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Pentode & Tetrode Amplifiers

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FAQ

FREQUENTLY ASKED QUESTIONS

Q. Is it ok to switch the amplifier on without speakers connected?
A. No. The speaker load is reflected to the output valve through the output transformer. There is a risk of damage to both the transformer and valve if left turned on for a period of time.

Q. How long will my valves last?
A. The output valves should last from 5000 to 10000 hrs with normal use. The rectifier valve should last 5000 to 8000 and the driver valves over 10000 hrs.

Q. When should I replace my valves?
A. The silver barium on the inside of the glass will almost have disappeared. When this is gone (or translucent) the valves performance will drop very quickly and should be replaced.

Q. Is it OK to use second hand used valves?
A. Yes, there could be a loss of performance, but it wont damage the amplifier in any way. (good old stock valves can increase sonic performance and listening pleasure)

Q. Where can I purchase replacement valves?
A. I do sell replacement valves to my amplifier customers, and they are also available from several Australian based ebay sellers at very competitive prices.

Q. Do the valves need to be matched?
A. Only in my push-pull amplifiers and just the output valves. They should be a matched pair for each channel, or better still all four matched.

Q. What happens if the valves are not matched?
A. There will be a slight increase in hum. If the valves are very mis-matched it may become distracting. It will not damaged the amplifier in any way. (please note, this only effects push-pull amplifiers)

Q. There seems to be a popping noise when ever the amplifier is tapped or I walk close to it.
A. This is most likely dust on the valve pins/sockets. Turn the amplifier off at the wall, remove the plug. When cool, remove each valve one at a time and replace it in the socket. This should cure most mystery cracks and pops. This can happen a bit with the old stock valves due to the oxidization on the pins. Remember, some old valves were made 60 years ago.

Q. My amplifier hums, and it seems louder in the left speaker.
A. All my valve amplifiers hum to some extent as they do not use music destroying negative feedback as nearly all others do. The push-pull amplifiers are very quite whilst the Single ended type can be heard from the sitting position if you have very sensitive speakers 100db+ for 1 watt. Generally speaking you shouldn’t be able to hear hum from more then 2 meters away. The 300B amplifiers may be slightly louder. The left side is always a bit louder due to the stray magnetic flux from the power transformer interacting with the left hand output transformer.

Q. The transformers are very hot. Is this normal?
A. Yes. Because all my amplifiers run in class A mode they are drawing full power even at idle. The larger push-pull amplifiers power transformer can get almost too hot to touch. This is quite normal, all my transformers are tested to 140 degrees Celsius.

Q. Do old stock valves really sound better?
A. Yes, especially the smaller driver valves. Most of the new stock valves do perform very well, but the old stock valves have a certain magic about them. And its fun to collect and try different brands. I have found the Sylvania 6SL7 and 6SN7 to be the most reliable and sweetest sounding. It isn’t critical for the driver valves to be matched or even both sections of each valve to be matched.

Q. How long does it take to “run in” my new amplifier?
A. Most customers have commented that their amplifier sounds better and better with time, so I guess around 200hrs would be a fair amount time.

Q. When I turn my amplifier on, how long does I take to sound its best?
A. As a rule I always turn my amplifier on last and off first. This saves any switching noise being transmitted to your speakers.
I usually start the music within 30 seconds of my amplifier being switched on and it takes around 20 minutes to settle for critical listening.

Q. Can I leave my amplifier turned on 24/7?
A. Definitely not. 2 reasons. Firstly there could be a risk of fire due to the excessive heat generated by the valves and secondly it wastes electricity which causes more greenhouse emissions.

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