TT JC18

TT JC18

It’s been a couple of years now, but the memories are still pretty present: the first contact with a real JCM 800. What a sound! One chord and you immediately felt like a real rock star.

Significantly smaller in size and with less output power is the JC18, equipped with the same preamp as the 2203, but with a pair of EL84 instead of EL34 in the power amp section. But this is not a disadvantage, quite the contrary. The JC18 offers the same feel as its inspiring example, but can develop the classic sound easier because of the lower wattage output stage, without the immediate risk of a hearing loss. Its 18 watts (measured 22 watts on the hi-input) make it also very universal. Whether at a club gig or at moderate volume at home in the living room, everything is easily possible.

Sound

Classic rock sound as known from the JCM800. Punchy and transparent, but no ultra hi-gain. It’s only Rock’n’Roll!

Files

Schematic as PDF (2 Pages, DIN A4)

Layout as PDF (1 Page, DIN A3)

The kit is available together with other accessories at the TT-Shop

Modification

To reduce interference from the tube heater, it is recommended to operate the V1 tube heater with DC voltage. This modification can be done in an easy and save way with the DC-Heater Kit which is available in the online-shop.
DC-Heater Kit

The following layout shows how to implement the kit in the amp:
Layout as PDF (1 Page, DIN A3)

Bias-Settings

Biasing is done with the trimmer Tr50, the current flowing through BOTH power tubes is measured across resistor R27. Voltage measurement in DC! The trimmer should be adjusted until the voltage measured across R27 is approximately 60 mV (which equals 60 mA for a 1 ohm resistor).

Warning!

Care is necessary during construction! Even though this is a lower wattage amp, the voltages inside are potentially fatal. This amp is NOT a beginner's project!

A successful build requires that you can read (and understand!) a schematic diagram, you know how to use various measuring devices, as well as you have some experience working with voltages over 60V.