The Hughes & Kettner User Forum

Would you like to react to this message? Create an account in a few clicks or log in to continue.
The Hughes & Kettner User Forum

The Unofficial guitar amp and cabinets forum for users of Hughes and Kettner products. We are not affiliated with Hughes and Kettner!!


4 posters

    Tubemeister 18 Plays in Standby Mode - What's Wrong?

    das234
    das234


    Posts : 7
    Join date : 2018-11-05

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by das234 Mon Nov 05, 2018 12:57 pm

    I'm hoping for some savvy advice. I have a Tubemeister 18 that was working just fine for a couple years. Last time I turned it on and tried to use it, there was no speaker connected (oops). I realized that within a minute or less and plugged in the speaker cab.

    Now, the amp plays in "standby" mode and makes an unpleasant loud hum in "play" mode. I don't know whether the problem is related to the brief time I had no speaker connected. It sounds awful in play mode but it seems to sound normal when I play through "standby". Anyway, something's obviously not right.

    I have opened it up and tested the standby switch. With the switch connected in the amp and no power, I get no resistance in play mode and I get 6M ohms in standby mode. When I take the switch out of the unit and test it, I get zero and infinity. While I was inside, I looked around at the various components that I could see and didn't notice any obvious burned resistors, etc.

    The TSC LEDs on the back both come on when I turn the unit on in standby and about 15 seconds later the right one goes out and the left one stays lit. When I switch to "play", both LEDs go out.

    I also checked with the tubes removed. Both LEDS are on in standby. In play, the left is on and the right one blinks.

    Finally, I checked with the two power tubes positions' reversed. The results are the same regardless of which tube is in which position:
    Standby - both LEDs on briefly and after 15 seconds, left on and right off
    Play - both LEDs off.

    I am about as green as can be with diagnosing and fixing amplifiers but I can wield a soldering iron and have built some effects pedals. Anyone have any helpful ideas?

    Khay124 likes this post

    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by bordonbert Wed Nov 07, 2018 9:40 am

    What happens if you use the TSC lights to read the bias current in the valves? By that I mean push the switch slot on the back with your plectrum.


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    das234
    das234


    Posts : 7
    Join date : 2018-11-05

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by das234 Wed Nov 07, 2018 1:17 pm

    bordonbert wrote:What happens if you use the TSC lights to read the bias current in the valves?  By that I mean push the switch slot on the back with your plectrum.

    Thanks for the reply.

    With the amp in standby mode, the right LED blinks 6 times and the left blinks 12 times.

    With the amp in play mode, the right blinks 8 times and the left blinks 12.
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by bordonbert Wed Nov 07, 2018 9:52 pm

    You have certainly done some really useful diagnostic work there and there is not much more I can suggest I am afraid.  Forget the Standby switch, it isn't the problem here.

    The fact that the valves can be switched and the problem remains with the same LED is not a good sign as you are aware.  It really sounds to me as though you have a TSC/bias problem rather than just a valve one but it would pay you to be sure before taking it to be looked at.  Can you not borrow a pair of known good EL84s to swap out to check that for definite?  I wouldn't buy a pair just for this but borrowing them just for a test would really help you.  Any friends have an EL84 amp you could raid or do you have a friendly local guitar shop who would help you out?  This would be the logical next step to take.

    Your slip with not connecting the speakers is not a good one to make.  The GM36 would have detected it and quickly switched to Quiet mode with the internal power soak acting as the load but I don't believe your TM amp has this built in.  Running an amp without any load on it is very stressful and can cause all sorts of problems even to the extent of burning out the output transformer.  That is a distinct possibility unfortunately.

    Other things which could be at fault here are in the TSC circuitry itself and that is processor controlled I am afraid.  Though it is rare the control MOSFETs which sit in the cathode circuitry can be damaged and it may even be possible that the problem is being caused by a fault in the PI circuit which feeds the output valves.  By the way, the Standby switch simply works by turning off these MOSFETs and shutting off current through the valves.  That's a step up from the old method of removing the output valves' anode voltage which actually kills the valves by cathode poisoning rather than increases their lifespan as is widely touted.  Old classic amp?  Don't use Standby, just turn down volume!

    So each EL84 has an independent bias setup with the TSC board controlling the current via that power MOSFET in each valves' cathode circuit.  The PI stage is a single triode type so one output valve is fed from the anode and the other from the cathode.  If one of the DC blocking caps feeding the output valve grids become leaky then they will allow the PI stage to influence the bias on that valve and it may go beyond the range which the TSC can adjust.  These are labelled C18/C19 and are 22nF 400V.  If it is in the TSC control circuitry it would almost certainly mean a PCB swap and H&K won't supply that to you direct, they only work through accepted maintenance sites.  A decent guitar workshop could do that for you.

    I know the idea of fixing it yourself seems a good one but if you haven't got much experience in working inside units like the TM18 it is a tall order to work at the level needed for such an intricate amp.  Most guitar techs prefer to steer clear of them and curse and spit at the design approach.  It's a state of the art piece of modern electronics not one of the old classic 'wet string and chewing gum' designs that they love because you can fix them with a hammer, a screwdriver and the internet for instructions.  And of course, as always, remember that the amp works at voltages which will kill you.  Really.  I mean stone dead!  Painfully!!!  A mains shock at around 220V (only 110V for woosy foreigners Wink ) is a nasty thing to experience.  That's AC and, despite what Edison and his elephant said, AC is much safer.  When you get an AC shock it kicks you away because the voltage is turning on and off and that allows you to release your grip.  A DC shock spasms the muscles into permanent contraction and can make you grip tightly the thing which is killing you so you can't let go.


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    das234
    das234


    Posts : 7
    Join date : 2018-11-05

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by das234 Thu Nov 08, 2018 11:52 am

    I might be able to track down some EL84s to try.

    I also have another piece of diagnostics to report. Someone I asked about this thing suggested I measure the resistance between pins 2 and 3 of Q14 and Q15 with the power off. I was told a high resistance would be a good thing. Q14 read 8.15M ohms (which I would consider "high" resistance) but Q14 was only 265 ohms (which, in contrast, is quite low). You seem to have a much better understanding of this circuit than I do.
    Does that mean anything to you?
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by bordonbert Thu Nov 08, 2018 1:56 pm

    Q14 and Q15 are the MOSFETs in the cathodes I talked about. If you have one of those damaged it would account for it and it has been known to happen before though it is not common. I've never tinkered with that part of this circuit but That 256ohms seems low to me. It looks as though you may have taken out one of those MOSFETs when you ran the amp without a load. The voltage spikes generated by running it with an infinite load are beyond what the valve and transformer and associated parts should see.

    The MOSFET test would really need to be performed with the MOSFET outside of the circuit to be more rigid but with one looking correct and one bad it seems very plausible. You do seem to have experience in this area so if you are going to try a replacement I would recommend replacing both here. Damage to one could imply the other has been stressed too and you don't want it to go in the future so you have to fix it twice. The MOSFETs are STP10NK60ZFP 600V 10A items and they are widely available and very cheap over here in the UK. It depends on your confidence in your ability to solder on PCBs but you sound pretty confident. It's another line to consider.


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    das234
    das234


    Posts : 7
    Join date : 2018-11-05

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by das234 Thu Nov 08, 2018 6:08 pm

    Oh, if only that's the solution that would be awesome! I'll get some on order, pop them in and see what happens.
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by bordonbert Fri Nov 09, 2018 1:12 am

    Just sat and thought about this a bit more and there is one thing I should have checked on with you.

    When you measured your resistances you did do it both ways round for each junction didn't you, swapping the probes of the meter? The MOSFETs have a zener diode across their drain and source. This will show a low resistance in one direction which may be what you were reading. You need to measure the drain/source (terminals 2/3) junction resistance in both directions. One way should be high and the other low. It may be that you have only measured the first in one direction and the second in the other direction which could account for your high/low readings.


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by bordonbert Fri Nov 09, 2018 1:23 am

    Have a look at this link and see if it makes sense to you.  The thing to go for is the table at the bottom of the page.

    MOSFET Testing with Meter

    You should take care with static too if you are handling these devices out of circuit.  Without having access to protective equipment like a wrist band earth or an antistatic mat the simplest way is to touch something earthed just before you touch the MOSFETs and try to keep your fingers off the Gate (terminal 1) as much as possible.  Rearding what I said earlier about taking them out of circuit to be valid, in circuit won't be a problem with them as they are hooked up in the cathode circuitry as the Drain is isolated with the valve turned off anyway so measurements in circuit would be valid.


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    das234
    das234


    Posts : 7
    Join date : 2018-11-05

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by das234 Sun Nov 11, 2018 2:48 pm

    Replace Q14 and Q15 and it works! Thanks a bunch for your help.

    Khay124 likes this post

    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by bordonbert Mon Nov 12, 2018 8:26 am

    Excellent result then.

    Well done on the removal and refitting, I was obviously worrying about nothing with your soldering skills. You have no idea how many people take on work like that armed with a massive poker sized iron and having only ever soldered a new jack socket onto their guitar - complete with dry joints! It's easy to do more damage than you fix if your equipment or skills really aren't up to it. This fault is a rare occurrence, those MOSFETs are specd so they are easily able to handle anything they should see in this role. It shows how stressed the amp output components get when you run a valve amp without a load.

    One trick which people could consider with all of their valve amps is to solder a permanent resistor load across the output socket. It needs to be about a 2W or above and any value around 470ohms would do. It can be put across the switching terminals of the socket so it is out of circuit when a speaker is attached but I prefer to put it straight across the live terminals so it is permanently attached whether there is a speaker jack inserted or not. That way it also covers you in the event of a cable break or speaker burnout too. A value that high means it will not affect the amp loading in any way when there is a real speaker attached. (16ohms // 470ohms = 15.5ohms and it is even less significant for the 8ohms and 4ohms.) This means that if you make that mistake again there is at least some loading across the transformer and the spikes generated are lower so the amp can cope with them in the short term.

    I use a Marshall 4x12 which I have split internally with a wooden baffle into two separate 2x12s. I can have two pairs of different speaker setups in there which I select via a pair of slider switches mounted into the handle. I can run either of the 2x12s at 8ohms, both of them in series at 16ohms or both of them in parallel at 4ohms as I choose. It is impossible to set the switches so there is no load at all, (unless you incorrectly set the slider switch in the middle of its travel of course). The series/parallel combos would mean plugging into a different impedance on my amp (another Marshall) so they are not usable on the fly but I can use the 4 speaker 16ohm setting with the GM36. However I can switch between each 2x12 without changing the amp if I really want to. The downside is that to change between them on the fly means an unloaded mismatch while a switch is in that indeterminate state in the middle which could cause nasty kicks if I am not careful. That permanent resistor removes that as a problem for me.

    H&K recognised this as a problem because in the more expensive GM36, for example, they gave it the ability to sense when there is no load and to automatically switch itself into Silent mode with the power soak in circuit. Unfortunately some of the less expensive models like the TM18 don't have that.


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    das234
    das234


    Posts : 7
    Join date : 2018-11-05

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by das234 Mon Nov 12, 2018 2:07 pm

    Thanks. Yeah, the soldering wasn't bad on this. It was disassembling the amp to get to the back side of the big PCB that was kind of a pain.

    I don't have any resistors beyond 1w right now since I mainly just build pedals but I'll track down a 2w 470 ohm next time I order some parts and put it across that output jack for some insurance.
    das234
    das234


    Posts : 7
    Join date : 2018-11-05

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by das234 Mon Nov 19, 2018 4:05 pm

    Just to make sure I put the output jack resistor in the right place when I get it, am I just jumping it from the tip of the jack to the sleeve? Or tip to ground?
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by bordonbert Mon Nov 19, 2018 7:18 pm

    You want it to be in circuit permanently so I would put it from the tip to ground.  That could be to the sleeve contact on the PCB but you must make sure it is the permanent ground side of that and not anything across the switching wafers. It's high enough to have it in place with a speaker load without bringing that load impedance down in any real relevant way, but it is low enough to let the transformer see some load so the spikes in the output valves when no speaker is put in place are kept down below dangerous.  When I get a minute I'll have a look at the PCB to see where that would be sensible.


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by bordonbert Mon Nov 19, 2018 8:14 pm

    I've had a look at the PCB drawings now.  The speaker output socket on the TM18 sits alone on the edge of the Rearboard PCB next to the Power Soak switch.  It uses only two of its four contacts, the switched ones take no part in its action.  The Tip and Sleeve are as you would expect and, as there is no switching action between the other wafers in the socket, those are redundant.  Both tip connections nearest the inboard back point of the socket are isolated from the main ground area on the top of the board and pass through to contacts on the bottom of the board.  The main tip connector, the outer one nearest the short edge of the board, has a thick PCB track to the far end of the power soak switch on the bottom layer.  That should be easy to identify.  That is the one you want to use.

    You need to connect the resistor to that outer contact of the Tip pair, that's the one closest to the short edge of the board and furthest in from the long edge with the PCB track to it.  There is a hole showing on the PCB drawing very near the Sleeve ground terminal on the outside edge of the board which I have no clue as to its purpose.  If it is a mounting hole of some sort or has anything else in bare  metal fitted into it, this may make mounting your resistor a little awkward as it should be kept away from things which it could short out on even though it is a ground leg.  If that would be a problem I would solder the resistor across the diagonal to the socket ground terminal furthest from the short edge of the PCB and closest to the long edge.  If that hole is actually not in use at all then you could use the two contacts closest to the short edge of the PCB.  Make sure to give just mm or two clearance between the resistor and the board, only a slight amount.  That resistor might get hot and lifting it slightly will help with cooling.

    This is IMPORTANT!!!  The square Tip pads on the PCB are isolated from the surrounding ground area on the top of the board under the socket by a narrow line clear of copper.  Make sure that nothing bridges that while you solder.  You should need the minimum of extra solder to attach the resistor legs to the pads under the board.  Make sure to tin the legs first before you fit them then you may not need any extra solder to get a good joint.  Extra solder can move up to the other side of the board and "blob" there with bad results.

    The socket Ground pads on the PCB Top side are designed in thermal relief as is modern practice.  That means they are partially isolated from the ground area around each corner leaving four short copper tracks from the terminal to the surrounding area.  This reduces the amount of heat required to correctly solder them in the automatic process and makes this more reliable.  This is perfectly normal.  Soldering to either Ground pad will do.  Even though the bottom of the board shows no PCB tracks going to these pads rest assured they are connected to the ground area on the top side of the board under the socket.

    It may seem odd that I suggest wiring the resistor in place from the permanent Tip connection and not form the switched Tip connection where it would be removed from the circuit when a plug is inserted.  If that does seem overkill just ask yourself what would happen if you accidentally inserted the speaker plug at the amp but it was not connected to anything at the speaker end, or if the speaker burnt out open circuit, or if one of the connections to either plug broke free, or if the cable core suffered a break.  They all remove the speaker load from the amp just as surely as not plugging in the speaker plug.  You are protected against all of them with the resistor in place even when the speaker is too and it makes no difference to the sound, action or safety of the amp.

    If anything else in unclear just let me know.


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by bordonbert Mon Nov 19, 2018 8:30 pm

    Might as well do this the easy way if others are going to benefit too.  Here is a pic.  Either position will do fine.  I would prefer the outer edge rather than the diagonal assuming the resistor length fits between the terminals and the hole near the ground is unused.  If the resistor is longer or something fits into that hole which may make the leg vulnerable to a short then use the diagonal position.  Make sure the resistor clears the bottom cover by a few mm too when that is in place.

    Tubemeister 18 Plays in Standby Mode - What's Wrong? XoXs9Il


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    Ramiro Garza
    Ramiro Garza


    Posts : 5
    Join date : 2020-01-28

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by Ramiro Garza Tue Jan 28, 2020 12:28 pm

    Hi bordonbert... I have same issue, stand by and bias... in a Tubemeister 18 30 Aniversary...

    I have open it and notice has different mosfets... mosfet 13NM60N

    So I read this forum before.... and ordered... the The MOSFETs are STP10NK60ZFP 600V 10A...

    I read that are similar... so I replaced... didn’t fix it. But the reading change...

    Now seems is trying to bias.... and after some seconds. .... right side blinks and left still on... I have tried 2 sets of tubes... my old ones that are ok... and the ones that came with.

    Before I had the status ... left on and right off...

    I got this tubemeister from ebay as a great deal... sounding and looking as new... so now I’m thinking to keep trying fixing with online help... like this forum and diagrams...

    So the mosfets are ok or I should get the mosfet 13NM60N...?

    What else can be doing this... thanks...
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by bordonbert Tue Jan 28, 2020 1:54 pm

    Hi Ramiro.  Well done for getting this far on your own.  Do be cautious and take care, apart from your own health and safety you don't want to risk doing more damage to your amp.

    There are differences in the two MOSFETs.  The Gate Threshold Voltages, (basically what voltage they start to turn on at), and the Rds(on), (their resistance when they are on and working under set conditions), are both slightly different.  The measurement conditions they are tested under in the spec sheets are slightly different so it is difficult to say how significant that would be.  It is very possible that it will make no difference at all as the system is a feedback loop so it will have a degree of self regulation.  If the conditions go beyond the range that the feedback loop can control then you would experience the problems you are getting.  It isn't mentioned in the manual but those MOSFETs are both controlled from a single transistor so there must be a degree of matching involved to allow them to set each valve to the same current from their shared gate voltage.  As far as I know you won't be able to get matched pairs of them.

    The other components which are relevant here are the resistors in the drain of the MOSFET.  These convert the bias current to a voltage and send it back as a signal to the digital circuitry for comparison against the set value.  If the voltage is too low then that means the current is too low and the control circuitry increases the current.  When it gets to be too high it does the opposite so the current settles to the set value.  If those resistors have changed their value then the bias circuitry will be deliberately trying to set the current to the wrong value.  These are labelled R89/91 and should be 1.5R 1W and they sit right next to the MOSFETs on the PCB.  Do they look scorched or damaged at all?

    Regarding the lights blinking, the manual says:
    TM18 User Manual wrote:One LED lights up continuously:-  The tube assigned to this LED is producing under-voltage. If the LED does not extinguish after a few minutes, this tube must be replaced.
    One LED flashes constantly:-  The tube assigned to this flashing LED is generating over-voltage. It has been shut down and must be replaced by a technician. If the second LED lights up continuously, this indicates it has also been shut down for safety reasons, but there is no need to replace it.
    It is possible that these warnings are being triggered by a fault in the digital side of the auto-bias circuitry rather than just the valves or MOSFETs being at fault.  If you have replaced the valves with a known good set then it looks as though there will be little more you can do.  You have replaced the MOSFETs and we have mentioned the sensing resistors but the rest of the control circuitry is digital and cannot be worked on.  If that is the source of the problem you will need to replace the control PCB.

    Do you have a decent tech near you who could get parts from H&K and fit them for you?  H&K will not send parts out to an owner, only service centres they recognise as being up to the standard of working on their amps.


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    Ramiro Garza
    Ramiro Garza


    Posts : 5
    Join date : 2020-01-28

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by Ramiro Garza Sat Feb 01, 2020 11:46 am

    Ok I will replace the mosfet again for the 13NM60N I found a pair ... online near.. anything with that number would be good... I saw STP STF STL ... 13NM60N ... I guess I will give it a try.... I have gloves and I’m intermediate level tech... I will give it a try and then if still bad... take it to a friend store... everything else look good nothing noticeable, and because the reading changed I think worth another try... before was kind of death and now is active... I guess the gate threshold and the specs are not matching... so another try... any 13NM60N would be good?
    Khay124
    Khay124


    Posts : 1
    Join date : 2021-06-09

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by Khay124 Wed Jun 09, 2021 6:05 pm

    das234 wrote:Replace Q14 and Q15 and it works!  Thanks a bunch for your help.
    Hi, I have this same problem which just happened today with my GM40, by q14 and q15 do you mean the preamp tubes like the 12ax7 tubes, I’ve never changed a tube before, but if changing the tubes will get rid of this problem, I’d do that to all my tubes at once even though it’s quite expensive.
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by bordonbert Thu Jun 10, 2021 7:13 am

    No!  Q14 and Q15 are not the valves at all.  If you read the whole thread from the beginning you will see that they are actually semiconductors, MOSFETs, in the cathode circuit of the output valves.  Without a lot of experience and decent equipment you will not be able to change them.

    What are your symptoms?  Please don't just put "the same as him", tell us in your own words what you personally are experiencing.  That way we can see whether it is likely you have the same problem.

    I also see you are talking about a GM40.  I would advise you to start your own thread in the GM40D forum and report your own symptoms from scratch there.  I'll keep an eye out for it and reply as soon as I can.  The information about the TM18 and GM40 will definitely not be the same and this could get very confusing for both yourself and other genuine TM18 users.


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie

    Sponsored content


    Tubemeister 18 Plays in Standby Mode - What's Wrong? Empty Re: Tubemeister 18 Plays in Standby Mode - What's Wrong?

    Post by Sponsored content


      Current date/time is Thu Mar 28, 2024 6:21 am