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Discussion in 'Amp Owners Clubs' started by Colo Springs E, Jan 1, 2013.
2 TAD 12ax7 s in V1 and 3. EL84 and V2 are both Ruby's. For now!
Update. TAD 12ax7 Mullard reproduction in position 2 is fantastic. Clean tones are stunning. Just can't decide which EL84 I prefer. Got JJ, TAD, and the original Ruby. They all sound very different driven. The JJ maybe lacks something when clean. May have to record all 3 and make a decision from there.
I have an L5T-112 as well. Not the studio version, but the last incarnation of the older model without all the bells and whistles. I think that would be revision 4.
I have a Tung-Sol EL84 in the power amp. It needs long to break in, and lacks something when compared to other brands.
The TAD EL84 it came with, wore out very quickly. The sound was very good though.
The absolute winner when tone is all you care about, was an old Philips EL84. It redplates when you use it in this amp, so it is not recommended to use this tube.
I still have to try some other brands. I never believed so much in tube rolling, but for a crancked SE class A amp it actually does matter.
One consideration with this amp is that you must use the standby switch when switching the amp on. If you switch on the high voltage before the tubes are warm, the DC coupled V2 might arc over.
I'd like to see a comparison video!
And halo thanks for the info. Tung sol might be the best?
Sticking with the TAD EL84. If it wears out I will try a Tung Sol. The JJ wasn't even nice driven, as if it were trying to push the amp into high gain and it just didn't sound nice to my ears. The TAD has more bass response than the others, but the master tone and bright switch sort that out. I always use the standby, as the mains is at the back of the amp. Thanks for advice though.
For good durability it is. For the best tone my current advise would be the TAD tubes.
I'm eager to try an EHX EL84M. They should be easy to break up, without too much volume. I'll let you know once I've tried one.
Cool - I find my stock tads to be harsh. That's the tubes that came with the amp
New in 2007, when I bought it used in 2011 it still had those in it. So they're likely shoot. They still work and aren't microphonic.
What's the m stand for on those el84m?
If I recall correctly, it stands for "Military". It might as well be marketing yibberish, I have no way of checking it.
I was mistaken. The tube I meant is the JJ EL844, not the EL84M.
The EL844 is a low output power low headroom tube, with approximately 9 watts of output (in push pull I suppose).
The EL84M is a Sovtek tube with improved mechanical construction. It is recommended for amps that put a lot of stress on the output tubes, such as Vox amps.
What I do know is that it is a very inefficient EL84, which has low output power and low headroom. If you intend to cranck your amp without the associated volume, this should be the tube you're looking for. For the settings I usually play in (theatres and churches) a 5 watt amp is actually already too loud before you hit the sweet spot on the volume dial.
I have been thinking about modifying the amp to lower the screen grid voltage, which should have the same effect. The tube sockets are not PCB mounted, so it should be an easy mod. If a different tube works though, I rather keep it original.
Well, I took the guess for €60,- and ordered a Sovtek, Mullard (new production) and Electro Harmonix EL84, as well as a JJ EL844. I still have a new TAD and Tung Sol, so next weekend I should have 6 different brands to try.
I'll update you once I have tried all of these tubes. Let the cork sniffing begin!
Yes do tell! If you're able you should do some recording.
Hi - I have an L5T 112 and have done a few things to it over the years:
V1 JJ ECC83S - fairly standard I think, nothing special, but yet to "run out" so have never really messed with it. Although I did move the Hi Grade to V2 and put that Standard TAD in the drawer
V2 TAD E83CC Hi Grade - again came with the amp and not messed
V3 Sovtek 12ax7 LPS - no complaints and not messed with it, however doesn't play nicely in V1, hums a lot.
V4 - TAD EL84 STR (Selected) - think this is code R030 in the TAD store and not thee ones they currently suggest are "best" for the Lionhearts. Sounds good though, but not compared to any others
Maybe I should try a Mullard - I am a bluesy, clean, crunchy kind of guy...?
2) Effects Loop - I have removed R28 and jumpered the FX Out-In jacks, so it is true series lop now and not a parallel one as it was messing with my pedals - each to their own for this one.
3) Power scaling - I have a London Power SV-2, and also a Dana Hall VVR.
VVR was the first scaling I used and I did the whole amp, basically broke into the power rail at the output of the fuse F3 into the VVR and back out to P24, the earth went to the shared ground pint of the power caps on the back of the PCB.
This works fairly well for mid scaling, but cleans up significantly and gets muddy/loses treble as you go lower. In the end I decided I wanted more control over the pre and power amps to choose what I wanted so I took it out and went onto.....
I installed the London Power SV2 just on the EL84, scaling both plate and screen. This is plugged into P24 (screen) and SP4 (plate) which are easy to spot and solder.
This keeps the preamp tone clean or driven - retaining the treble and "Presence", the only trade off being you have to manage the Drive Volume (on Drive channel!) or Clean Volume as the EL84 gets very fuzzy/buzzy if overdriven *too much* (yes there is such a thing).
One thing with doing power-only scaling is that the preamp voltages go up as the scaling goes "down" to offset the unloading of the supply. I was uncertain about this at first so delved into lots of amp theory books, and worked out that the 12ax7/ecc83's are fine at those higher voltages (max plate on v1a is 290v), and are still fairly linear in their response.
I checked the tone from them at the new voltages vs the old by using my new series FX loop - I just took the out into another very clean amp and listened as I turned the EL84 scaling up and down (even though this bit was not output to speaker - or actually never got the input!)
Turns out (prob as expected) on Clean channel, V1a stays clean all the way up - no crunch at all regardless of plate voltage or "gain". This also means I didn't have to work out how to get a Master Volume on the clean channel to keep any v1/v2 crunch..as there was none
V1b (AKA the Drive Channel) clips asymetrically with a fair amount of gain as well, and this tone stayed constant too, no cleaning up or increase in drive tone with the el84 scaled/unscaled.
V2a- just a gain improver (lots though), no clipping here anyway regardless of what is fed into it as per clean v1a above feeding into it.
V2b just feeds the tone stack, again no clipping here.
The above were all checked with guitar straight in, and with various boost pedals in front - I think I might have got V2a to clip but not 100% sure with a cascaded Rocket Archer and Compressor on max level....suffice to say the preamp structure remains constant re tone with the EL84 scaled.
Happy days - except I had forgotten about V3 - the "phase inverter" even though it is an SE amp this still sort of follows the Marshall template, and i had read that the PI is also responsible for a lot of power stage clipping, so back to the drawing board to somehow find a way of testing/hearing v3 clipping
Aha! I still had the VVR in the drawer - so this came out and is now scaling V3a on its own. I thought, if this triode is clipping then scaling it will make that stand out. So with the EL84 on full power (clean as can be) and the preamp on clean and turned up.....v3a didn't clip at all. I could only get it to clip when scaled *right* down, and to be honest the volume drop at that point was more of a noticeable thing.
So what I can deduce from all this - the L5t really only uses EL84 power tube clipping when the clean preamp volume is dimed, and on te3h Drive channel v21b only adds in "traditional" asymmetric clipping as well as gain increase, but probably not enough to clip at v2b or V3a (PI/Driver))
So your best bet is to just scale the EL84 - you won't be losing out on anything by leaving v1/2/and 3 exactly as is.
As I say though, judicious use of Volume/Drive Volume is called for though to keep the signal into the EL84 just right.
Footnote 1- to answer the point I quoted - I looked at just EL84 screen scaling, but everything I read pointed out this doesn't really "fix" anything and just moves the current/voltage operating points around in a non-optimal way i.e the responses to change in input isn't consistent and it really doesn't work well.
Footnote 2 - looking at the plate voltage, cathode resistor etc of the EL84 I suspect it is biased on the "quite-to-hot" side, so it asymetrically clips when driven hard
4) Finally mod but in no way least (IMHO) - I added a switch to "remove" the negative feedback loop via an SPDT toggle inserted where the 4ohm speaker jack connection (brown wire I think) goes out the back.
The SPDT has normal connection one way, and inserts a 100MOhm Resistor in series with R52 the other way, so the connection isn't lost (can cause popping if totally unconnected although the switch itself has a slight make-break-make action) that effectively stops the NFB voltage getting any further.
Effect is ......
Probably the best thing you can do with this amp - increases volume a bit and "roughness", but the touch sensitivity is simply amazing.
Set for clean preamp, or even a little driven, into a scaled EL84 for a touch of crunch you can now totally do that 57 Deluxe 5e3 thing, screamin' blues overdrive down to clean just by picking. This was the one thing I thought the stock L5t wasn't good at at all, so a huge relief not to have to get another amp !
very happy with the way things have turned out - however I now have the "Shock Brothers" bug methinks....
Until I build my own, anyone got any other ideas for mods (thinking of somehow getting a 0.1uF coupling caps in there somewhere, or changing the preamp plate resistors for 220k like the 18w has....or changing the Cathode r/c's) - unfortunately a lot of these are surface mount so are fairly untouchable
Should just say - all this was with a tele, so single coils rule.....I have no idea if the above holds true with HBs (although I suspect given my boost pedal tests it will be ok)
The NFB mod sounds promising. I might actually try that. How does removing the NFB affect the tone knob? I suppose it becomes a top cut control like Vox has?
How did you check for distortion? It is really hard to spot a small amount of distortion on an oscilloscope. I would expect V1a to distort at least a few percent, and the other stages (except the CF) too.
If desired, I can hook up my ancient distortion analizer and measure the amp through. The analizer needs a revision though, so measurements are not accurate. It should measure down to 0.05%, but since it is out of spec it won't go down 0.5% or so. It is full of carbon composition resistors, if you were wondering
Anyway, the tubes came in today. The Sovtek, EHX and Mullard look exacy identical except for the filaments. The Sovtek does not have spiral heaters, the others do.
The EL844 is completely different. The plates are closer together and elliptical shaped. On one side there is a gap between the plates, showing the grids. That should look very cool in an amp.
Now wait for a day when the wife is not home. It will get loud
I just checked it with my ears and the preamp tone didn't change much if at all (either clean or Drive channels) - certainly not from a clipping point of view.
I suppose the 12ax7 transfer curves may have a slightly different asymmetry at different voltages so some harmonic content may be changing *technically*, but I couldn't spot it.
A good go through an oscilloscope would be interesting, but I don't have one
The Tone circuit isn't affected at all by the nfb loop change Tone ground still happens through R54 and then R53, regardless of what the nfb is doing. I put my SPDT *not* on P16 but on the other end of that real wire when it gets to the actual 4 Ohm Output jack.
(Wish I could insert a pic of the schematic, but not sure a) how to, and b) if allowed - although it is readily available as a pdf)
Out of interest, what serial is yours ? Mine was bought in Jan 2014 prob a few months before they changed it to China production or something - and is number 3000 )
Got a report?
I put in the EL844 to see if it would work at all, and it does.
I can't crank up my amp until next monday, so stay tuned
Has anyone else noted that there is a high pitched noise when using the bright channel?
Don't know about "high pitched" but certainly got mains him/buzz until I opened up the chassis and tweaked the hum trimmer.
With no guitar or lead in I would say its a very quiet amp, clean channel with Bright on.
Where about is the hum trimmer inside?
It is called VR10 on the schematic and PCB.
With the amp bit separated from the chassis and looking at it so you see the insides the trimmer is on the left hand side, a small flathead screwdriver is all that is needed.
What does turning it left vs right do?