SPE/Flex 6xxx drive control

I have 2k-fa and 1.3k-fa.

I use 2k-fa with K3. 2k-fa went 4 time for repairs, with at most one due to overdrive. 
I use 1.3k-fa with 6600. Low power drive mod. Numerous bad antennas and high SWR. Never a problem. Automatic power control for LOW/MID/HI works well. 

Ignacy, NO9E

FWIW, I had my 1.3K-FA go up in smoke three times with my 6700 driving it. The last time was on the Low power PA setting on 80 M FT8 (probably 600-700 W RMS power) into a tuned dipole with SWR of less than 1.1:1. Half of the RF board was immolated by the heat, but there was no alarm or other warning before I smelled the magic smoke coming out of the amp. 

I suspect it was more of a heat dissipation issue than a spike causing the LD-MOSFET to pop. I've seen that happen with another SS PA. 

My opinion is that the SPE PAs should not be used for digital modes, period. The heat dissipation leaves a lot to be desired. My PGXL arrives today, and I intend to baby it quite a bit. I will use my Alpha 9500 and Acom 2100 for the digital modes. They can handle all sorts of insults and just keep on humming along.

If it were true that "..SPE PAs should not be used for digital modes, period" and were effectively not fit for digital they would not be fit for much, given the high percentage of digital operating that now takes place. But their respective user manuals state they are "able to mange all (digital modes) currently in use". Further, Gianfranco I0ZY posted to the SPE Forum that there is no restriction on use for digital modes. False moves are one thing but when they fail through no fault of the user, that is a different matter. 

This is not my experience. With low power drive, about 4W for LOW, 6W for MID, and 8 W for HIGH. More on 10M. 

One way to determine the optimal driving power is to increase drive watching output power, and stop when teh increase is much less than linear.

For instance if 1 W produces 100W, 3 W produce 290W, 5 W produce 450W, and 6 W produce 470W, 5 W seems OK and 6W is too much. 

One can drive with 8 W in Low and the amp will work but will be greatly distorting on SSB. Probably no effect on CW.

Setting different power levels on many bands is trivial with Flex setting in SPE.  

I have a 6500 linked to SPE 1,5k and works fine. It is possibile band by band to decide the Power input generated by 6500 to avoid any kind of overdrive.

Best 73 and DX

Luciano I0JBL

Have the Expert 1.3FA and home brew cable with no issues. Maybe this is just an issue with the 1.5FA. See my post on wiring.

Make sure you go into the SPE setup for each Amp level and set the desired input to the amp via the menu

for low, Mid and High. This takes a little bit of time for all bands but is worth it as never have overdriven the amp.

Mine is the low pad SPE Amp so 10-12 watts will drive it to full power.

Have run the amp over two years and has worked flawlessly.

My feeling with SPE is they work like BMW, very well but may break from time to time. There may be more reliable choices but using SPE is so easy (antenna switch, settable power levels with Flex, pretuning for each antenna separately). My SPE 2k failed 4 times, 3 times covered by SPE warranty and one by credit card warranty. No problems for the next couple of years. After learning of my problems, Gianfranco of SPE volunteered to take it back. I decided to keep the amp, and it was a good decision retrospectively.

I was cured from tube amps by TenTec Centurion. In one year 2 faults of BK board, one high voltage flashover and a broken band switch.

There is a problem with digital modes, with guys falling for 50% power just by lowering the drive power as the duty cycle increases. As someone noted, lowering the drive power at same voltage can actually increase dissipation as efficiency plummets. Disisipation power is U * I but output power is I*I*R. So if an amp has an efficiency of 60% at KW out, it takes 1600W W and dissipates 600W. At 50% drive with same voltage, it produces 500W, takes about 1100 W (1600w * sqrt(0.5)) and dissipates 600 W, same as with a KW. With voltage reduced to 35V, the efficiency is restored (more less) and the amp would dissipate around 300W.

SPE owners have a choice of using the lower voltage to boost efficiency, unlike e.g. KPA1500. PGXL has MFFA, not sure whether this is the same thing as reducing the voltage to maintain efficiency. But PGXL does not have an ATU, which limits its appeal mainly to hams with low SWR antennas (higher level contesters). Personally, my antenna are low SWR except 40m (2 el shorty with 150 KHz 2:1 bandwith) and 160m (80 KHz 2:1 bandwidth). With pretuning by SPE, QSY is instantaneous even on 160 and 40m. No pressing buttons, no turning knobs....

Ignacy NO9E

Been a while since anyone has posted here but I wanted to thank all of the posters on this thread. Though I’m not new to SPE Amps, I am to the Flex 6400 and SmartSDR. This thread was IMMENSELY helpful to me in getting my REV 1.0 Expert 1.5K-FA set up with proper RF Pwr levels so it would quit going into Protection mode from INPUT OVERDRIVE.

I will post the following information that was sent to me from a friend on drive levels but before I do, let me say this, and I learned this from this thread…. The 0-100 RF Pwr: slider is NOT 0 watts to 100 watts, it is 0-100% of whatever RF Prw the radio has and it differs band to band. Use a watt meter between the radio and the amp to verify what rf power the radio is actually putting out at 100% using the TUNE button and then adjust your drive levels according to your watt meter, not the SmartSDR slider value. I found that the radio was putting out significantly more than 100 watts on 160, 80, 40, and 20 meters.

Thanks again to the OP of this thread and to all the posters.

Paul - N5DUP

P.S. Start at several watts under the 30/20/10 MAX/MID/LOW maximum settings

When the SPE linear is in Standby, you can set the SmartSDR's RF power control where ever you want. When the SPE linear is in Operate, the linear will take over the FlexRadio's drive level based on what you set it for on the linear.

When the SPE linear is in Operate, just press one of the Left/Up or Down/Right arrow buttons on the front of the linear. When you do this, you will see the "PC:****" appear above where you see "BAND" on the linear's front panel. This is the percent of drive the SPE linear is telling the FlexRadio to use. Basically, for a 100 watt transceiver, 0 to 100% equals 0 to 100 watts of RF output. While the PC:**** is displayed, you can use the same arrow buttons to change the value. The default values used to be 20, 40 and 60 for LOW, MID and MAX outputs of the linear. I think they are different now. Ultimately, the 1.3K-FA/1.5K-FA will need something like 10, 20 and 30 for LOW, MID and MAX. Start out with lower numbers and work your way up to where you want or you see no difference in amplifier output. Again, this needs to be done with the linear in Operate. It cannot be done in Standby. You will also need to make these 3 adjustments for each band.