Bewitch KT88 Valve Amplifier

The Bewitch KT88 valve amp is a real piece of heavy weight kit. Mine came supplied with Electro-harmonic KT88 tubes & Chinese pre-valves & rectifier valves, all of which are in fact quite good.

The amp is designed to run on 220 volts, so don't just plug into the "UK" mains, yes I know we are suppose to be on 230v now, but if you check the voltage at the socket you'll find it's about 240 plus! In my area it swings from 243-251 volts.

What you must take into account is the HT (High Tension) side of the amp, even at 240v that's a 20 volt overload to start with, but that results in about a 40 volt overload on the HT rail, no amp's going to take that for too long.

I run mine with a variable transformer (Variac), that way I can run it

at a dead 220 volts, you will need to do the same.

The amp came via e-bay from Hong Kong & was very well packed, it took about 7 weeks to arrive & was all ok.

The first thing I noticed was a hum on both channels, it was not loud, but very noticeable.

The hum increased with the volume control & was on all inputs with or without anything connected, so an input problem.

The fault is minor & is an easy fix if you have basic electrical knowledge & can use a soldering iron.

The trouble is the wires to the volume control, they are not shielded, just bare wire going to three pins on the circuit board about 25mm away. The trouble is these pins are about 20mm away from the first Rectifier valve, running at about 400 volts.

NEEDLESS TO SAY DO THE FOLLOWING WORK WITH THE AMP UNPLUGED!

The answer is to remove these wires & solder good quality screen cable to the volume pot, but don't solder the other end to the pins on the board, follow the tracks from the pins back to the inner pre-valves & solder the volume control wires directly onto the solder joins at the end of the tracks, by the pre valves.

Then CUT the tracks at the pre valve end so the interference from the rectifier valves can not feed back into the pre tubes.

Result No hum.....all nice & quiet.

Sound quality : She sounds ok, being KT88 based it have a very clear & sharp top end with a solid mid range, however bass is a little on the light side, it your use to a EL34 based amp this may come as a bit of a shock. I did change the pre tubes 6SN7's for Electro-harmonic's & the 6SL7GT for Tung-Sol tubes, which has cleaned up the mid range & improved timing.

This of course is with the amp set in "Ultra Linear" mode, but

with the amp switched to "Triode" mode it's a different beast, the bass is better plus the overall sound image is more coloured/deeper.

To sum up it's a good amp, yes I'm pleased I bought one & would buy another, but I guess I would have to say that in Ultra linear mode it seems like it's trying to sound like a transistor amp, but in Triode

mode it sound like a real Valve amp, meaty with feedback, but still lacks the bass of a decent EL34 based amp.

She puts out 60 watts in ultra linear mode & 30 watts in triode mode, power consumption on mine is 206 watts

The amp is well built & reasonable well designed, but for the volume control location! most components seem to be of good quality, the output transformers sure have a lot of iron in them which no doubt goes a long way to giving the amp it's quality sound. At about £500 it's a result!