How do you know when your valves have died?

[CaptainChoptastic]

Perhaps an obvious one this, but what are the symptoms of your amp's valves being on the way out?

I've got a Laney LC30 that must be over 10 years old now, and has never had the valves replaced. The clean channel seems fine (although it never gets cranked), but the lead channel - well, one man's lovely overdrive is another's wasp in a jam-jar - but it's frankly sounding a bit harsh.

I've not being using it massively over the years - doing a bit more Guitar Rigging these days - so it's hard to remember how it used to sound, but I'm pretty sure it was smoother than this.

A full set of valves is likely to cost me around £100, or maybe around twice that if I go for a speaker upgrade too (HH Invader to Celestion V30), so I'd like to be sure that I'm replacing the right bits, or that I'm not just better off scraping this amp, and buying something shiny and new.

If new valves are the way forward, who makes the best ones these days? Is there anything in this "Cryo" stuff, or just marketing hype?

Cheers,
Si

[Daniel Davis]

From the Marshall site:

The most important thing to remember about valves is that they have an indeterminate lifespan, rather like a lightbulb. There is no real way of saying categorically what sort of life they will have. Generally speaking, if used two or three times per week, a set of EL34 or 5881 output valves will last 18 to 24 months. Pre-amp valves [ECC83/12AX7] as a rule have about double the life of the power valves, so about 3 to 4 years under normal playing conditions. As different makes of valve operate at different bias settings you should always ensure that matched power valves are used, otherwise their life will be drastically reduced.

When the time comes to change the power valves you will definitely know as valves only have two states, working or not working. The most common symptom of valve failure is the blowing of the HT fuse. On some occasions after replacing the fuse the amp will work for a while but will blow the fuse again when it reaches full working temperature. This is the first warning sign that a valve is failing. If both the HT and mains fuses blow, then blow again on replacement, then it is pretty definite that at least one of the valves has short circuited and needs replacing. Although not absolutely essential, I always recommend that the entire set of power valves should be changed together [two in a 50 Watt model and four in a 100 Watt].

Where pre-amp valves are concerned, the most common fault is microphony : a high pitched whistling noise which is apparent all the time, whether anything is plugged into the amp or not. This is often caused by the first pre-amp valve in the chain and can sometimes be cured by simply swapping pre-amp valves around. Other pre-amp valve related problems include; lack of volume, loss of bottom end, thinning of the sound and loss of all top-end frequencies. Again it is best to replace all the pre-amp valves at the same time.

[Folderol]

Good grief! If that's the 'official' response then {deity} help us

Output valves do not just work or not work. By far the most common aging result is a slow drop in output and power handling.

Microphony has nothing at all to do with whistles. It is a totally self-descriptive term. The valves behave like microphones! Usually a microphonic valve starts out that way. The more common symptom of aging in pre-amp valves is poor gain and/or early distortion.

[zenguitar]

Full set of valves and a Celestion G12 for the Laney LC30. Just under £150 from Watford Valves. And you can get the Service Manual here on pdf.

Too good an amp to discard, definitely worth some TLC. You won't get anything close for what it'll cost you to replace the valves and upgrade the speaker.

As for cryo, my personal jury is still out until I get around to making a few personal comparisons, but I remain highly cynical. Previous discussions here have tended to fall against there being any real benefit to cryo.

Andy

[ef37a]

Morning Si,
Something a bit off about your "diagnosis" IMHO! Generally as output valves age they deliver less and less CLEAN sound, especially if you demand a lot of LF "grunt" from them.
You say it is the OD sound that is harsh? Impossible to call remotely but I would say NOT EL84 trouble!
That "official" info is flawed to my mind. EL34s should last a lot longer than 2 years (well, maybe if you run them into a soak at 150% overdrive every night for 6 hours you will kill them sooner!) Good quality EL84s should last 2.3.4 years easy unless as I say, you demand 30W clean power all the time. In fact in an amp such as that Laney (and most 15&30watters using 84's)the valves are working just as hard whether you drive the amp or not (so don't leave amps on if you don't need to and don't leave them on standby for hours either!). Pre amp and PI valves are the same, signal/no signal, they wear at the same rate but for pre valves the lifespan is nearer a decade IMO not years. All this of course depends upon valves of the quality of 20+years ago, not easy to find! PIs in particular can be very hummy and front end triodes need selecting for a decent noise/crackle/microphony performance.

I am suspicious of "matched sets". I had several such sets of 84s and 34s to pick through and found :madas:r

[ef37a]

Matched sets..I found better matches BETWEEN sets than inside them!
In fact with cathode biased amps such as the Laney you can just buy 4 valves of the same brand and whack them in. Check the hum levels (all controls at zero). Barely audible? Leave it and mark the valves 1 to 4. Bit hummy at 1mtr? Swop one inner for one outer. No better? Try the other pair. This is really all a matched set does, balance the anode currents for minimum hum and a TEEENSY bit of extra power.

You will read elsewhere of all sorts of claims for certain valves and the Iceland treatment. Peeps will slobber on about "tightened bottoms" and "shimmering highs" What you WON'T ever get is a before and after VOLTAGE table or a 1/2 decent A/B .wav recording!(and WHY do they always use a fekkin' 57!)

Lastly, and I have no axe to grind here nor any experience of the firm but Watford Valves have come in for some criticism recently. A phone call to test the water would be in order methinks?

Dave.

[CaptainChoptastic]

Full set of valves and a Celestion G12 for the Laney LC30. Just under £150 from Watford Valves. And you can get the Service Manual here on pdf.

Cheers Andy, I should have known that your fetish for all things diagram and documentation would come to the rescue!

I did spot that on Watford Valves' site, and also a similar kit with the Vintage 30 (which I think I marginally prefer the more open top-end on - Ahem, judging by the MP3 demo...) for slightly less.

However, if you check the small print then add on delivery and VAT (yes, VAT gets added to the delivery too!) then it's more like £200. Granted, it's unlikely I'd get anything remotely similar to the LC30 for that sort of money.

Lastly, and I have no axe to grind here nor any experience of the firm but Watford Valves have come in for some criticism recently. A phone call to test the water would be in order methinks?

You care to elaborate on that Dave? Are we talking showing something as being in stock then it never arriving? ("Next week, honest Guv!") Or not actually getting what you thought you were ordering? I seem to recall getting some kit from them when I was building a valve amp for a college project, and think they were fine then... but that was over 15 years ago...

Cheers for the other advice too. Consensus seems to be, given the amp is 10 years + old, that even if the valves aren't completely fecked, then they're probably due a change. And that there's probably little point in paying a premium for cryos.

What valve brands are decent nowadays? The Watford kits mentioned earlier come with Harma. My amp currently has Sovtek, and apparently Laney currently uses TAD and Ruby Tubes. Are all modern valves "not like they used to make 'em?"

Oh, and as a footnote, Dave, part of the reason for me getting my LC30 up and running again, is so I can run my recently acquired HT-Dual through it!

[ef37a]

Hi Cap'
Re Watford Valves. I really do not like criticizing people or companies in forums. Any firm can have a bad patch due to key staff going crook or a myriad other things.
I have seen a few references to poor service in Music radar but that is all. A phone call would I am sure give you a very quick impression of the company for good or ill.

Valve suggestions? I have handled probably 500 valves in the last 2 years but mainly from a limited number of sources but FAWITIW here you go...
EL84: Sovtek, ok. EH, ok but might "redplate" in some amps if the mains is at top tolerance. J.J, ok.TAD OK.
ECC83/12AX7,Sovtek, ok generally but I struggled to find low noise, low crunchies, low microphony, low hum in high gain front ends. 10% were too hummy as a PI.
TAD 7025 High Grade. much better but still some selection needed for sensitive front ends (or maybe I am just a fussy bastard!) Rubies? Only saw 3, miccy as flip!
EF86: Only ever changed about 2! Not a problem with any brand.
EL34. No brand stands out. Some of all were good, some of all were unreliable *hit!
KT88. As EL34. Wrapped.....

[ef37a]

Note that I am rating these valves on reliability and "out of the box" performance re noise (yes I had MICROPHONIC output valves!) and hum and mic'phonics. I am NOT going to blather on about "focus" and tight fekkin' mids bollox.
Having got your new set, run the old set up and if possible record the amp. Swop the set then do it again. Listen carefully for any increase in hum. hiss or microphony (belt the box!).Swop all the pre amp valves around and test at each plugging, all should be equally quiet. You are paying top dollar RETAIL prices. My valves were bought in 50s and 100s at a time (and supposed to be the same grade supplied to the factory in most cases)Any that don't come up to scratch send back.

And lastly. IF at the end of the re valve the amp does not, hand on heart, sound any better..Well I did say!
Dave.

[zenguitar]

However, if you check the small print then add on delivery and VAT (yes, VAT gets added to the delivery too!) then it's more like £200.

It's a fair cop Chop, needed to put my reading glasses on

Andy

[Folderol]

It just occurred to me that we may be falsely accusing perfectly good valves.

In your first post you say the clean channels sounds OK, it's just the lead one that sounds rough. If you can get a reasonable volume from the clean channel, then there is no need to think about changing output bottles.

Do you perchance have ECC83s in both channels that you can carefully swap (noting which came from where)?

If you have, and doing so makes no difference to the harshness you describe, it's quite possible that you have a leaky cap somewhere that's making a mess of the pre-amps bias.

P.S.
As I said when the subject came up previously. Considering that under normal operation conditions the metalwork in a valve approaches annealing temperatures, any possible 'fixing' of crystal structure by freezing would be undone in a few minutes!

[ef37a]

Hi Will,
In fact that Laney circuit uses, unusually for a cathode biased EL84 amp, a bit of feedback to the PI and so the op valves will have to degrade to a pretty crap level of emission before the fact is noticed.
BTW the valves share a 56R cathode resistor. I would up that to 68R if'twere mine, some 84s will red plate at high mains in with that value.

Dave.

[Folderol]

Hi Dave

Had a hunt for (and found) the diagrams of that amp. It has some quite interesting features - and no shortage of '83s to swap around. Notice the drawing error in the 84s?

I have seen that see-saw phase splitter and output stage before, but in a hifi amp. However they were using just a pair of ECL86s and there was no decoupling cap on the common cathodes. I was told the reasoning was that in a class A amp there should be no net AC at that point so the cap wouldn't be doing anything. I don't for one minute think saving money came into it

Curious using a ganged pot on the overdrive path. Does it maybe give a log-log response? it looks like there's a misprint 2 x V2B?

The second one (V3B) would be my suspicion for being on it's way out if that cathode resistor is right. At only 820 ohms the valve is working quite hard. I'd be inclined to swap V2 and V3 and see how it sounds.

Interesting idea, paralleling up 2 TL072s to drive the reverb spring drive coil.

[ef37a]

"Interesting idea, paralleling up 2 TL072s to drive the reverb spring drive coil."

Better would be both sections of an NE5532! Not only is the TL072 not happy driving loads below 10k (per section) but all the TL series FET op amps suffer from latchup (to the neg' rail I think) at switchon and if overdriven. A guy I talk to a lot on another forum says he changes quite a few Laney verb tanks with blown input coils!

Nowt wrong with the TL072 in the right application. B'star use shedloads of them (but an NE5534 for a special purpose in the Series Ones!)and I have changed fewer than 3 I think in 2 years.

Dave.

[CaptainChoptastic]

A guy I talk to a lot on another forum says he changes quite a few Laney verb tanks with blown input coils!

Ummm - curious you should mention that... The reverb tank on my LC30 died quite some time ago. I thought it was related to a rather damp flat I was renting at the time (possibly also responsible for killing my then Digitech FX unit). Initially the reverb would only switch on intermittently - I had to really mash the footswitch to get it to latch - then it died completely. A bit of testing has revealed the input on the tank to be OC.

I'll maybe take Will's advice and swap round V2 and V3 to see if that changes anything, but at the end of the day, I think all the valves are probably pretty tired after 10-odd years. I'm veering towards buying direct from TAD, as they also supply replacement reverb tanks: unless a new tank is just as likely to get blown...

[ef37a]

A guy I talk to a lot on another forum says he changes quite a few Laney verb tanks with blown input coils!

Ummm - curious you should mention that... The reverb tank on my LC30 died quite some time ago. I thought it was related to a rather damp flat I was renting at the time (possibly also responsible for killing my then Digitech FX unit). Initially the reverb would only switch on intermittently - I had to really mash the footswitch to get it to latch - then it died completely. A bit of testing has revealed the input on the tank to be OC.

I'll maybe take Will's advice and swap round V2 and V3 to see if that changes anything, but at the end of the day, I think all the valves are probably pretty tired after 10-odd years. I'm veering towards buying direct from TAD, as they also supply replacement reverb tanks: unless a new tank is just as likely to get blown...

I think a lot of the trouble is the DC coupling of the tank. I would insert a 22mfd cap. If the reverb goes a bit "thin" and bass light, keep adding 22s until it sounds right but fit the smallest value you can.
Dave.

[Folderol]

Some good points here. However I'd suggest going a little further.

All the recommendations I've seen (and my own experience) suggest that reverb tanks are most responsive when current driven. This one is very solidly voltage driven - the two 100R resistors don't could as they are inside the Op-Amps feedback loop.

Although you are unlikely to be able to find out the actual impedance of the drive coil you can measure it's DC resistance. If you then put a resistor in series of about twice the measured value you will be somewhere near the impedance and achieve a number of things.

The drive will seem more current orientated so there will be less damping on the springs.

The maximum possible LF/DC current will be reduced to a third of what it was, but the output in the wanted range will reduced by no more than 3dB worst case.

The frequency response will probably seem a little broader.

The Op-Amps will be less stressed (I would still take Dave's advice to change them).

Add the cap as Dave suggests, and you can positively define the LF response better. A spring over-driven at LF just sounds mushy

[CaptainChoptastic]

Thanks for all the advice guys. Looks like I might have to dust of those particular brain-cells to get my head around this one. Originally I was just looking to make good on the wear and tear, but we're now discussing improving on the original design. Admittedly, not a bad idea if I don't want to have to replace my reverb tank every couple of months!

Although you are unlikely to be able to find out the actual impedance of the drive coil...

Not so fast, Mr. Will:
TAD Reverb Can

In fact, it looks like the "model number" here, and in the schematic for the LC30 actually identifies the specs of the reverb tank:
TAD Reverb Datasheet

OK, so just to make sure I'm clear on what you're saying: between the output of the op-amp's feedback loops and the Send socket I need to place an approx 150ohm resistor and a cap in series. The cap and the impedance of the tank's input coil form an HPF. If I'm using the right formula, then the 150ohm i/p impedance and a 22uF cap will give a corner frequency of around 48Hz. Does that sound about right? Or too much bass in the signal?

Regarding the TL072: Dave, where you suggesting that I replace that? Not that it's a great expense (about 50p from Maplin), but I'm not sure if my soldering is up to the task any longer.

Dave, your suggestion of upping the cathode load resistor: I'm not entirely clear on what the effect of this will be. I'm assuming that Laney picked the original value to get Class-A bias on the EL84s. Will changing this value not affect that? Will break-up start happening at slightly lower gain? (Possibly that's a good thing for home recording?)

I'm beginning to think that now I have the schematics for this amp, I might use it as a bit of a test-bed for refreshing my electronics "skills". I was wondering if it would be possible to switch-out one pair of EL84s in the power-amp to give a 15W o/p? Is this as simple as pulling two of the valves (V6 and V8, say), or does that muck up the internal impedances?

Lots of questions....

Cheers,
Si

[ef37a]

Si, the TL0 72 I would leave if it isn't in a socket (hah!). If you have not desoldered a chip before don't start here! Do the cap' mod.
Cathode R: Mullard data works out for 68R for a 320V anode supply for 4 valves (but they would say 4x270+caps!). If the screen grid feed Rs are not 1k, make them so, valves will never get less expensive! 82 Ohms for Rk would not go amiss yes the valves are biased colder but I doubt you would tell.
No such thing as class "A" for guitar amps!

DO NOT PULL VALVES! You can if you like in fixed biased amps but not cathode biased jobbies.
To drop the power you can arrange to switch off the drive to 2 valves or/and run them as triodes by strapping G2 to anode but in truth 15watts is still B loud, better bend you efforts to making a power soak, not hard or exensive for 30watts.

Dave.

[Folderol]

Well done Capn' for finding those links

Unfortunately the pictures just aren't quite clear enough to tell for sure, but before condemning you existing tank, look very carefully at the leads from the drive coil to the socket. What I can't quite see is whether the leads go directly into the coil, or whether they go to very short pins. In either case, at the socket end, pull the leads very gently. If they seem to stretch, or immediately come away from the socket, then you had a fracture from repeated bending at the highest stress point. If the coil has pins then try the same trick that end.

The corner frequency is going to be 1 over (2 x PI x (Coil Imp + Resistor) x Cap)

However, at low frequencies the coil impedance will be very much lower than the stated figure. Probably in the region of 50 ohms. I would tend to go with a 10u Cap, that then gives you around 79Hz, or just below your bottom E string. It is something you would really need to experiment with for best results.

I never unsolder chips from boards. I use small flush cutters to chop off the legs tight against the body of the chip, then ease the pins out of the board one-at-a-time using an ordinary soldering iron and a pair of tweezers. Solder wick or a solder sucker will then clear the holes with the least chance of damage.

Don't solder the new chip in directly - use a socket. Much safer and easier.

"No such thing as class "A" for guitar amps!"
Humble apologies. I've spent too long in the domestic and HiFi markets - well known for their corrosive and corrupting effect on people

[ef37a]

Yes indeed, chop chips out and fit a socket. Even if you bugger some print, and we all have, a socket makes it almost always possible to repair, might not look good tho!

Class A Will? no harm, tho my flippant remark should probably be explained so as not to perpetuate myths and admens halftruths in the mind of the OP?
Class A is a biasing and drive condition that means neither of the output devices (for they could just as well be transistors)is ever completely turned off by the signal. Another consequence of this is that a pure class A amp would draw the same average power from the PSU whether it was driven at its rated output or not driven at all. This gives low distortion but at the cost of greatly reduced efficiency.

Those classic EL84 amps such as the AC30s were indeed biased to operate in class A for much of the time but as the drive got to some 16 watts or so the working point of the valves shifted and they did in fact pull more power from the supply (and thus was born the myth(?) of "sag"!). Check the cathode volts of any EL84 cathode biased amp and you will find the 10volts or so under no signal conditions shifts to about 19-20 under heavy drive..THAT ain't class A! (and as for "class A" mic pre amps..don't get me started!).

Dave.

[CaptainChoptastic]

OK - I've taken the time to dismantle my amp, and have discovered the following:

Contrary to what I previously implied, although the EL84s are Sovteks, only V1 in the pre-amp is a Sovtek (7025/12AX7WB). The rest of the pre-amp valves have a logo on them of "Ei" in a circle, and the text Yugoslavia ECC.83. Not a brand I'm familiar with from my recent investigations.

I removed the reverb tank and measured the DC resistance across the input and output coils. To verify my findings I went right inside the tank, pulled off the molex-type plugs that mate the external sockets up to the drive/recovery coils, and measured the resistance at the pins of the coils directly: the input coil is fine, returning a DC resistance of around 25-26 ohms. It's the output coil that appears to be open circuit.

Lastly, the construction of the amp is a bit of a hybrid, as you might expect from this generation of valve amp: there's a mixture of PCBs and point-to-point, with the valve bases being mounted on the chassis and some of the valves' associated components wired directly across the pins. What's especially unusual in my eye is that the main PCB is both through-hole (for the components on the top) and surface-mount (for the components underneath). The TL072s appear to be of the latter type, meaning that to get to them will mean removing this PCB from the chassis, and that will involve removing all the knobs from the pots, and the nuts and washers from the pots and jacks. And then I might have to phanny around trying to unsolder SMT DIPs (assuming I can easily source replacements).

Given this, I think my plan is to replace the valves with TADs and plug in a new reverb tank. I think that trying any of the mods/repairs we've discussed might be more hassle than it's worth. Maybe something to look into at a later date.

I suppose my only question from this is whether or not it's worth replacing the reverb tank at all? Does the blown output coil suggest other faulty circuitry which might blow the coil in the new tank, or is it more likely a symptom of age/gremlins?

Cheers,
Si

[Folderol]

Hmm all rather an embuggerance (as Mr Pratchet would say).

I think sorting out the valves has to be the first priority. You can decide about the reverb afterwards if the amp as a whole comes up to expectations.

Don't even think about changing the TLOs if they are surface mount. Without the proper tools you'd be in for a world of pain.

Very unusual for the O/P coil to go an a tank. I suppose the following chip could have latched up its input, but I can't recall having heard of that.

Am I right in thinking you said there were actual pins on the coils themselves? If so, there is more testing (and a possible recovery) you can do with the aid of a magnifying glass, a razor blade or fine craft knife, and a steady hand

Looking closely at the pins you should see a very fine wire going from each of these and disappearing into the coil former. You need to carefully scrape just the insulation from the top of these wires - trying to not disturb the wires themselves. Next, measure across these points. If you get continuity, then moisture has managed to creep in right at the soldering to the pins and corrode through the wires.

My usual way of dealing with this is to solder a short, very fine wire to the pin itself, then with tweezers or thin pliers bend it down till it lays along the top of the section of wire you just bared. A quick, gentle dab with a hot iron and fresh solder should then do the trick. This is an exceptional situation where I clean the iron completely, put solder to the iron then immediately, iron to the joint. Cored solder usually actually has too much flux for this sort of operation so doing it this way gets rid of some of it.

Good luck!

[CaptainChoptastic]

An embuggerance indeed!

Anyway, my valves turned up this morning from TAD, but I've slightly gone and embuggered myself (if that doesn't present too uncomfortable a mental image...) with regards to the reverb tank:

I thought I'd go ahead and order the reverb unit at the same time, to save on two lots of delivery costs from Germany. Of course, so caught up was I in the checking of i/p and o/p impedances, that I forgot to check the physical size of the thing. Turns out it's about twice the length of the unit I'm replacing! I'm going to put that - and any spelling/grammar mistakes in this here post - down to this flipping head cold I've been nursing for the past few days...

On the plus side, it's not a complete disaster. The new tank will physically fit inside the combo, it just won't fit inside the old reverb's vinyl bag.

Any idea if it's OK to just screw the new tank directly to the base of the combo? There's a rubber grommet/metal collar mounting point at each corner of the tank, so I'm assuming it's OK. Will it affect the sound over stuffing the tank in a bag, notwithstanding that the new unit will sound different to the old one anyway? And not that I can remember if I liked the sound of the old reverb or not, it's been that long since it was working.

[Folderol]

Oops
I've seen them with and without bags. I'm not aware of any acoustic reasons. I think the bag is just to keep the crap out. Mounting it upside down should take care of that though

P.S.
Don't overtighten any screws on those grommets, only just enough to keep the thing in place.