Problem with Metro 12000 100W Volume Jump

[julkke]

I don't know where the 8 to 16 ohm comes from. Tried it and it sounded like poo, lost punch and gain. OT is happier when matching impedances.

[Dunkmop]

Just to bring some life back into this thread; the sound is still a problem with this amp, and it stays in a low volume state most of the time.

I just want to ask the people here what your bias voltage is at i.e mine is 90.8VAC going into the first 27K resistor in the bias circuit and joins the PI twin 220K resitors at -35.46VDC.

My B+ is approximately 400V


Just want to see what other people get here

[Dunkmop]

Finally found it guys!

It was the frigging PI cap where the couplers are. Probably saw too much heat over the years with circuit/component changes, and decided to give up.

Cheers for those that threw ideas in!


One worth noting; sudden drops in volume, and looser (maybe slightly gainier) sound!

[neikeel]

Finally found it guys!
It was the frigging PI cap where the couplers are. Probably saw too much heat over the years with circuit/component changes, and decided to give up.
Cheers for those that threw ideas in!
One worth noting; sudden drops in volume, and looser (maybe slightly gainier) sound!

Well done!
Which one the 47pF or one of the couplers?
Usually if PI output coupler goes leaky you get redplating on that bank of output tubes.

[Dunkmop]

Well done!
Which one the 47pF or one of the couplers?
Usually if PI output coupler goes leaky you get redplating on that bank of output tubes.

It was the 'fizzy' cap. It was 47pf silver mica, but I only had 100pf silver mica to throw in there for now.

What a difference; the amp is easier to play now, cleaner (distortion), and much louder. Back to how it should be!


Might try some ceramics and dog bone caps in this position now. I was almost ready to bolt her into the head cab, but I'm waiting for these new Sozo's to come out first

[neikeel]

You can actually play without one

[Dunkmop]

Yeh, interesting. It's one thing I haven't tried yet. The fizzy cap is there to reduce oscillations, is it not?

Will it sound more raw with this cap off? I do like the way it sounds with the 47pf, so ill see how the 100pf does.