Possible issue with my Ashdown ABM 500-II

ishouldbeking · #1 09-01-2010, 08:50 PM

So I haven't ruled out the possibility of another issue here, such as cable, input jack or the power at my rehearsal space... but it has happened a couple times, so I thought I'd ask all y'all. A few times now when I first fire up my rig, I'll start playing and find there's hardly any output. And then the volume will start to fluctuate, getting closer to normal levels, then dropping back down. Usually I start unplugging things, and making sure all my bass's knobs are set correctly, and eventually things seem to go away. But it's worrisome.

I have isolated it to the point where I know it's not coming from my pedalboard. The last time it happened I plugged straight into the amp and it kept on doing it. So I ran around for a few minutes and eventually swapped the cable out, but by then it had either stopped or the cable was the cause. I've since used that same cable several times with no issues. The reason I think it might be the amp is because when you fire up the amp it usually takes up to 30 seconds to "warm up" and deliver full volume anyway, and this felt like it might be an extension of that. However, the input needle on this amp was showing hardly any input level when the issue was taking place. Could this mean i need a new preamp tube possibly? Or should I be looking at external non-amp related factors?

Thanks guys.

1kinal · #2 09-01-2010, 11:04 PM

I'd try a new tube first. For $10 it's always good to have a backup.

ishouldbeking · #3 09-02-2010, 12:52 PM

i've never swapped a tube before, is it something I can do on my own? i don't know how to bias a tube or any of that stuff, if that's a part of it, haha. obviously i'm a bit green when it comes to tubes, this is my first hybrid amp.

1kinal · #4 09-02-2010, 01:03 PM

Quote:

Originally Posted by ishouldbeking

i've never swapped a tube before, is it something I can do on my own? i don't know how to bias a tube or any of that stuff, if that's a part of it, haha. obviously i'm a bit green when it comes to tubes, this is my first hybrid amp.

No bias needed for preamp tube (as it's the case with the ashdown head). Just open the amp by removing the top screws, remove the tube and put the new one in place. Anybody can do it. Make sure the amp is not plugged in and it's been turned off for a few minutes.

As for replacement, I really like the JJ/Tesla when I had my ashdown amp. It's cheap and sounds great.

http://thetubestore.com/tesla12ax7.html

eyeballkid · #5 09-02-2010, 01:05 PM

alright,
first: try turning it on without the tube drive button engaged.
It is TOTALLY NORMAL and expected for it to take a few (5-15 seconds) to "warm up" with the volume fading in from '0' to full volume potential when you turn it on with the tube drive engaged as the preamp tube warms up.

if the problem is the tube and ONLY the tube you will have immediate volume upon turning it on with the tube drive off.

(this means you have to have the button OUT, not just the knob turned down to minimum)

if you have full volume, then yes, its the tube.
to replace it, simply unscrew all the screws on the chassis, gently lift off the lid, pull the 12ax7 straight up and out, and replace with a new one making sure the pins are placed in correctly. dont touch anything else!.....

no biasing is needed for preamp tubes, its just pop, and drop.

now if you have turned the tube drive off and you STILL have volume fluctuations upon turning it on, you have other more serious problems.

but its probably the tube.

eyeballkid · #6 09-02-2010, 01:08 PM

if that wasnt clear... what i mean is

turn the amp off
turn the tube drive off
leave it off for a few
turn the amp back on..
do you have immediate and stable volume (which may be a little quieter than with the tube on)?
yes? then its a bad tube...replace the tube.
no? oh no! its trouble.

kayakbass · #7 09-02-2010, 01:49 PM

Quote:

Originally Posted by ishouldbeking

So I haven't ruled out the possibility of another issue here, such as cable, input jack or the power at my rehearsal space... but it has happened a couple times, so I thought I'd ask all y'all. A few times now when I first fire up my rig, I'll start playing and find there's hardly any output. And then the volume will start to fluctuate, getting closer to normal levels, then dropping back down. Usually I start unplugging things, and making sure all my bass's knobs are set correctly, and eventually things seem to go away. But it's worrisome.

I have isolated it to the point where I know it's not coming from my pedalboard. The last time it happened I plugged straight into the amp and it kept on doing it. So I ran around for a few minutes and eventually swapped the cable out, but by then it had either stopped or the cable was the cause. I've since used that same cable several times with no issues. The reason I think it might be the amp is because when you fire up the amp it usually takes up to 30 seconds to "warm up" and deliver full volume anyway, and this felt like it might be an extension of that. However, the input needle on this amp was showing hardly any input level when the issue was taking place. Could this mean i need a new preamp tube possibly? Or should I be looking at external non-amp related factors?

Thanks guys.

Plug into your FX return directly. This will bypass your preamp and allow you to see if the prob is with your preamp part of the head or output. Sounds like a Preamp issue. Change that tube out!

ishouldbeking · #8 09-02-2010, 02:06 PM

seeing as it doesn't do it every time, I think i'll be proactive and change the tube anyway. thanks for the JJ/tesla recommendation, that's the general consensus I've gotten so i'll probably go that way. Now, I've got one last possibly dumb question... how many and what type of tubes does my head have? I've never opened it up, and a quick google search turned up nothing, and believe it or not the ashdown site and manual don't have any details.

i'm guessing it's a single 12-ax7 but i wanna make sure before i order anything.

funkytoe · #9 09-02-2010, 02:29 PM

This may sound really simplistic, but you say the meter on your amp is showing hardly any input when this occurs? Do you have an active bass? Maybe its time to change the battery in your bass's preamp?

Krispy · #10 09-02-2010, 02:43 PM

Tube. I replaced mine (same amp) with these and love the punchy sound. The JJ's were a bit muddy to me.

Good luck!

Quote:

Originally Posted by ishouldbeking

seeing as it doesn't do it every time, I think i'll be proactive and change the tube anyway. thanks for the JJ/tesla recommendation, that's the general consensus I've gotten so i'll probably go that way. Now, I've got one last possibly dumb question... how many and what type of tubes does my head have? I've never opened it up, and a quick google search turned up nothing, and believe it or not the ashdown site and manual don't have any details.

i'm guessing it's a single 12-ax7 but i wanna make sure before i order anything.

ishouldbeking · #11 09-02-2010, 02:44 PM

Quote:

Originally Posted by funkytoe

This may sound really simplistic, but you say the meter on your amp is showing hardly any input when this occurs? Do you have an active bass? Maybe its time to change the battery in your bass's preamp?

nah, I've only been using my Ric and Precisions lately. But I appreciate the suggestion... I can remember a studio session where my stingray started to sound terrible, and I spent an hour trying to figure out why. Suddenly I remembered the battery power, and sure enough, I tested it and it had almost no juice left.

1kinal · #12 09-02-2010, 04:17 PM

Quote:

Originally Posted by ishouldbeking

seeing as it doesn't do it every time, I think i'll be proactive and change the tube anyway. thanks for the JJ/tesla recommendation, that's the general consensus I've gotten so i'll probably go that way. Now, I've got one last possibly dumb question... how many and what type of tubes does my head have? I've never opened it up, and a quick google search turned up nothing, and believe it or not the ashdown site and manual don't have any details.

i'm guessing it's a single 12-ax7 but i wanna make sure before i order anything.

right, a single 12ax7 is used in the preamp stage. No tube in the power section.