Metropoulos Forum

This wasn't a kit but it is a JTM45 so I am posting this here...M e r r e n OT, MM PT, NOS mustards, McMurdo octal sockets, custom made head and 2x12 cabinet. I'm really happy with how it turned out, even though I ran out of wire and had to use orange in some spots.

Next up is a Marstran spec OT and PT build with NOS Mustards, Pihers and a Bulgin...

Nice work. So pretty.

Looks good, and I am sure orange wire will sound better too

Thanks Neil, I am not as good as you but my next build is mostly NOS parts so I am excited about it.

I can't shake the thought that this amp is too grainy at high levels...I added the "flying resistor" and increased PI filtering but once I get above 6 things get really gainy. Is this the nature of the M e r r e n Drake OT?

Neil, do you seen anything in my build that would cause grainy, gainy overdrive?

No, it looks good.

It will need some running in hours and your tube choice will be very important (a Mullard ECC83 works wonders), lower filtering will be better than higher).

Also check the bias on both outputs and go up and down until it sounds best - temporarily forget the numbers.

New builds do sound brighter, stiffer and slightly harsher than originals but they do settle down with hours.

The cathode resistors on v2 look like Metal oxide which you usually don't see other than the b+ line, but that's really just voodoo mojo stuff.

I will always be suspicious of modern silver micas. I'd try some ceramics in there to see of it holds together better.

Doug H wrote:The cathode resistors on v2 look like Metal oxide which you usually don't see other than the b+ line, but that's really just voodoo mojo stuff.

I will always be suspicious of modern silver micas. I'd try some ceramics in there to see of it holds together better.

I agree re the micas but they are smoother and less grainy than ceramics.

The MOs are voodoo, but if all else fails you can use cc plate resistors on V1 and on v2 and 2w cc in the B+ line

Thanks guys. My B+ is high on this PT, right at 460. I might try closer to 400 to see how I like it.

I have some vintage GEC KT66s, I'll give those a shot today.

I do have some ceramic disc caps I could use, I'll consider it. Plenty of carbon comps, I used the metal oxide because I found them first when building!

I have watched Johan's videos on YouTube and the originals do get very aggressive when cranked. My first JTM45 build was a Metro kit and it was very soft and round...400 B+.

I need to take back my "quiet as a mouse" report...at high volumes there is some heavy buzz/hum coming on. My house was built in 1951 and the electrical is very noisy, but I need to tighten this up some.

Neil - any advice on lead dress to make her run a little quieter? It's too late for Larry Grounding.

Generally looks pretty good, only bit I see is the red heater wires on V2 which are directly under and parallel with the signal wires.

I think if you shorten the wires so they go direct to the socket you may be able to cross them at 90 degrees. Other things to do are push the plate wires down to the chassis floor and raise the green grid wires up level with the board then dip them down to the socket at the last minute.

Oh and cut the pot bus shorter so the bass pot is not grounded and the presence pot only has a dedicated ground wire to the lug on the PI can.

Bass pot is not grounded. The ground connection from my Presence pot to the lug is the connection for the entire bus.

I will work on the heaters etc.

where are the speaker jacks grounded?

In a ground lug off a power tube socket. Why?

just curious, couldn't see it anywhere.

The Aiken site has a fantastic page on grounding, maybe you can find a gem there that can be worked into your build easily and will help with the noise.

Are the OT primary and secondary leads bundled together? it sort of looks like they might be in the pic.