Ampeg Portaflex PF-50T Bass Head

Vintage Heritage, Moderate Power, and Great Tube Tone

Tube time ....

by Phil O'Keefe

Ampeg - makers of such legendary tube amps as the SVT and B-15 - is without a doubt one of the most famous names ever in bass amplification. These two amps sit at different ends of the wattage spectrum: the SVT is a high-wattage stage-dominating monster, while the B-15 takes a very tuneful lower-wattage approach that led to it becoming one of the most cherished and oft-used recording amps ever made. The Portaflex line that the B-15 established has included many other tube and solid state models since it was first introduced and while all have built upon the foundation it established, lately the line's emphasis has been on higher-power solid state Class D heads like the PF-350 and PF-800. These are complemented by the vintage style "flip-top" and shelf-ported cabinets that sport the classic B-15 grille cloth. Ampeg was no doubt aware of the recent lack of tube Portaflex head offerings, and having heard the requests from their customers have taken action. Let's look at a brand new all-tube Portaflex amp called the PF-50T, and see how it stacks up.

What You Need To Know

• The 50-watt PF-50T is joined by the 20-watt PF-20T, which while similar, has a more basic three-band EQ section.

• The PF-50T's tubes are all from Ruby Tubes. There's a a pair of 6L6GC-MSTR power tubes and three nine-pin preamp tubes - two 12AX7s, with one for preamp and gain in V1, and the other handling EQ and amp drive in V2, and a 12AU7 in V3 that functions as a phase splitter for the power amp section. The PF-20T uses a similar all-tube setup, but with two 12AX7's and a pair of 6V6 power amp tubes. All the tube sockets are ceramic, and tube retainers are provided for the power tubes, with shields for the preamp bottles.

   

• The PF-50T uses a solid state rectifier. Power output is rated 50W RMS at 20% THD when feeding a 4 or 8 ohm load, with a maximum available amp gain of 66 dB (54 dB for the PF-20T).

   

• Physically, the PF-50T is a bit of a beast. The enclosure is topped off with a protective metal cage over the five tubes, as well as two beefy transformers. The box itself is made of heavy-gauge metal, and feels quite rigid and substantial. Of course, all of this comes with a bit of a weight penalty; the PF-50T weighs in at 19.4 pounds - not unreasonable by tube head standards but certainly not insignificant. Still, I'll take rugged construction I can rely on over light in weight but cheap and flimsy any day. The head measures 7.3" H x 13.0" W x 10.4" D. The PF-20T shares the same dimensions, but is a bit lighter at 15.2 pounds.

   

• The Ampeg Portaflex PF-50T has a rather cool dual-color, bar-shaped power indicator located directly beneath the front Ampeg logo. It illuminates red when the power is on but the amp is in standby, and glows purple when the amp is on and ready to play.

• The front panel's controls are straightforward. You get dual inputs; one of which is attenuated -15dB and is well-suited for use with hot active pickups. The other input is unattenuated and designed for passive basses. I tested the PF-50T with both active and passive basses, using both flatwound and roundwound strings.

• Like most good tube heads, a nearly unnoticeable amount of tube distortion is a basic ingredient in the PF-50T's tonal recipe, giving it warmth and subtle coloration. If you want more apparent dirt, the amp can certainly oblige. There are separate gain and volume controls, which makes it easy to dial in just a little growl when you dig in, or even a pretty healthy amount of tube grit - just push the gain past noon and set the volume level to taste.   

   

• Expanding on the two band EQ of its B-15 ancestor, the EQ on the PF-50T is three-band, with traditional boost/cut bass and treble controls. The Bass control offers +/- 10 dB of boost or cut at 60 Hz, while the Treble control provides +10/-20 dB at 8 kHz.

   

• The PF-20T has a more stripped-down midrange EQ with a single knob for boost and cut, but the midrange on the PF-50T is a bit more complex, with a second five-position knob to let you select the frequency you want the boost/cut knob to adjust. This gives the midrange EQ band quite a bit of flexibility, and provides a considerable amount of tonal control in this vital frequency range.  The five-position switch can be set for +5/-20 dB at 200 Hz, 400 Hz or 800 Hz, and has a +5/-15 dB range for the 1.6 kHz and 3 kHz settings.

   

• Another difference in the EQ between the two models is the inclusion of two additional EQ switches on the PF-50T labeled "Ultra High" and "Ultra Low." When active, the Ultra High switch adds 5 dB at 8 kHz, while the Ultra Low adds 2 dB at 50 Hz and simultaneously subtracts 10 dB at 500 Hz to reduce midrange mud.

   

• Around back, you'll find the power and standby switches, a fuse-protected IEC power cable receptacle, a bias adjustment screw with two LED indicators to help you set it properly, an XLR preamp output that can be switched for pre or post-EQ, a transformer balanced XLR line out with a switchable ground lift, and a single 1/4" speaker output jack. This speaker out jack has a switch that allows you to set it for 4 or 8 ohm loads. 

• The Line Output can be used even when a speaker load is not attached; the only caveat is that Ampeg says you need to switch the impedance selection switch to the 8 ohm position when doing so. Being able to run without a speaker load is a great feature for recording, as well as when using the PF-50T as a preamp alongside a more powerful power amp.  

   

• One of the cool features of the Portaflex line is the way that the heads can be physically attached to the removable top panels of some of the Portaflex cabinets, then flipped over so the amp is tucked away within the cabinet for storage and transport. Once you get to the gig, you unlatch the top and flip it over, plug in the cables and you're ready to go. While Ampex didn't include a cabinet as part of this review, they assure me that the PF-20T and PF-50T tube heads will work in exactly this manner with the PF-115HE and PF-210HE "flip top" cabinets from the current Portaflex line.  

   

Limitations

• While it can get reasonably loud (and the loudness will also depend on the efficiency of the speaker(s) you have connected to the PF-50T), it's still only a 50 watt amp, with all the limitations that come along with a lower-powered amplifier.

   

• There's only one speaker output jack, so if you want to run two cabinets your only option is to daisy-chain them.

• Tube access isn't horrible, but it does require a Phillips screwdriver to remove six small screws. Such screws can be easily lost on a dark stage; a tool-free "captive" thumb screw arrangement for the tube cage attachment would be an improvement.

   

• The tube cage can get very hot during operation. There's a warning printed clearly on the cage, but it bears repeating - be careful not to lay anything on top of it (or touch it) when the amp is in use.

   

• Some modern conveniences that many bass amps offer are not included, such as a onboard compressor/limiter, effects loop, headphone jack, dedicated tuner output jack and line input.

   

Conclusion

With heavy-duty construction and a beefy sound that respects the past but isn't stuck in it, the Ampeg Portaflex PF-50T is a worthy descendent of the legendary B-15 and a cool new addition to the Portafex line. While it lacks the high wattage of some other contemporary bass amps, it makes up for it with tons of delicious tube tone and tonal flexibility. At only $899.99 "street," the PF-50T can be coupled with a PF-115HE flip-top cabinet for a combo with a lot of the sound, look and vibe of Ampeg's Heritage series B-15N ($2,999.99 "street") for less than half the price.

Some players may be tempted to opt for the even less expensive ($599.99 "street" price) PF-20T. While I have not tried that amp, I wouldn't be surprised if many ultimately purchase the PF-50T instead due to its higher wattage and more flexible EQ. The EQ on the PF-50T is quite powerful, and I was able to dial up tons of cool-sounding tones quickly and easily with any bass, including sounds reminiscent of the classic 60s era B-15 tones. The gain and volume control arrangement allows for similar user control over the amount of grit and growl in the sound, from clean and warm-sounding all the way to significant amounts of tube overdrive.

While the original B-15 was only 25-30 watts, even 50 watts is relatively low for a bass rig today. The PF-50T also lacks some of the other modern conveniences that its Class D powered Portaflex stablemates have, such as an effects loop and compressor. However, don't underestimate what you can do with a amp like this. First of all, it's louder than you might think. I was able to generate levels that hit 115 dB with this amp (measured one meter away from a cabinet rated at 99 dB @ 1 W/1m), so for situations where you don't need earth-shaking volume levels (such as rehearsals, small venues and when recording), it's a great choice. It has plenty of power for live use in small to mid-sized clubs, cafes and coffee houses. With PA support, larger gigs could be covered too, courtesy of the line output. And best of all, the PF-50T has the same kind of rich, all-tube tonal sweetness and ease of use that made Ampeg's most legendary amps famous, so no matter where or how you use it, you'll be doing it in style. That makes the PF-50T a winner, and it's bound to be a big hit with bass players.  

Resources

Ampeg Portaflex PF-50T tube bass head ($1,259.99 MSRP, $899.00 "street")

Ampeg's Portaflex PF-50T product web page.

Ampeg's Portaflex product lineup page.

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Phil O'Keefe is a multi-instrumentalist, recording engineer / producer and the Senior Editor of Harmony Central. He has engineered, produced and performed on countless recording sessions in a diverse range of styles, with artists such as Alien Ant Farm, Jules Day, Voodoo Glow Skulls, John McGill, Michael Knott and Alexa's Wish. He is a former featured monthly columnist for EQ magazine, and his articles and product reviews have also appeared in Keyboard, Electronic Musician and Guitar Player magazines.