First off, my sincere thanks to everyone for subscribing to our very first email newsletter...sent to 550+ hams!
By now, most receiving this newsletter have seen the website, emailed or talked with me personally regarding our new amplifier design, which is still very much a work in progress.
In the months since this project began, there have been small changes made (filament supply design, blower positioning, etc), somewhat larger changes made (input circuit design, major component positioning, etc)....and we have, at times, made some fairly significant changes (chassis design, tank design, and even a change in vacuum tubes).
The story on the tube change....
The change from the 3CPX800A7 to the current 8877 was done for a few reasons - and not two months after this decision was made, the wholesale cost of the smaller triode rose nearly one-third, despite the fact we were purchasing these from Eimac directly in Palo Alto, California.
For hams purchasing our amplifier using (2) of the '800A7's, this would have meant about $600 extra just in tube cost, and around $900 extra for the 3-tube export models. This volatile increase aside, the decision to go with the trusted 8877 has proven to be the right one. The tubes, frankly, have been the singular area in this project where the input (parts) cost is being given attention.
The forward plan (in phases) is mapped out like this:
1) Design / development (coincides with 2x prototype build)
2) Internal prototype testing / de-bugging
3) Initial build of five (5) amplifiers (single 8877 only)
4) Field prototype beta testing of hardware and firmware
5) Apply changes as necessary, based on performance
6) Retest beta units until performance is optimum
7) FCC & CE Mark certification
8) Initiate production
Steps 4, 5 and 6 above could (and likely will) take significant time, all dependent on results from the initial (5) beta units. Real production will occur only after thorough beta testing has been performed for some time, and we are totally convinced of superior performance.
A few of the preliminary specifics....
Groundbreaking for an Amateur Radio amplifier....a powerful Graphical User Interface (GUI) on a touch screen device.
From the tablet:
* Power up and power down the amplifier.
* Monitor Plate & Grid Current, Plate & Filament Voltage, Exhaust Temperature, Power Output, and load SWR.
* Monitor, reset and adjust certain fault settings, including trip-points.
* Take the amplifier into manual mode with virtual Tune & Load knobs using the capacitive touch screen.
Put the amplifier where YOU want it, and simply use the tablet at the operating position, running our custom HTML interface.
We supply the tablet, or you can provide your own.
Because our intent is to offer our same Amateur-spec amplifiers to commercial and government users, we needed continuous coverage HF spectrum resonance.
While models intended strictly for Amateur service will be band-specific firmware locked to meet FCC type acceptance, hams will still benefit from this inductor design offering the perfect value of inductance over the HF spectrum at every individual frequency, as opposed to the more typical approach of using a single tapped tank coil.
This inductor is mandrel wound using a 12 HP South Bend lathe here in Somerset, Pennsylvania. The 1/4" center shaft rides in oil-impregnated bronze rod bearings tested in our shop at over 86,000 revolutions to ensure longevity.
The specific material in this inductor coil is 17200 Alloy, TD02 Temper Beryllium copper, 3/8" wide x 1/16" thick. Turn spacing is 5/16" (0.3125") on center.
Designing this inductor contactor wheel has become a meticulous project in itself. We are using a large diameter, 1-1/4" OD one-piece wheel, machined from solid billet TD04 grade beryllium round rod, which tightly contacts both sides of the coil to eliminate any chance of arcing, even in dusty conditions. We're still perfecting the correct ratio between wheel wall thickness, wall center-to-center spacing, and material spring rate.
Our matching pair of vacuum variable Tune & Load capacitors. We've sourced these from (2) separate offshore suppliers, and are currently working with an independent testing facility to perform HiPot testing, where the capacitor is run back and forth thousands of times, testing the HiPot each time, as well as a destructive rotational "stress" test, where the capacitor internal bellows & inner workings are basically tested until failure occurs.
Doing this gives the internal bellows a real workout & gives us the accelerated stress testing we need to determine which capacitor is the most ideal. We'll then make a determination on the specific manufacturer to go with, based on the test results, and further testing in an actual amplifier.
These will be used in both the 1x8877 and the 2x8877 amplifiers. Ratings on these capacitors is 10KV (working voltage) and 14KV (peak test voltage).
These each measure 9" long, and over 4" in diameter.
And for those wondering what the inside of a vacuum variable looks like, we cut away the ceramic on one....
The large copper bellows pictured in the center expands and contracts with clockwise / counter-clockwise rotational turns, thus varying the capacitance.
The prototype input tuner board is complete and is soon to be tested. Glen has spent significant time the last couple of months designing this specific to the new amp, and he is presently building the frequency lookup tables to be stored in the processor. On this board the bias circuitry is on the left, as is the bias relay. The orange relay is the PTT.
This board has a serial port visible in the upper left used for testing and adjustment using a VNA. For production boards, this serial will not be added.
Input SWR of 1:2 or less should be achievable on all bands.
Our custom spec Toroidal HV transformer, weighing in at a massive 79 LBS.
We told the Maryland-based transformer manufacturer that we needed a real 100% CCS rating at full rated load continuously, and they delivered.
Some specs:
Designed for 4,027v UO (Unloaded Output) at 1.8A.
100% CCS (Continuous Commercial Service) at rated output.
Multiple primary inputs for a variety of voltages (typically in 10 VAC steps) to work in conjunction with our auto-sense AC input circuit.
The temperature rise at rated load is 55 Deg. C.
Core loss is just 24.6W.
Designed for 1,500W FM carrier forever, 100% duty cycle, and no de-rating curve.
As of now, the intent is to use the same power supply in the 1x8877 amplifier as we will in the dual 8877 model for export / commercial users.
Above shows a simple water pressure test being performed on our dual blower, simulated with a mocked-up tube plenum chamber made of cardboard. Air volume & pressure (as they relate to blower output) are significantly reduced with increasing elevation, as opposed to sea-level, and we have tested to ensure our new blower meets the specs provided on the datasheet that accompanies it.
The bottom line here is, we performed this test to ensure our blower will move enough air to satisfy the cooling requirements of the tube at high elevations (10,000 ft) with no reduction in duty cycle.
That's it for now! We'll distribute these newsletters periodically, or as significant updates are made.
73
Dan KK3AN
