Anyone thought of making an Orange Tiny Terror?

peesinstew · Post by **peesinstew** » Mon 05/14/07 9:51 am

Wicksy wrote:I got confused by the two 500K audio pots either side of V1b. From the schematic it looked like they might be a dual ganged pot.

This is a dual ganged pot which controls the gain by simultaneously attenuating the signal both going from V1a to V1b and from V1b to the PI.

Wicksy wrote:Also, there seems to be a 500K pot in series with a 2.2nF cap across the two 100nF power section coupling caps.

This is the "Tone" control of the amp. It acts like the classic Vox "cut" control by allowing higher frequencies to cross between both sides of the post-PI circuit, where they get cancelled out. Adjusting the 500KL pot will change the cutoff freq.

At least this is my understanding of how this works. There may have been a better description in one of the other threads about the TT on this site.

Whoops! Sorry Phil! I take too long to type.

Wicksy · Post by **Wicksy** » Mon 05/14/07 10:42 am

Nice one. Cheers guys for the clarification. However the Tiny Terror has three controls and there appears to be only two indicated in the schematic... I'm guessing theres a master volume in there somewhere?

conger · Post by **conger** » Mon 05/14/07 11:02 am

AdmiralB, who I believe drew the TT schematic said about the MV - "I omitted the master from my drawing. It's a 500K dual-pot post-PI master with an extra set of .1uF caps."

... and also about the PT:

"The power switch is on my drawing, it's on the HV secondary. It selects between two 'ends' of the winding - HV winds up with about 325V and LV about 250V."

Wicksy · Post by **Wicksy** » Mon 05/14/07 11:43 am

conger wrote:AdmiralB, who I believe drew the TT schematic said about the MV - "I omitted the master from my drawing. It's a 500K dual-pot post-PI master with an extra set of .1uF caps."

... and also about the PT:

"The power switch is on my drawing, it's on the HV secondary. It selects between two 'ends' of the winding - HV winds up with about 325V and LV about 250V."

Cheers mate! Thats a typical PPIMV then. Brilliant!

Boprikov · Post by **Boprikov** » Mon 05/14/07 11:58 am

I think the master volume pot is included in that schematic. "500 KA dual" between the PI and tone control.

Post by **zaphod_phil** » Mon 05/14/07 12:07 pm

Yes, that's correct. The dual-gang 500k pot in the power stage is the post-PI MV.

So taken in order, this amp has:
Gain control (dual gang 500k)
Master volume (dual gang 500k)
Tone/Treble Cut (single 500k)

Wicksy · Post by **Wicksy** » Mon 05/14/07 3:36 pm

I've had a quick read about the PPIMV mod on NMV amps. Theres a nice thread over at Metroamp talking indepth. However i dont see much mentioned about the mod on cathode biased amps. I'm not sure how that would work.

The Metroamp thread is here for reference:

http://forum.metroamp.com/viewtopic.php?t=4390

Post by **zaphod_phil** » Mon 05/14/07 4:12 pm

In this case the post-PI MV is already part of the amp. And it makes no difference whether it's a cathode-biased or fixed bias amp. It works the same way in both cases. You just need to have a reasonable amount of gain in the preamp and PI, which is certainly the case with the Tiny Terror.

Wicksy · Post by **Wicksy** » Mon 05/14/07 4:49 pm

Yeah, i just had that pointed out on the Metroamp forum

I had a copy of the schematic without the MV. The one posted on this thread already has it. That answers a lot of questions. Cheers!

jac · Post by **jac** » Mon 05/14/07 5:06 pm

So is someone going to make a layout?. Not trying to get greedy, but I'd love to try to build this.
Thanks in advance.

bradleyt · Post by **bradleyt** » Mon 05/14/07 5:42 pm

The half power switch on this amp interesting but raises a question; would this be considered a form of power scaling? I know there is another thread on this subject but I am looking at it from this amps perspective. I normally think of a half power switch as a pentode/triode switch.

Thanks.

loyjdockery · Post by **loyjdockery** » Mon 05/14/07 7:19 pm

Yeah it's reducing the B+ voltage to all the tubes. Although power scaling could mean reducing B+ voltage to 1) all tubes 2) power + PI 3)power tubes. This circuit is option 1.

bradleyt · Post by **bradleyt** » Tue 05/15/07 10:54 am

Thanks Loy. After looking at a picture of the tiny terror I see its labeled 15 watts - 7 watts. I suppose one could use a power resistor to drop the B+ coming from the rectifiers to achieve the same result, or to place the resistor before the rectifiers.

With the PPIMV wouldn't you achieve similar results of low volume vs. tube distortion, or is there something to power scaling I'm missing?

btw Loy one of these days I'm gonna get to work on that 18 watt amp; I'm to the fun stage of wiring everything up.

Wicksy · Post by **Wicksy** » Tue 05/15/07 4:37 pm

I'm working on the layout. The MK 1 version should be posted when i get it roughed out then put into electronic format. The half power switch is basically switching between two taps of the HT winding on the PT secondary. Barry Plows in the UK sells an 18 watt PT that can do just that. All you need is a two way switch (with three prongs on. The two PT taps go either side of the switch and the middle goes to the rectifer. That way you can switch between different B+s.

I'm thinking can caps might be easier with the hand-wired layout. A dual 50uF + 50uF and a single 100uF should do most of the filterign while the 22uF cap can be accomadated onboard.

It should be interesting to see whether i could build one from scratch cheaper than i could buy one. I intend to tear down by Ampmaker 18 watt lite for much of the bits and should just need to order a few pots and power resistors. I'm even going to have a go making my own chassis from a PC case...

straycat · Post by **straycat** » Tue 05/15/07 6:45 pm

What would happen by using a PT with 290/215 taps verses the 325/250 taps stated in another thread as the original voltages. Would this set of transformer work OK for the 7/15 watt drop?

http://www.brownnote.net/bntransformers.html

Wicksy · Post by **Wicksy** » Wed 05/16/07 6:03 am

I would imagine that will be fine. You will just have to tailor the dropper resistors in the power section to get it right.

Do you have the URL for that thread with the stated voltages BTW?

straycat · Post by **straycat** » Wed 05/16/07 6:52 am

here is the thread

http://music-electronics-forum.com/show ... php?t=1477

Wicksy · Post by **Wicksy** » Wed 05/16/07 7:03 am

Cheers Stray Cat. I have a rough version of the layout which i'm going to tidy up and get in electronic format. I might have that up by tonight.

ing that thread, there is a suggestion about replacing the power selector switch with a double pole switch to also switch in another cathode resistor when going from 7 watts to 15 watts thus keeping the bias of the output tubes consistent at both power levels. Thats a really good idea. I might try and implement that later on...

populartsl · Post by **populartsl** » Wed 05/16/07 7:20 am

Wicksey its good of you to do this. I got a trex i built with barry's iron so thats going to get butchered to make it.

Thanks Ben

jac · Post by **jac** » Wed 05/16/07 4:50 pm

Wicksey,

Hate to be a bother.

Wondering how the layout came out, like to try to build the terror, just not good enough for the schemo yet.

Thanks in advance.
Jac

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Anyone thought of making an Orange Tiny Terror?