DSL or Pickup howl?

Xiderpunk · 10-30-2008, 06:48 AM

Recently at rehersal ran into a new problem occuring with my DSL 50 or Jackson DK2, I am not entirely sure which is the cause as yet, hence asking for opinions based on others experience.

First the DSL 50 is tubed with 1 original ECC83 in 1, JJ ECC83S in 2,3,4 and two JJ E34L for power tubes. I had all JJ's but the first 1 died within hours in position 1 so put the original back in. All the remaining JJ tubes probably have around 10 hours of play time on them.

The settings I tend to use are Lead 2 with gain at around 7-8 and volume at around 4.5 (earth trembling loud). EQ wise, deep switch in, pres 4, treble 3, mid 6, bass 7, tone shift out. Basically a real Megadeth heavy type tone.

Prior to retubing had no particular feedback problems with these settings, other than the usual, damping strings would stop it immediately. However now with these settings I am getting a mid-range howling (imagine a large dog howl), strings dampened or not, only reducing the guitar volume or playing stops it. Even from 15 feet away from the amp.

My initial thoughts was OK this is probably yet another JJ tube problem, with one of them going microphonic. However I checked all tubes using the pencil tap method.. no difference between tubes.. no sound generated through the speaker with guitar unplugged using very high volume/gain settings.

On the guitar I mainly use the bridge pickup.. a Seymour Duncan TB4 which is a very hot pickup. Using the two single coils (SD STK1's) I have found the howling doesn't start till around vol 6-7 (ears bleeding level), however it is the same howl.. starting at the same pitch and gradually increasing.

Reducing the gain or volume on the amp eliminates the issue, however naturally this is not desirable.

In trying to diagnose this I have tried several different cables to no avail also and also going straight to amp with nothing in the effects loop.

So I still suspect that 1 or more tube is responsible, however after failing with the pencil technique I am questioning whether my guitar could be the cause. Anyone seen these symptoms before?

Xiderpunk · 10-30-2008, 07:46 AM

Ah just still experimenting and discovered a new or perhaps related issue.. unusually quiet clean channel. For example I can turn up volume and gain to around 8 each and whilst loud, would not get over a drum kit, it's about as loud as a marshall 15w solid state clean on around 9 or 10. Now totally confused..

Brett Blackmore · 10-30-2008, 08:25 AM

Hi,

if I understand rightly you have recently changed all but 1 new tube. One tube went down within hours so you put in an original again... right?

Was that a power tube or a preamp tube? If it was a main power tube then you might have a mis-matching bias. You will need to re-bias it.

It might be a failing pre-amp tube but it does not mean they all go microphonic - some just die quietly. And of course plenty of new tubes
die even when new...

A change of tubes often changes some minimal characteristics of an amp. It could be that the new values are darker than before and you might need to re-dial the EQ to suit. I use gain1 at 8-10 and do not use the push button for extra bass. Maybe you need to use a little less boom and gain now.

The fact that one channel is wrong points to one or more preamp tubes. Rotate them and see if you rotate the problem somewhere else. If so change the bad tube.

ps. the usual safety point - switch the amp off when you change things!

Cheers Brett

Xiderpunk · 10-30-2008, 08:35 AM

Hi Brett good advice and yes it happened to be in position 1 before so the original went back in, at the moment I am altering around the various tubes between 1 and 3 and leaving the PI in 4 alone, also cleaning all the pins etc. Will post back how it goes.

Xiderpunk · 10-30-2008, 12:21 PM

Oh well, guess it is back to Marshall for a service. Unable to bias the amp, 1 side is reading 9 mA and the other 51 mA. No matter what I can't raise the left side beyond 20 mA. It bias'ed correctly to around 41 mA when I did the tube change but has now drifted enormously.

solarburnDSL50 · 10-31-2008, 06:45 AM

If you have the other power tubes or access to another set put them in and check the bias. See if you can get it to bias. IMO you are just having tube trouble. Putting another set of power tubes in to see if it can bias will sure tell you alot. You may have a bad preamp tube as well. Keep trouble shooting.

Yes...brand new tubes can be bad!

10-30-2008, 06:48 AM	#1 (permalink)
Xiderpunk Senior Member Join Date: Apr 2008 Location: Farnborough, UK Posts: 122	DSL or Pickup howl? Recently at rehersal ran into a new problem occuring with my DSL 50 or Jackson DK2, I am not entirely sure which is the cause as yet, hence asking for opinions based on others experience. First the DSL 50 is tubed with 1 original ECC83 in 1, JJ ECC83S in 2,3,4 and two JJ E34L for power tubes. I had all JJ's but the first 1 died within hours in position 1 so put the original back in. All the remaining JJ tubes probably have around 10 hours of play time on them. The settings I tend to use are Lead 2 with gain at around 7-8 and volume at around 4.5 (earth trembling loud). EQ wise, deep switch in, pres 4, treble 3, mid 6, bass 7, tone shift out. Basically a real Megadeth heavy type tone. Prior to retubing had no particular feedback problems with these settings, other than the usual, damping strings would stop it immediately. However now with these settings I am getting a mid-range howling (imagine a large dog howl), strings dampened or not, only reducing the guitar volume or playing stops it. Even from 15 feet away from the amp. My initial thoughts was OK this is probably yet another JJ tube problem, with one of them going microphonic. However I checked all tubes using the pencil tap method.. no difference between tubes.. no sound generated through the speaker with guitar unplugged using very high volume/gain settings. On the guitar I mainly use the bridge pickup.. a Seymour Duncan TB4 which is a very hot pickup. Using the two single coils (SD STK1's) I have found the howling doesn't start till around vol 6-7 (ears bleeding level), however it is the same howl.. starting at the same pitch and gradually increasing. Reducing the gain or volume on the amp eliminates the issue, however naturally this is not desirable. In trying to diagnose this I have tried several different cables to no avail also and also going straight to amp with nothing in the effects loop. So I still suspect that 1 or more tube is responsible, however after failing with the pencil technique I am questioning whether my guitar could be the cause. Anyone seen these symptoms before? __________________ Marshall JCM2000 DSL-50 with 1960A 4x12 (2 x GT-75's + 2 x Vintage 30's) V1: NOS Mullard 12AX7 V2: Sovtek 12AX7-EH V3: JJ ECC83S V4: JJ ECC83S Power: JJ KT77 or JJ EL34L http://www.myspace.com/taintedgraceband

10-30-2008, 07:46 AM	#2 (permalink)
Xiderpunk Senior Member Join Date: Apr 2008 Location: Farnborough, UK Posts: 122	Re: DSL or Pickup howl? Ah just still experimenting and discovered a new or perhaps related issue.. unusually quiet clean channel. For example I can turn up volume and gain to around 8 each and whilst loud, would not get over a drum kit, it's about as loud as a marshall 15w solid state clean on around 9 or 10. Now totally confused.. __________________ Marshall JCM2000 DSL-50 with 1960A 4x12 (2 x GT-75's + 2 x Vintage 30's) V1: NOS Mullard 12AX7 V2: Sovtek 12AX7-EH V3: JJ ECC83S V4: JJ ECC83S Power: JJ KT77 or JJ EL34L http://www.myspace.com/taintedgraceband

10-30-2008, 08:25 AM	#3 (permalink)
Brett Blackmore Senior Member Join Date: Apr 2008 Location: Bingen, Germany Posts: 344	Re: DSL or Pickup howl? Hi, if I understand rightly you have recently changed all but 1 new tube. One tube went down within hours so you put in an original again... right? Was that a power tube or a preamp tube? If it was a main power tube then you might have a mis-matching bias. You will need to re-bias it. It might be a failing pre-amp tube but it does not mean they all go microphonic - some just die quietly. And of course plenty of new tubes die even when new... A change of tubes often changes some minimal characteristics of an amp. It could be that the new values are darker than before and you might need to re-dial the EQ to suit. I use gain1 at 8-10 and do not use the push button for extra bass. Maybe you need to use a little less boom and gain now. The fact that one channel is wrong points to one or more preamp tubes. Rotate them and see if you rotate the problem somewhere else. If so change the bad tube. ps. the usual safety point - switch the amp off when you change things! Cheers Brett

10-30-2008, 08:35 AM	#4 (permalink)
Xiderpunk Senior Member Join Date: Apr 2008 Location: Farnborough, UK Posts: 122	Re: DSL or Pickup howl? Hi Brett good advice and yes it happened to be in position 1 before so the original went back in, at the moment I am altering around the various tubes between 1 and 3 and leaving the PI in 4 alone, also cleaning all the pins etc. Will post back how it goes. __________________ Marshall JCM2000 DSL-50 with 1960A 4x12 (2 x GT-75's + 2 x Vintage 30's) V1: NOS Mullard 12AX7 V2: Sovtek 12AX7-EH V3: JJ ECC83S V4: JJ ECC83S Power: JJ KT77 or JJ EL34L http://www.myspace.com/taintedgraceband

10-30-2008, 12:21 PM	#5 (permalink)
Xiderpunk Senior Member Join Date: Apr 2008 Location: Farnborough, UK Posts: 122	Re: DSL or Pickup howl? Oh well, guess it is back to Marshall for a service. Unable to bias the amp, 1 side is reading 9 mA and the other 51 mA. No matter what I can't raise the left side beyond 20 mA. It bias'ed correctly to around 41 mA when I did the tube change but has now drifted enormously. __________________ Marshall JCM2000 DSL-50 with 1960A 4x12 (2 x GT-75's + 2 x Vintage 30's) V1: NOS Mullard 12AX7 V2: Sovtek 12AX7-EH V3: JJ ECC83S V4: JJ ECC83S Power: JJ KT77 or JJ EL34L http://www.myspace.com/taintedgraceband

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode