In the landscape of tube high fidelity, the names Klimo Merlin and Klimo Merlino are often confused, due to an extremely similar naming that leads many enthusiasts to mistakenly believe they are the same device or a direct evolution of one another. In reality, these are two distinct preamplifiers, designed in different periods and with different design philosophies, sharing only the brand and a certain general approach.

For this very reason, I decided to bring both workshop experiences together into a single article. In the past I had the opportunity to repair a Klimo Merlin, while more recently a Klimo Merlino was brought to me for inspection after being purchased on the second-hand market. Unifying the two cases makes it possible to clarify once and for all the differences between these devices and to avoid misunderstandings, which are very common online as well.

The Klimo Merlin represents the more historical and ambitious project. Produced in Germany with exceptional artisanal care, it was conceived to deliver extremely high technical performance. The declared bandwidth, ranging from 3 Hz to 450 kHz, a maximum output of 25 V, and a total harmonic distortion below 0.07% place it firmly among the reference tube preamplifiers of its era. The Merlin embodies a very precise design philosophy: letting the tubes speak with their own voice, placing them in a circuit that respects timing, dynamics, and naturalness, without unnecessary forcing.

This Klimo Merlin was delivered to me in completely original condition, but affected by a noticeable hum and several signs of aging. In addition to some capacitors that were already out of specification, the main issue was the layer of dirt and old soldering flux that had never been removed, which over time had begun to attack and corrode the PCB traces.

I carried out a thorough cleaning, brushing and washing the circuit with specific non-oily products suitable for removing residues without leaving conductive traces. The PCB proved to be extremely delicate. Years of acidic flux and oxidized solder joints had likely made it fragile and, despite the use of a desoldering station, removing the components without risking lifted traces or detached vias was a rather demanding operation.

In the image below you can see the replacement of the four capacitors located in front of the two transistors. The original ones, in plastic cases, were well out of tolerance. On the right, the electrolytic capacitor of the filament circuit is also visible, replaced because it had a broken lead.

All the other capacitors, in particular the orange ERO and the yellow Frako units, were tested individually with an RLC bridge. Not only were they perfectly within tolerance, they showed capacitance values even higher than nominal and an ESR surprisingly lower than that of many modern audio-grade capacitors. When components this old show excellent instrumental performance, it is correct to keep them in place. I emphasize this point because too many indiscriminate maintenance interventions end up unnecessarily altering the original sonic character of the device.

The unit, after the interventions, returned to correct operation. Below are the instrumental measurements.

Bandwidth

RIAA section bandwidth

THD

Second part: Klimo Merlino.

This unit was brought to me simply for a general check, as it had been purchased used online. The device was in overall healthy and well-kept condition.

In the past, a capacitor upgrade had already been carried out, replacing the originals with Mundorf components. The work had been done correctly, with tidy wiring and clean solder joints, without improvised or invasive modifications.

During the checks, only one anomaly emerged: one of the two Electro Harmonix ECC88 tubes had a completely exhausted section. I therefore replaced only that tube with another ECC88 EH, keeping the other one of the pair, which tested perfectly efficient, practically as new.

I carefully verified that there were no circuit anomalies that could explain the selective exhaustion of a single triode, but all voltages and operating conditions were within normal limits. Once the faulty tube was replaced, the unit was closed and returned to the owner.

I did not consider it necessary to acquire instrumental measurements in this case. The frequency response is flat well beyond 100 kHz and there were no anomalous behaviors or particularly interesting elements to document. The inspection was therefore concluded without further intervention.