UPDATED 3-14-2023
SUMMARY: This is a 5-Star solid state amplifier for yesterday and a 4-Star amplifier for today in light of newer products that are half the weight, much smaller, more power efficient and more powerful. Regardless - this is a VERY good HF/6M amplifier. Not something I'd want to lug on a DXpedition, though!
DETAILS: The 1 KW Quadra VL-1000 HF/6M amplifier and it's separate VP-1000 power supply is large and heavy (78 lbs.) compared to more modern and powerful solid state HF/6M amplifiers (like the 1.5 KW Elecraft KPA-1500 which weighs just 39 lbs.). Visually, its looks a lot like a late '80's high end component stereo system tuner/amp, with concealed control buttons and a large but monochrome, low-res LCD panel. It will supply 1 KW PEP (HF)/500W PEP (6M) when running from 240 VAC and up to 500 W PEP on 120 VAC (not recommended). High duty cycle/digital modes should be limited to 500W, per Yaesu. A built-in, motor AND relay driven automatic tuner allows matching of most resonant (~3:1 SWR) antennas at full power. While it has excellent peak/average power and SWR/SWR map readouts, it curiously lacks a PA temperature indicator, other than overheat and fault.
Like the Icom PWM-1, the Yaesu Quadra was an elite solid state amplifier when introduced in 1997/98, and its heavy, no expenses spared, quality build still reflects that.
For anyone considering buying a used Quadra (they were discontinued in 2020) Adam Farson, AB0J, has a great set of web pages on the Yaesu Quadra with a lot of resources, including FAQ's, repair info, operating experiences, etc. (Thanks, Adam!): https://www.ab4oj.com/quadra/main.html
The Quadra design is dated and uses eight (8) MRF-150 transistors in four complementary pairs (hence the name "Quadra") whose outputs feed a fairly lossy combiner tree, and so it's not the most efficient solid state amplifier out there today. Newer LDMOS amps usually eliminate the combiner tree by using a single, higher power complementary pair of transistors, sometimes with both in the same module (looks like a single transistor). But the good news is that the Quadra's MRF-150 transistors are relatively inexpensive and readily available as of 2023, if repairs are needed. In fact, a pair of their close cousins, the VRF-150's, are used in the much newer, 200 Watt Yaesu FTDX-101D/MP.
But as all things Yaesu - the Quadra has a few quirks...
The Quadra should be turned on in a specific 3-step sequence. FIRST: rear VP-1000 mounted MASTER circuit breaker which I just leave ON, SECOND: VP-1000 front panel "hard" POWER switch, then THIRD: VL-1000 front panel "soft" POWER switch. Turn off in reverse order.
If just the VL-1000 soft switch is used to turn the amp off (VL-1000 power supply left ON), then it will actually be in "standby" mode and will periodically "exercise" its relays with a noticeable "clicking" sound. The VP-1000 power supply is also prone to damage from AC mains fault events, so its best to turn it and the VP-1000 off completely, from its front panel 'hard" switch - AFTER shutting the VL-1000 off via its soft switch.
When used with non-Yaesu rigs, the Quadra/VL-1000 requires pushing a front-mounted button to "auto-sense" and move to the correct frequency based on exciter output. But it can be set to follow band moves automatically and instantly via a dedicated control cable with Yaesu (only) rigs. This works fine with the FTDX-101D/MP, FTDX-5000/-3000/-1200, FT-991/991a and many other Yaesu radios.
The VP-1000 has two separate radio control ports (and linked exciter input ports) to allow automatic band switching by Yaesu HF/6M transceivers. But each port has slightly different auxiliary control lines in addition to the band selection lines. Yaesu recommends use of the #2 control and exciter inputs for the FTDX-101D/MP, FTDX-3000/-1200 and FT-991/991A. Unfortunately the amplifier passes through only the #1 exciter input to the #1 antenna output when off, so for any other configuration it must be powered up but disabled for amplifier pass-through.
The Quadra includes a low power mode where final transistor voltage is reduced from 50 VDC to 35VDC. This low power mode improves crossover distortion and lowers power dissipation/heating when running at or under 500W output - great for high duty cycle/weak signal digital modes like FT8.
There is also a switchable 3 dB INPUT attenuator pad that INCREASES required drive by 3 dB (doubles it). This attenuator is intended to allow safe operation of the Quadra with exciters putting out more than 100 Watts (like the 200 Watt FTDX-101MP) by providing more overdrive margin. It's also handy for reducing amplifier power output significantly in one "jump", or for going below 100W output with the amplifier still in line when used with transceivers like the the FTDX-101/-3000/-1200 and FT-991/991A, etc., that have a minimum 5-Watt output level.
A 20 dB OUTPUT attenuator is automatically switched in-line during antenna tuning to reduce interference to other hams. The good news is that it works very well. The bad news is that tuning REQUIRES about 70 Watts of drive from the exciter for successful tuner activation - otherwise it aborts. I put the amplifier in BYPASS mode for antenna tuning just to be safe as 70 Watts of drive can actually OVERDRIVE the Quadra in normal operation, which usually requires no more than 40 Watts drive for full output and forgetting to back off drive after tuning can be problematic. Yet another "quirk"/feature/operating procedure that is not well explained in the manual.
There is no direct temperature readout on the VL-1000 but final transistor heating can be gauged as amplifier gain drops slightly - about 5-10% (it will require more drive for the same output) as the amp warms up. The only indication of temperature beyond this is a warning on the amplifier front panel that the PA is getting too hot, followed by a mandatory, automatic disable if this goes too far. Due to it's size and design, the Quadra has LOTS of thermal mass and heat sink area plus FIVE fans (3 on the VL-1000, 2 on the VP-1000) - so overheating is very unlikely when operated within specs. Still, I LIKE a temperature readout and so installed two thermocouples on the (huge) VL-1000 heatsink, leading to an external meter, just to keep an eye on things.
Despite the number of fans, the amplifier is pretty quiet, emitting a slightly louder and periodic "Whoosh!" when transmitting for a while. You KNOW when the Quadra is working hard from the tone of the fans, but it's never obnoxious. It's certainly quieter than my Elecraft KPA-500 at 500 Watts out in back to back digital QSOs (but I really don't mind that fan noise, either).
After four years of (very happy) intense use on SSB and digital modes one of the MRF-150 transistors failed and was replaced (by John Stanford at Island Amplifier in Placentia, CA - GOOD JOB, John!). I had run the Quadra with FTDX-1200, -3000 and FT-991 radios with resonant antennas ranging from a Cushcraft/MFJ A3S Yagi (now DEAD), Mosley TA-33-MW/40M (working just fine), to a an EFHW-8010-2K end-fed wire (great to fill in the band gaps on the Mosley). One of these antennas suffered an intermittent insulation breakdown at 500 Watts, and this apparently lead to amplifier damage before the protection circuits kicked in. Many amplifiers are subject to this same failure cause/effect so I do not fault the Quadra for this.
I'm currently running the Quadra with an FTDX-101MP and am rediscovering the pleasure of using it - AFTER running my backup amp for a while - an Elecraft KPA-500/KAT-500 amplifier/tuner combo.
The KPA-500/KAT-500 combo is a small fraction of the Quadra's size and weight, is more power efficient, runs happily off of 120 VAC, can seemingly run at 500 W on FT8 all day in back to back QSOs (but with significant fan noise), has no visible "gain droop" when hot and automatically goes into bypass mode (up to 200W "through power") when OFF. Also, the KPA-500 status panel can display finals temp continuously in 1C increments. Effectively, the relatively tiny and convenient KPA/KAT-500 can run FT8 QRO just as well as the super-sized Quadra.
But the Quadra CAN support SSB and CW at 1 KW, one (Yaesu) S-unit (3 dB) greater than the 500W KPA-500, just by pressing a button, and this CAN make a significant difference on those modes.
The Quadra also has two separate and switchable exciter RF input ports and two control ports to go with them ( the KPA/KAT-500 has just one). It has FOUR switchable antenna output ports (KPA/KAT-500 has 3). The relatively slow built-in motor + relay driven tuner is a throwback to yesteryear but seems to handle all of my (resonant) antennas across their respective bands without trouble and has quite a few memories to speed things up.
At 1KW out on SSB some microphonic noise can be heard from the Quadra VL-1000, but this does not seem to affect output signal quality.
Overall, the Quadra is a "tried and true amplifier" that has stood "the test of time" well, but has a few small issues, mainly due to it's dated design: Size, weight, power efficiency and lack of finals temp readout.
Regardless - If you have the space, 240 VAC outlet and a strong bench (and back!) to support it, the Quadra is a pleasure to use. What it does, it does VERY well. And so I've put it back in operation and put the KPA-500/KAT-500 (a GREAT combo) next to it, on "STANDBY".
Best Regards,
Brian - K6BRN |