TSC Light Still On After Tube Replacement

Hello There,

So I bought a Tubemeister 36 form Craigslist. When I fired it up I noticed the sound was a little treble heavy and then noticed that the right most TSC light was on (closest to power). I planned on replacing the tubes anyway, so ordered and installed a full set of JJs for poweramp and pre-amp tubes. Got them all installed and fired it up again and the same light is still on I am wondering what my next step should be. My first thought is that maybe the TSC has to be reset or something, but am not sure. Any help you can provide is appreciated. Starting to wonder if I might have been ripped off, if there is something else wrong with the amp.

If it's any help I had a similar problem with my TM36 when I put in 4xJJ EL84 replacements. I fitted them and tried it out, no problem. So I decided to burn them in for a couple of hours and left it on standby. When I came back and tried it again, nothing! The TSC on the back was now reporting a duff valve. Be still my beating heart!!! I just switched it off, waited a few minutes and ran it up again. It worked. Running the TSC plectrum test showed the valves in good balance and I haven't had a problem since.

Has yours shown the same one off behaviour and you're not using it now because of you're worried about the fault, or is it a permanent problem every time you run it up. It is possible you have been sent a rogue valve. I would first swap the outer pair over and see if the problem moves with the valve or stays with the socket.

Thank you for the response.

So I took your recommendation and swapped the two outside tubes, and the same light still comes on.

All of the tubes themselves light up, so they are all getting power.

Not sure if it matters but when test it I get 10-13 flashes, not sure if that matters.

I am wondering if maybe it is just that sensor that is wonky?

I also noticed that the metal shield on the V1 tube is missing. I think they guy who had this before me is not telling me some things about the amp.

I also tried playing through it and it works. The cleans are still a little treble heavy...but maybe that is just the amp. The distorted channels sound good. I am just wondering if I am getting the full tone and power if one of the tube lights is still on.

All of the tubes are lit up physically so does not look like power is not being sent to the one.

The tubes lighting up is a separate issue Kwestin.  The heaters for the valves almost always have a separate supply, often just AC from a dedicated tap on the mains transformer.  This means that they will all light up as soon as the amp is switched on.  They stay heated up at all times as heating up and cooling down is the main area of stress they will encounter and it shortens their lives.  Hence, when you turn on Standby all you have done is to remove the high voltage supply from their anodes, the heaters still chug along as normal and the little chaps glow happily.

This is from the manual:

One LED lights up continuously: If only one LED lights up, then the tube assigned to this LED is not delivering enough current and has been shut down. If the LED does not extinguish after a few minutes, this tube must be replaced.

Assuming that describes your symptoms accurately, you have done that.  And when you swap the valves over the problem persists in the same socket so it shouldn't be the valve.  Unless the indicator for the opposite valve is faulty.  Do you see all 4 LEDs light up when you are in standby?  If so then the indicators are working.

As a final test for your valves, try swapping the inside pair for the outside pair.  See if you still get the problem occurring in the same way then.  Make sure you have the full 36W setting selected, (all power soak lights on the back panel extinguished.)  Your amp should have no LEDs showing.  Then select 18W and a pair of the LEDs should light up.

Having 10-13 flashes is not a problem.  The important fact is to have each pair showing similar numbers of flashes.  In the manual it says that 13 flashes shows a valve with H&K rating 5 and with 17.2V bias.  This is right in the middle of the range.  There should be a difference of no more than 4 flashes between the valves in each pair for best sound.  I would count the inner pair and the outer pair separately, your eye can be fooled so simplify the test.  Note, a mismatch in the count is not a problem which will damage the amp, only impair the sound.

The valve cover missing will not harm the amp either, but it will make it more prone to picking up noise.  Search on ebay for "12AX7 screening can" and you'll find a few cheap ones.  You don't want the valve base, only the screening can.

On the last score, too much treble, check out the other threads here, there are a few which will advise you on this.  Speakers are crucial and the wrong ones can create a really fizzy spiky top end.

Do you have a copy of the manual?  If not you can get it here:  http://hughes-and-kettner.com/wp-content/uploads/2014/03/BDA_GrandMeister_1_4_7spr.pdf

Hello,

Yes I have the manual, that is what I have been using to guide and troubleshoot the problem. I tried switching the power tubes around and it is the same problem, they are a matched quad.

When I turn on the power soak no matter what all but one of the LEDs lights up.

Think I got sold a lemon. I guess I have to try and find an amp tech, or see if H&K can help me out. This will be the last tube amp I buy used, would have been better to buy new so I can get a warranty. The fact the screen is missing indicates someone was fiddling with the amp at some point so think the guy I bought this from was well aware of the problem.

OK another thing I just noticed, when I play loud like on a lead channel the light turns off....

The light going off when you play hard might be a normal thing, I'm not sure.  In a class B amp, (and class AB as we have is almost the same), each valve is only working for half of the signal with a tiny overlap around 0V to smooth things out, and being off for half the time might be enough to shut off the bias detector.  If we had a schematic we could help but they aren't out there I'm afraid.  Good to hear you can still use the amp though.  If you get three LEDs lit when the power soak is on then I would have thought the amp would have cut out if there was a serious fault.  The matching pair of LEDs is lit because their two valves, (probably inner I think), are switched off to drop the power selection down to 18W.  The other one is supposed to be on because the TSC has cut that valve off but it sounds as though you still have a working amp.  There may just be something causing that LED to light up when nothing is actually wrong.

I think it looks like a trip to the tech might be in order.  Pick a good one, don't go somewhere just because it is cheap!  If there is a problem and it's easily fixed this might not be as expensive as you would first think.  It might still turn out to be a bargain depending on how much you paid in the first place.  I would try asking H&K about it first.  The advice most people seem to give here is to use H&K's Facebook page.  I don't know about that, but if you think about it, it will make your problem public and might induce them to reply a little more, (their reputation is pretty poor at getting back to you with advice on a problem).

Sounds like you could be right about the amp having been fiddled with, but I would think this may have come about because there is something that already looked faulty, rather than the fiddling  has caused a fault.  Most people figure, "if it 'aint broke don't fix it"!  Don't be put off altogether buying valve amps secondhand.  I have both my TM36 and GM36 bought that way and they are both mustard!  It's a question of learning what to look for and then not being frightened to say "No"!  I'm in the UK and Craigslist doesn't seem to be as big over here yet, but we have Gumtree which seems similar.  I wouldn't use it for buying anything expensive and delicate which I couldn't see first.  The reason is that the site doesn't give you any support in the event of buying a pup!  Ebay is a little different, there you have some comeback if the item doesn't match the description or turns up faulty.  They may not be absolute but they do help.

Try the Facebook route to get H&K.  Give them a full description of the nature of the problem and wait.  Keep us up to date here, it may help someone else to know what is going on.

So I have an update on the issue. I reached out to H&K through their website and got no response. I reached out to them on Facebook and got a response, explained what I have done and the fact the light now goes out when I play, they could not explain it and asked me to contact their US distributor to help find a tech:
Yorkville Sound, Inc
4625 Witmer Industrial Estates 14305
Niagara Falls Tel.: +1 7162972920
hk.usa@yorkville.com www.yorkville.com

...I got no response from them either. I reached out to a tech here in Portland, OR who was incredibly knowledgeable regarding tube amps in general, I learned a ton just talking with him. He does not think there is anything wrong with the tubes or anything as the amp sounds great, gets plenty loud and since the light goes out when playing thinks it is a glitch in the TCS sensor. He suggested I not worry about it, especially since I am not going to get any help from H&K and if I do it will probably cost a lot of money to fix something that does not affect the sound of the amplifier.

So, some things I have learned through this process:

1) Don't buy tube amps via Craigslist, if I went through Reverb or Guitar Center I would have some recourse to get my money back or exchange it. I have usually had good luck with Craigslist for gear, but think for bigger ticket items like this I am going a safer route.

2) H&K makes a killer amp, but the tech support process needs to be improved. It is great if you buy new and have a warranty I guess, but even then some of the lines of communication and their distributor in the US could use some work

3) JJ Tubes make a big difference in the sound of the Tubemeister amps, I am really happy with the tone now that I have things dialed in and it integrated into my effects unit.

4) A big geekier, but I have my amp setup in stereo now using the 4 cable method with my HD500...I set the other output through a .44 Magnum power amp pedal to another cab...it sounds great. This approach allows me to use the H&K tube preamp, outputs that through effects loop where I then add reverb, stereo delay and other stereo effects, run one side back into the effects loop of the H&K and the other out to the other power amp and cab. It is still a pretty compact setup using two 1x12 cabs.

I have a similar issue in a TM18 which may lead to how this issue started before you bought the amp. No LEDs were lit before tube swap. Replaced stock china tubes with New JJ's and The amp rejected them. First a crackle followed by Varying volume and electronic burning smell. We shut off the amp immediately! We tested the JJ's and they were working fine, some better then others. We put the Stock Power tubes back in and the Right LED lit up solid meaning "BAD Tube" we tested it and The stock China tube was even better then the new JJ's lol (not so funny though). We also noticed that the LED light would go away when the amp received the guitar signal and would come back when there was a pause in playing.

At this point we put the JJ's that tested GOOD back in with the same outcome as the re-installed stock tubes. Right LED Solid that goes away when receiving the guitar signal. Volume sounds correct, Tone has a bit more gain on the Clean CH. (Fender Bassmanish w H&K sparkle) but Sounds Good. So I am at the point where is there an issue with my Amp not the Tube so the TSC is throwing a Code, Or did the TSC simply malfunction and blew a portion of it circuity. Because the amp sounds fine, I believe its just the TSC and not the amp its self. Which i'm fine with because i'm out of the warranty period.

Any Updates whether your H&K is still operating Fine? Or will I need to have this issue looked at to prevent further damage as its my practice and gig amp. Love this amp, everyone loves my tone so I do not want to move on from H&K. Hope this has given some insight on how your issue originally occurred. And hope to hear some insight whether this is a issue I will face later down the road. Hopefully not on the road... .

Do NOT like the sound of the burning smell!   Sounds very much to me like something very bad happened on first switch on.  It's possible you had a bad valve.  Very occasionally there can be minute bits of debris left inside the valve after manufacture from the formation of the getter in there to attract gas molecules.  Usually reputable suppliers test and burn in their valves and this aspect is sorted in the first few hours of running.  If yours have been supplied in tested condition it's unlikely to be this, but it's always possible that damage occurred in transit.  It may be enough to just shove the valve out of range for its type, maybe running way out of whack on its current.  We can't really know without testing again.

Alternatively, it could be the new valve pins didn't make contact properly and spluttered and the resulting arcing somehow has caused a fault in the bias control circuitry.  That is solid state of course and will not cope with high voltage switching currents like another valve would.  It may have only affected the way it displays its status with the LED, or it may be more sinister.  If you can look at the pins on the new valves can you see any evidence of any tiny scorch marks?  One valve, one pin, small area, big ask.  That would be tiny as it would only be on the portion where the pins actually made contact, you may even need a magnifying glass to see anything, (and it may not be that at all of course).

Sounds like when you now put a signal in there it generates current through the valve which the sensing circuitry is then reasoning contains a bias current and temporarily says everything is apparently ok.  The fact that you may have the valve still working even when it is marked as 'in a bad state' is obviously a contradiction.  I would have expected the pair to have closed down.  If there is genuinely no bias in one valve then you are running the amp in an unbalanced state with DC through the output Tx.  This may not cause any long term problems but isn't how it was meant to work.  And it shows something out of whack in teh control circuitry at least.

How does the amp react to the magic plectrum test?  You know, push the plectrum into the slot on the back and count the pulses for each valve?  Does that still work and show reasonable results or is it also SNAFU?

I would think that ultimately your best bet is to assume that there is a fault and have it looked at by a proper H&K knowledgeable tech if you can, to get an estimate of costs of fixing it.  Sorry if this sounds a little disrespectful to many excellent non-H&K techs but, in an amp with this sort of unique control complexity, I would personally prefer to go to someone who has the correct full documentation and has had some official training however brief on what does what to what.  It's basically just a valve amp with a couple of wrinkles and personal foibles but, it's + an extremely involved, specialist programmed, microprocessor controlled section which mostly cannot be serviced or repaired, only replaced direct from H&K.  It sounds like that second section is where your problems may lie.  If I am right with that, it is on the small PCB mounted on the end of the Main PCB at right angles to it.  It's obvious once you look inside.  If you do open the amp up to have a look at it, see if there are any frazzled wires or scorched components on that small board, or if it smells at all, (the burning smell lasts for quite a time close to the damaged components).  Also look at the two MOSFET power transistors Q14/15 laid flat on the board near one of the output valves, and their resistors R89/91 between them and the valves for signs of burning.

Any decent tech would be able to deal with the amp bits, they are similar to many amps of its type, and if it lies in the unique parts most would just make an intelligent guess as to where the fault lies then immediately change out a board, (if they can get them).  As long as they aren't clocking up hours trying to fix a digital board manually I would guess you would be at the bottom end of the charge market, parts + minimal time.  My worry would be as you asked, that this may lead to further damage through continued use.

Just take trained advice first of all.  You could even get in touch with H&K via their Facebook page and give them a quick rundown of the problem and see what they say.  That's a search for 'Hughes & Kettner Product/Service' in Facebook.  They respond to a query faster there than by email.



For anyone else reading this, we can see it is an ultra rare occurence for new valves to cause a problem on fitting as this has not come up before as far as I can see.  Now it has, it highlights something that had never occurred to me to say before as most of us would take it for granted.  With new valves, check and if necessary wipe off the pins before fitting.  You shouldn't attack them with a file or emery, just give them a wipe with a cloth to remove any grease or obvious tarnishing.  (No arguments about gold plated pins please!)  That way your new valves will bond happily with their new home without upsetting the neighbours!

Geez, thanks... Yes I am in contact with HK first through Facebook now waiting for Service from Germany Techs they directed me to, though afraid I wont hear back from them. The Bias test on the back works 13-14x +2 on the right which is the same value that the LED glows. Would it make since to have my amp looked at locally, particularly where the mishap happened before I looking for a specific HK tech. Also the amp cost 500$ new, at what price/cost% would it make sense to just move on and use it for recording/practice purposes and buy a new amp for gigging if its deemed not reliable and costly to fix. I know that is up to me but with your knowledge, all and any advice is a big help. I have rehearsals and 1 gig this week and my back up would be a 120w 5150II which I haven't used in ages. My tone is dialed in with the TM18 even with the new JJ's and mishap. The HK still sounds mint so I feel it is hard not to use it seeing has it operates fine other then the tsc  

One bit of evidence I would like to share with you is that when we took out the stock tubes the pins seemed not to be perfectly straight, slightly bent out of shape. if that can point us in any direction. Wishing I had replaced the tubes while it was still under warranty now.

Update: Switched back the Power tubes at home to the stock china ones to compare the tone if the differnce was in the amp or tubes. They are Sovtek not JJ, Pre amp is JJ. Tone change was in the Sovtek Power Tubes and not the amp its self so that is at least a possible sign that the amp may not have been affected. I actually prefer the China Power tubes, think the Sovtek were to bluesy for my Metal needs (too much breakup) Same situation with the LED though and No sign of heat on the Pins either.

From H&K

"Hello Lukas,

sorry to hear you have trouble with your amp.

We have not observed this behavior yet but we have a assumption:

Sometimes tubes need to “burn in” that means in the first minutes of their lifetime some impurities can “burn” in the tube. This could cause a short over current.
This over current probably results in a heavily loaded screen grit resistor (which could cause the smell). Further this screen resistor can decrease or increase it’s resistance so the TSC shows a bad bias.
When playing, the TSC does not work anyway so it’s normal, that the LED does not light.

So please let your tech check the amp. He should check the screen resistors and all parts in the Power amp.


Freundliche Grüße / Kind regards
Simon Marx
Leiter Service / Manager Customer Service"

Told you those guys are good!  Just the fact that they have passed it on to someone tech who has looked into it properly is an indication of something VoodoJeff has always maintained, their customer support is top class.

Yes, their explanation makes sense.  I suggested the 'valve burn in' idea myself earlier when I talked about bits of debris being left after manufacture.  The screen grid resistors are R92/93 and they are 1k 2W.  You will find them directly next to the valve holders for the output valves on the side towards the fuses and big power supply caps.  If they have been badly scorched enough to change their value significantly it should be obvious.



This is a commonly available pic on the interenet of the TM18's guts.  The original poster is talking utter bollocks when he says the grey resistors are the screen grid resistors, they are the power soak components!  The two resistors you are looking for are the ones ringed in red which are sitting behind them on the other board running from top to bottom rather than across.

You may even be able to see them through the ventilation slots under the amp, it's awkward with the lighting but if I get the angle right I can see mine in the TM36.  If not you must make a decision whether you are able to remove the bottom panel for a look see or whether to take it to a tech and get him to investigate and replace it/them.

Keep us up to date.

I had a similar problem with my TM18 - I tried several sets of tubes all with the same problem

I replaced the last 12ax7 (i.e. not the input tube - my rational being that would be the phase inverter and would be sending signal to the power section, if one half of that wasn't working correctly maybe that would confuse the monitor circuit). I have no idea if that actually makes sense for not , but it seems to have worked.

'Streuth Streuth, that's excellent thinking!  Never occurred to me to question that area.

I can't see at first glance how it would work but in the TM18 the PI stage before the output valves is a single triode cathodyne "concertina" type.  (Technical lowdown here for anyone interested: Cathodyne Phase Inverter).  It generates the two signals for the output valves by being a cathode follower with an in phase signal from its cathode, and with an equal anode load resistor sitting on the same current it generates an equal out of phase signal at the anode.  If the burning smell came from one of those resistors and it had gone out of spec, (they are 56k 1W), then the stage would be out of kilter and the valve certainly could not balance it up again, but that shouldn't affect the bias conditions.  There is also the valve itself of course, if that is doubtful....  However if it has sorted out your problems, it's an easy task to swap the preamp valves to see if things improve.  If there is a duff valve it will go elsewhere and cause other problems there but the output could settle down with a better PI in place.

Here is a better pic I sourced to see which they are for investigation:





EDIT: Another link for the higher res full size picture of the whole underside:

TM18 Underside

Half way down the page. Looks like these issues are out there!

Update: Took my amp in to my local Tech and Just as Bordonbret and HK tech said, The Screen Resistor blew from the burn off of a new tube. Waited a week for the part. Otherwise was a cheap and easy fix 65$ for Labor and Tax 1$ for the Resistor. Been playing my amp for a week now. Finally got to hear her with the new tubes (Stock Power/JJ Pre amp). JJ's Added a bit more body to my tone while keeping the overall tone of the amp w some slight tweaks to the amps EQ and my 10 band MXR. Still Glassy cleans but no longer sterile gain.Boost is nice and Beefy now which I use as my Metal tone. Thanks for all the Help and assurance!

Thanks for getting back to us with the update Nin. Good to hear you're back thumping out the riffs again. Isn't it a joy to see that the TSC was only doing its job and wasn't damaged as easily as we thought it may be. The credit has to go to H&K who came up with the original assessment of that screen grid resistor. Told you those guys were on the ball.

Just wanted to update, the TM18 isn't my main gigging amp so I wasn't totally sure that replaceing the phase inverted truly fixed my problem, but gigged with it on the weekend with no problems. So sure seems like that was the problem with mine.

This is an old thread, but am responding since I just went thru similar problems with a used TM36 that I bought online this summer, where TSC kept showing only 3 out of 4 tubes delivering power in 36W mode despite a brand new set of JJ EL84's, and where going from 18W to 36W mode gave no perceptible volume increase. Off to the local amp tech I went, who discovered that the problem lie in the analog portion of the bias circuitry. One tube socket had over twice as much bias voltage as all the rest, which I believe he was able to fix by simply replacing a bad resistor. Everything's working fine now! Might even keep this amp instead of the Grandmeister 36 I also bought shortly after...

Ok so if bordonbert is correct and I have no reason to believe that he is not,

If the PI is a "Cathodyne Phase Inverter" then why are we paying extra for a balanced 12AX7 for the PI?

Craig

It depends which model you have Craig. I can confirm for definite:

The GM36 is a dual triode Long Tailed Pair type of PI as it has 3 x 12AX7s to work with giving 6 triodes in total. There are 3 triodes in the gain stages, a cathode follower before the tone controls and the two triodes used in the PI. (The cathode follower is actually very significant as it introduces a characteristic type of valve distortion that no other stage is really able to.)

The TM18 is a single triode Cathodyne PI as it only has 2 x 12AX7s to work with giving only 4 triodes. That gives it 3 triodes used in the gain stages, no cathode follower to drive the tone stack, then the single triode PI.

I do not have absolute definitive info on the other units in the GM/TM range but those two I can be absolutely certain about. It is usual to follow a family approach with this sort of thing. That is, if the GM36 has a particular setup the TM36 is very likely to have the same, and so with the TM18 and the GM18.

And you're right, in the case of the single triode PI models there is no advantage in getting a balanced 12AX7.

Thanks for the explanation bordonbert, mine's a TM36 combo so I guess I didn't waste an extra £2 on a balanced valve.

Craig

I'm having an issue at the moment on the tubemeister 36, where the 2 inside lights of the TSC are on while playing. All 4 lights are on during standby mode though. I tried replacing the 2 middle tubes but still no luck. Is it likely that the new tubes I bought are faulty too, or is there something else which may be the issue?

The simplest things which jumps to mind is how is your power soak set Kev? If you have it set to anything other than full 36W the two valves will be turned off to drop the power so it would be correct to see those two LEDs turned on.