Metropoulos Forum

danman wrote:I don't think we have discussed how the amp sounds either. Are you getting any output at the speaker? Is it producing the expected volume or is it weak?

This is normal. Check this thread http://forum.metroamp.com/viewtopic.php?f=4&t=37397

Statick wrote: I can't get more than about 28mA of cathode current with the bias pot max'ed out, so it looks like a resistor change is in order. That's easy enough.

I had one set of Tubes that I could not bias beyond 14ma. Had to change resistor too.

Glad that you got it sorted out!

Dan, it all sprang from your question about how it sounds, so thank you.

Now that I've got it working well in "stock" form, I need to read up on the best way to de-blanket channel-II. I'll probably start by trying other combinations of R-C in place of the 820/220u that is there now.

Statick wrote:Now that I've got it working well in "stock" form, I need to read up on the best way to de-blanket channel-II. I'll probably start by trying other combinations of R-C in place of the 820/220u that is there now.

Yes good place to start, try 25uF or 10uF with a 1k5 resistor and a 100pF bright cap on that channel. You will not lose the flavour of that channel abd will be able to blend it with the other channel.

neikeel wrote:Yes good place to start, try 25uF or 10uF with a 1k5 resistor and a 100pF bright cap on that channel. You will not lose the flavour of that channel abd will be able to blend it with the other channel.

Great suggestion Neikeel. I went with the 10uF/1k5 and the 100pF bright cap. Now that channel sounds amazing and it points out that the other channel needs some work. Channel 1 is awfully harsh. I'll probably start with other values for the bright cap.

Statick wrote:

neikeel wrote:Yes good place to start, try 25uF or 10uF with a 1k5 resistor and a 100pF bright cap on that channel. You will not lose the flavour of that channel abd will be able to blend it with the other channel.

Great suggestion Neikeel. I went with the 10uF/1k5 and the 100pF bright cap. Now that channel sounds amazing and it points out that the other channel needs some work. Channel 1 is awfully harsh. I'll probably start with other values for the bright cap.

What do you have now (and what is on V2a and your NFB)?

neikeel wrote: What do you have now (and what is on V2a and your NFB)?

Channel 1 (V1b) cathode bypass: 0.68uF/2k7
Channel 1 bright cap: 500pF
V2a cathode bypass: 0.68uF/820
NFB: 47k

Today I moved the NFB from the speaker jack to the 8ohm tap and replaced the 500pF with 250pF. It's better. I think I'll run with it like this for a while.

Further tweaking is inevitable. I may try a 100pF bright cap and raising the NFB resistor to 100k.

I prefer 47k on 8ohm tap, I find 100k on 4ohm a bit loose but you should decide for yourself. 100pF works well