Refurbishing a Nikko TRM600, 2026
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This page is written using English language only.
This Nikko is a very nice looking example of the "Silver era" of the seventies vintage amps.
I bought as a defective piece, one channel was supposed failed, apart from dirty switches found, this actually was the case.
My comments, as usual, assumes the reader aquired the technical info already from the internet.
Nikko TRM-600 overview.
This Nikko is a typical "no frills budget amplifier" from the seventies, though having more than enough power for a normal living room. It's only "extra frill" is the Microphone input.
Opening up the Nikko, a simple layour reveals itself at the top, and at its bottom a cheap way of attaching wires, directly to the circuit cards, is something catching attention.
There are many small stain/rust places on the chassis, I could address this by cleaning.
The nikko trm600 power supply.
The power supply incorporates a TO-3 rather oversized rectifier feeding two 6800 Microfard capacitors, already generous for this size of amplifier. I replaced them using two less old premium quality Philips ones of 10000 Microfared 63 Volts ones.
There is an axial capacitor mounted on the bottom of the amplifier feeding the preamp power regulator to be found on the pre-amplifier card. Of course, also this one was updated, the left picture resembles the old situation.
The yellow wires from the transformer did power the small power lamp, they are not used anymore as I used a LED solution for this.
The nikko trm600 main amplifier.
The first picture, on the left bottom next to the Q651 transistor, the actual reason this amp lost a channel reveales itself.
The little trimmer potentiomet lost its rotary slider.
On the left picture below, one can see the temperature pickup transistors for bias purpose, I retained them as well as the power transistors.
The other picture shows part of the HFE measurements.
Part of the 2SC484 are considered somewhat low on HFE, as part of the 2SC627, so all small transistors were replaced. KSA1220/KSC2690 for the drivers. They are high HFE so they are capable of providing enough drive for the rather low HFE 2SD188 output transistors.
The big power transistors were retained.
The Nikko TRM600 preamplifier card.
This card contains the turntape amp, tone amp and voltage regulator.
The nikko trm600 "mixer" microphone pre-amp.
This little card was much too sensitive, so amplification was lowered, changing the 47 Ohms resistor in the feedback path to 430 Ohms, the red arrow points to it.
The nikko trm600 mode selector switches.
The switches were rather intermitting and influencing each other, they needed a good clean, so they were taken apart, cleaned, and reassembled.
The nikko trm600 loudspeaker protector.
I decided to add a delayed relay and dc protection on this Nikko, based on the Tandberg TR2075MK1 protector card.
I used a high-end quality relay (higher-end than average audiophiles-high-end quality ;-) .
On the protector circuit card, I also mounted a potentiometer and resistors to feed a LED, replacing the power indicator lamp.
As the relay itself went rather hot to the touch when getting some 25 Volts (it is rated up to 28 Volts!) and it engages at 15 Volts already, I lowered its voltage to little over 20 by upping the 5W series resistor to 220 Ohms.
Various pictures
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