other IC's are a standard 7404 TTL (74LS04 sholdd work as well, ) @ $0.29, and a CMOS CD4040B @ $0.39.

Before you give up and pronounce the Com Ports DEAD, you need to consult the documentation for the motherboard, and MAKE SURE the connectors you are using between the motherboard and DB-9 or DB-25 are correct!  I have run into situations where the pin out on the motherboard is unusual, and naturally the Serial ports will appear dead!
    Also, be careful with adapters and mice or other pointing devices.  If hey are not SPECIFICALLY designed to be PS-2/Serial compatible, and you use an adapter, you CAN cause damage to the pointing device, serial port, or PS-2 port.
    The fact that some serial devices seem to work, or at least partly so seems to indicate a problem with the Com port set up, not the hardware itself.
    Good luck.

I've been looking for the same myself!  Some programs will function tolerably, but I haven't found anything that works specifically with the 790, or provides all the functions.  I hope somebody responds with a positive answer!
73,
Larry WA9SVD
P.S.  It's a GREAT rig, nevertheless!

Hi,

    Windows 9x operating system already has a terminal program, if this is any help.  You may have to re-run the install from the Windows CD, but it's called "Hyper-terminal" and I've used it to control a Kantronics KPC-3 TNC, so it should work with most other hardware-based TNC's.  Good luck.  WinXP, you're on your own!

Hi Jim,
    Don't pay any attention to snide remarks.  There are a few terminal programs out there that are simple to use, and should work in a DOS window.  (As I said, they are simple.)  I've accumulated a few over the years, and if you e-mail me at:  wa9svd@juno.com and describe what you want the program to do I can point you in the right direction.  
    Welcome to Amateur Radio, and Congratulations on Extra.  (I just upgraded last month after 35 years.)
73,  Larry