Showman Modification

HAS ANYONE (here) modded a Fender Showman to separate the PreAmp from the Power Amp? This would allow the preamp to go to a more powerful amp, and conversely, allow the power amp to be used separate from the preamp. Seems simple to do ... just looking for experience

 

I'll certainly defer to your expertise, but I thought "FX In/Out" - typically after the first tube half (?) was different than "Preamp Out / Power Amp in", which would seem a logical "functional dividing point" in an integrated amp.

P.S.: No Slave Out this era (August '65)

 

I lucked into a tuned cabinet, so I'm also 1x15 D140. Interestingly, it sounds really different in various locations around my studio - I'm building a little dolly to mount it so I can easily move it around in here.

 

And for clarity: I have an "old blue" Alembic F-2B (heavily modded), and the driver for this idea was to be able to flex* that preamp into the existing showman power amp (4x6L6GC + Single D140)

The F-2B heavy mods include 5691 tubes in lieu of 12AX7, and one side Fender Tone Stack the other Marshall Tone Stack ... I like the Marshall side better these days, but that might just be novelty of it. Normally that preamp goes into a Million Watt QSC Class "D" then various cabinets. Variety - the Spice of Life!

* "Flex" ... means use it or don't use it, depending on the weather and my daily mood swing.

 

Thanks ... Turns out, I personally know Greg at Bass Pluckers ... but I'll probably pass on one more piece of gear. (if you only knew, lol)

 

I heard ya,

Alembic shares your concern - see last paragraph:

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The F-2B was inspired by the Fender Dual Showman amplifier. In the late '60's, we routinely added preamp output jacks to Dual Showman amplifiers and substituted an external power amplifier for the built-in quad 6L6's, most usually a MacIntosh 75.

The F-2B came about to provide the same preamp functionality in a rack-mounting package, as the Dual Showman was considerably wider than the standard 19 inch rack.

We took the opportunity to make a small improvement in the input jack circuit, while providing identical functionality. Plugging into Jack 1 alone gives full sensitivity, while Jack 2 alone is attenuated 6 dB. If signals are plugged into both jacks simultaneously, mixing resistors combine the signals and give isolation to the two input sources. In the original circuit, the mixing resistors are always in series with the grid of the first stage, and contribute a small amount of Johnson (thermal) noise. Our jacks have additional contacts which completely switch out the mixing resistors when using Jack 1 and the ultimate quietness of the tube is preserved.

As in its predecessor, the instrument signal is amplified by the first stage before any volume control. Without the wide dynamic range provided by the 300 volt supply, the first stage could be easily overloaded by large transients which are characteristic of electric instruments.

The tone control section follows, with a circuit attributed to Tom Walker, wherein the Bass and Treble controls contribute mostly boost and the Mid control provides cut only. While there is no absolutely flat position, the response is reasonably flat with the controls set at 2 - 10 - 2, with the bright switch off. The circuit can be described as interacting, such that the frequencies affected by each control is changed somewhat by the settings of the other controls. Additionally, when all 3 tone controls are turned to 0 then no signal is passed at all. These effects, while not suitable for a music reproduction system, have nonetheless proved highly pleasing for electrical instruments and have been adopted by a wide group of manufacturers.

The Volume control immediately follows the tone control section. The Bright Switch connects a capacitor around the volume control, the value of the capacitor being selected to bypass only the high frequencies. The effect of the Bright Switch is also interactive with the Volume Control, and there is no effect if the Volume control is turned up to 10, and the magnitude of the effect changes, depending on the setting of the control.

The signal loss of the passive tone controls and the volume control is made up by the second stage, also a common-cathode vacuum tube stage. The second stage plate circuit feeds the output jack. Since the output impedance of the tube circuit is fairly high, the power amplifier(s) should be located adjacent to the F-2B so that short connecting cords can be used. While the output circuitry of the F-2B can satisfactorily interface with the vast majority of power amplifiers, the F-2B does not work well if the power amplifier input impedance is lower than 10 K Ohms or if the power amplifier has very low sensitivity.

 

Late 70's they were selling those 1x15 cabinets - asking $400 each - and while it'da been a fun talking point, I passed the opportunity.

 

Might be ... been literal decades, and they didn't have an infinite supply - iirc, there were two of those rigs - leap-frogged across venues until even that was too much "work" (or something) .. I saw it once and it was pretty cool. Say what ya want about the music, but their tone was always to die for, state of the art - especially the drums.