top of page

JF-C500 "Ultra C500" Hi-Fi Monoblock

  • Model No. JF-C500 'Ultra C500"

  • Point-To-Point Hand Wired

  • 50 Watts Class AB Ultra Linear Monoblock

  • Matched Pair Classic KT88 Output Tubes

  • Vintage Octal 6SN7 Preamp Tubes

  • 5U4GB Heavy Duty Rectifier Tube

  • 4-8-16 Speaker Impedance Switch

  • Classic Banana Post Speaker Connector

  • Input Level Control

  • Presence With Loudness Boost

MSRP: $1895.00



FREE 1YEAR-TECH-made in usa11.27.22 - 125px.jpg




The FRENZEL JF-C500 "Ultra C500" Monoblock was designed for the audiophile that loves ultra fidelity  sound. It was inspired by the vintage 1950's Craftsmen C500 series. The C500 is famous for its pure tones and it was an incredible amp, but we have added some new features to make it even better. If you love the vintage hi-fidelity will love this amp. A pair of them hooked to the output of your CD player or IPOD will give you stereo sound like you have never heard before. This amp will faithfully reproduce what you put into it.

For those of you not familiar with the original Craftsmen C500, it was basically a modified Williamson design that used  one-half of a 6SN7 for the first gain stage, and the other half  for a split-load phase inverter. The output of the phase inverter was coupled to another 6SN7 which was used as a push-pull driver to drive the output stage. The output stage was a push-pull Class A using two KT66's wired as triodes. There was a feedback loop that was connected from the speaker output to the first gain stage.  All in all a great design which made it one of the most popular Hi-Fi amps of the 1950's.

The JF-C500 follows the basic concept of the original C500, but we have upgraded  it with many new features including  KT88'S...which are considered the "king of the audio output tubes" today. The KT88'S operate Class AB1 ultra-linear fixed bias mode. This gives more headroom and more power...50 watts versus the 15 watts in the original C500. The KT88's were designed specifically to run in the Class AB1 ultra-linear mode  so we upgraded the output transformer to a classic Hammond ultra linear which has ultra low harmonic distortion and a  flat 20-20,000hz frequency response.  The end result of all the upgrades is an  absolute  treat for the ears.

There are a lot of other features we have added such  as an oversized power transformer and filter choke coupled with larger capacitors in the power supply for better regulation, a LEVEL control which allows you to match the output of your driving device with the amp, and a PRESENCE control and a NNFB ( no negative feedback ) pull switch which gives you more dynamic sound and unbelievable highs....and for users with custom speaker cabs, we  added a 4-8-16 ohm impedance selector to allow a larger selection of speakers. We also included all of the classic features in the "Ultra 500" that our amps are known for. A list of the features is shown below:

Standard Features:

  • Input Jack isolated from chassis to eliminate noise or eddy currents and hum  from the chassis.

  • Star ground system to reduce induced current chassis noise.

  • LEVEL control to allow you to match the input level to your driving source. 

  • Classic PRESENCE control for extended highs coupled with a Unique NNFB "Edge" switch on the PRESENCE control that transforms the power amp section into a No-Negative-Feedback style amp for more dynamic bass and less compressed tones.  

  • Class AB cathode biased for the purest of sound reproduction. 

  • Power Output @ 4,8 or 16 ohm  - 50 watts RMS.

  • Heavy duty 5U4GB rectifier for optimum sag and regulation. 

  • Standard IEC three prong grounded power cord socket. 

  • Class AB  ultra-linear KT88's. 

  • Ultra-Linear output transformers for the purest high-fidelity tones.

  • Heavy duty power transformer with " flux band" to eliminate 60 cycle hum radiation and noise.

  • Choke  filtered high voltage with 5 filter capacitors to eliminate 60 cycle hum and noise.

  • DC Voltage on preamp tube filaments to eliminate hum and noise.

  • ​Input and Output Jacks isolated from chassis for the lowest possible  noise, and hum.

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

  • High quality commercial grade parts  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.

  • Star ground system to eliminate induced current chassis noise.

  • Speaker Impedance Selector Switch  allows you to use 4, 8, or 16 ohm speakers.  

  • Heavy Duty Three Way Banana Type Speaker Jack 

  • Classic knobs and open style chassis.

  • Vintage jewel pilot light and chrome toggle switch.

  • Compact 12" x 8"  x 2" lightweight non-magnetic aluminum chassis with vintage style oak wood side panels and bottom cover plate with rubber feet.  

  • Tube compliment: 2 - 6SN7's, 2 - KT88's, 1 - 5U4 

Electrical Specifications: 

  • Frequency Response: 20 to 20,000 hz

  • Harmonic Distortion: Less than 1% 

  • Input Impedance:   1 megohm

  • Input Level:  1.0 V RMS (Line Level) for full output   

  • Output Tubes - Class AB Push-Pull KT88's - Fixed Bias

  • Output Power: 50 Watts 

  • Output Impedance: Selectable 4 - 8 - 16 ohm

  • Power Consumption: 120V 60hz - 230VA


Physical Data: 

  • Chassis Dimensions - 8" Wide x 12" Deep x 2" High. 

  • Weight - 15 lbs. 

  • Chassis - Heavy gauge aluminum with welded corners and oak side panels.

  • Front Panel Controls - Level Control, Presence, Loudness Boost Switch,   Pilot Lamp, Power Switch

  • Rear Panel Controls -  Power Cord Connector, Fuse,  Input Jack, Speaker Output Connector, Speaker 4-8-16 Impedance Selector Switch,  

bottom of page