Koch Twintone II - The Guitar Tube Amplifier that no one's heard of..

 

"I've never heard of it..."
Standard response when someone sees this Amp for the first time.

Hand make Dutch engineering.
Three quality assurance signatures.
See for yourself:

The chassis as it came out of the Cabinet.

Those HT Caps still look good.

Not bad for an 18 year old Amp.
Couldn't find any significant component drift.

Populated with TAD Tubes except for the two JJ EL34's

Transformers are 18 years old.

Pretty sturdy.

Feeling a bit more confident seeing the chassis.

The cabinet is not appealing I'd say.

Here's an ad. for one:

Koch TwinTone 50

Features All-tube circuits, matched Ruby EL34 power tubes, built-in power soak, Accutronics reverb tank, 11-ply birch plywood cabinet, two-button footswitch, independent clean and overdrive channels, independently voiced inputs for single-coil and humbucker pickups, rhythm/solo boost circuit.

Price $2,150

Bias 'out-of-the-box'

Changed generic Chinese Phase Inverter Tube for a 12AX7EH
Changed BIAS to 35mV

Vox AD30VT guitar amp motorboat? You are not alone!

 

It can be fixed, apparently.

Read the comments section. But not for long I'm afraid to say.

My suggestion, sorry my question actually: what made you buy one of these?

Vox AC30 TB Before restoration photos

 

Vox AC30 TB After restoration photos

 

Brian May's Nine Vox AC30 Amplifiers On Stage

Vox AC30 (circa 1963)

My favorite Tube guitar Amp.

I enjoy restoring them more than any other Amps that I work on. Probably on account of the relationship the musicians develop with these gems over the years.

Testing out an Ibanez TSA-30 after repair

An Ibanez Tube Screamer guitar amplifier, on account of its unreliability and propensity to hum, came into the workshop for investigation and repair.

It became apparent that the engineers decided to compromise on the way the amplifier provides power to the valve pre-amplifier stages and the solid-state signal processor.

Proposed changes to the circuitry were modeled, prototyped and implemented.

After the amplifier passed all the lab tests, it was time to get real.

I invited Greg Gunther, an astute musician and teacher, to answer the client's question, "Is the amplifier bullet proof?"

The recording was not rehearsed and done in a single take with the amplifier set to run between 70% to 90% of its rated output power of 30W.

No equalization, filters or soft clipping were used, in the post processing.