Hi Adriano. You posted this same comment of two unrelated videos, emailed me and also posted it on my forum. The answer is the same, these caps cost $14, hardly "very expensive" and if there was a cheaper solution that sounded as good, I would have used it. Feel free to toss whatever cheapo caps you want into it and ruin the sound signature being cheap. And in the future please don't SPAM ever available place you can find when you don't get a reply in 25 milliseconds.

You could try using a different rectifier tube like a 5U4 to see if the voltages come down? The 6.8V is a little high but shouldn't kill tubes.

Sorry, I haven't seen any of their kits yet in person to comment.

Once a rectifier tube arcs its junk and it will continue to Arc and blow fuses. First make sure there isn't a short circuit in the wiring, that would do this But most likely was a weak rectifier tube and the solution is to hunt down a new old stock 5ar4. The modern ones are junk from my experience and about 50% of them don't meet specs. If you are intent on using a new production, the only ones I've had any luck with are the TAD and sovtech.

Not so much "shooting in the dark" but doing some trial and error testing using our "best guess". Shooting in the dark implies just throwing stuff at an amp with no idea why or what is should be doing. Yes there is synergy between a circuit, the tubes used an a specific output transformer, this is why built circuits many times don't perform the same way they do in a computer simulation.

As long as you aren't laying wired directly against stuff, (which is a bad idea for other reasons) the insulation rating isn't a big concern.

I honestly think the A50 modified is a MUCH better amp than the Willsenton R300

If you don't have a volume pot, just use something like a 250K for the grid leak would be my recommendation. Leave the 1K resistor alone.

It's not really needed. But one other option would be to put a switchable 100VDC meter directly across the cathode resistor and you would have a way to monitor the output tube current that way.

Unfortunately not. This meter was designed to work across the cathode resistor of a cathode biased tube amp.

I would 100% NOT split the board and put it in another box. EVERYONE that I have seen do this fought hum problems. 100% of the people having hum problems get "creative" on their build or follow some mod website. It's not the EI core transformer causing hum, I've sold dozens of these built with an EI core transformer, single board, used a choke instead of a resistor for the first filter and use parts and tubes as marked on the board. As soon as you starts changing tubes and parts values, it screws up the RIAA curve, then you have to start changing other parts trying to fix the problem you created. A 12AT7 isn't as linear and isn't a drop in replacement for a 12AX7. I also don't buy them with those super cheapo china caps (I use legit sourced caps), use high quality mica caps for the RIAA section and I hand select resistors to get within 1% of the marked value. Most of the resistors they populate the center part of the board with are the wrong values/out of spec. These also were designed to have a lot of gain, I don't understand why people think that's a problem.... Just turn the volume down on your amp. The extra gain is not going to "create hum". Every one I have listened to where changes were made to reduce the gain didn't sound right to me. The last thing is I see so many of these built with no ventilation. It will work for a while but will end up cooking the caps. There is a reason for this: "tube heaters" make heat, heat kills caps.

I have no hum using EI core. It's all about the grounding (single ground point). Most of the problems I see people have with these are from doing a bunch of mods or overthinking things.

You'd need to just measure the voltage to see if it's OK to use that cap.

When I first started playing with this on a KT88 amp, I used a center off DPDT switch and would "hot switch" two values of feedback + zero feedback to listen to the changes A/B. That amp also had a triode/UL switch. I learned I don't really care for the sound of a triode trapped pentode in a SE amp. Yeah you will hear a "pop" but didn't seem to hurt anything. For this amp, try a 5751 tube in place of the 12AX7, the gold pin JJ sounds really nice! I tried between 300K and 470K and ended up with 360K as the sweet spot for me.

This is AMAZING work!!!

They are actually like 2 watts, even after the mods. And sorry I don't mod amps for people, but I am doing a total gut and rewire series on these little amps right now that should get them closer to 5W.

It's to balance the phases. Earlier designs were either slightly unbalanced or had a "balance pot" to adjust it. It corrects phase alignment distortion in the output transformer.

Thanks! :)

Add $230 shipping..

Nice build!