Cornford Hurricane layout

[10thTx]

Single 12AX7 triode driven reverb - that will be "limp".

Sounds pretty decent to me & I'm not sure I'd want more verb on a distorted tone?

http://www.youtube.com/watch?v=mcDVkB73VKc

http://www.youtube.com/watch?v=GC3vm9T5DtU

With respect, 10thtx

[Phil_S]

Isn't it conventional amp-building wisdom that the AC line-in ground be isolated to the chassis and away from circuit grounds (speaker and rectifier grounds in the diagram are tied to the AC-line ground)? Or am I not seeing that correctly?

It is more than simple convention. I've been told by a licensed master electrician who is also a gigging musician and amp tech that it is required by NEC (for USA). Besides that, common sense will tell you, in the event of a fault the way it is pictured your chassis is potentially tied the the mains HT, which couldn't be a good thing. I understand that, as pictured, it introduces AC hash into the ground scheme potentially contributing noise. Now, that's 3 reasons to do it like Nick says.

[vibratoking]

Thanks for those clips. That amp sounds very nice.

[Blackburn]

Yeah, that amp sounds great! Never really heard a Cornford before, at least to my knowledge. Nice sounding verb too, in a new amp.

[Phil_S]

Thanks for those clips. That amp sounds very nice.

+1 on that. I found a youtube video where the guy calls it a one-trick pony, but adding that it does the one trick exceptionally well. I really liked what I heard, and the amp looks very "doable." I think one of these just made my list. Soon, though, I'm going to have to thin the herd. That's going to be really hard to do.

[10thTx]

Has anyone noticed that the PT is 295V using a solid state rectifier?


295V X 1.4 = 413V on the plates of the EL84's?

That doesn't sound right to me?

Comments?

I would think a PT that is 275-0-275 with GZ34 rectifier creating around 350V on the plates of the EL84 might make more sense.

With respect, 10thtx

[Phil_S]

Has anyone noticed that the PT is 295V using a solid state rectifier?
295V X 1.4 = 413V on the plates of the EL84's?
That doesn't sound right to me?
<snip for brevity>

I saw that. It says, "...secondaries are 295V 130mA~, heat 6.3V~3.A" and on the diagram it shows 295V between the voltage source wires.

IMHO, B+ =413 is all wrong for EL84's and the 10K dropping resistor is too small to depress the screen voltage by much. I am guessing you'd need to drop screen voltage below 300 to make Va=400 workable.

I took this to mean 147.5-147.5, no center tap. There are no voltages on the schematic except for 295V. So, blew past it thinking, well, 147.5 X 1.4 = ~206VDC. The sum of the dropping R's in the B+ ladder is 14,200 ohms, so I figured the preamp tubes would run somewhere in the upper 100's, maybe a bit less.

One of us must be right! Does anyone actually know from personal experience?

[da Geezer]

The Hurricane does indeed sound good, and seems relatively simple, at least compared to my last few multi-channel, relay laden builds.

I note from the manufacturer info that the original amp has the 1st 2x gain stages controlled simultaneously by a dual ganged pot, although I will probably use two separate pots just for experimentation sake.

http://www.cornfordamps.com/docs/hurricane.pdf

Geezer

[10thTx]

Does the reverb look right ?


Insertion points OK?

Does the grid of the return reverb triode need a resistor to ground?

With respect, 10thtx

[cbass]

Has anyone noticed that the PT is 295V using a solid state rectifier?


295V X 1.4 = 413V on the plates of the EL84's?

That doesn't sound right to me?

Comments?

I would think a PT that is 275-0-275 with GZ34 rectifier creating around 350V on the plates of the EL84 might make more sense.

With respect, 10thtx

I don't know butt he 220 ohm cathode resistors suggests that this amp maybe running higher voltages.And of course with a load the plate voltage will be under 400 still pretty dang high for an el84

[JazzGuitarGimp]

Does the reverb look right ?


Insertion points OK?

Does the grid of the return reverb triode need a resistor to ground?

With respect, 10thtx

I would use a 100K to 1M resistor here. As long as the reverb tank is connected, there's no need for the resistor. But if the amp is run without the tank, it's probably better to have a GND reverence than to leave the grid floating.

Also, R35 appears to be 1.5R. SHould it be 1.5K, or is 1.5R correct?

[10thTx]

I thought some more about this schematic and how I would consider approaching this build.

I am not a fan of EL84 amps, so I drew up a 6V6 version. I have found with a 275-0-275 150ma PT, that by using a 330R/10w resistor that I can switch without rebiasing between:

6K6 with 5Y3GT
6V6 with 5V4
5881 with GZ34

I am not sure the reverb is drawn correctly in the original schematic, & since I prefer delay in an active FX on board, I added that. The active FX makes a great Master Volume also.

I change some component values to ones I like. Note tone stack and coupling cap changes compared to original schematic. I'd use Orange Drop PS caps.

I added an "enhance cap" across the LTPI plate resistor instead of the 10pf snubbing cap (which has always been a tone killer on my amps when I tried it)

I like smaller value filter caps going towards the preamp tubes in the B+ chain. It seems to add some transparency in my experience.

Anyway, I have not built this so it's totally a DRAFT idea ......... but I thought I'd share it for comments. CHECK for ERRORS.

** added a layout Compare with schematic & check for errors. Go with schematic IF there is a discrepancy.

With respect, 10thtx

[67Mopar]

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[10thTx]

The V1b plate resistor is incorrect... It should be 220k. The V2b coupling cap is also incorrect... It should be 33n. The V2a 470pf cap should run parallel with the 220k plate, not over the treble cap. Also, the treble cap should be 330pf, not 220pf. There are other mistakes as well.

I am understanding this to be in regards to the original schematic posted?

Any errors that you are aware of regarding the reverb insertion points or other reverb errors?

With respect, 10thtx

[67Mopar]

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