Subminiature Terror with PP Triodes

[sneakers563]

Hi all,
I've been working on implementing a version of the Orange Tiny Terror circuit using subminiature tubes. I'm using 6112s for the first two stages and LTP, and a 6021 or 6111 for the "power stage".

I have to say though, that I seem to be much better at turretboard layouts than PCBs, so I was hoping that you guys could take a look at the layout and offer any suggestions, particular with regard to component arrangement and the grounding layout. As I've had more experience / success with turretboards, the layout generally follows how I would do it there, but with slightly more variable spacing. I've tried to keep the various subcircuits separated by about 0.375", while component pads within the subcircuit are spaced horizontally at about 0.2" apart.

I don't have schematic made that includes the off-board components, so I'll just describe what's generally going on.

Here's version 1:

Submini_TT_V1.png

The subcircuits are (R-L):
V1A cathode circuit: C1, R1
V1A anode circuit: R2, C2, R3
V1B anode circuit: R5, R6, C5. I'm not sure if C4 and C14 are really necessary, but they are equivalent to the anode bypass on the real TT.
V1B cathode circuit: R4, C3
LTP cathode circuit: R7, R8, R9, R10, C6, C7
LTP anode 1 circuit: R11, R13, C8
LTP anode 2 circuit: R12, R14, C9
Power cathode: R17, C10
Power grid: R15, R16
PS reservoir and bleeder: R18, C11

Here's another version with a slightly different ground layout. Here, I tried to follow Merlin Blencowe's "star of stars" / James O'Connor's "galactic" grounding scheme. I dunno whether this one would perform any differently. The grounds obviously are a bit more controlled where they come together, but at the expense of longer traces.

Submini_TT_V2.png

I've also added a zip of gerbers below in case anyone cares enough to want to take a look at them.

Thanks for any help you can give. Ultimately, I'd like to attempt a subminiature version of the Orange Rocker 30. It has an extra gain stage, so I'd really like to get a good idea of what I'm doing right or wrong before attempting that one.

[bmx]

would someone volunteering to check your layout need a schematic to check against?

[sneakers563]

I was kind of hoping that the particular component values would be irrelevant, and that the info above about the subcircuits would be enough. The Tiny Terror is not, after all, a particularly complicated circuit and it's mainly the grouping of the various components and subcircuits that I'm interested in feedback on. However, yes, a full schematic would make it easier. I'll try to get one together and post it. Thanks!

[katopan]

I built a 2W version of the 18 Watt Superlite TMB with subminiature valves years ago. I used 5902s in the power stage to keep with proper power pentodes.

Just be aware that contrary to Dana's Lil Devil, I found that the 6112 didn't bias the same as a 12AX7 so I couldn't just use the same plate and cathode resistor values. Also they don't deliver as much gain and once again I had to change component values to get as much out of them as possible to get an adequate level of drive into the power stage.

[sneakers563]

Thanks Katopan,
Yeah, I'm aware that everything needs to be rebiased. Luckily, I have a uTracer, and have been able to run some tests on the 6112. It seems like the plate resistance is around 36K, so I'm going to be using 75K load resistors.

How did the 18W with 5902's turn out? And did you make a pcb? If so, do you recall what kind of spacing you used between components?

[katopan]

It worked out really well. Great little amp!

Yes, I designed my own PCB. I soldered the submini valves into 8 pin DIP IC sockets and soldered another set of the same sockets onto the PCB to make the valves plug in, which is an idea I stole from somewhere else. Posted about it in detail on 18Watt.com at the time, but that was years ago and even if you found the old thread all the photos would be gone. But I've got some photos of it here:
https://sites.google.com/site/chosenaud ... otscreamer

As you can see there's plenty of space on the PCB, mainly dictated by the valve spacing I was working to. But when I design more compact PCBs for pedals and other things the spacing is more like what your pics above look like.

I was never happy with any low powered triode push-pull output amp and that is what drove me to build this in the first place.

[sneakers563]

Oh cool, I've look at your page before. That amp was/is one of my inspirations.

Re: the push-pull triodes, I know what you mean. I've gone back and forth on whether to use triodes in the output stage or whether to try to use some small pentodes. I actually have a couple of 6397 tubes, and it appears that if I lower the B+ to around about 100V, my 22.5K transformer will work and give me around 0.4W or less. Unfortunately, the 6397 is directly heated, but I was going to use DC heaters anyway, so maybe that would be ok. The lower B+ means I could probably use the (cheaper) 6021 tube in lieu of the 6112.

[katopan]

Sounds good Sneakers563. Looking forward to seeing it come together and what you think of the 6397s if you end up using them.