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Currawong Valve Amplifier Is Motor-Boating
I recently completed a Currawong
Valve Amplifier (SILICON CHIP, October to December 2014). All appears
to be well apart from the level of
“motor-boating” noise which is easily audible.
I have attached a scope screen
shot which shows the output of the
left and right amplifier channels. As
can be seen, there are positive and
negative spikes superimposed on
2mV or so of 50Hz.
The stated signal-to-noise ratio is
-70dB and what I’m seeing doesn’t
seem to be within that limit. The
ripple on the HT appears to be as
expected. Any suggestions please?
(D. H., via email).
• We have not had any other reports
of motor-boating; yours is the first.
We would be inclined to suspect defective capacitors or associated poor
soldering. Check the power supply,
the feedback network and the 100µF
bypass capacitors for the 6L6 valves.
Also, check that you have the correct
47kΩ and 6.8kΩ decoupling resistors
installed in the HT rails.
Advertising Index
Altronics.........................loose insert
Australian Asset Disposal............ 40
Electric Factory (ELFA).................. 3
Emona Instruments........................ 8
Hare & Forbes.......................... OBC
High Profile Communications....... 95
Icom Australia.............................. 29
Jaycar .............................. IFC,45-52
KCS Trade Pty Ltd...................... IBC
Keith Rippon ................................ 95
LD Electronics.............................. 95
Ask SILICON CHIP
. . . continued from page 95
wonder why a practical solar panel
array would have such a wide range.
Such a regulator would require a stepup and step-down circuit, one to step
up from 5V to 12V or 24V and the other
for reducing voltages above 12V or 24V.
A major factor is how much current
needs to be supplied from the regulator.
Problem with ultrasonic
anti-fouling unit
I have purchased a kit for the Ultrasonic Anti-Fouling unit (SILICON CHIP,
September & November 2010) and
completed the assembly. When I connected the unit I got a brief red light
and the fuse blew. I have run the test
as stipulated in your article that came
with the kit and have set a 5V output
on the potentiometer but still nothing.
I am attaching the pictures I have
from the top. Kindly note that the
blue wire coming from the battery is
positive and the brown the negative.
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Also the transformer arrived with
a minor damage. The top left black
plate was broken but we sealed it. (J.
J., via email).
• From your pictures, the construction looks good on the top side.
However, the transformer clip behind
Mosfet Q1 is not actually holding the
ferrite core in place and that might
be the problem. The core seems to
be fractured also on the side near the
SC
2200µF capacitor.
Master Instruments...................... 95
Ocean Controls............................ 10
Sesame Electronics..................... 95
Silicon Chip Binders..................... 89
Silicon Chip Online Shop........ 84-85
Silicon Chip Subscriptions........... 11
Silvertone Electronics.................... 5
Threadboard................................... 9
Tronixlabs..................................... 95
Next Issue
The November 2015 issue of SILICON CHIP is due on sale in newsagents by Thursday 29th October.
Expect postal delivery of subscription copies in Australia between
October 28th and November 10th.
WARNING!
SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such
projects should be considered dangerous or even lethal if not used safely.
Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or
high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you
are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone
be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine.
Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability
for projects which are used in such a way as to infringe relevant government regulations and by-laws.
Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the
Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable.
96 Silicon Chip
siliconchip.com.au
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