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Unread 12-01-2009, 11:23 AM   #1 (permalink)
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Exclamation Issue with preamp tubes in a JCM DSL 2000 100 watts

Hi everyone,

I've had my JCM 2000 DSL 100 watts head since around year 2000. It always worked fine until one day it was losing volume so I took it for repairs and they changed an output trasformer I think.

About a year ago I had it fail and a new board from Marshall was sent and installed. That time I had volume problems and one of the power tubes went totally orange

Currently the amp works fine but burns the preamp tube in position V2 quickly. I mean, it lasts some months but after a while I get a massive drop in volume and replacing the tube fixes the issue.

I'm using KT77's on the power section from JJ tubes and 12AX7LPS from Sovtek for the preamp positions. I had to put other tubes in that V2 spot but I'm out of of preamp ones for the moment.

In the end I'd like to avoid permanently damaging my amp... again -.-. I should also mention that another head of mine, the Blackstar HT-5 had the preamp tube fail in a similar dropping-volume fashion. I thought it was the speaker cable which I replaced and it worked fine until the same preamp tube blew in a rehearsal...

Finally, I'm using a 1936 2X12" cab with the 8ohm connector (mono). Does anybody have an idea what could be causing this recurrent problem?

Regards and many thanks!,
-David
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Unread 12-01-2009, 01:07 PM   #2 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

It sounds like whomever fixed your amp didn't do a good job. I'd bring it in to a Marshall service center.
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Unread 12-01-2009, 09:14 PM   #3 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

I was told by the guys who repaired the amp that they measured with another exact same amp side by side and readings were the same :S
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Unread 12-01-2009, 09:42 PM   #4 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

Maybe you got got a bad run of preamp tubes. Try some Mullard reissue or tung sol 12ax7 tubes to see if they longer. If your tech really did the work right, maybe the amp is fine and you need some better quality tubes.

I've bought new tubes that were bad right out of the box!
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Unread 12-01-2009, 10:07 PM   #5 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

Hey David. Just to be clear, you are talking about the tube right next to the tube under the shield. Is this correct? I ask, because a lot of current production tubes do not last very long in V3. I always recommend an NOS tube for that slot. It has higher operating voltages and is hard on most CP tubes. However, the Mullard RI and the Electro-Harmonix seem to do a good job in that slot.

V2 is just a gain stage. If it is in fact the tube that you are having trouble with I will say this. Sovtek tubes are not very good. The WA and WB were horrible. The LPS is not much better and it is not recommended for combos and tends to be microphonic.

As JCMJMP said, it may be time to go with a different brand. Right now, I can't recommend a Tung-Sol in V3, but it will be fine in V2. Try it or a Mullard RI.

Also, when the amp is on for about fifteen minutes, try touching the V2 tube and see if it is very hot. It shouldn't be.

Lastly, it might be a good idea to clean the socket with some spray Detox-It. Do this with the amp unplugged. Allow ample time for the cleaner to evaporate before installing the tube and powering the amp back on.
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Unread 12-01-2009, 11:20 PM   #6 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

Marty, you're right... it's the tube next to the shielded one. I assumed that was the V2 position but it seems like it's V3 right? In this post Replacing DSL 100 tubes? it's labeled as V2.

I was thinking on buying a JJ, a Mullard RI and a couple Sovtek LPS's as spares... might need to change my plans a bit. How would you rate the JJ, Mullard RI, Tungsol and EH against each other?

I wanted to buy 3 brands to try other tubes out, with 2 of the same brand to change positions V2 and V3 and save a spare LPS just in case.

Last but not least, thanks a lot for your great advice much much appreciated since I'm about to order some new tubes as you can tell!
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Unread 12-02-2009, 12:34 AM   #7 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

Quote:
Originally Posted by David Corrales View Post
Marty, you're right... it's the tube next to the shielded one. I assumed that was the V2 position but it seems like it's V3 right? In this post Replacing DSL 100 tubes? it's labeled as V2.

I was thinking on buying a JJ, a Mullard RI and a couple Sovtek LPS's as spares... might need to change my plans a bit. How would you rate the JJ, Mullard RI, Tungsol and EH against each other?

I wanted to buy 3 brands to try other tubes out, with 2 of the same brand to change positions V2 and V3 and save a spare LPS just in case.

Last but not least, thanks a lot for your great advice much much appreciated since I'm about to order some new tubes as you can tell!
Yeah, I remember that thread. Well that is the V2 tube. I would say go with the Mullard RI, Tung-Sol or EH's. Get two Mullard RI's, a T-S and an EH. Use either a Mullard or the EH in V3.
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Unread 12-02-2009, 06:54 AM   #8 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

The whole thing about Tung Sols in V3 might very well be internet myth. Mine have been running fine for 2 years.
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Unread 12-02-2009, 09:35 AM   #9 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

Quick update: I already order 2 Mullard RI's, 1 Tungsol and 1 JJ to try them all out. Thanks guys for the help I'll post back with results hehe
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Unread 12-02-2009, 02:47 PM   #10 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

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Originally Posted by jcmjmp View Post
The whole thing about Tung Sols in V3 might very well be internet myth. Mine have been running fine for 2 years.
Well, I have personally dealt with people who have had these problems and it is not just with the Tung-Sol. Here is a link to Metro Amps.

MetroAmp.com Forum • View topic - Tung Sol Reissue 12AX7 not for CF stage !!!

Here's a link from MEF:

12AX7EH CF Failure

Now I will say that these links are about two to five years old. There is a possibility that the tube problem has been rectified, but because there was a problem, the "rumor" got started.

I have bought CP tubes to test in the gain stages. I do not use CP in the TS/CF or the PI. Once I do my testing the CP tube is put back up and an NOS tube is put back in the amp. The most recent batch of CP tubes I bought was about four months ago and I bought everything from Sovteks, EH's, Mullard RI's, Tung-Sol's and JJ's. However, none were used in the CF slot. I guess I could do a run on them in the CF slot and see if any of them fail. Apparently the VOX circuit is a real CP killer in the CF slot.
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Unread 12-02-2009, 03:57 PM   #11 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

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Originally Posted by MartyStrat54 View Post
Well, I have personally dealt with people who have had these problems and it is not just with the Tung-Sol. Here is a link to Metro Amps.

MetroAmp.com Forum • View topic - Tung Sol Reissue 12AX7 not for CF stage !!!
Yes, I'm familiar with the MetroAmp thread. Maybe the quality improved?
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Unread 12-02-2009, 04:12 PM   #12 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

Well I haven't seen anything current on either the Tung-Sol or the EH, so I think I will lift my ban on these in the CF slot. As far as the Sovteks go, I just don't like them anywhere in a amp. I see guys on the forum the are running these in all positions and to be blunt, they sound like cardboard.

Right now, my three favorite CP 12AX7's are:

1.Tung-Sol Short Plate ($14.95)
2.Mullard RI Long Plate (16.95)
3.EH Short Plate (Best Buy @ $10.95)

Actually, if you order an EH and request a high gain tube, they are pretty solid in V2. EH is advertising their tube to be safe in all tube slots.
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Unread 12-02-2009, 05:44 PM   #13 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

The CF stage in a DSL is V3, right? V2 in a JCM800? If so, I've never had premature failures of the TS 12AX7 in the CF stage.
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Unread 12-02-2009, 06:35 PM   #14 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

Quote:
Originally Posted by jcmjmp View Post
The CF stage in a DSL is V3, right? V2 in a JCM800? If so, I've never had premature failures of the TS 12AX7 in the CF stage.
Yeah, on a four tube preamp, the TS/CF is V3 and on a three tube preamp it is V2.

I always wondered how an 800 got its sound with just one gain tube? Pretty awesome at that.
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Unread 12-10-2009, 10:57 PM   #15 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

Update: Today I got my tubes and I love Marty's recommendation I'm currently using a Tungsol in V1, Mullard RI in V2, JJ in V3 and Sovtek LPS in V4. I couldn't change all tubes you said but it sounds really nice, I love the V1 sound

I do prefer still the Sovtek LPS in my Blackstar HT-5 head. It has the more "defined" sound of them all.

Thanks again for the help
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Unread 12-10-2009, 11:31 PM   #16 (permalink)
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Re: Issue with preamp tubes in a JCM DSL 2000 100 watts

Glad it worked out. I think you will get a lot of enjoyment out of them.
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