Alembic F-2B mods?

[Lorcan]

It looks like it's a Bass rig only, standard Alembic clone. Saw the pictures of Lorcan's Alembic build on his website, and I must say the Aluminium faceplate, and general layout looks sexy. Also easier to drill to mount the panel pots, compared to steel. Thought you would've used shielded cables earthed at the star point to avoid RF interference, rather than twist wires? Gilmour definitely uses an extra stage for gain or 'bite' as Cornish quotes. I guess due to the fact the F2B is stereo, would you run the output of 1 channel into the input of the channel 2, (only using the first ecc83 triode of the 2nd stage for gain)? Then by using a ecc832, use the 2nd ecc82 triode for the cathode follower mod? Tempted to buy a 2nd hand Alembic to do this, although building from scratch would be a rewarding achievement in itself. As Lorcan states, the hardest part is getting the materials sourced from various vendors and pcb fabrication (which I'm still to learn about). The assembly itself would be, in comparison, more of a straight forward process. In my particular case, I'm looking at running a wet/ dry rig. So split off from the preamp output, into the wet 'delay'  effect input, and the other into the dry power amp input. Hence cathode follower is probably required. Anybody know of a worthy 'Dummies Guide' Book to DYI PCB manufacture? We all started somewhere!

I use twisted wire for AC heaters, which is standard practice for tubes. If you'd want to use shielded wire, you'd have to find a 2 signal + shield braid capable of handling the current (admittedly quite small for 12ax7s) ... I did of course use shielded wire for jack-to input and output wiring. You could go as far as shielding the wire going to the pots and switches if you find the need to or feel paranoid about noise, but mine is fine without this. Just keep them as short as possible and plan your layout before any drilling

[Jarno]

...plan your layout before any drilling

+10.000
I just "winged" it on my first build, and it shows!

[POGFROGULPOP]

O.K. guys, Thanks for the inspiration. The voyage of discovery has begun. I'm off to the electronics shop tomorrow to buy a 1u 19" rack enclosure. The list is being prepared. YouTube had a few good clips on DIY PCB fabrication. Nowhere near as hard as I expected. Will update this thread on future progress for those interested. Still a bit of a mod to the original design, to get my head around. But as they say, "A man who never tried anything never got anywhere."

[Jarno]

Alternatively, you could use terminal strip board, or turret board, saving you the necessity to get to grips with making your own PCB's.

[POGFROGULPOP]

It might be a cheaper option as I would need to buy a monochrome laser printer, for the PCB method. Seem to be twice the price of a normal laser printer, not good. Have a friend who does screen printing, could be worth a call.

[POGFROGULPOP]

Looks like my cheap  Brother Monochrome Laser Printer 1200 dpi is capable of printing on to glossy photo paper. Cool.

[POGFROGULPOP]

My DIY voyage of discovery so far.... Started trying to learn how to design my own PCB drawings by trying to come to grips with a free version of Eagle version 5.1. Found too many obsticals and limitations due to maximum allowable PCB size (4" by 3"), and being unable to transfer 9 pin 12ax7 tube designs, from the user library, to the free version. Was also going to use the 'Toner Transfer' method, using a Laser printer, and modified Laminator. My Brother printer doesn't use a re-fusable toner, unlike the old HP Laser printers. Think I've found a better way to do the PCB method. A good friend, being a Screen Printer, has a old version of Photoshop 7.0. I gave him Lorcan's Alembic pdf, which was created using Eagle version 5.6. Being a bitmap drawing, we sat down for 2 hours and modified his circuit design to add a ECC832, for the extra ECC83 stage, plus ECC 82 Cathode follower. Unfortunately JJ Electronics are the only manufacturer of this tube. Have heard their quality control has slid in recent years on their preamp valves. Will probably need to buy half a dozen, then test on my other friends Amplitrex AT-1000, before getting a usable ECC832. At least it will help keep the circuit design simple, for now. This could change for version, 'Mark 2' though, if the JJ's consistently fail as a Cathode Follower. What my Screen Printer friend has suggested, is Screen Print the circuit designs onto the copper of the PCB, using his finest mesh screen. Then use Ferric Chloride to etch the design. Will update this thread with my future results, for those interested.

[Jarno]

I would be amazed if JJ would produce that many mediocre/ bad tubes, I just bought three of the ECC832 and fully expect them to be "A ok". IMHO any company selling duds will be bankrupt within a week. But we'll see.

[Ben N]

If you have some gain to spare, another way to lower the output impedance is with split plate load resistors.

[Ronsonic]

My DIY voyage of discovery so far.... Started trying to learn how to design my own PCB drawings by trying to come to grips with a free version of Eagle version 5.1. Found too many obsticals and limitations due to maximum allowable PCB size (4" by 3"), and being unable to transfer 9 pin 12ax7 tube designs, from the user library, to the free version. Was also going to use the 'Toner Transfer' method, using a Laser printer, and modified Laminator. My Brother printer doesn't use a re-fusable toner, unlike the old HP Laser printers. Think I've found a better way to do the PCB method. A good friend, being a Screen Printer, has a old version of Photoshop 7.0. I gave him Lorcan's Alembic pdf, which was created using Eagle version 5.6. Being a bitmap drawing, we sat down for 2 hours and modified his circuit design to add a ECC832, for the extra ECC83 stage, plus ECC 82 Cathode follower. Unfortunately JJ Electronics are the only manufacturer of this tube. Have heard their quality control has slid in recent years on their preamp valves. Will probably need to buy half a dozen, then test on my other friends Amplitrex AT-1000, before getting a usable ECC832. At least it will help keep the circuit design simple, for now. This could change for version, 'Mark 2' though, if the JJ's consistently fail as a Cathode Follower. What my Screen Printer friend has suggested, is Screen Print the circuit designs onto the copper of the PCB, using his finest mesh screen. Then use Ferric Chloride to etch the design. Will update this thread with my future results, for those interested.

For a dual triode that has high and low mu sections why not just use a 12DW7?

It's a standard number. Might even be the same thing as that JJ, Hell, it'd make a lot more sense for them to produce that than invent a variant.

[Jarno]

Not sure about the availability of 12DW7, but ECC types are easy to get this side of the ocean american types somewhat less so.
They might have made a new tube though, because they even offer a mirrored variant, ECC823, which has the ECC82 section on the other three pins. Presumably so you can plug it into an existing amp and modify the gain structure.

[Jarno]

If you have some gain to spare, another way to lower the output impedance is with split plate load resistors.

Does that lower the Zout or just the gain of a stage? Will this allow the tube to drive a transformer with more current? I've been trying to find some pictures an explanations but there's not that much info, I've read a short snippet done by Paul Ruby on Ampgarage.

[Ben N]

You know, I had always assumed it lowered Z-out, but now I'm doubting myself. I found this by Steve Ahola at Blue Guitar, but says nothing about impedance, and I can't find anything else about it.

Oh, RG? PRR?

[jaysg]

I'm not sure how to insert an image on this site.   I skipped the extra tube with a MosFet -- an IRF820.  It's in Keen's MosFet follies stuff.   If you're going for the full two channel version, then you may as well add the tube I suppose, as long as your power supply can take it.

[POGFROGULPOP]

I would be amazed if JJ would produce that many mediocre/ bad tubes, I just bought three of the ECC832 and fully expect them to be "A ok". IMHO any company selling duds will be bankrupt within a week. But we'll see.

I've decided to steer clear of the JJ's, on the advice of my friend who now refuses to sell them based on the fact that he had to return 50% of them to the supplier because they were out of spec.(<65% gain), after testing them on his Amplitrex AT-1000. Then the supplier probably just passed them on to some other unfortunate retailer. Also many that did test within factory spec. were burning up in a short period of time. He still sells and recommends JJ Power Valves like the EL34L, but refuses to sell their preamp tubes. Tung-Sol re-issue 12ax7's are apparently better and more consistent, as far as test results, so he recommends these instead. They dont make ECC832's though. I took a big punt and bought some NOS Mullard 7247 (12DW7 Equivalent) from Ebay from a fairly reliable seller, to be used for the cathode follower. Just love the warm sound of Mullards, so couldn't resist.

[POGFROGULPOP]

I'm not sure how to insert an image on this site.   I skipped the extra tube with a MosFet -- an IRF820.  It's in Keen's MosFet follies stuff.   If you're going for the full two channel version, then you may as well add the tube I suppose, as long as your power supply can take it.

Another though I'm having is just to keep the original Alembic F2B 'ala Lorcan' design, and just buy a separate Tube Cathode Follower, that has a Drive Adjustment, as well as a 'Send' and 'Return' adjustment from a company called Ceriatone, that do clones of all sorts of amps, including Dumble. For $250, you can buy a 1 unit rack mountable Tube Impedance matcher(Serial Tube Buffer), cloned from a Dumble design. It uses a 12ax7 though, which I found a bit weird, as I thought the ECC82 was a better tube cathode follower. Heard some clips of it on YouTube, and it sounded good. Here is a link for those interested.......http://ceriatone.com/productSubPages/C-lator/C-latorComplete.htm

[POGFROGULPOP]

I'm not sure how to insert an image on this site.   I skipped the extra tube with a MosFet -- an IRF820.  It's in Keen's MosFet follies stuff.   If you're going for the full two channel version, then you may as well add the tube I suppose, as long as your power supply can take it.

Here's a good YouTube link showing how the c-lator serial tube buffer works, with the 'drive' control giving the extra bite needed. I must say I'm impressed, as it really does thicken up the raw preamp tone nicely, before hitting the poweramp. I think you can buy a DIY version of the kit that you solder yourself for US$160 + postage. Have a listen........ http://il.youtube.com/watch?v=ZPB4X17p7Oo

[Ben N]

I would be amazed if JJ would produce that many mediocre/ bad tubes, I just bought three of the ECC832 and fully expect them to be "A ok". IMHO any company selling duds will be bankrupt within a week. But we'll see.

I've decided to steer clear of the JJ's, on the advice of my friend who now refuses to sell them based on the fact that he had to return 50% of them to the supplier because they were out of spec.(<65% gain), after testing them on his Amplitrex AT-1000. Then the supplier probably just passed them on to some other unfortunate retailer. Also many that did test within factory spec. were burning up in a short period of time. He still sells and recommends JJ Power Valves like the EL34L, but refuses to sell their preamp tubes. Tung-Sol re-issue 12ax7's are apparently better and more consistent, as far as test results, so he recommends these instead. They dont make ECC832's though. I took a big punt and bought some NOS Mullard 7247 (12DW7 Equivalent) from Ebay from a fairly reliable seller, to be used for the cathode follower. Just love the warm sound of Mullards, so couldn't resist.

Well this sort of confirms my experience with JJ preamp tubes. I got a complete set for my Deluxe Reverb from Eurotubes, and I ended up taking them all out--every last one was microphonic.