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CAUTION:

Tubes may be extremely hot after the amplifier has been used.
Never touch a hot tube.

The great thing about a tube amplifier is… the tubes.
Tubes are the components that provide your amplifier with a heart and soul together with that unmatched organic, dynamic response.

But as light bulbs, the tubes need to be replaced at some time and can occasionally malfunction. How frequent you need to change tubes is depending on how often you use your amplifier and how hard you push it. Normally you need to replace the tubes every 1 – 2 years, but if you are a pro-guitarist on tour, you might want to replace them even more often to be sure your tubes are performing at an optimal level.

A shortened lifetime of a tube can also be dependent on shocks during transportation, incorrect speaker load, peaks from the power supply or other abuse.

Microphonics is a term used for high-pitched clanging noises that can occur from bad tubes. You can test for microphonics by gently tapping the tubes with a wooden pen, or similar, when amp is turned on. It’s normal to hear some noise when tapping the tubes, especially the pre-amp tube located closest to the input jacket is sensitive.

If the output power of your amplifier is getting weak and your tone is flattening, try replacing the power tubes. Power tubes can short-circuit when malfunctioning, making the main fuse blow. If your amplifier should act strange and/or then be out of business – first replace the power tubes – and, if needed, check the main fuse and replace with a fuse of the same type. The main fuse is located at the mains inlet.
The power tubes should always be replaced in matched pairs or quartets for best performance. See tube socket for match grade. Always use the same type of power tubes as the original ones. If the replacement tubes have a different match grade – the amplifier needs to be re-biased by a certified service technician or similar. Bias instructions can be sent upon request.

If the amplifier is still not working properly, there are fuses inside the amplifier that needs to be checked by a certified service technician or similar.

If you experience noise, un-normal feedback - rattling or fuzzy sounds from the output of your amplifier – it is very likely to be caused by a bad pre-amp tube. The best way to diagnose a bad pre-amp tube is to use a replacement tube of the same type, that is known to be good and substitute it in each possible tube location, one at the time, until the problem disappears.
See tube chart for positions and functions for speeding up your diagnose.

To access the tubes, place your amplifier on a stable surface, remove the screws holding the back-grill using a crosshead screwdriver and then remove the back-grill.
(For M90 Modena, pay attention to unplug the fan-connector. Remember to connect it when assembling)
See tube chart below for positions and functions for speeding up your diagnose.

M60 / M90 MODENA and BONNEVILLE 50 – Any 12AX7 (ECC83) of good quality.
PreAmp tubes need no calibration or biasing.

M60 MODENA and BONNEVILLE 50 – Any EL34 of good quality.
KT66, KT77 and 6L6 can be used if preferred, but needs different biasing.

M90 MODENA – Any KT88 of good quality.
EL34 can be used if preferred, but needs different biasing.

Always check the match grade of your Power tubes before replacing them.
If replaced with tubes with a different match grade the amplifier may need to be re-biased. The match grade should be visible at the power tube sockets.

To access the tubes in the Stinger Combo, remove the 4 screws (2 on each side) placed on the top-front sides of the Combo and gently pull out the amp chassis. Place the amp chassis on a stable surface and then remove the screws holding the top plate.

Any 12AX7 (ECC83) of good quality.
PreAmp tubes need no calibration or biasing.

Matched quartet of JJ Electronics EL84.
No biasing is needed since the output circuit is cathode biased.

Elmwood Amps, its employees and its representatives, do not accept any responsibility what so ever, including, but not limited to, responsibility for negligence, physical damage, personal injury, economic loss, costs or expenses of any kind, or any other loss or damage suffered or incurred by anyone as a direct or indirect consequence of performing any action that includes tube replacement, other technical operations and/or disassembling of any of Elmwood Amps products. All actions that includes tube replacement, other technical operations and/or disassembling of any of Elmwood Amps products are taken at own risk.