I've heard great distorted tones coming from a Hot Rod Deluxe.
First either stick the amp on some crates, or angle it towards your ears so you can actually hear it properly. So many people complain that they can't get a great tone, when the speakers aren't even pointing at their head. Set the volume of the channel you're using to the sweet spot where the amp *just* starts breaking up when playing a power-chord with the guitar volume on full. Might be a bit loud.
My Vibrolux does this at about 3 with my strat though
Use the amp's distortion channels for the drive before you start messing about with pedals. Make sure the guitar volume is on around 8 and twist the dirty dial (or whatever it happens to be called

) to around 25%.
This should give you a very light crunch. Now it's time to start playing with the tone controls. First set them all at the middle position.
Now take the treble right up and get a feel for what it's doing. Now cut it completely. Leave the other tone controls flat while you do this. Really get it set in your head what the control does. Take it in. Really listen. Getting the idea now?!
Cutting can be as important as boosting.
Do this many times with each tone control until you know them intimately. After about five minutes of sweeping them to their extremes, you will be ready to use them in combination. Now your brain actually knows what the controls are capable of you should be able to dial in 'a tone'.
OK, now it's time to play with the gain a bit more. Ha! No it's not - it's time to go listen to the guitar sounds you're trying to emulate - or get close to - or combine to make your own unique sound. I'd listen to Bloodsucker from Deep Purple In Rock myself. Make sure you're listening to somebody who plays humbuckers. If you tried to get Deep Purple sounds (for instance) you might find it frustrating as I think Ritchie used single-coils for most stuff.
OK - now it really is time to play with your dirty knob (ohhh matron).
First whack the volume on your guitar to full. Notice how the amp reacts - since you're using a nice valve amp it won't get much more loud, but it will become more compressed and dirtier. OK, now keep raising the dirty knob on the amp and playing with the volume on the guitar.
You'll find that the tones on this amp are pretty bluesy on the whole, so you may want to engage your pedal (on the clean channel probably) if you want that really compressed 'metal' tone. Make sure you're thorough in the way you play with the controls and you should have more success. Also bear in mind that 'full' isn't always the best setting for the gain or 'drive'.
Much of rock music doesn't actually use that much distortion. I'm listening to Bloodcucker now, and the guitar is just a touch crunchy.
Same goes for many Led Zep tracks.