Alembic F2-B

[oatmeal769]

Alembic F2-B refit

Sorry for the looooong delay in posting pictures.

I'm pretty well done, I've decided to forgo the balanced output, but the rest of the suggestions made here I have implemented.

The result is a unit which is much MUCH quieter - almost silent, even at extreme volumes / gain. A bit of thermal tube noise, and maybe just a tiny bit from the remaining CC resistors (which I may still change out to MF resistors), but a huge improvement. No hum whatsoever. The active EMG electronics in my bass are now far and away the noisiest part of my signal chain.

It has also regained the punch and clarity I felt it had been lacking.

Here's a rundown, and pictures.

New wiring as needed.

ALL capacitors were replaced.

All new metal film resistors and diodes in the power supply.

Channel CC resistors replaced with MF resistors where needed.

New grounded power cord, re-wired for proper grounding.

Added choke in the P.S.

Added 100nf caps between tube output and tone stack.

Tinned circuit board, & riveted board to chassis.

Cleaned or replaced all jacks, cleaned chassis, tube mounts, new screws as needed.

[Jarno]

Looks great! Good that you've kept it original, I don't think I could have resisted to urge to put in DC heaters :-)
By the way, which tubes are you using? I have Tung Sol ECC803S, and that's an excellent tube. Different makes do make a difference!

[oatmeal769]

Thanks!
I've kinda settled on a pair of early '60s smooth plate Telefunkens for now. I will sometimes put Mullards in there, they seem to be a bit brighter. I had wanted to try some Tung's or some Valvo's but I'm kinda settled for now.

I bought it with what I think are the original tubes - some early 70's RCA orange labels. I think their life may be closer to 'done' as they seem to not output as loud, but I have not had them tested.

Tubes do make a difference, but I think as long as one uses good vintage tubes rather than new Russian or Chinese stuff, the differences are probably pretty subtle.

------------------------

Hey, check this out -
I'm thinking of making another pre-amp, really more of a direct box, based on this circuit. More of a simplified reverse engineering job than anything...

What I'd like to do is make the same power supply, and then use a 12AX7 - and nothing else - as the preamp. No tone stack, extra caps, etc.
I'd just run the input jack straight to the first stage, and connect the pins to go directly to the second stage, and then straight to the output jack. The only thing might be a first and /or second stage gain control. The tone would then be entirely based on the tube, and the bass plugged into it.

I'm a complete novice, but I think it will work (?) My curiosity as a 'minimalist' has had me thinking about this for some time now. What do you think? Any suggestions?

Also, what is this DC heater thing you're talking about? Aren't the tubes already heated DC?

[Jarno]

The F2b, and a host of other tube equipment with indirect heaters, use AC to heat the tubes, and that can be a bit noisier than heating them with DC. Wire dress is more important with AC heaters.

I have been thinking about doing a sort of a lunchbox studio pre myself, maybe see if I can score a UTC output transformer on eBay. I was thinking of using a pentode (EF86) with a triode pentode morph, and maybe a rudimentary tone control (high roll-of with a cap and a pot).
Don't really need it right now and plenty of projects in the pipeline so it falls in the "sometime/ maybe" category (any GTD fans out there?).

[MaxPlankton]

nice work, oat!
makes me regret selling my Alembic years ago..
now being used by Harry Bruz in Leo Sayer's band..heh
I'm a guitarist tho', but they're great for a stereo guitar rig
I bought a Rivera 60Wx2 head, but it wasn't so great..
now I run through a Hughes & Kettner valve Leslie thingy (Roto-plooker?),
bass rotor into a blackface Super Reverb, treble rotor into a Princeton Reverb
works pretty good, except the H&K Rotoflex has died on me and I'm not a tech...heh

Cheers

[Groundhangers]

I havent been in for ages but i see the Alembic woes still go on.
When i get time ill draw up and post a full layout including the power supply And put and end to all the miss-leading schematics out there, i wish they were all banished to the black hole.

Greg

[oatmeal769]

Originally Posted by Groundhangers

I havent been in for ages but i see the Alembic woes still go on.
When i get time ill draw up and post a full layout including the power supply And put and end to all the miss-leading schematics out there, i wish they were all banished to the black hole.

That would be VERY cool, Please PM me when you do it. I don't read schematics very well, but at the end of the day, I just wadded up the one I got off the net, and tried to figure out what does what just by looking.

I'd love a layout sheet, rather than a schematic anyway, it makes things easier for those of us who are musicians first, and technical engineers a far off second, LOL

[Jarno]

Originally Posted by Groundhangers

I havent been in for ages but i see the Alembic woes still go on.
When i get time ill draw up and post a full layout including the power supply And put and end to all the miss-leading schematics out there, i wish they were all banished to the black hole.

Greg

Well, my clone worked off the bat, so not much woes going on overhere.
If you do make a layout, make one with regulated DC heaters And B+, that would be great

[oatmeal769]

Originally Posted by Jarno

... make one with regulated DC heaters And B+, that would be great

+1

[oatmeal769]

Hey Jarno -
I did some swapping and listening last night, I'm still using the Telefunken for overall smoothness, and a Mullard for loud, bright and punchy. They were the two that stood out the most, although all the 'old stock' tubes were better than the JJ or Electro-Harmonix one.
I am still hearing that people love the Tung-Sol in there. Any idea where I can get a bona-fide NOS one? ebay doesn't seem to be turning up much these days - unless you want to pay through the nose.