tiny terror clone -> just humm, sound

[iWishmaster]

I finished building an orange tiny terror clone a while ago, mainly using information from the thread on this forum. The sound was good, but there was a _lot_ of hum and shortly after building it, it broke down as a result of poor internal design. So I decided to redesign the internal layout and redo all the soldering work. I finished all the work, but now, the amp doesn't produce any sound, just some 50 (or 100?) cycle humm and can't seem to find the problem. Here's what I tried / concluded sofar:

-The tube filaments glow as they should
-The internal DC voltages (power supply) are correct (though somewhat lower with load, which is to be expected)
-There is a very mild hum coming from the speaker. Turning the gain knob clockwise makes the humm slightly louder (expected behaviour). Turning the tone knob clockwise decreases the humm slightly. Turning the volume knob does absolutely nothing.
-Plugging in the guitar decreases the humm slightly and touching the tip of the plug increases the humm slightly.
-Tested the guitar on a different amp: works.
-I don't have access to another speaker cab, so I can't test it, but the cab is brand new, so I doubt it's broken.

As far as I can tell all the connections are correct (I haven't finished checking the entire signal path though). Any thoughts on what the problem could be? Snce I can hear some humm my guess is that the problem is not in the signal path... Maybe a busted (decoupling) cap? How can I test that? I only have acces to a digital multimeter, no scope or such.
The tubes have taken quite a hit due to some design faults earlier (see previous posts), can I measure somehow whether they are dead or not? Any clues on what the problem could be, or where I can start looking?

Thanks in advance!

Roy

[Twist]

What are the voltages on the pre amp tubes (Plate and cathodes / pins 1,3,6,8)?

[iWishmaster]

Darn, I was called away to work for a couple of days and didn't have the time to read here or work on the amp, I'll be working on it again tonight.

Originally Posted by Twist

What are the voltages on the pre amp tubes (Plate and cathodes / pins 1,3,6,8)?

I measured all those voltages a while ago and I don't remember finding anything odd but I'll recheck tonight.

I did notice that the preamp tubes aren't getting warm and they glow far too faint. I only just realized this. The preamp tubes are fed by DC, so maybe there's something wrong with the AC-DC converter circuit (merely a diode bridge, a cap and some diodes to drop the voltage a bit). The converter wasn't there in my original design ...

What happens to the sound / amp when the tubes run (very) cold? Besides potentially damaging the tubes ...

[iWishmaster]

Allright, I finished measuring everything. There was a problem with the heaters: they were running at a FAR to low voltage as a result of a busted diode-bridge. That's fixed now, but more problems arose ...

The guitar's sound is now (barely) audible, but it's distorted (very nasty) and fuzzy). THere's also squeling and humming coming from the cab which changes in volume and frequency when turning the tone and gain knob. The volume knob still does nothing.

These are all the DC voltages:

V1:
Plate1 = 173V
Plate2=175V
Kathode1: 1.3V
Kathode2:1.3V
g1: 0 V
g2: 0 V

PI:
Plate1: 215V
Plate2: 230V
Kathode: 63V
g1:43V
g2:40V
Note, nearly all the humm disappears while measuring the grids.

El84's:
Plate1: 313V
Plate2: 312V
Kathode: 11.3V
g1: 0 V
g2: 0 V
Note: Measuring the grids causes lots of humm.

I'm not sure what al these voltages are supposed to be, but to plate's seem OK. Preamp seems allright. Power amp seems allright: I'll have to recheck the volume pot and circuit to find that problem I guess.

The kathode and grid on the PI are most definetly wrong. But what could cause this?