Laney Iron Heart IRT 120H head problem

[Howdy Doody Time]

My Laney valve head has started making a regular noise. What happens is that when it has warmed up for a couple of minutes, it begins to hiss and the hiss increases in pitch until it ends with a pop, then the process begins again, Hiss - pop, hiss - pop, hiss - pop , making the thing unusable.

It's like a capacitor is filling up, then discharging, over and over.

Anyone have any ideas as to what it might be? Much obliged for suggestions.

Howdy Doody Time.

[Howdy Doody Time]

Mmmmm.. There was a massive thunderclap recently and I mean dogs and cats terrified. I heard a sizzle a millisecond before the crash seemed to come from a wall socket. The next morning my shower had tripped and wanted re-setting. However the TV which was plugged into the socket was OK.

I checked where I'd plugged the Amp in and rather stupidly, I had not plugged it into one of the outlets from the battery box things (I forget what they are called) that protect from surges and spikes.

So now I'm wondering if that huge bang recently fried something in the Amp. Warranty useless I suspect.

[ef37a]

Valve gear, especially big amplifiers is usually pretty immune to mains spikes, even big storm induced ones. Any damage sustained is usually primary side of the mains transformer so, IEC socket black, mains fuse black and shattered, mains switch black, possibly blown asunder but the secondary circuits usually survive unscathed especially in this case where the amp was not switched on.

But I am a little confused as to the timeline here? Was the amp hissing and popping before the storm and is it now dead? If the "hiss/pop" is post flashing blade then yes, likely a valve has been damaged, maybe a resistor burned out.

If the amp is still working you could be lucky! With the amp disconnected from the mains, remove all the small valves (mark where they go with a Sharpy first) Then power up the head. If it still hiss/pops you have a dud output valve or/and other damage and since OPV replacement requires a re bias, that is tech time. If all is quiet, replace the valves one at a time starting with the one closest the big ones.

As far as warranty is concerned, YOU have done nothing wrong so if it is faulty just send it back. The retailer will soon give you grief if they suspect there is "wriggle room"!

Our 13A ring main system with fused plugs saves a lot of kit from storm damage.

Dave.

[Howdy Doody Time]

Much obliged ef37a, Amp was OK before the storm, and now has hiss - pop. I notice a bit more about it now, the hiss does not increase in frequency, just in volume, then the pop. The amp still works fine during the hiss, then the volume dips during or right after the pop, and returns to normal volume a fraction of a second later. Then the cycle starts again.

I have come to think the storm is a red herring. Nothing else is affected (the shower heater has been known to trip before and is easily reset)

I bought the whole rig very recently second hand (but looking so brand new I think it must have been a demo unit) from a clearing shop used by the big local Music Store. I never tried it in the shop before buying, but it worked fine when I got it home. However, I never left it on long enough to activate the hiss-pop until a couple of days ago when I decided to sit down and explore it with me new Gibson LP.

I will try what you suggest, which sounds very logical and sensible, and let you know the outcome.

Thanks again Much obliged.

[ef37a]

Ok HDT, if the fault does prove to be a pre amp valve, probably an ECC83 AKA 12AX7*, you might find the offending article is fine next the the OP valves as the Phase Inverter but pops in other situations.

I don't know what the consumer law is out there but here, any registered business has to give you a reasoanble warranty of 12 months (but they can claim just 90 days on valves) so if it is not just a small bottle worth finding out. Just a re bias and 4 new OP vlaves is going to set you back over £100 and if fault tracing is involved, somewhat more I would think.

*I always found the TAD 7025 a quiet, reliable 83 equivalent and not expensive at around a tenner. Do not in any case pay silly money for "specially selected" or "Cryo" valves, never seen a shred they were any better than decent, standard fair. Avoid "NOS" as well since they probably ain't!

Dave.

[Howdy Doody Time]

I took the first little one out, they are all ECC83's and no popping from the Amplifier. So I put the first one back in and the popping came back.

So I put the first one in number four, and number four in the first socket, and it's warming up now. So far no pop.

I ordered four new ones from Lazada at 300 Baht each (7.20 GBP at current prices - used to be six quid when I first came here)

Still no pop.

Popping is back. So I'll juggle them around a bit. Lazada will deliver 20th April (has to order from overseas) If no luck, I'll replace the lot when they come. Meanwhile I have some small amps I can be playing with.

The Laney 120 Manual reckons all valves can just be replaced, including the output valves. There is a Bias switch on the back which one selects according to the type of output valves being used, so maybe in my case there would be no additional bias adjustments to be made by a tech ?

Number two is now number four and what was number one in now number two.

No pops yet.

Pops back.

[ef37a]

Sorry mate Should have said you don't need a full set of pre amp valves!

Two would do, one to replace the popper and a spare. No matter, you seem to have got a good deal.

Regarding the biasing, some amp makers bias so cold that there is no need (usually!) to check and adjust it although the practice can result in an amp that has little or no clean sound. Not likely I admit with a 100 wattter!

Personally I would always check the bias because modern valves can vary a great deal and it is possible that one of a bunch could "redplate" and fail rather quickly. If you ever do replace the OP valves run the amp in a dark room for an hour and check the anodes remain slate grey.

Dave.

[Wonks]

The dark room is just so that you can see how hot the power valves are glowing. It's not because it has a headache and needs to lie down.

Don't forget that the power valves need to be matched (which is a normal buying option). So you should be able to get a matched set of four. If not, then two matched pairs is better than unmatched. But install the pairs together so that they are next to each other in the line.

[Sam Spoons]

OP valve pairs on a Boogie mk4 are inner and outer (or 1+4 and 2+3). If you can't get a matched quad check which way round they are on the Laney.

[Wonks]

Sam's probably right. Laney simply say replace with a matched quad set. The power valves are labeled V9-V12 in the IRT 120. In the IRT 60, the two power valves are V10 and V12, so it seems likely that the inner two are one pair, the outer two another, though Laney don't specifically state this.

[Howdy Doody Time]

OK, well I ordered a set of four Power Valves and four of the preamp smaller ones, so I might as well change em all out when they arrive. My money says it will still pop, and a 30 Baht capacitor is to blame - not because I know anything about amps, but I do know my luck

Much obliged to all for assistance, - Ta very much

[ef37a]

Now, I know this was a one off test, once by one person but a few years ago I was given a collection of "matched" EL34s and asked to check how closely they were in fact matched.

Not that well was the answer in that the grid voltage needed to hit 25mA was closer for some samples OUTSIDE of the quads than those in it. As I say, a one time test on a tiny sample but it did make me a bit cynical of matched sets.

One easy safe way to "match" output valves if you have a DMM and access to speaker terminals is to measure the residual hum and note the reading. Mark the top of the valves with a sharpie and then swap the outer pair. Power off of course and use a rag! Power up and let it settle for 5mins. Hum worse or better? You are of course looking for minimum hum voltage. You can then try various combinations. (of course, SOME nice amp peeps give you not only a bias pot AND a sense resistor to measure Ik but also a balance pot! )

Dave.

[Howdy Doody Time]

Dave

What would be the effect on the audio (at studio volume levels rather than club blasting) of a badly matched output quad set, or would the problem be more likely to upset the amp / damage the valves ?

Not being Guitar Amp savvy, I tried all sorts of stuff last night - some of which appeared to work, but in fact only delayed the onset of the hiss-pop.

For example the Cab is a Laney thing which has different input jacks for 4 Ohm 4 Speakers 8 Ohm 2 speakers, 16 Ohm 4 speakers and 8 Ohm 2 speakers while the Amp Head has outputs for 2*8, 2*4, 1*16 and 1*8 and some configuration for stereo via a slide switch.

I had been using 4 Ohms out to 4*4 on the Cab, using a patch bay lead because it was a nice short length. Then I switched to a high quality guitar lead for the audio out, and used the 1*16 out to the 16 Ohm 4 Speaker in on the Cab.

Also I used another of those Power UPS things solely for the Amp connected to the only guaranteed earthed circuit (because I made it using a long copper rod driven into the ground)

I very nearly posted success because the hiss pop took about an hour to appear, but appear it did.

[ef37a]

The effect of badly mismatched output valves would be excess hum and increased even harmonic distortion*. You are unlikely to hear the latter in a guitar amp context, might even like the effect!
But even a gross mismatch, three valves say, will do no damage (in a fixed biased amp. Cathode biased another story) but the hum would be horrendous so you would not continue to run it.

I am sorry the hiss/pop has returned, since you are getting a complete set of valves the quickest thing would be to fit them all (number them!) and then leave the amp running. If the noise returns you obviously need the ministrations of a tech'.

The speaker loading on the amp is not that critical, so long as the load is within 50% or so of the setting on the amp you will be safe. If you drive the absolute be-whatsits off the amp try to stay bang on "matched". Not likely with a 100 watter as you would be very unpopular!

*It is often said that good matching/balance reduces even harmonic distortion and so it does but the balance has to be extremely good and over a wide bandwidth. Not something you will get in any guitar amplifier!

Dave.

[Wonks]

Basically, each valve in a pair is ideally amplifying half of the output waveform. One the positive half, and one the negative. But each valve has a different value within the tolerances allowed, so for a given bias value, it may conduct for more than half the cycle (a 'hot' bias), or less than half the cycle ('cold' bias).

With well matched valves, adjusting the bias should allow (in theory) for each valve to produce exactly half the cycle, and so produce exactly the signal passed to it from the preamp.

With mismatched valves, one valve can be set to produce exactly half the waveform, but the other valve will either produce less or produce more than half, and so introduce distortion of the output waveform. With a small mismatch, this only affects the signal near the zero crossing point, so isn't that noticeable, but the bigger the mismatch, the more noticeable it gets.

[Howdy Doody Time]

I love this forum - my first foray into Guitar Valve Amps, and I'm getting one to one tuition from experts. Thanks so much Dave and Wonks!

[ef37a]

I love this forum - my first foray into Guitar Valve Amps, and I'm getting one to one tuition from experts. Thanks so much Dave and Wonks!

There is one gitamp book I can recommend (many are crap) Valve pre amps for Guitar and Bass by Merlin Blencowe.
Yes there is SOME maths in it but you don't need Calculus (or I couldn't handle it!) just simple equations and graphs. You don't even need the little maths there is because Merlin gives lots of wee schematics with values and tables.

I DO wish he would buckle down and do power stages before I am totally ga-ga!

Dave.

[Howdy Doody Time]

GOOD NEWS!!

The power valves arrived this morning from Lazada. I changed all four out for the new ones, powered up, and waited...

Now it's been running about half an hour, and it's quiet as a church mouse. No hiss, no hum and no pops.

The preamp valves will arrive about the 20th, but I'll just store those away.

The valves came in a pack of three, plus a single in a different package. So no hope of matching them. Nevertheless I am not hearing hum, so whether I was lucky, or Laney (since they don't mention matching) must have designed the circuitry somehow to account for mismatches.

Anyway, I want to thank you all for responding, I've always been terrified of valve equipment but your advice and guidance has helped me sort that, and the amplifier out.

Much obliged

Dominic (HDT)

[ef37a]

Good stuff!
When the pre amp valves arrive I strongly suggest you make time to check them.
Just swap out the first valve, usually the most critical for noise and hum. Go through the batch that way and if any seem unduly noisy get back to the supplier. No good complaining 2 years down the line!

I am not surprised the valves "matched" pretty well, that was my experience with EL34s and EL84s. In any case, with 4 valves any differences are averaged out better than pairs.

BTW, keep the old OP valves. They are only ever going to get more expensive IMO and I bet three of them are perfectly ok!

You are right to be wary of valve gear! The stuff inside the chassis takes few prisoners. If people are really stuck I will tell them how to bias amps in a PM but not post the procedure.

Dave.

[Wonks]

The valves came in a pack of three, plus a single in a different package. So no hope of matching them. Nevertheless I am not hearing hum, so whether I was lucky, or Laney (since they don't mention matching) must have designed the circuitry somehow to account fora mismatch.

As I said in one of my posts, Laney do state in the manual that the power valves should be replaced as a matched quad set. It's not made that obvious (nothing in bold type or in any warning section), but it's there. Almost on the last page of the English section of the manual, rightbefore the signal flow diagram.

Just mentioning it for correctness.

Great news that it's working!

[ef37a]

The valves came in a pack of three, plus a single in a different package. So no hope of matching them. Nevertheless I am not hearing hum, so whether I was lucky, or Laney (since they don't mention matching) must have designed the circuitry somehow to account fora mismatch.

As I said in one of my posts, Laney do state in the manual that the power valves should be replaced as a matched quad set. It's not made that obvious (nothing in bold type or in any warning section), but it's there. Almost on the last page of the English section of the manual, rightbefore the signal flow diagram.

Just mentioning it for correctness.

Great news that it's working!

Yeah, Manufacturers put a lot of A saving stuff in manuals! Some will state that you MUST use exactly the right impedance speaker when there is no such thing and it is not THAT critical anyway. Some say use of a power soak will wear out the OP valves. True but no faster than playing 7 nights a week at full chat in a club.

Some warnings are I understand required by law? Electrical safety is paramount of course but I always smile about the SPL charts? The punter has bought a 50W combo with two V30s in it..What's he gonna do?

As far as valve matching goes, a very big unbalance will lead to hum and some reduction in clean power but where balance really matters it has to be much better implimented. Not only DC balalnce of the OP valves but LF and HF balance of the drive from the PI.

Dave.

[Howdy Doody Time]

Mr. Wonks, indeed you are correct:

"Typical output tube problems can include a blown HT fuse, sound lacking in punch, sound lacking extreme highs or low, and low level hum. The output tubes can be replaced singly if you replace them with the exact same type AND grade as factory fitted, otherwise they should be replaced as a matched quad set in the IRT120H, or a matched dual set in the IRT60H"

Nevertheless, the 3 plus 1 thing didn't make a hap'orth of difference, thankfully.

[Wonks]

They often get graded and a number or letter put on the packaging, so they will send out all no. 40s or letter Bs etc.

[Howdy Doody Time]

Well after all that, I plain don't like the amp. It's not that I don't like it really, more like I bought the wrong one, on impulse, and it was fairly cheap, and handy, and big, and impressive looking.

So I bought another one. A Laney L20 Combo. New this time, didn't fancy another round of Valve swapping.

Well I must say I love the L20. Creamy British retro tone and retro looks. Wouldn't be out of place on a mid '60s stage.

Handy thing about the 120H and Cab is that the L20 sits very comfortably on top of it (ok maybe a little high for adjusting the knobs)

Lovely thing.

[Howdy Doody Time]

Aww shucks!

The new preamp valves came today so I thought I might as well change them. So now the 120 has all new valves, 4 preamp and 4 power.

And it sounds great.

What the hell, having 2 valve amps never hurt anyone.

My problem is I have no patience.