Monkeymatic Angry Ape

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xtian
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Monkeymatic Angry Ape

Post by xtian »

Starting my Tiny Terror build, using Hammond AO43 chassis, Fender Blues Junior transformers, and parts from the beaks and feet collection.
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xtian
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Re: Monkeymatic Angry Ape

Post by xtian »

Finished wiring. PtP. What a sucker's game. I mean, I made it this far without injury or melting any components with the iron, but if I have to change any wiring, it's going to be a bitch.

Odds on first startup working?
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Smokebreak
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Re: Monkeymatic Angry Ape

Post by Smokebreak »

Depends on how you define "working" :D
You've got pretty good luck, but I'll give you 2:1 . $5 in caps?
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xtian
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Re: Monkeymatic Angry Ape

Post by xtian »

Sorry, betting window is closed. Amp fired up and works great--no issues.

Very minimal hum audible (though I am using mismatched, old Hammond EL84s, which may contribute to the hum) and old, USA long plates also, but they sound good.

319v on plates, 73mA total cathode current (~37mA per tube is 100% dissipation). 323v on screens, though, but that seems to often be the case in cathode biased amps, I've seen.

At bedroom volume levels, amp is too bright. Sounds best with tone control at zero. And I already changed bright cap from 1000p to 500p before I even started it up. Not much chunk or chug available.

Dual-ganged gain and volume controls are very nice. Smooth.

Measured 12.5 watts clean.
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drew
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Re: Monkeymatic Angry Ape

Post by drew »

Have you got the Damned Dirty Ape on the drawing board yet?
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xtian
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Re: Monkeymatic Angry Ape

Post by xtian »

Sure, the Chuck Heston model!
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Re: Monkeymatic Angry Ape

Post by RJ Guitars »

Nice work Aaron, that looks like one bad Monkey to me! I would be curious if any of that hum could be due to the steel chassis but we can wait until you swap out the tubes before it's worth looking into that.

Funny little side note - I just read a post in a HiFi forum where they are lamenting that guitar amp builders have bought up all these old Hammond amps and you can't hardly find one for a reasonable price any more to make into a HiFi amp.
Good, Fast, or Cheap -- Pick two...

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xtian
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Re: Monkeymatic Angry Ape

Post by xtian »

Tried a matched pair of JJ EL84s. Decreases the hum by about half. A very small (must put ear close to speaker) hum remains, but certainly not surprised--my grounding scheme is far from optimal...I ground to the chassis at four or five different points!

Also, sounds better (less tinny and harsh) with the bright cap removed.
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pdf64
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Re: Monkeymatic Angry Ape

Post by pdf64 »

Independent power tube cathode resistors (eg 240 ohm each instead of 120 ohms shared in this case) generally allows 'good but mismatched' power tubes to settle to closely similar cathode currents, thereby getting rid of the dreaded hum.
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Re: Monkeymatic Angry Ape

Post by xtian »

Excellent tip, Pete.

I'm wondering about the screen voltage (323), which is higher than the plates (320). Worth bringing that down to save some stress on the power tubes?
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pdf64
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Re: Monkeymatic Angry Ape

Post by pdf64 »

Well, the stock TT screen grid node only seems to have a 150 ohm dropper.
So if that's what you've used, I'd consider increasing it, to at least ~500, and then see where they sit.
But the original AC15 screen grids must have sat quite a bit higher than the plates, as the plates and screens used the same node, after a Pi filter.

In use, I can't hear a difference between shared and independent p-p cathodes; however, Merlin notes that a shared cathode arrangement can promote even harmonic distortion, though I'm not clear what the mechanism for that may be http://www.valvewizard.co.uk/pp.html
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xtian
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Re: Monkeymatic Angry Ape

Post by xtian »

I'm revisiting this amp (has been sitting unsold for a while--unwanted amps often become victims of "improvements" if they sit long enough).

The tone control is a post-PI Cut control, like TW Rocket. Does nothing to the tone when the gain is up. Why?

Here's the schem I used:

http://www.prowessamplifiers.com/schema ... terror.pdf
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Re: Monkeymatic Angry Ape

Post by JazzGuitarGimp »

That's weird. I could see how the position of the Volume control would affect the usefulness of the Cut contol, but not the position of the Gain control.
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xtian
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Re: Monkeymatic Angry Ape

Post by xtian »

Hmm. Maybe that's it. Because I have the volume set low when the gain is set high. I'll test.
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Re: Monkeymatic Angry Ape

Post by JazzGuitarGimp »

If it turns out to be an interaction with Volume control, you might be able fix it by moving the Cut control from the Wiper terminals to the Clockwise terminals of the Volume pot, though you will likely need to increase the value of the Cut control's capacitor to get the range of the Cut control back to where you like it.
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