Hybrid amp design

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If you want to get the Orange Tiny Terror (OTT) sound (which is very good), build it in full, up to and including the Phase Inverter (PI) which is an integral part of the sound.
Just replace the last 220K grid resistor with an attenuator: 220K+10K to have a proper value level and impedance to drive a chipamp, LM3886 recommended.
The PSU can be simplified, because the preamp needs only a few mA.
You van use the back to back transformers trick:
120V:12V(1A) > 12V (0.5A or 1A):220V .
You'll get almost 300V DC which is fine.
 

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Ok so this is my.. 4th or 5th revision. Dave I think I may go with the bad boy right here 262F12 Hammond Manufacturing | 262F12-ND | DigiKey, the one thing that has got me scratching my head is R6, R7 and R8. I know what R8 is, but I'm a little unsure of the correct value for this application. I would like to say I did read your link dave, but now there are more questions than answers. lets just say I know enough to know, I don't know enough. P.S. the examples you all have been providing really help, thanks.

Edit: directed at JMfahey, your right I could. I was wanting to build the thing around 1 duel triode though, think I may jump ship on this thing. Not much of a analog guy there pushing digital devices and such at devry (don't laugh I know its the best school)
 

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Wow, why would you go with that crazy transformer to drive only one heater? haha... Are you realising the snowball effect of tube amp design already? soon it will have two more preamp tubes and at least two power amp tubes. LOL ;)

R7 is to stop noise on diode switching, but I'm not exactly sure what R6 is for. In my last design I tried the R7/D3 protection circuit and found that it did in fact affect the sound. I don't remember exactly how it affected the sound but I know I didn't like it. I also have no resistor between the triodes (R6 on your sch). You should also get rid of C7.

Once you build it you will no doubt experiment a lot with C2 and R18. Right now I can tell you that C2 is far too large. You will likely get a muddy tone. You can use that RC as a "gain slope" control, effectively making a treble boost/bass cut if you want. Download the PDF here The Valve Wizard and check out pages 25-30 or so. If you haven't seen that PDF already I would highly recommend reading the entire thing. Great read and it will teach you a lot.
 
Better with a 12AU7 I think, they work better at low voltages. Something like this?

An externally hosted image should be here but it was not working when we last tested it.


It'll fit in 4 sq in... showing ground traces... still needs a bit of work. I think the tone controls are the wrong way round (anticlockwise for boost)

An externally hosted image should be here but it was not working when we last tested it.


Here's the tube stage driven with 10mV

An externally hosted image should be here but it was not working when we last tested it.


And with 1V... you can improve the symmetry a bit with the trimpots

An externally hosted image should be here but it was not working when we last tested it.


50 watts into 8 ohms. It'd probably be better not to throw the full 35V at it.
 
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Better with a 12AU7 I think, they work better at low voltages. Something like this?

It'll fit in 4 sq in... showing ground traces... still needs a bit of work. I think the tone controls are the wrong way round (anticlockwise for boost)

Here's the tube stage driven with 10mV

And with 1V... you can improve the symmetry a bit with the trimpots

50 watts into 8 ohms. It'd probably be better not to throw the full 35V at it.

That's a completely different concept. I count 16sq inches, 4 inch square ;)
 
Hi friends, I *think* I have solved the mystery.:confused:
Like most others, I clicked m145 's link provided in post #43 , and landed in DigiKey's page attached here:
there we all clearly read its description:
Description TRANSFRM 120CT FILMNT 12.6V 26VA
where we can "decode" the following:
120 and 12.6V = clearly primary and secondary voltages, huh?
FILMNT = the intended use, huh?
CT= well, that one is easy for old hounddogs like us, it means it has a centertap somewhere, huh?
Being a filament transformer, that's a very common spec.
So the standard deduction would be that it has a center tapped 12.6V filament secondary ... which would be fine to feed "6.3V only" tubes, huh?
Well, everything above is wrong :eek:

Very intrigued and somewhat pissed off at the mistery, got into Hammond's own site.
And found that said 262F12 is properly described as:
*115VAC primary
*dual secondary; 120V and 12.6V AC
* NO centertap anywhere
Oh well :p

So, in a nutshell, M145 can power his preamp with it. :D

EDIT: just in case it was not clear, I was quite worried that he might try to rectify line voltage to power his preamp.
In the last 6 months I saw it twice in Forums; in both cases OPs said "ah !! but I'll be *careful* " :mad:
 

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Pardon my absents, I have been reading. So I think I have come up with something that should work.. maybe. Tube = 12ax7 HT = 150vdc Rl = 330k and if I remember right I biased at -1.5, I fear I may destroy a good tube with this one, and the clipping may not be symmetrical. Thanks to those who have taken an interest in my thread. Especially the crazy SOB who came up with a real design, which I will be referring too after I read some more. Oh... anybody know of good cad software that supports tubes, the the behavior of the triodes in multisim are very in-accurate.
 

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Please disregard my last design (If you can call it that). what I'm posting now should actually work, If somebody could give it a quick look over that would really be great. I have been reading Merlin Blencowe's book on preamp designs I think its helped.
 

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That looks a lot more sensible but.... you want some grid stoppers (R2 & R7 in mine). What's the point of 1M after C1 when it's shunted by (in parallel with) 115k? I don't see much point in throwing away the gain at R4/R3, and R10/R11, better to put a pot in there, although the 12AX7 does have a lot of gain. R12 should be 10* R11 minimum anyway. R11||R12 = 2857 ohms, neglecting pot setting and loading. C4 is too big, cuts off @ ~160Hz (3pF cuts off @ 160kHz).

It's not too bad, but it won't work as it stands, it's full of beginner's errors.

Changed mine around a bit...

An externally hosted image should be here but it was not working when we last tested it.


Crazy SOB huh?
 
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