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VHF and HF amplifiers
This section will ("wip", pictures will follow) contain an overview of my current and past HF and VHF amplifiers
plus my evaluation and comments for each item.
This at present still is "wip" ("work in progress").
VHF amplifiers:
Compact-1000 2m amplifier by I0JXX
For our current 2m EME set-up we have chosen to get the I0JXX Compact-1000 amplifier.
This is a ready-to-go 144 MHz MosFET amp offered by I0JXX and besides the pure amp stages it's got a
built-in and reasonably well-designed low pass filter.
Reason for choosing this amp was quick availability (and delivery) plus expected ruggedness of the amp.
The amp easily delivers up to 1100 watts output, measured with an high-quality PEP watt meter, without
getting any hot. For our JT65B operation at our EME site it easily delivers the legal 750 watts at the antenna
without any complaints.
It's got built-in protection circuits, e.g. shutting-off with too high an SWR (and yes, they work and we had to
test this, not by intent but by accident!).
However, there is no protection against overdrive. So you really need to take care about this issue.
At power-on you'll get a warning at the amplifier status LCD to take care about adjusting your driving power
and you better follow these instructions!
Another feature especially beneficial at our /portable EME location is the built-in switching-type PSU.
It covers a wide range of AC input voltage swing and keeps the amp DC supply voltage and the power output
up to the desired level.
We have more than 100 meters of AC supply line length from the power outlet to our EME shack. The voltage
swing along the AC line is such, that at the legal limit power output we see as much as a 40 Volts AC voltage
swing (dropping from the nominal 230 Volts AC supply)!
For the rest of our EME equipment we are also using switched-type PSUs and they act with the same behaviour,
no issues with that in face of the large AC voltage drop along the AC line.
The only complaint we've had so far with the Compact-1000 are the rather noisy fans. They are really "loud"
but on the other hand keep the "thermals" of the amp at a quite safe level even under extended key-down
operation.
For more details on the amplifier see the I0JXX website here.
HF amplifiers:
As I am working CW QRP most of the time these days, my HF amps are sitting on the shack shelf without
being used at all.
However, I would like to give you an overview of what I still have sitting in my shack and what I have used
in the past, and my experience with the various pieces of equipment. I will try to keep the information rather
short on this page and place an internal link whenever I'd like to add some more information and/or pictures.
Tokyo Hy-Power Labs HL-700B (still in the shack):
This is a bi-polar transistor (13.6V DC transistors) HF amplifier sold by THP, Japan.
The amplifier delivers between 500 and 700 watts of output power. At this power level it calls for a DC supply
of about 80 to 90 amps at 13.6 volts! Which basically means you need to connect the amp to a switching-type
of PSU. At present I've connected it to a 120 amps switching PSU and made the DC supply lines (thumb-thick
wire) as short as possible. There is still a bit of voltage drop along the DC supply line which I could eliminate
by installing 2 voltage sensing wires from the amp back to the switching PSU which compensate for the voltage
drop.
Although the HL-700B only has push-buttons for selecting the "conventional" 5 ham
radio bands, it also works on the WARC bands by selecting the next higher band.
E.g. when used on 18 MHz you need to push-in the 21 MHz button.
However, it will not be wise to use it on 1.8 MHz, as there is no dedicated low-pass-filter
for that band and the 3.5 MHz LPF filter will definitely not be good-enough to get rid of
the 2nd, 3rd and possibly 4th harmonic of 1.8 MHz! Don't use it on 1.8 MHz without
adding a dedicated low pass filter for that band (not too difficult to implement).
(click on picture left for HL-700B picture gallery)
The HL-700B uses 4 pairs of custom THP bi-polar tarnsistors implemented as 4 sets of amps combined together,
each sporting 2 transistors, giving a total of 8 transistors.
A very unique feature of the HL-700B is that by flipping an internal switch you can configure the amp such that
1 amp unit is been taken out of the final amp configuaration and instead being used as a driver.
As a result you can drive the amp with a low power transceiver (5 to 10 watts of output power) and still get out
something like up to 400 watts PEP from the remaining 3 amp units! A very clever and flexible design!
Fan modification / updated 21-Oct-2009:
As the original fans were much on the noisy side I exchanged them (2 pieces) with Pabst fans. I used a pair of
3412 NGMV fans because that was the best I could get hold of re. noise level at the time of the mod. I do not use
their thermal voltage control line, though. The fans are spec'd at 28 db(A) and 72 m^3/h.
Today (2009) Pabst also offers 3412 versions NLE and NGLE which are spec'd at 23 db(A) and 61 m^3/h. That's a
5 db(A) difference which is a lot!
It's certainly also worth-while looking at fans from "Noiseblocker" (www.noiseblocker.de). They have a version of
their "blacksilentfan", XE1, which is spec'd at 21 db(A) and 50 m^3/h. Max. DC voltage is spec'd at 13.8 volts DC.
So it might be a good idea to insert a small value resistor into the fan DC supply line in order to have the fans
running within spec'd supply voltage range. However, I do not have used their fans so far, so no experience re.
quality and reliability of their products.
Heathkit SB-220 (not in the shack any more):
I've used this amp over many years back in the 80s of the last century. It sports 2 Eimac 3-500Z tubes which
are no longer manufactured by Eimac but are offered from Chinese supplies plus some US NOS etc.
Good point with that amplifier was: you were never able to over-drive it as it needed about 120+ watts to
be fully driven to the limits. I had no such transceiver at that time which would drive an SB-220 over it's limits.
Relay switching line was at about -120 volts, calling for an amplifier switching interface when using the amp
with contemporary transceivers and their ability of switching voltage and currents. So watch out for that!
Adjusting Pi-Net input circuitry was extremely awkward! A big hazzle! This is more important if you intend
to use an SB-220 with a transistorised transceiver and in case you may need to correct the amp's input SWR to
a safe level. Extremely cumbersome to do this job as the circuitry was hidden inside the midths of the cabinet!
Rather difficult to get there and dangerous as far as HV contact is concerned!
Else: a very reliable and strong amp!
Heathkit SB-200 (not in the shack any more):
SB-200 is a still very usable amp. It sports a pair of 572B tubes which come from China these days.
Power output is at about 600 watts, maybe 700 watts. It's got an input Pi-Net filter as well as on the SB-220.
However, adjustments to that is much more easy than with the SB-220.
It is said to also perform on the WARC bands. However, I cannot confirm this as I have never used the amp
on those bands.
Relay switching voltage: as with the SB-220, it is negative at about -120 volts, calling for a dedicated amplifier
switching device when used with contemporary transceivers. Else, you may just "freeze" your transceivers
amp switching relay! You should better watch-out for this!
Collins 30L-1 (still in the shack):
This amplifier sports 4x 811A (triode) tubes and covers all ham radio bands (please see 30L-1 instructions manual
for details!).
It's a pretty good SSB and CW amp and is still quite usable these days. Very clean TX signal!
I've not used it on the WARC bands, as I do not run high power there anyway. It's not an appropriate amp for
running key-down modes as RTTY etc., as the per tube dissipation power is only rated at 65 watts per tube and
with respect to the tube data sheet.
But it is said to be one of the cleanest tube-type HF amps on the market!
Yaesu FL-7000 (not in the shack anymore):
Actually, I have owned 2 versions of the Yaesu FL-7000: the "old" version (2nd hand purchase) and the "new" version,
which I had bought "brand-new".
The amp had various issues, where a few of them were related to the amp design:
E.g. the internal antenna tuner was very slow and had trouble of finding the appropriate SWR settings quick-enough.
The amp was very sensitive for TRX driver spikes. I was not aware ot his TRX issue until I had purchased my first
FL-7000. I did have issues with TRXs from all of the big 3 Japanese brands. I finally touched-up the FL-7000 internal
protection settings until I could achieve a stable working condition. After that it performed rather well.
to be continued...
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