Hybrid amp design

[doozerdave]

That's just an example. I'm not saying that's exactly the one you want (although it would work for you, and has a CT so you can easily elevate the heater to protect your cathode follower), but DigiKey carries Hammond.

[JMFahey]

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.

[m145mcc]

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)

[doozerdave]

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.

[m145mcc]

Thanks, I will. I could check again but I'm prety sure the transformers secondaries are 120vac and 12.6 vac so I wont have to back-to-back two twelve volt tranys.

[JMFahey]

Thanks, I will. I could check again but I'm prety sure the transformers secondaries are 120vac and 12.6 vac so I wont have to back-to-back two twelve volt tranys.

And how will you get 250/300V for the plates?

[Robert Kesh]

Originally Posted by JMFahey

And how will you get 250/300V for the plates?

B+ on this circuit is ~150V

[JMFahey]

OK, 150V. That's not the point.
The question remains.

[Robert Kesh]

Originally Posted by JMFahey

OK, 150V. That's not the point.
The question remains.

120VAC= about 160VDC

[counter culture]

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.