** Hi,

does anyone still use germanium transistor amps - anywhere ?

Had a late 60s "Nikko TRM40" stereo amp on the bench this week, in sad looking condition. I reckoned it been in storage for a couple of decades and was surely uneconomic to repair. There was plenty of dust inside and ALL the transistors were germanium types plus the power stages used driver transformers for the TO3 outputs, see pics of similar amp:

Front panel:

http://img.usaudiomart.com/uploads/l..._amplifier.jpg

Insides:

http://www.zmdz.com/bbs/incomefiles/...8521149767.JPG


Initially, almost nothing worked since corrosion was causing bad or no contact in all the pots, rotary and slide switches plus both loudspeaker circuit breakers. However, after some TLC and a little WD40 in the right spots, those problems disappeared and I had a working amp. Amazingly, all electros tested good on my ESR meter.

The next step was to test power output & THD at 1kHz which resulted in 10 Watts into 8ohms at about 1% for each channel. At the 1 Watt level, THD dropped to 0.35%, mainly third harmonic which agrees with the maker's specs.

However, THD increased at higher frequencies soon reaching double digits. Visible slew rate limiting on a scope began at *3kHz* becoming severe above that frequency - square wave testing showed it was a mere 0.3V/uS in the negative direction !! TIM & SID must have been well pleased.

The damping factor tested around 9 or 10 and the amp was fairly noisy on all inputs. The Nikko was affordably priced in 1968 and competed with budget valve amps with similar power ratings.

A least you never had to feed it any new valves.



..... Phil