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Super Twin Plexi 

"Unique One of a Kind Amp For the Serious Creative Player"

Frenzel Super Twin Plexi 800 Guitar Amp

Sample Image -  Panel Design May Vary Depending On Upgrades    

  • Model No. STP -50 (50 Watt Standard)

  • Model No. STP -100 (100 Watt Upgrade)

  • Push-Pull 6L6/EL34 Guitar Amp

  • 4-8-16 Speaker Impedance

  • Multi Power Level  1/4 - 1/2 - Full

  • Dual Channel Twin & Plexi  Preamps

  • Separate Channel Gains, Master, Tone Stack

  • Bright & Deep Switches
  • 3 Band Tone Stack

  • Presence With Edge Boost

  • Buffered Effects Loop

  • 6L6-EL34 Bias Switch

  • Post OT Line Out With Level Control

  • Tubes: 5 -12AX7, 2 -6L6GC

MSRP: $1865.00



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The FRENZEL STP50/100 "Super Twin Plexi"  was designed as the ultimate amp for the serious player.  It  has a lot of soul that is generated by two separately voiced preamps each with its own separate Gain control, 3 band tone stack,  and Master level control. The CLEAN preamp is voiced like the classic Fender 5F8A Twin…the BOOST channel is voiced like the Marshall Super Lead Plexi. This amp is a unique one of a kind designed totally for the creative player in mind. It will give you just about any sound you ever dreamed of.  

The heart of any amp is the preamp…it generates the signature tones. The preamp in this amp is a killer tone machine like none you have ever heard. It has High-Low separate input jacks for each channel. This allows you to match your pickup output impedance and to use an AB-Y switch select either channel or both to create your own unique tones! Each channel has separate F and M preamps each with its own Gain Control with a Bright pull switch or voice mode pull switch,  a 3 Band Tone Stack with a Deep pull switch on the Bass, and Master Level Control.   Both preamps share the same Presence control which is part of the output negative feedback circuitry. Also, we have put an Edge boost pull-switch on the Presence control that reduces the negative feedback level to produce a boost in volume and a soaring uncompressed sound for dynamic leads. The combination of all these options generates a wide ranges of tones from Clapton warm to Van Halen hot!  

No matter how good any preamp is, it can always be fine tuned an Effects Loop to create your own unique tones with pedals.  The  Effects Loop uses a passive buffer amplifier to match low or high impedance pedals with the high impedance tube circuitry of the amp. This prevents tone suck and volume loss. 

We left the output stage design of the amp pretty much undisturbed from the vintage design except  we replaced  the 5881’s  used in the Twin with the new higher plate voltage JJ 6L6GC'S to give more headroom and warmth, but we also added a bias switch to select EL34's for a more Marshall sound. For the output trannie we chose a vintage Marshall for the original classic vintage sound. This trannie provides you with extended low-end warmth and those  incredible enhanced Marshall overtones. All the while, maintaining a perfect balance between the highs, mids, and lows. The trannie  has  4, 8, and 16 ohm output taps which are selectable by a switch on the back of the amp. The output transformer feeds a passive three power level attenuator that provides a selection of 1/4, 1/2 or FULL power.  A post output transformer Line Out with Line Out Level control is provided for recording or driving a power amp. The Line Out can be used without a speaker plugged in.  It has an auto switched internal load to simulate a speaker if a speaker is not plugged in. This allows you to produce true clean and overdrive distortion tones when recording without a speaker.

For the power supply section we used an oversized custom power transformer which provides great voltage regulation so that you don’t sag too much when you get on it hard. The high-voltage is filtered for very low hum by an equally large choke and 8 filter capacitors.  We stayed with the Marshall choice of solid state rectifiers, but chose the newest type FRED ultra fast recovery rectifiers for tight dynamic bass response. 

The amp is built on a compact 17” x  10”  x 3” aluminum chassis and come with a retro steel mesh cage. All the parts in the amp are top-of-the line  including polypropylene coupling caps, precision mica tone stack caps, metal film resistors, Alpha pots, Neutrik jacks, high voltage sockets, etc…  This is a rock solid point-to-point hand wired amp….a real one of kind collectors item...designed to last for generations! 


Standard Features:

  • Dual Channel - Each channel has High/Low input jacks, separate Gains, Tone Stacks & Masters.

  • Channel 1  - Fender 5F8 Twin smooth  warm clean tones.  Channel 2 - Marshall Super Lead Plexi high-mid rock tones .  You can use an AB-Y switch to select or blend the channels to create your own distinct tones.

  • Bright Pull Switch On F and M  channel Gain controls.

  • Classic Bassman 5F6A style 3-BAND TONE STACK for extended flexibility in shaping your tone.

  • Deep Pull Switch on Bass controls.

  • Master level controls so you can crank the GAIN's up and overdrive the preamp without overdriving the output tubes.

  • Presence control  - used to adjust the high-frequency response and damping factor of the power amp section.

  • Boost - Unique NNFB "Edge" boost switch on the PRESENCE control that transforms the power amp section into a No-Negative-Feedback style amp for soaring dynamic leads. 

  • Effects Loop - pure tube buffered serial effects loop designed to perfectly match the low impedance solid-state pedal levels with high impedance tube levels.

  • Line Out - post output transformer LINE OUT with LINE OUT LEVEL control for recording or driving a power amp, Auto switched internal load to simulate speaker if speaker is  not plugged in. Inject great tone directly into the PA system with the Speaker Simulated Direct Interface.

  • Custom heavy duty output transformer for extended low frequency performance with 4 - 8 - 16 ohm outputs selectable by a rotary switch.

  • Three Power Level Selector Switch - Provides three power levels. 1/4 -1/2  FULL.

  • EL34/6L6 Bias Selector Switch - Allows you to use either 6L6 or EL34 power output tubes.

  • Solid-State FRED ultra fast recovery rectifiers for tight dynamic bass response.

  • Standby Switch - Protects tubes from cathode stripping during warm-up

  • Tube Complement: comes standard with 5 - 12AX7,  2 - 6L6, but you can substitute 12AT7's or 12AU7's in the preamp and driver for different tones and overdrive sounds. You can also substitute 5881's, KT66's, KT88's, 6550's, or EL34's and KT77's when using the EL34/6L6 Bias Selector Switch  in the output stage for different sounds. 


Electrical Specifications: 

  • Input Power  120 VAC 50-60Hz - 225 Watts Standard IEC plug-in three prong grounded power cord. (230 -240VAC available. See Upgrade Options) 

  • Output Tubes - Class AB Push-Pull 6L6's - Fixed Bias

  • Output Power - 50 watts RMS (100 Watt upgrade available)

  • Speaker Output Impedance - selectable by switch 4-8-16 ohms.

  • Output Power Selector Switch - provides three power levels. 1/4 - 1/2 - FULL power.

  • Line Out Impedance - 10K ohms

  • Effects Loop Send Impedance - 10K ohms

  • Effects Loop Return Impedance -  470K ohms

  • Instrument Input Impedance - 1 Megohm

  • DC on filaments to eliminate 60 hz hum.

  • Star ground system to eliminate induced current chassis noise.

Physical Data: 

  • Retro Vintage Cage Head  - heavy duty lightweight steel mesh cage provides protection and excellent ventilation for tubes. Comes with easy carry Fender style strap handle. Overall  Dimensions - 17" Wide x 12" Deep x 10" High (Includes feet, handle and knobs)

  • Chassis - Heavy gauge aluminum with welded corners.

  • Weight -19 lbs. 

  • Rock solid point-to-point hand wiring with military style tie-wrapped wiring harnesses for long life and reliability.

  • Input and Output Jacks isolated from chassis for low noise, eddy currents, and hum.

  • Components:  Only the highest quality parts are used including heavy duty transformers, low noise tubular polypropylenes capacitors, metal film resistors, Micalex sockets, Neutrik jacks. All parts are rated for commercial high use conditions. Wherever possible we use parts made in the USA.

  • Front Panel:  F Input Jack, M Input Jack, F Gain with Bright Pull Switch, M Gain with Bright Pull Switch, Bass with Deep Pull Switch, Middle, Treble, Presence/Edge Boost Pull Switch, Standby Power Switch, Pilot Lamp, On/Off Power Switch

  • Rear Panel:   Power Cord Connector, Fuse,  Effects Loop Return Jack, Effects Loop Send Jack,  Line Out Level, Line Out Jack, Output Power Level Switch,  Speaker Output Jack, Speaker 4-8-16 Impedance Selector Switch.

Upgrade Options: 

These options allow you to  customize your amp to meet your special individual requirements.

100 WATT POWER OUTPUT -   STP800C-100 model Increases power output to 100 watts. Uses quad of 6L6's.   Add $300.00.

HIGH GAIN JCM800 M CHANNEL PREAMP - Pull switch on M Gain control  changes  M  channel from Marshall Super Lead Plexi to Marshall  JCM800 High-Gain Lead.  Add $95.00​  

5U4 DUAL RECTIFIER POWER SUPPLY - This upgrade comes with a 5U4GB tube rectifier which provides that classic smooth warm  tube compression on peaks  and a  solid-state rectifier  for  tight dynamic bass.  A switch on rear panel selects the mode of operation. Add $75.00 


Review By Featured Artist Anthony Ambroso 

Hi Jim, I wanted to send you a more detailed rave review of the Super Twin Plexi (STP-50) after having had more time to play the amp with different guitars. 

The negative feedback defeat switch is a great feature, and the amp becomes a whole different beast depending on whether you leave it in or pull it out. With it in, you get a tighter, more compressed sound, and with it out, you get a more dynamic, open sound with more harmonics. Pulling it out sounds great with single coil pickups and gets you Clapton-esque 60's blues leads. Leaving it in sounds great with PAF-style humbuckers and gets you into Angus Young territory, with singing sustain and crunchy power chords.

The clean “Fender” channel also does beautifully with single coils and give you a spanky, full American amp tone with lots of dynamic sensitivity. The 2-rectifier setup gives the amp just the right balance between natural “sag” and defined pick attack. Having an ABY footswitch allows me to switch to the clean channel for greater clarity when I engage my fuzz pedal, rather than feeding the fuzz into an overdriven amp. Combining the two channels with the “Y” on my footswitch sounded great with my Tele and really fattened up the bridge pickup.

The “Marshall” channel puts out rich even-order harmonics and upper mids. As expected, it does great with humbuckers but I was also surprised at how good this channel is with single coils, and how nicely it cleans up with the guitar’s volume knob. 

The build quality is top notch and the chassis is easy to remove and work on. When I first tried out the amp, I removed the chassis from its wooden cabinet and looked it over. I then played the amp for a while before re-mounting it in its cabinet. 

Thanks for making such a great amp!  Cheers, Anthony Ambroso (Pennsylvania)


STP-50 - Dear Jim,  I just absolutely love this amp.  It has such a pure tone, even when I put a small chain in front or in the loop . I still prefer nothing in front or in the loop, but I have found, surprisingly, that I can pretty easily get into high gain territory on both channels with a boost.   Matt C..(Missouri)  


STP50-800 - Really excited about my new amp! Can't find a bad tone yet! Thanks, guys! John M. (Texas)


STP50-800  Hi Jim, I have received my STP800 amp and put a few hours on it. I have to say it is an absolutely beautiful amp, well laid out, well built, all the controls are just where they need to be, very impressive.  Now, the tone. With the KT-88's, I have found that I have been struggling with trying to EQ in what other tubes lack. The KT-88's give me everything I want in a tube, and the EQ now responds to what I want to remove or add in the signal rather than trying to EQ the tubes and the signal at the same time. The tone on both channels is rich and full - I practice and test on speakers that go to 8k Hz - and I find myself playing a lot more clean. Every knob, every pull does something meaningful. I can go on and on, I'll put that up on GearPage, but I just wanted to say thank you for a beautiful, beautiful amp. The amp of my dreams, and then some. I do have a suggestion, since you had told me you were going with the wood shells which got put on hold. If you do go with the wood shells, I suggest using the perforated metal on the front, for both ventilation and people can see the tubes glow, versus a closed wood front. Even with the cage I have it gets pretty hot without a fan. Second, I would still offer the cage as an option for studio players and studios that want to have a Frenzel on the shelf. With the cathode/fixed bias option, it would be a lot easier to roll pre- and power-tubes with the cage off, rather than pulling the chassis out of a wood shell. I'm surprised I don't read more reviews of your amps in studios, my amp will get Tweed Fender/scooped Fender, old Plexi/new 800 tones, and everything in-between by bridging the channels. It's the perfect studio amp. Thank you again for a great amp, and have a great week! Bill D. (California)

STP-100 - Jim, I got my amp and it is awesome!!!  Thank you!!!  Mark H. (Utah)

STP50 Hi There, I recently purchased a Frenzel STP-50 used  (2008), and I am loving the amp!  Best, Anthony

STP50-800 - This is a great Amp! Very simple and sounds great! Thank you! Brad A. (Oregon) 


 STP50-800R - Hi Team Frenzel, I love the amp, it is a joy to play through! Wallace B. (Wisconsin)

STP-100 - Great amp! I checked the amp on the bench instruments  and on speakers. It puts out a solid clean  100 watts RMS, and that sounds like 200 watts  through a pair of 12" Vintage Jensen C12N's. It will rattle the windows. If you like playing clean you will love this amp…but it will also kick and crunch and sing when you crank it up.  The sound is clean and crisp and develops three distinct types of  crunch and distortion depending on whether you are overdriving the preamp tubes, output tubes, or both.  It will give you the great high mids of the SLP Plexi and the warmth of the Twin….plus a lot more!  Gus M. (Texas)

STP100 - Here is a video of me (Bob Salihar) and our band The Lost Monarchs performing with my Frenzel Twin/plexi and 5e3 Retro Deluxe. You're hearing the Twin/Plexi in the video. This is a song by the Lost Monarchs called "Just cant wait for the Summertime ". Hope you all enjoy it as much as we do. Feel free to use the video. Thanks so much. You guys make awesome amps. I've used them exclusively for the last 4 years love them and never will I switch to other amps. Love the tone I get at any volume with any effects I've tried. Again thank you all, Bob Salihar. 


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