Metropoulos Forum

I just wired up a c. 1986 reissue BB combo head (JTM 45/T) using SDM BB layout, the JTM instructions, and a few tweak before the PI.

It is basically a bastard 800 series MV model up to the PI, then a 10k/8.2k dropping string, stock PT, Classictone OT for EL34s and Classictone choke.

Fired it up and everything passed voltage checks. Went out of standby and I have a motorboater. Put put put put put not whump whump whump.. I see the 34s blinking halos with the put put, and I left it on about 30 seconds with the NFB disconected and it ate an HT fuse.

I swapped the primaries and it howled. I was proud of that, so I swapped them back.

Checked all grounds. Good. New F/T filters, everything up to the PI is old mustards and piher/iskra/lemco..

If I pull all the 12ax7's, no motorboat. I have the trem socket still wired but no tube there, no dress, just a wired socket.

Imma bit stumped. Any suggestions?

Check your swamp resistors.

It was a bad 150k at bias entrance! No more boating for me.

Have many tweaks to go, but the power supply is done. (and my least favorite part of it!)

Thanks, buddy!

Those are the best problems - the ones you figure out and fix yourself!

Funny though! I was having another problem a little later. Couldn't get a bias reading on v5 worth a crap. Stayed at socket with tube swap. Stayed similar with tube change. Always about half of other socket reading.

-44 on v4, -17/-19 or something v5, for instance... so I plugged in anyhow. Sounded pretty good until I started across the room to change cabinets, and the floor bouces enough in this old house to make it roll off the 1x12 onto the floor taking out the whole tube set including an old mullard in v2.

Now I can't get any bias reading on either socket and it sounds like a robot singing the national anthem.. the Antarctican National Anthem..



Crap, and such. heh too old to cry.

This was built on the last Metro BBRI board. It had SOME mistakes. One of the ones I found early was a bus wire dropped in the NFB circuit insted of the bias, one other small one, and the wrong resistor out there on the end of the bias. I think the trimmer is also bad right out of the gate, but all that is just a little annoyance at this point.



lol

Post some pictures so we can see all the mistakes in one shot.

I repoulated the board up to the PI and assembled the amp. No pictures of steps or anything. I only had 2 days to do it!

Mustards and big Pihers in cathodes some iskras then mustards up to the PI couplers where I like Sozos. I can upload the 4-5 pics I did take after work. Can't from ipad because of size restriction. Grrrr