6J1 Valve Preamp, Vacuum Tube Preamp Valve Preamp Amplifier Board Audio Amp Assortment Kit

Just built this little guy last night. It seems to have decent output. I’m currently running it on a larger transformer as I had no small ones. I’m reading 30.1 volts on each of the boost circuit rails coming to 60.2 volts total. The sound seems decent from it. Easy to put together if you have experience in soldering circuit boards. It was worth what I paid for at $14. We’ll see how long it survives. All the circuits are cheap if any blow including the tubes which I’m considering upgrading to 5654W tubes.

This kit is good if you have some circuit board experience under your belt. No instructions, but a few other kits taught me you go small to large in order of soldering, Diodes, Resistors, Small caps, tube carraige, In/Out, DC in, then finally your big caps. As far as sound quality, it works best at 50%. It starts to break up when dimed. Which is what you want for guitar amplification, so I'm going to do that with mine.

Trying to avoid using terms like "warm," this little circuit produces all the transparency and clarity one would expect from a tube amp. After all, most of the tube amp magic happens in the preamp stage. Every element within the mix is more audible, without being overly dominant or blaring. Yes it's counterintuitive for inherently noisy tubes to sound more clear than transistors. But CD quality digital audio must be dithered. The intentional injection of noise. Clearing up any confusion surrounding capacitor polarity: inside the silkscreened circles marking where the electrolytic caps are placed, the negative lead should ALWAYS go in the hole marked with the series of stripes. No doubt those of you ohming out the solder pads will say, "Hold on! Half the pads without the stripes are connected to ground." That's because this board uses both positive and negative voltage. The caps receiving negative voltage will see the ground as positive voltage. Positive compared to the negative voltage on the negative lead. So connecting the positive lead to ground is in fact proper. If anybody is unclear, a polarized electrolytic capacitor connected backward will in fact explode. As at least one reviewer has reported. If anyone is having trouble finding a 12VAC power adapter, a DC adapter can be fairly easily converted to AC. Provided it has a transformer. Most modern power adapters are no longer built around transformers. They simply rectify the voltage to DC, and regulate it down to the desired output voltage. The trick in conversion is to disconnect and bypass the rectifier circuitry. Connecting the output cable directly to the transformer output.

Just a bag of components. Nothing else. Not one shred of information on the assembly aspect. No schematics, no website, nothing but a bag of frustration and disappointment if you buy it for learning purposes.

Putting the kit together was fun. It was a pretty easy build. The PCB was clearly labeled and easy to follow. Installing all the components was straightforward with basic soldering skills needed. However, I'm not sure how to properly use this preamp. I've tried using it as a headphone amp, a preamp for my turntable, and as a preamp for a small guitar amp and in all scenarios, the sound is barely audible even when maxing the gain knob. On top of that, the sound is lacking low-end and warmth. It's very unsatisfactory as a preamp...If anyone has any ideas on the input/output impedance needed to get this preamp to preamp, let me know...

This unit requires an A/C power source of 12 volts ac as the amplifier also requires a different A/C source of 18vac which I would have to invert with a voltage divider just to bench test it.

Actually a clone of Musical Fidelity X10D-Tube Buffer Pre-Amplifier. Great tone from cheap record player that sounded so flat. It acts like a great buffer. Was confused that I had an extra part (diode) and it was on the list of sent components. I contacted the seller and got a Chinese manual with schematic and found I didn't need it. Also saw they don't use negative feedback loop or cathode bypass capacitors so I will be modding mine after I get all the data I need from "stock" I'll swap all the cheap caps and do some mods. Most likely will use this for my record player but will add a switch and jack for a tube gain guitar pedal.

I bought this because I needed a preamp for an old Heathkit amplifier. It works pretty well, good gain, little added noise. Please note the following: first, there is no documentation that came with the kit. If you are used to building kits and know how to read resistor values, etc, that should not be a problem. If this is your first kit, you will not have a step-by-step assembly instructions or schematic. Next, this calls for 12VAC for power. This voltage is rectified and filtered for two separate purposes: it provides the power (12.6VDC) for the tube filaments, and it's used to generate the Plus voltage for the Anode and negative voltage for the cathode. The acceptable voltage range for the anode and cathode is quite large, but that's not true for the filaments. Tube life shortens significantly if the filament voltage is too high. there is no separate regulation for the filament voltage, and when i used a 12VAC transformer to power the board, the filament voltage was almost 18V. I am now using a variac to insure that the filament voltage isn't too high.

I thought as the ad says it comes with a pair of 6J1 tubes, it did not but 6j4 instead. And also, returns to this Vendor are paid by the customer- not a pre paid postage. Make sure its worth it, if you changed your mind, you ll be lining up at the post office and will be paying for the shipping. Just saying.