Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tonedef on March 19, 2023, 05:37:38 pm
-
I absolutely love @SILVERGUN 's son of a breadboard (https://el34world.com/Forum/index.php?topic=16551.0). I finally decided to build something similar. I'm about to start wiring the preamp section soon, would love to hear anyone's pointers if you have any. Mostly concerned about the best layout for minimizing noise and ease of building. I've got a scrap piece of aluminum channel for the preamp section, and I'll run the heater wires along the back of it (ala merlin's guide (http://www.valvewizard.co.uk/heater.html)). The circled numbers are the tube pin numbers:
-
Looks like a fun project.
If your builds look anything like mine, you'll have a rat's nest of wires running around soon enough. Glorious!
-
:laugh: Totally! You should see my midibox keyboard project. I swear, half the weight of the thing is ribbon cable.
-
I'll probably also add the option to split the heater supply in two. A DC supply for the first gain stage (I love high gain amps as you might have guessed from how far away the second bottle is), and an AC supply for the rest.
-
What I made a few years back with the intention of experimenting before the real build
Never used it though, as it seemed more of a hassle,
and the builds are almost always relatively easy to change a value here and there
And many of the designs are already in the EL34 schematic library.
Then a lot of the issues have to do with lead dress and chassis layout which is only observed in the real deal.
Unless there is another purpose that I haven't seen yet.
-
Layouts are definitely very critical. Even as simple as where you want to ground something. But tube breadboards, I think, are very much useful, especially when you're going off the reservation. For example, I plan on making a slo-clone, but I also want to swap out to a PPIMV. I also want to try making it a "bedroom" friendly 6V6 20 Watt, while keeping the FX and clean channel, etc. There's a lot of playing around. I think you can find some interesting things very quickly (or abandon terrible ideas) with breadboards. Even if it's suboptimal, the point isn't the perfect amp on a breadboard, but a great idea that you refine.
-
Congrats on your build and I'm glad to hear you were inspired...
Looking back at my build, there isn't much I would change or add except that I should have left room to the left of the cap cans for a tube rectifier socket. I didn't realize at the time that I would care, but sag is an important component in the feel of an amp and a tube rectifier is the original way to get there.
Other than that, I have never really wished for anything different. When necessary I use a Variac driven power supply to try different input voltages. (not included on board)
One of the nice features that isn't well documented is a ground bar that starts at the power supply at the back of the board and runs to the front rail. It is under the board but bolts through the board and that front rail. It is a piece of 1/8" aluminum flat stock that I had laying around. I put it in a vice and bent a 90 degree angle so it would stick up in the back. Available at Home Depot (but not necessary)
-
there isn't much I would change or add except that I should have left room to the left of the cap cans for a tube rectifier socket
Oh, awesome! That's great advice, I was originally thinking to just nix the tube rectifier and go solid state - I totally did not think about voltage sag. I'll update my layout
When necessary I use a Variac driven power supply to try different input voltages
Nice! I've been musing over a Variac + isolation transformer anyway. This seems to be a great way to adjust things without a lot of hassle. I built into the board a mini clamp to make swapping out transformers easy, but in practice, I'm probably going to just leave it in place till I dial in what I need for a final build.
One of the nice features that isn't well documented is a ground bar
Totally! I've got loads of scrap Al hanging around (I do a modest amount of CNC work). I was going to use a 1/16 sheet that covered the entire bottom of the board, but that's def. a waste. A thicker, inch wide strap would be better.