So I am building out a Harris Analog TV SSPA out for a 1KW 6 meter amplifier for running meteor scatter and when some openings pop up. Here is a picture of most of the parts I have, I have most of everything just need a 30ua meter movement for my bird Line Section and a 1.5KW bird slug. I already have the Power supply and voltage divider circuits for the fans. I have to build a buck circuit for the RX/TX switching relays to kick the amp in and out of the circuit. This Amp has 16 transistors, 2 per pallet board, and an input and output combiner circuit that is good for 10db of gain. So 1 watt in is 100w out, 10 watts in is 1KW out.

These amps are hard to get parts for so even though it will run legal limit, they were designed to run 100% duty cycle in the TV service at 1kw with 250cfm of airflow. So I plan to keep this amp at 1KW for efficiency's sake.

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Now one of the issues with these amps is they are commonly destroyed by radios that have an ALC oversoot on key up. I am going to be running this on an IC-7300 and the overshoot on most of them is there, it is usually the first 1-2ms after key up you get a 100w spike for around 1ms. This can be enough to smoke the finals even when the power is reduced to say 10% for a 1 KW out system.

Currently, I have a W6PQL 4 even sequencer that can hold off the amp keying for 300ms so that would keep the spike out of the amplifier circuit and would just hit the antenna. The other option I have is to pad the input of the amp with a 10db attenuator circuit. That way if I forget to turn the power down, I would not damage anything, in fact I could leave my radio at full power at all times and run the amp for 1kw, or kick the power back for reduced power on the amp. That is the way I am leaning, just because as we get older it seems that we forget things more often. Like to get some opinions on what direction you would go on this?

Very cool project!

How much drive power does this amp require for full power out, i.e. how much gain does it have?

Each of phillips devices is spec for 150w output each x16 so max theoretical power is 2.4kw. Harris claims the quarter modules are rated for service of 275 watts out per module @100% duty cycle. Testing of these 1/4 modules showed that they were able to keep linearity and power dissipation rating under the Phillips specs with 400 watts out and the 3rd order was about -28dBc doing a 2 tone test. So even driving this to 1600w output of SSB maintains linearity. The commercial standard for 3rd order IMD is -30dBc, and ham gear specs are -20dBc. Total gain varies from amp to amp, but the average is about 20db on the low end and around 18db on the high end.

Power requirements are 50v with voltage sagging at 1500w output to around 49v @ 44.6 amps. I have a modified HP 50v server power supply that is rated to 3kw so around 70 amps supply using 220v.

So I should be able to key down on this amp at 1kw indefinitely.

The TV  station that these came out of ran a rack of 100 of these for a 100kw output. They were hot-swappable modules and if a fault occurred they would yank the module while still transmitting and then slide a backup in and be back up and running. The guy I got this from tested this amp with a weak bench power supply and with 23 watts in got 960 out on the Bird meter. His buddy's amp tested at 950 watts and when he got his on the air using the same supply I have, he was getting 1390w with 22 watts of drive.

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The challenging thing with this is output filtering, and TX/RX switching, size, and cooling. I have a 2kw low pass filter for this, 3rd harmonics is the issue since at 1500w out there are effectively 25 watts on 150mhz. I am considering padding the input but that would limit me to around 10w input with a 10db pad. If I sequence the ALC spike out of it, then I can adjust for full legal limit on SSB and kick the power back to 1KW on digital modes and keep this thing happy.

I have several of those amps, which I have not yet put into service, and I am planning to drive them with either an IC-705, which probably maxes out at around 10W out on 6m, or else I also intend to drive them with a recent-vintage Hermes board from Apache Labs, driving either the companion 10W amplifier (which may possibly have reduced output on 6m), that is, if Apache Labs ever gets around to fulfilling my order that I placed a long, long time ago (for which they are not responding to my customer support inquiries, which is par for the course for Apache Labs), or else I will be driving a 10W amplifier kit that I got from QRP Labs (which I have not built yet).

Neither of those options should encounter the transmit spike problem.

However, depending on the output power that I see from driving the Harris with either of those radio/amplifier combinations, and depending on whether I may decide to drive a pair of the Harris amplifiers (with a splitter on the inputs and a combiner on the outputs), I may later decide to use my IC-7300 as the driving rig.

Either way, I will be using an older W6PQL sequencer to handle the sequencing.

So take my comments with a grain of salt.

But if it were me, I would not want to hot-switch the input to the Harris via the sequencer as a way of protecting against a possible rogue spike.

So, in light of the potential severe consequences should such a spike become an issue, personally I'd be more comfortable running the IC-7300 at full output, and putting an appropriate attenuator between the output of the IC-7300 and the input of the Harris.

Yes, the attenuator will get hot - but either a fan or a higher power rating for the attenuator should take care of that. You might have to experiment with different attenuators to get things 'dialed in' to your liking.

I'm hoping (and hoping) that I'll be ready before the June VHF contest. But that was my plan last year as well

Are these only usable at 50ish MHz, or are there others useful at 2M, 222 and 432MHz?

My VHF/UHF multimode setup outputs 10w on all modes - SSB, CW, AM and FM. A couple FT-762Rs, a couple FTV-901Rs and the odd assorted VHF-only transceiver (e.g., TS-660) round things out. These RF decks would be perfect for my application and drive levels.

They can be moved up into VHF but they require no modifications for the 6m conversion. They require quite a bit of modding to move up. The Larcan amps that were used for TV are bettery served for VHF operations from what I was told by most of the guys running them.

It is my understanding that the spike that is known on many of the rigs is only for a millisecond or 2 so I am not worried about hot switching the relays. The more I think about it the more I believe that by the time the sequencer kicks the relays to the amp, then kicks the amp I am looking at 60 ms. The spike should be gone and I should be able to run this with the IC-7300 with no issue. There is an option on the 7300 to hold off RF after keying for 30ms on the different bands, so I think this is a moot point.

I just ran a bunch of tests and was unable to find any indication of Overshoot on 6m with my radio. I may just use a W6PQL ALC circuit on the input of the amp to control the power input into the amp. For now, I think I am going to Proceed with the initial setup and build out of this amp. I also looked at the model of this amp and it appears to be a newer Harris that does have an overdrive, temp, voltage, and SWR lock-out feature. So I will likely move the front mount LED into the Amplifier control box I have. I plan on having the voltage of the power supply, relay indicators, bypass switch, and a power output meter from my line section. I am going to build some legs on the bottom to make a shelf for the pallet. Mount the power supply to the bottom of the pallet and have a break out to supply power to other 50v amps as I build out the next amp for 1296.

Changed the title, and ordered the final parts so I am going to make this a build thread.

30ua watt meter was ordered for the Bird Line section and a peak kit with 2x and 4x will be included in the control head I am building for the amp.

Amp will be converted to a cabinet that is going to double as a 50v power supply and a 12v 75amp supply.

Its Alive!

I have an issue with my microwave down key that I have for the output as the TX/RX. Its a wire mess while I wait for the a project enclosure to come in for the relays, power distribution and the Keying Circuit I am going to have to build. Next up is the remote head with Voltage and Fault Monitoring, analog power meter for the Bird Line Section with a peak reading kit with the 2x and 5x switch. Even with the LPF with 20 watts of drive I am getting 1KW out and the antenna rebuild seems to handle it fine. With a KW out I have about 4 watts reflected.

Started testing on a dead band this evenng and using FTB and increasing the power and duty cycle to check the fan system efficiency. Got it up to Full power for me so just a needle width Shy of 1KW, and i get a response from a guy 30 miles north off the back of the beam. They are coming in at -7 on WSJT. So I make the contact. Get a signal report of +39! About fell out of my chair and kicked the the power down and finished up testing.

Next up cleaning up the wiring, and building the remote head, and hitting some MSK for meteor scatter. My

Awesome project!

You are doing  all this cool  6 meter High Power solid state fab..... and then using an IC7300 for exciter ???
 ???? WHY ?
                   Use a better radio,one  without inherent 130 watt key-up pulses.

I have been testing this radio and there has not been any RF during key up. Tested on Oscilloscope and spectrum analyzer.

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These are some of the parts for the remote control head. I built the relay control using solid state relays. From key down to full path switching is 15ms total. With the delay on the radio and delay in WSJT i have about a .3 second buffer going on. Right now the control head is not being used. I have to build it still so I added an option of RCA plug keying from my sequencer. Its is working well. With 10 watts of drive it is make 600w out. 17 watts of drive is good for 1kw. Ran a test last night of a 10m cycle of JT65 eme and ran 10 transmit sequences and the amp was only 75 degrees on the fins. The fans are a bit loud even at half voltage so I will build a thermal control circuit. Here is the meter from last night on the test. This was 17 watts of drive, 500w bird slug with the peak kit on 2x and calibrated.

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Been working on the noise I had from the DC to DC converter to drop the voltage from 50v to 28v for the antenna relays. And some noise from the 50v switcher. Bad news was I ran through my supply of FT240-31 cores, good news is my RX level of noise has dropped dramatically and now able to pull some really weak signals out. Had a great morning on Meteor Scatter with it.

Outstanding! Just in time for time for the 6m season.