r/diytubes

Dead family member, I know nothing about tubes. Are there any resources out there to help me sell these or get them to someone who might find use for them? Thanks

Hey guys this is my first amp. It's a MarkIIC+ with a couple changes in the circuit it's got independent controls for the 2 channels except for presence because it didn't really seem to make sense to me when I was designing the PCB it's a 50Watter with 2 6L6GC. For the first 2 preamp stages I've used 2 triodes in parallel because they reduce the noise of the stage by the squareroot of 2 which in the first stages is pretty interesting because it lowers the overall noise of the amp by a lot. I've used this same noise reduction tecnique in my thesis so why not use it here too. The pcbs have a couple of small mistakes but nothing that compromises the amp functionality I just had to wire the channel switching circuit and the Master pots the other way around. The EQ is mostly smd with gyrators instead of inductors because the inductors are really hard to find where I live. I havent installed it in the cabinet yet because some screws are missing but the last photo is a mockup of how it will look once all is done.

Made this build after my Tweaker 15 112 died on me. Gutted it and reused the transformers and chassis. My first non-kit amp build. Used diyLC to plan the board layout, and then cut and drilled a blank 3mm bakelite sheet to fit and swage the turrets. Had to retrofit a few things so not the most ideal(e.g board mounting screws are under some capacitors) but works well and has very little noise.

The turretboard layout is my own layout based off Robrobs optimised 5E3 layout. Made a few changes to:

1. Got rid of standby switch cuz its useless

2. Togglable input bright/normal switch to reduce 4 jacks to one. No one need the low input jacks anyway

3. 3-way toggle for: stock, cathode bypass cap lift for V2A, and adjustable negative feedback loop from 5k to 55k

4. 470ohm screen resistor on power tubes to extend tube life. I know 1k is better but i alr had 470 on hand

5. Uf4007 for solid state rectification as space constraints prevented tube rectifier. UF to reduce diode ringing.

6. Upsized cathode resistor to 10w as that thing runs hot

7. Pre cathodyne phase inverter master volume. Initially used robrobs master volume method but it was q ineffective. So i just did a classic volume pot with an additional coupling cap

Had a few issues like due to reusing power transformer and solid state rectification, the B+ was around 390vdc instead of 360vdc. Power tube dissipation was at 130%(blew a jj6v6s) so i had to lower it. Initially used Geofx’s mosfet folly but even with a heatsink it got really hot and i felt uncomfortable using it. Couldnt find high wattage zener diodes so I settled on just using a 10w resistor before everything else to lower B+. After some trial and error i landed on 150ohms, which lowered B+ to a comfortable 355, giving me an ideal 93% dissipation. 10w B+ dropper resistor dissipated around 1w so no worries there. Temperatures internally dont go above 55C so the F&T ecaps should last me a good while.

Designed my ownfaceplate in cad but getting it made satisfactory was q difficult to do as locally(singapore) everyone used a CO2 laser, so they couldnt get the word engravings to look nice and rounded. Importing from the west prices were also crazy due to shipping, ended up with a chinese manufacturer who gave satisfactory results.

Thinking about replacing the 1/4w grid stopper resistors with 1w resistors on the preamp tube grids on V1AB and V2B for both aesthetics and mechanical stability. But havent fully decided, advice whether to do so is welcome. Lead dress is a little messy, but im happy with how it turned out. It sounds great thru the made-in-uk V30(idk y ppl hate this combo i think it sounds good) with very little noise and hiss. I get some slight oscillation if I play with the master and feedback knobs at certain positions but its negligible. Shouldnt have the classic 5E3 sag but Ive never played a vintage accurate one so Ive no basis to compare to.

All in all pretty happy with how it turned out. Especially with all the retrofitting of the hardware and drilling/filing needed to be done.

Any feedback or advice would be welcome as im still pretty new. Looking towards building an Orange rocker amp or a JohnH attenuator with log vu meter soon.