andreus A-22 Manuel d'utilisation - Page 11

Parcourez en ligne ou téléchargez le pdf Manuel d'utilisation pour {nom_de_la_catégorie} andreus A-22. andreus A-22 13 pages. Head and combo

TUBE REPLACEMENT

Precautions: Always unplug the amplifier and allow the tubes to cool

completely before touching them.

After years of experience with various available tubes, we have chosen specific tubes

for this amp. This decision has been made for tone and reliability reasons.

You can safely replace any of the three preamp tubes any time without concern about

biasing. ECC803S, ECC83S and 7025 are variations of 12AX7 and are

interchangeable. In the V1 position (far right, looking from the back), a 12AX7 or its

variations will give the maximum amount of gain. The JJ ECC82 (12AU7) also sounds

very nice in the V1 position if less gain is desired. Larger plate tubes such as the

ECC803S or 12AX7LPS work especially well in the V2 and V3 positions. Different

brands will give slightly different tones which may be preferable to some players.

However, some brands have reliability problems and may have more noise,

microphonics or hum.

For output tube replacement, we strongly suggest using JJ brand EL84 tubes. Sovtek

brand EL84s are also reliable and long lasting but may not sound as full and smooth

when new compared to the JJs. This amp applies very high voltages to the output

tubes and lesser quality tubes may not be reliable in this model. Also, it is absolutely

necessary to adjust the bias when replacing the output tubes. Please check our web

site periodically for updates on recommended tube brands since tube production is

constantly changing and new brands are becoming available.

When to replace tubes: 12AX7 preamp tubes will generally last for many thousands

of hours but occasionally problems can development before they "wear out". If you

hear cracking, popping, ringing, or other strange noises, try replacing your preamp

tubes; one at a time. This may resolve the problem. Also, if you hear a scratchy

sound when turning the VOLUME control, try replacing V2.

Output tubes usually have a somewhat shorter life – They will often start to sound bad

long before they fail. If you notice that your amp is gradually loosing volume,

headroom or "punch", or if you notice that low notes are sounding a little "flabby", or

you notice that you are hearing unpleasing harmonics or overtones, it might be time

for a new matched set of high quality output tubes. This could happen after a few

months or it might take several years, depending on how much and how hard the amp

is played. Don't forget about biasing the output tubes. These symptoms can also be

caused by a worn out speaker so be sure to try the amp on another cabinet to be

sure.