When I I blew my pair of 4.7 Ohm resistor-fuses, it was mainly my fault. I had the volume turned up at an AKG K-1000 level (way, way up). This is too much initial power for the RKV! You should wait for the red light inside the RKV to go out before turning up the volume.
To avoid problems, you should follow the following steps.
Turning on the RKV...
1. Turn the RKV's volume all the way down.
2. Turn on the RKV.
3. Wait for the red light to go out after one minute.
4. Plug in your headphones.
5. Turn up the volume.
On the transformer...
The RKV's transformer should be screwed to the bottom plate. Most amp manufacturers do this to avoid damage during the amp's shipping phase. I believe Mr Becker should do the same to avoid warranty problems. This security feature makes a lot of sense to me!
EDIT: Jan Meier says that this design flaw has been corrected in recent amps. I hope this correction includes a bolt, securing the transformer to the bottom plate.
On Mr Becker...
In my experience, Mr Becker has been very helpful and very nice. With Mr Becker's e-mails and photos, I was able to repair my RKV rapidly. Sure, to do these repairs, you need a little bit of DIY electronics experience. If you don't have any experience, any repair shop can use Mr Becker's text and photos to repair your RKV in the USA. You don't have to send it to Germany for repairs. Actually, most repairs entail changing resistors. That's not hard at all!
My RKV...
With the AKG K1000 headphones, I simply love the sound I get. It is 1st class--the best! The RKV's bass is tight due to its very high damping (3400). Midrange? It is gorgeous, esp with female voices. Now, unlike some posters, my RKV is not clipped in the high frequencies. I get everything up there! Most likely, this is due to the 4 NOS Telefunken PCL805 tubes I have in the RKV. These are very high quality NOS German tubes!
Edit
I've got to add something. Peter Millett, the designer of the Wheatfield Amps, says that a tube amp must have a very low output impedance in order to drive the AKG K-1000s. If the output impedance is too high, the K-1000s lack bass and sound thin. Hmm...not good! Usually, tube amps have an output impedance of 30 to 40 Ohms. Now, the RKV is in another league: It's output impedance is below 3! What does this mean? It means that RKV produces excellent bass! You don't need a sub-woofer besides you. Ha!
Oh, the sub-woofer solution gives me the giggles. Got to go! With my happy-go-lucky attitude, I have a tendency to crack up with laughter. Bye!