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Triode Hum & Squealing, and Firmware 2.0 (2 loosely related questions!)

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Hi all,

 

I bought my DT25 second hand on eBay a couple of years back. The seller said he'd replaced a couple of the tubes himself (I got the feeling he was a little clueless). Anyway, since having it it's been getting a bit - well - weird on me. 

 

Around 6 months ago, flipping the pentode -> triode switch causes notable hum. Knocking back to pentode resolved it so I've just used it in this mode.

Around 1 month ago, flipping pentode -> triode makes the amp scream out with what sounds like feedback squeal (loudly). The volume control has no impact on the volume of said squeal. Pentode still works fine however. Is this likely to be a tube thing?

 

I should also say that I'm clueless about tubes but have spent hours on these forums reading multiple old posts. I'm thinking if it is, I'll get them replaced. But, since I don't have the originals I'm not sure *exactly* what to replace them with. The knowledgebase says "Chinese-branded 12AX7 preamp tube (1) and Electro-Harmonix EL84 power tubes (2)." but which ones? ie EH 12AX7's? Or what? So confused. Can anyone point out which ones from say here or perhaps another UK based shop?

 

Finally - on a separate note, I just upgraded my DT25 to the 2.0 firmware. I can't find any instructions on how to use the update! The only link on the L6 web site is now dead :(

 

Thanks everyone :) 

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Just an update - I found these tubes. Would they be okay? I'm having most difficulty finding a Chinese branded 12AX7, but Tube Amp Doctor have them. Is it okay that they're not Electro Harmonix tubes? It's all so confusing!

 

1No. 12AX7

2No. EH EL84s

 

Cheers, J

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Thanks and I'd agree - except that the Line 6 official knowledgebase says to specifically to use a Chinese-branded 12AX7 preamp tube on the DT25. EH are Russian! In fact the one in my amp at the moment is an EH (Russian) 12AX7, so should I be replacing it anyway?

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12AX7EH for the pre-amp valves.

EL84EH, have to be a matched set for the power stage.

 

What elegault2 said,...

 

http://line6.com/sup...nd/#entry198956

 

You can get away with using the China 12AX7's, but that's more used on the Spider Valve and Alchemist amps.

Sticking with the EH valves is the best bet.

 

Saw Mike Mathews, owner of EH the other day at a trade show and had my annual chat with him about valves

(tubes), so you know my info is current.

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12AX7EH for the pre-amp valves.

EL84EH, have to be a matched set for the power stage.

 

What elegault2 said,...

 

http://line6.com/sup...nd/#entry198956

 

You can get away with using the China 12AX7's, but that's more used on the Spider Valve and Alchemist amps.

Sticking with the EH valves is the best bet.

 

Saw Mike Mathews, owner of EH the other day at a trade show and had my annual chat with him about valves

(tubes), so you know my info is current.

 

That's really useful thank you - I don't doubt you one bit! Why does the official L6 guide suggest China 12AX7's for the DT25 and 12AX7EH for the DT50? I wonder what the logic is behind that - any idea?

 

Also, do you think this is likely to sort the issue I've described above? And if I replaced them, would I need to bias them (or get them biased)? Bit of a newbie in that sense!

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EH's are what's officially approved by engineering, and I concur. But, probably the pre-amp is not

as crucial with DT25 as it is with the DT50. So the China ones for the DT25 are okay. Just make certain

that for the soft, medium or hard, that you get mediums,... no compromising on that. It's what these are optimized for.

 

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Just make certain that for the soft, medium or hard, that you get mediums,... no compromising on that. It's what these are optimized for.

 

In the UK, all the valve shops I've looked at (6+) stock them, but they don't offer soft, medium, or hard. The only place I can see that is on musiciansfriend online. If they don't specify, is it therefore likely to be medium by default, or just potluck?

 

EDIT***

 

Don't worry I spoke to the store and they said they can provide medium (something to do with Groove tube - I'm a bit clueless obviously!)

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I know Aspen Pittman who used to own Groove Tubes. Love Groove Tubes, good product,...

just not in a DT amp. It would be fine if it were an all analog amp, but it's not.

 

The digital half needs to talk nice to the analog half and vice-versa, or something will go wrong.

That's why getting the correct tube is crucial. Can't get away with the same willy-nilly of tube

swapping we used to do with "all analog tube amps" back in the 1960's and 70's.

 

Soft, medium and hard has to do with the ratio of gas-to-vacuum within the tube.

 

50/50 it's default medium. Tube suppliers should know this stuff and know what they have.

That's why sticking to the EH's is the best bet, the ones we get for these amps are mediums,

since that's what these amps are optimized for.

 

Stick with the Medium EH's,... no Tung-Sol, Mesa, JJ's, Groove Tubes or Ruby Tubes in a DT amp.

 

Just had my annual tube chat at NAMM over the weekend with former Groove Tube's Aspen

Pittman and EH's Mike Matthews, they keep me current.

 

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Thank you for all that - very useful indeed. Therefore I've bought some paired EH EL84 (medium) and a 12AX7EH as suggested.

 

UQAHH5P.jpg

 

So my next question is about changing them.

 

I'm fully aware it's a risky process and don't particularly want to die! To change the tubes alone, is that something I can do without too much fuss/risk on the DT25? I appreciate biasing them is a little more tricky and needs more disassembly (and therefore more risk). Can I change them and have someone else bias them? Or can I change them and just see if it's any better off the bat and not bother biasing?

 

Thanks!

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Don’t change the tubes without biasing. It’s not difficult but you need to have your wits about you as it can be dangerous. If you are unsure take it to a pro.

Where did you get your tubes from?

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I've FINALLY had the tubes installed and biased. Apparently one of my tubes was massively underperforming and the other was taking all the load.  The loaded one was giving a reading of 68mV whereas the other wasn't providing any voltage whatsoever. 

 

2 new tubes biased at 25 mV +/- 3 mV and it's works BEAUTIFULLY. The amp sounds so much nicer - even better than when I bought it second hand. I suspect the guy who changed them was a bit clueless. 

 

Anyway, over the moon, so thanks for all your help earlier this year.

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On 5/14/2018 at 5:33 PM, psarkissian said:

Awesome!

 

 

Some strange things are happening now. They might be perfectly normal, but as I bought it second hand I'm unsure of the intended manufacturer behaviour.

 

1. The thing is loud. I mean really really loud. In a gig practise situation, I would have the HD500X output set to max, the channel volume set to high on the amp, then the master volume at around half way. Now, if I have that I get serious volume/feedback from the amp. I've had to reduce everything quite a lot. So much so it's messed up a lot of my presets!! Sounds like a stupid comment, but I'm wondering if it's supposed to be quite that powerful (subjective I know).

 

2. If I roll my guitar volume down to 0% I get a quiet weird clicking/hum sound. That's even if I plug directly into the amp. It's not so much of an issue, but highlights something that might not be right.

 

Any ideas?


Thanks :)

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1- pull on the volume knob gently, the shaft should come up and the volume drop by almost half, the adjust volume from there.

 

2- sound like just background noise. The processor board is digital, so it's digital quiet, vacuum tubes aren't.

 

 

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