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THD - Type-O

THD Type-O - built-in Variac control, switchable rectifier (Hard & Soft) and can be biased to use 6L6, EL-34, 5881, 6550, KT-88, KT-90 or KT-100 output tubes. Variable "Output" control works in the output stage instead of in the preamp. This allows you to dial up the preamp volumes for distortion, yet back-off the Output control to lower the overall volume and retain the warmth and drive. When the Variac control is in the normal position, 50 watts. Stepped-down Variac mode, 28 watts.

THD - Type-O. $1699-2890. 50 watt all tube combo. Plexi and Tweed style circuitry. Built-in Variac control. fx loop. Options: headonly version, reverb and tremolo. Black, brown, cream, tweed, paisley [note], or Big Blue Flowers [note].


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I have a THD "Plexi" 4x10 reverb amp. It sounds fantastic!!
The "plexi" version (as well as the new "Type-O") has a
"variac" switch that allows you to drop voltages to the tubes.
It came with EL34's, but for a change, I recently put in NOS
GE6l6's and a 5751 preamp tube--sounds great that way too!
More Fenderish. I wired my speakers with two jacks and three
toggles so I can get 4x10, 3x10, 2x10's series, 2x10's parallel, etc.

Another element of flexibility: the four input configuration allows
you to "jumper" channels in various ways, and use both the normal
and bright volume controls together.

My amp has a fantastic, dynamic clean tone, and great overdrive.
I prefer to set the volume(s) in the 6-9 range, and use
a Centaur overdrive pedal--this gives me a better balance
of clean and lead tones, than if I cranked the amp all the way up
and simply used my guitars volume control.

It's a top notch, well-built amp, but it's not going to give you a huge variety
of tones on the fly. But you can use a variety of preamp, driver and
power tubes [see below].

For lower volume, in addition to the "variac" which drops the power
to around 25 watts, I highly recommend a THD HOTPLATE.
(The newer THD's come with post-phase inverter master volumes,
ala Ken Fischer.)
Also: you can get a pair of THD YellowJackets--these allow
you to run the amp with 2xEL84 in class A cathode bias, for
around 18watts.


Some THD Comments:

* * * * * * * *
My amp:
1992 THD "Plexi" 4x10 Combo

4 input/ 2 Channel (Bright and Normal)
Non-Master Volume
2 x El34 Output (or 6l6)
Footswitchable tube driven series EFX loop
EFX loop can be used for added gain stage
"Variac" Control [see below]
THD "Longhorn" 10" speakers (mono/stereo wiring)
THD solid state Rectifier

Currently THD has combined the "Plexi" amp features with their
previous "Blues" and "Rock" variations into the "Type-O" Model.

* * * * * * * * * * * * * *

"The new THD Type-O amplifier is a combination of our former
Blues, Rock, and Plexi models. It features a built in variac control,
switchable rectifier (Hard and Soft) and can be biased to use
6L6, EL-34, 5881, 6550, KT-88, KT-90, or KT-100 output tubes. All
preamp tube positions can accomodate 12ax7, 12au7, 12at7, 12ay7,
12az7 preamp tubes without adjustment. This gives you tremendous
control over the amplifiers feel and sound. All Type-O amplifiers
include our footswitchable variable efx loop."

"The Type-O features a variable 'Output Control' which works in
the output stage instead of in the preamp. This allows you to
dial up the preamp volume for distortion, yet back off the Output
control to lower the overall volume and retain the warmth and

"When set-up with the EL-34 output tubes, all 12AX7 preamp tubes,
and the rectifier switched to 'hard', the amplifier exactly
emulates the sound of early plexi-glass front Marshall JMP 50
amplifiers. The original JMP 50 Marshalls are renowned for their
tight low end, phenomenal dynamic response, and smooth output
distortion. This is especially true when using a Variac to drop
the wall voltage from the normal 120 VAC to 90 or 100 VAC. Dropping
the voltage lowers the overall output power of the amplifier [to what? need wattage specs - still far too loud?] and
decreases the output transformer saturation. This allows for
more of the power tubes' harmonic overtones to reach the speakers
without being squashed by the transformer's distortion characteristics,
resulting in the tighter, more transparent overdrive."

"When the rectifier is switched to 'soft' and soft 6L6 tubes are
installed with a 12AY7 in the first preamp stage, the Type-O
can provide the sweet, clear 'Tweed Fender' sound desired by
many blues guitarists and harmonica players. When driven hard,
it breaks up gradually, giving you an even transition from
crystal clean sounds to cello-like distortion. This is the
sound and feel of our previous Blues model."

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