On 10/06/2016 7:34 PM, Phil Allison wrote:
** 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
**If you need germanium devices, Rockby have some interesting ones in
their specials list. Amazing those caps were all good. I just serviced a
3 year old M-DAC. I started marking the bad electros, until I realised
it would be easier to mark the good ones. I have to replace around 60
caps! In a DAC!
--
Trevor Wilson
www.rageaudio.com.au
---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus