changing tubes in all tube amp?

[Mr. BassmanPT]

first of all, this is somewhat related to guitar amps but maybe the same principle applies to bass amplifiers?

i went to a friend house and he had 2 amps, both all tubes.. a jcm800 and a mesa stiletto.

when he played with the distortion channel, there was a noticeable hum, with annoying levels.. when he played with the clean channel, there was no hum.. this happened in both amplifiers!

do the valves need to be changed? is it normal to have hum with tube amps?

i also would like to know what can cause tubes to be changed! and how often these tubes need changing.

regards

[coreyfyfe]

Try an instrument with better shielding or a different instrument cable first. Minor hum which may not be loud when you first plug in will definitely be noticeable when you crank up the gain (ie use the distortion channel).

As far as when tubes need to be changes and how to do it, there is a ton of information available to those who search. Google is your friend. For most of the basics, this is a great resource: http://www.geofex.com/tubeampfaq/tafaqndx.htm

[RickenBoogie]

To anyone unfamiliar with the inner workings of an amplifier, having a trained, professional amp tech do the work is smart thinking. There's alot more to it than just "changing the light bulbs".

[NecroticImbecil]

Originally Posted by cmaranhao

first of all, this is somewhat related to guitar amps but maybe the same principle applies to bass amplifiers?

i went to a friend house and he had 2 amps, both all tubes.. a jcm800 and a mesa stiletto.

when he played with the distortion channel, there was a noticeable hum, with annoying levels.. when he played with the clean channel, there was no hum.. this happened in both amplifiers!

do the valves need to be changed? is it normal to have hum with tube amps?

i also would like to know what can cause tubes to be changed! and how often these tubes need changing.

regards

Hum levels depend on a lot more than just tubes: EQ, gain, and volume settings, cords, effects pedals and the settings thereof, and instruments used, as well as volume and tone settings on the instrument. Pickups in the instrument, proximity of guitar to amp, and a half a million other things also make a difference.

A technician familiar with tube amps should have the equipment and experience to determine when tubes need changing. Experienced tube amp owners sometimes can tell by listening that something is "not right" with an amp they are familiar with. There is no law that says YOU MUST CHANGE TUBES EVERY X MONTHS/YEARS. Not too long ago I retubed an amp that had the original tubes from 1974 in it. It still sounded fine; I only retubed it so I could sell the originals, which were worth more than I paid for the amp. Is hum normal for tube amps? Some tube amps hum. Some solid state amps hum.

[countrybass007]

I change my power tubes, I just order a matched, properly biased set direct from Mesa Boogie. Anything beyond that RickenBoogie's advice is correct, let a tech do it.