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Page 61
When you turn on the amplifier – if all the tubes light up and all is well then we need to check a couple of key voltages to
make sure all is well…
• Check pin 8 of the 6SH7 – it should be 180V-190v DC.
• Check pin 1 of the 300B – it should be in the 440V range.
•
Check that pin 4 (1K5 in parallel attached - cathode) to ground is approx 65-70v range.
•
Check that there is 5v DC across pin 4 & 1 on the 300B - these are the filament pins.
If all these 4 voltage checks are good then move onto the final testing phase next…
Mono Block Testing Kit
• Grounded RCA input Plug
• 8-Ohm Resistor Load (Parallel Resistor Pair)
• Audio Test CD
You have now completed all the wiring on the Mono block kit along with the checklist and the voltage checks. If all is good
then you can use the kit provided to do the following checks.
To check for audio signal you will want to do the following - Attach the Dummy Load 8-ohm resistor between the speaker
posts this will act as the speaker load - it is basically 2 16W resistors in parallel that will act as an 8-ohm load. Now plug a
CD player into the input of the mono block and insert the Audio test CD. The first track will play a 1Khz sin wave - you can
use your voltmeter in the AC position and measure the signal on the input RCA - you could measure on the input pin of
the 6SH7 pin 4 to GND and you should measure around 100mv depending on the output of your CD player.
Then measure the output speaker posts – put a probe on one speaker post and one on the other and you should see
approx between 0.65 and 0.7 volts AC rms.
If all is well then we have correct audio signal amplification.
The last test you will want to perform will test for hum - Turn the amplifier off - Use the Grounded RCA plug and plug it into
the input RCA input of the amplifier - connect up speakers to the kit - when you turn the amplifier on you should hear a
hum for about 20 seconds and then it will go completely quiet. If you have a quiet amplifier with all the previous DC
voltage and audio checks then you are ready to listen to music. The amplifier will smooth out over the first 3-4 days of
listening and continue to improve over time!
Congratulations on your completed Mono Block Kit !
AC Wall Voltage Checks and Adjustment
Wall voltages vary around the world - for example in North America the wall voltage is rated at 120V AC - I often read
117V.
Usually lower is fine - sometimes in 240V countries we find that higher than expected AC voltages occur - for example
247v etc…
It’s usually not a problem but if you would like to tweak the Voltages in your kit so that they fall into our levels that describe
in the manual then the best thing to do is add a larger resistor value between the output of the 5U4g/ 5Y3 - A typical value
here is 47 ohms but we can add up to 100 or 200 ohms - the higher the voltage the more load on the Power supply and
the lower the resulting DC voltages will be.
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