The Velleman K4040 is not hard to build although you will need some experiance and patience. I expect that you can build it nicely in two days, so perfect for a rainy weekend.
The parts that are delivered with the kit are from good quality but can also be improved. If you feel like replacing signal capacitors or resistors i would advice to look into that before you start building it.
The tubes delivered are from Sovtek (EL34, 12AX7 and 12AU7).
In the first place i advice to leave the tubes as they are untill you build and have tested the amplifier.
The power and output transformers are massive and from good quality. You manage the bias easily from the front panel and LED bar meter. When you have the older K4000 you will need to use normal meter and test points personally i prefer this method.
The instruction manual is complete and clear. When all components are in place (except the tubes) You need to do some measuring to be sure all is fine.
If you have a pair of test speakers available i would advice to use these the first time you connect the amplifier. When all is fine be sure to leave the Amplifier running for some hours. The tubes need some burn-in time and verify the bias several times. Especially in the first hours you will see that it will need adjustment.
I’m sure you will be amazed by the sound you will hear…tubes are magic not?
But…it can sound better if you simply replace the tubes. You can use any ECC81/12AT7 and ECC82/12AU7 available. Personally I would advice Telefunken. For the EL34 it will be expensive and difficult to find NOS. Since you would need a matched octet if you want to do it well.
So for that i would advise the re-issued Mullard EL34 or the new Electro Harmonix 6CA7. But remind that once you replace the end tubes you always need to verify the bias. Something you should do at least once a year anyway.
Enjoy the sound!
For High-End Audio Tubes visit us at: High Fidelity Tubes
