Anyone know what the "tiny terror" circuit is?

[Steve Conner]

Yes! Bear in mind that the traditional sound of tube guitar amps comes from cheap underrated transformers, it logically follows that Mercury make overpriced cheap underrated transformers

You might struggle to get a PT with the required extra secondary winding for half power. If you're looking for a custom unit in the UK, someone from BLS Electronics hangs out on this forum and they seem tube amp friendly. I've also heard Majestic Transformers recommended.

However, many custom builders have a minimum order of 10 or so, which would make it cheaper to just buy a MM transformer set or even a complete Tiny Terror

[bob p]

Yes! Bear in mind that the traditional sound of tube guitar amps comes from cheap underrated transformers, it logically follows that Mercury make overpriced cheap underrated transformers

That's very true. And very funny!

You might struggle to get a PT with the required extra secondary winding for half power. If you're looking for a custom unit in the UK, someone from BLS Electronics hangs out on this forum and they seem tube amp friendly. I've also heard Majestic Transformers recommended.

I have an OTT, and I don't find that half-power feature to be all that useful, so I wouldn't even worry about custom transformers.

With the ability to use the master and gain controls to dial-in and dial-out an extra gain stage, the amp has really nice chimey to overdriven tone in the 15W setting. In the 15W mode the B+ is designed to put the amp right in the sweet spot for EL84 chime. The amp does get significantly more quiet with the half-power mode engaged, but running the power tubes at those lower voltages tends to rob the amp of it's chimey capabilities. If you run the B+ too low on a set of EL84 they just lose their chimey magic and become too dark sounding. Being a fan of Voxy chime, to me the OTT just doesn't sound that good in the 7W setting. I don't like the low power setting at all, and I avoid using it.

If I were building one of these from scratch and I had to source iron for the job, I would definitely skip the second/low-power tap on the power transformer and design the amp to sound it's best with a 15W output. Then if the amp is too loud I'd consider some sort of attenuation to drop the volume.

I ended up buying one of these OTT-15 amps, even though I had intended not to buy one. I did a lot of research on what makes an EL84 amp sound good, and I was convinced that I wanted a Vox AC15 type of circuit for the chime factor, plus another gain stage that could be dialed-in or dialed-out to spank the power tubes a little harder to get the full-on overdriven EL84 tone when needed. When the homework was done I was considering building something along the lines of a Matchless Spitfire or Lightning.

Part of doing my research involved scouring a lot of threads at various sites to find the best mods, and I need to give some props to Chuck H for his excellent contributions here on this subject. Several of his posts on the subject of what makes a good EL84 amp should be "sticky" as required reading for anyone interested in building an EL84 amp. There are one or two posts where Chuck summarized everything that you need to do to eliminate the dreaded EL84 buzz, what voltages are needed to hit the chimey sweet spot, and what sort of biasing changes it takes to make the little EL84 behave more like bigger bottles when you push them hard instead of little ones.

In the course of doing my research, I compared schematics for every circuit that I considered building, and I compared them to Chuck's recommendations, with the plan that I was going to buy all of the parts and build something from the ground up. But in the course of doing research I found that there was one commercially available amp that had almost every one of Chuck's recommended mods already in the circuit -- the OTT-15. As a platform, it was a well-built commercial amp that was already 99% of what I wanted it to be -- the only thing that was missing was the Zener trick. So I found a used OTT-15 that was in like-new condition and bought a complete amp for less than the price of the parts to build something equivalent. The only mod that it needs is to have a little daughter board installed to do the Zener mod. But the amp sounds so good as it is that I keep putting that project on a back burner.

Props to Orange for doing their homework. They really have a good design in the OTT-15.

Props to Chuck for his excellent recommendations on what's needed to make an EL84 sound great.

[Dave H]

I was planning to use the mercury magnetics trannies for my build, but they only supply with US/Canada mains. I'm entirely new to all of this (I've built one of ampmaker's kits and done a few mods) but fancied giving the TT a go. This thread is really great for everything, so thanks to all previous contributors!

Why don't you use the PT from Ampmaker? It has a half power tap. Link

[Zozobra]

I've used that ampmaker PT and matching OT. It's good stuff. As Dave H said it can be switched between full and half power. It can be run at 1/10th power too. I've built Merlins VVR into an amp using these transformers and it works very well and is easy to do. I only scaled the plates and screens in this case. The amp was cathode biased so there is nothing to worry about there. If you do want to go custom then I can recommend toroidy.pl for custom wound toroidal power transformers. Much much cheaper than EI construction. The shipping is a bit steep but they don't charge a great deal extra for adding secondaries. I got a custom wound toroid for a preamp I'm building and it was 42 quid delivered.

[mhuss]

The output cathode cap should be 63v or better. The other cathode caps can be 16v. The rest of the caps should be 400v or better. All the unmarked resistors can be 0.5w. I generally use 1w CC resistors because they look good and are easy to work with.

--mark

[huuubert]

Hi Guys,

I plan to build my OTT Clone and I have questions about transformers.

I've used that ampmaker PT and matching OT. It's good stuff.

Can I use this PT with 275V - 190V - 160mA secondaries without any components values modifications (Tiny_Terror_Layout_v.1.11) ? I ask this because ciambom said :

Your transformer must be:
- primary: 240V
- secondary1: 250V 125mA
- secondary2: 180V 125mA
- secondary3: 6.3V 3A

For the OT, can I use this one?

Thanks for your help.
Huuubert

[isaac]

I would recommend not solid core wire, it fatigues worse.

[Tom Phillips]

I would recommend not solid core wire, it fatigues worse.

A primary requirement is to insure that the solid wire is not nicked when the insulation is removed. A nick will propagate through the wire and cause the wire to break if it is in an area that is subject to movement. The damage during stripping is a significant problem for hobbyists and anyone else who does not have the proper tools and technique. If you do have the ability to properly strip the wire then there is no inherent problem with copper fatigue. Push back insulation prevented this problem for Fender in the early days. Lots of other old equipment was successfully built with stripped solid hookup wire.

[jergenoman]

Hi, benjy!

Basically they mean probably this:



Unfortunately the statement "But it does come after all of the the preamp's tone-shaping and gain circuitry." is IMO not 100% correct - Tiny Terror uses even overdriven PI (PI = Phase Inverter) made by second ECC83, to achieve more distortion (it's one of it's most unique features). So you cannot get full preamp distortion of OTT into FX loop this way (and frankly there's no any other reasonable way).. but you can try this, maybe it will work for you (it depends on the way you use your OTT).

Sorry, I have to leave for now..

T.

I am planning an OTT clone and i want to add an fx loop. I'm not very familiar with tube cirquits and i wonder if this will work:

[jergenoman]

I am planning an OTT clone and i want to add an fx loop. I'm not very familiar with tube cirquits and i wonder if it will work to add these output and input stages between the preamp and the PI:

[jergenoman]

Will this work on the TT?

[isaac]

That quote is a very simple loop. And would technically work, but being unbuffered, might not work well. I'd recommend the image you attached.

[J M Fahey]

It *is* buffered!!
In fact it's made out of 2 cathode follower, unity gain, tube buffers, go figure!!!!
The unbuffered one was the first one.

That said, effects loops are not of much use in TT because it achieves its distortion *after* the loop, plus loop level is very high for most floor pedals.

[isaac]

That's what I said. The one inside the quotes wasn't buffered. The attached image had a nice looking loop. Maybe you just misunderstood what I said. If I remember correctly, I said it a little bit vague... Being up late does that to you.

[J M Fahey]

Same here
And trying to beat it with too much coffee does not work very well either