Metropoulos Forum

Hey guys!! I love my Metroamp 50watter, but it's time to make some changes. Already did the PPIMV(thanks George!) Now I need to get help from you all. I really want to get more gain (more distortion) out of this amp!! I removed the 500uf bright cap, I'm thinking of trying a 100 or a 220 . You guys understand, I want this baby to roar!! I prefer not to use any boxes on the front end. My MMPT puts out (last time I biased) 430v. I'm also biased at about 40. I'm open to whatever you may suggest!!
Oh, my 50 is also tube-rectified, 3.3 Henry MM choke, and MMOT.
Thanks.
Rick

the most noticable thing you can do is lower the value of the first cathode resistor. like to a 4.7k or even lower, or to throw a .68uf cap across it. or both. it might screech like hell after you do this so you will have to tame it by finding the right balance. i went through this exact same thing until i finally got pissed and added 2 additional gain stages, now my amp rages like a soldano, or can be turned down to a crunchy plexi. if you want i could send you a schematic for adding more gain stages without adding more tubes but by adding a different tube to the pre-amp. makes it roar.
mike..
mike@thegetawaysloths.com

myker wrote:the most noticable thing you can do is lower the value of the first cathode resistor. like to a 4.7k or even lower...

Uhm, I thought the first cathode resistor was 820 ohms?

Try to install a .0047uf cap or even a .0022uf cap in between your negative feedback resistor wire and your impedance tab.......whatever your are using there..........4-8-16ohms...

This will give you a "resonance" type of control (if you use a 1 meg. pot to control it....) or perminant effect without the pot.....

This will tighten up the bottom. A la Soldano a little!!!!!

myker wrote:
the most noticable thing you can do is lower the value of the first cathode resistor. like to a 4.7k or even lower...

Uhm, I thought the first cathode resistor was 820 ohms?

Klark,
oops, i assumed that the 50 watter was a mkII or a master volume 2204 styled amp which would make the first cathode resistor 10k. sorry!
note to self: Quit assuming shit!
Thanks for catching that Klark!
mike..

I think swapping a 330uf cap on V2A in place of the exsisting .68 cap adds gain, isn't this the "Eddie" Spec?

It is, yes, with a 1.1k resistor instead of the 820ohms (Apparently......), but I didn't try it yet don't know if its good..........

5150loveeddie wrote:It is, yes, with a 1.1k resistor instead of the 820ohms (Apparently......), but I didn't try it yet don't know if its good..........

Well, actually V1 and V2 resistors were actually 820 ohms, but they drifted to up to like 1.1k. I'm sure you've all read the witness reports so I won't bother providing a link to it.

When I get my 100 watter built I was gonna try some 1k's instead of the 820's to see how it sounds.

As those old cathode resistors drift up in value, the tube operates in a different part of it's linear curve. That makes the the tone a little different. It's subtle, but you can hear it.

George