Anyone know what the "tiny terror" circuit is?

[FatGaz]

Hi all,

I've got a old project amp that I want to rebuild - I was never happy with the design i tried SO i want to strip it down and try again.

Anyhow, the amp has two 12ax7's and 2 EL84s plus an EZ80 or EZ81. At the moment it has the power stage arranged as one 12ax7 as a phase splitter into the two el84's using i think the circuit of a marshall 18 watt amp. The pre is the two triode stages of the other 12ax7 in series with a tone stack in between. The preamp was my own design; unfortunately it sucked !

I happened to try an orange tiny terror amp in a shop last week - WOW this is just what i want my amp to sound like !!!

anyone know what circuit it uses ? it's got the same set of tubes - but uses a SS rectifier.

(also my amp happens looks very similar to the tiny terror - it's a shoebox sized metal head with a handle on top)

Anyone know if orange are in the habit of including schematics with their amps ?

Peace and Season's greeting,

Gareth.

[FatGaz]

some links orange TT secrets..

http://www.orangeamps.com/tinyterror/

only info i have been able to find on the web is from this link (and it's a very interesting description of an amp design possibly closer to the kind of tricks 'london power' amps use than a basic circuit from an ac15 or 18-watter etc.)

http://www.musicianshotline.com/issu..._orangeusa.asp

from which i quote :

"Inventing Terror
The Tiny Terror utilizes class A valve technology with a 100% analog signal path that eliminates any and all digital clipping output characteristics. Driven by a pair of EL84 power valves and a front end that utilizes a duct of 12AX7 preamp valves. Switchable from 7 to 15 watts of output, Orange designers have designed the gain structure of the Tiny Terror to work in a very unique way; utilizing a dual gang gain pot, one side turns up the first gain stage to the point of very heavy compression, while the other side changes the impedance of the second gain stage so that it to compresses to the same degree.

It utilizes a five section fully filmed interleaved output transformer that is very closely balanced to primary. The EL84 output tubes are cathode biased to around 90% in the 15w position, and 96% in the 7w position. In short, the Tiny Terror is designed to produce as much gain as a four stage gain pot, but the output tubes are driven evenly all the way through. The tone control is also designed in a unique way, where the tone circuit is not on the preamp side, but actually part of the phase inverter (power amp) so the gain structure of the amp is unaffected by the tone control. "

[AdmiralB]

It's an AC15, with an extra gain stage cascaded on the front end. PI and power amp are 100% AC15. The gain pot is a dual 500K that serves as simultaneous voltage dividers after each gain stage.

The amp is actually biased at over 15W per tube static. It's insane. I swapped the 100 ohm cathode resistor for a 180 ohm, made no difference in the sound but made the tubes a lot happier.

[steve]

Admiral,

How does the 7/15 watt switch work?

steve

It's an AC15, with an extra gain stage cascaded on the front end. PI and power amp are 100% AC15. The gain pot is a dual 500K that serves as simultaneous voltage dividers after each gain stage.

The amp is actually biased at over 15W per tube static. It's insane. I swapped the 100 ohm cathode resistor for a 180 ohm, made no difference in the sound but made the tubes a lot happier.

[AdmiralB]

It selects a different HV tap on the PT secondary. One leg remains tied to one side of the bridge rectifier, the other side has two taps and the switch selects between them. The result is something like 250VDC rather than about 325VDC.

It affects the entire amp, not just the power tubes, and it does NOT do anything to the bias state - so, in stock form the amp is severely (IMO) underbiased in 15W mode, and just about right in 7W. But I think the low voltages affect the feel in a negative way.

I replaced the power switch with a DPDT and also switched a second cathode resistor in parallel when I selected 7W. That made both modes idle happily.

[steve]

Cool. Thanks for the info.

steve

It selects a different HV tap on the PT secondary. One leg remains tied to one side of the bridge rectifier, the other side has two taps and the switch selects between them. The result is something like 250VDC rather than about 325VDC.

It affects the entire amp, not just the power tubes, and it does NOT do anything to the bias state - so, in stock form the amp is severely (IMO) underbiased in 15W mode, and just about right in 7W. But I think the low voltages affect the feel in a negative way.

I replaced the power switch with a DPDT and also switched a second cathode resistor in parallel when I selected 7W. That made both modes idle happily.

[Steve Conner]

That's "underbiased" as in running too hot, I guess? I always think of underbias as meaning cold with a lack of idle current.

BTW, thanks for the info, I played through one of these in a guitar shop a while back, and was wondering how they were made. It struck me as a real dirt machine of an amp. I read all the PR blurb on the Orange site, and it gave me the impression of some top secret cutting-edge technology, not an AC15 clone ;-)

[bob p]

It selects a different HV tap on the PT secondary. ... the switch selects between them. The result is something like 250VDC rather than about 325VDC.

didn't Randall Smith/Mesa claim a patent for B+ switching back when they first used that in the Mark series amps? I know that my Mk IV uses a toggle switch to tap different coils on the PT for its lower voltage "tweed" mode, and its higher voltage "full power" mode. IIs Orange licensing that, or has that patent expired already?

[AdmiralB]

didn't Randall Smith/Mesa claim a patent for B+ switching back when they first used that in the Mark series amps? I know that my Mk IV uses a toggle switch to tap different coils on the PT for its lower voltage "tweed" mode, and its higher voltage "full power" mode. IIs Orange licensing that, or has that patent expired already?

Smith's patent selects different taps on the primary - in practice, one is 120V and the other is around 160V, which when fed 120V gives the result of 120V variaced down to about 90V. It browns out the whole amp, HV, heaters, bias, etc.

The TT switches the HV secondary only. Heaters don't change.

[drewl]

Judging from the assesment, it seems pretty close to the rocker series....here's one I had to bring back from the dead.....it blowed up real good!

http://img.photobucket.com/albums/v3...1/100_1918.jpg

http://img.photobucket.com/albums/v3...s/100_1917.jpg

[gtrboy]

oh yes!!

please post the schematic on this one... it kicks butt!!! i played one. its gotta have 3 gain stages and not be push pull. the dual pot thing has been on ax84 forever. no news there.

[AdmiralB]

Ask and ye shall...

gotta have 3 gain stages and not be push pull.

Why do you say this? It is neither of those things.

[gtrboy]

thats one sexy circuit!!

[mak]

TT Tone

so, has anyone tried to mod the tone circuit to brighten the mid/hi response? great amp, but a really foggy tone and not much authority in the tone circuit
Cheers
mak

[FatGaz]

ampage rules once again !

Hi All,

I've not been here for a while after posting my query - but ampage proves what a fantastic set of people post here ! both the circuit and constructive critisism of it !

I am now spurred-on to get the soldering iron out and turn my failed project amp in to a terrible-tot !

I using a hammond universal PP OT, 125E i think is the model number. I have a tube recto too (ez80 i think) so the amp will probably feel fairly different.

Questions for A.B. re the schematic....

I notice that there is the 7/15w hv switch is not shown and that there is also no master vol shown - which master vol circuit is used ? post PI ?

I will mod my preamp to match that of the circuit and put two preamp gain controls in. I will leave my poweramp as is - it has switchable NF and a post PI master vol that shorts across the power tube outputs. I'm not sure if i'll bother putting in the ac-15 alike top-cut.

I don't have any dual 500K or 1mge pots at the moment - maplin don't do them worst luck - so i'll need to think what els i need for a big enought mailorder.

If anyone has any ideas about tweaks i might want to do or where I may need to tweak component values to suit my particuar tubes/ ot/ B+, post them here !

Gaerth.

PS
since i last posted i've hot rodded my jap squire strat (kinman woodstock plus pups and a switch to put the bridge pup in series) and finally set it up properly with a new bone nut, bridge bits and I read a decent book and borrowed an imperial feeler guage to set it just right - it's such a better guitar now - bridge and neck in series is a great new tone too.