Metropoulos Forum

Hello, I have a few questions.

I bought the amp built, and appears to be a Metro. It is identical to the 50 watt build instructions. All the values are per instructions as well. It has a PPIMV and Metro Loop added.

1. The Normal channel (II) is extremely bassy and flubby. Channel I sounds fine.

2. With PPIMV up and out, there is sound when playing out of either channel I or II with both vols on 0. When either vol turned up, they seem to notch and get sig louder at about 1-2? I also notice that if I jiggle the wire at the terminal on Vol II, it will make it go wide open, or shut off completely. Is this a sign of pot going bad? Already checked solder joints.

3. The wires off of vol II pot inside seem to be microphonic, especially with PPIMV up, is this normal? Tubes are only slightly microphonic.

Thanks in advance!

Bring it over I'll test it and fix it

Little too far away to just drop it off!

I'll figure it out, just looking for a little advice!

Thanks

What you describe on the Normal channel is normal. Can we see some gut shots?

I'll see what I can do, I've got it all torn apart now, gonna just order 2 new pots for the vols.

Would it be wrong to say that if I matched the values of the cathode caps and resistors of V1a and V1b, both channels should sound the same? Both bypass caps are .022.

If so, I think that is where I will start once the vol pots are replaced.

Thanks

Post pics before you rip it apart.....oh you have already

Mxzx wrote:I'll see what I can do, I've got it all torn apart now, gonna just order 2 new pots for the vols.

Would it be wrong to say that if I matched the values of the cathode caps and resistors of V1a and V1b, both channels should sound the same? Both bypass caps are .022.

If so, I think that is where I will start once the vol pots are replaced.

Thanks

Those are not by pass caps normal cathode by pass caps are 250uf and .68uf

Maybe I should have clarified, both V1a and V1b Plate Bypass Caps are .022uf.

Yes, as per the Metro 50 watt instructions, V1a Cathode Cap is 220uf and V1a Cathode Res is 820. V1b Cathode Cap is .68uf and V1b Cathode Res is 2.7k.

My thought was that if I make V1a and V1b 220uf and 820, both channels should sound the same?

Thanks,
Michael

As Art mentioned they are not plate bypass caps. They are inter stage coupling caps. Plate resistor bypass caps sit across the plate resistors only.

Changing to the values you suggest on both stages would probably sound horrible, a better option would be both 1.5k cathode resistor with 25uF bypass cap (like my late 60s Laney 60 plexi)

Hmm, ok. Here is the diagram that I am referencing.