by bordonbert Thu Jul 08, 2021 10:53 pm
Hi there Snaggs. Congrats on your find. A TM36 is a pretty awesome beast to own and play through. Here is a long diatribe of advice on aspects of noise with your TM36. Please be patient, some of it will be relevant to you.
Noisy? Well that really can be a subjective thing. My own GM36 is certainly not noisy - to my ears, but then I don't play high gain metal. All guitar amps will exhibit some noise and it isn't always the amp which causes it. The whole guitar electronic generating process is "tiny signals at very high impedances". That is an absolute recipe for disaster noisewise. I have known guitarists who expect their rig to be as quiet as a high quality hifi. That's an unrealistic unachievable aim. The best I ever expect is that the noise should not intrude while I am playing with a band. For recording there would need to be a higher level of noise immunity than that, but there is always a limit as to what is achievable. Then we go to noise gates, of which there is a good one on the GM! Unfortunately I have just noticed you have a TM36 which doesn't have that feature. The possibility does exist that you could get a noise gate pedal if this remains a problem for you. I would consider that if you have not already.
The noise level on Clean will be very very different to the noise level on high gain Lead of course. But you describe your problem very clearly and I would say that is not how things should be. So what can be done? First let's consider the info you have given. The output valves are pretty much ok according to the TSC count of 14. The manual, (available online for download if you don't have it), shows 14 flashes to be in the middle of the acceptable range. Are they all matched at or very near 14? They should be matched pairs as the outside two LEDs the same and the inside two LEDs the same. Make sure the two valves in each of those two pairs are within four flashes of each other. The difference between the pairs is not as important. However, that may be interesting but being the output valves it should not cause too much of a problem with your noise situation.
Is your guitar and cable ok in other amps? It may just be poor grounding on your guitar. Shielding with copper sheet does nothing for hum, that's down to the Physics and can't be denied, and it improves high frequency buzz only a limited amount. Industry spends millions trying ultra complex solutions to remove noise in its sensitive electronics but guitarists can do it with a bit of tacky copper foil? Naaaaah, it doesn't work like that in the real world of Physics! Check that ground leads in your guitar are clean and good. The leads connecting the pot covers and the output socket are all good. The output socket must be soldered cleanly and its terminals must be clean. The wire through the body which usually connects the bridge or tailpiece to the pots is sometimes just pinched under the metalwork. This must be clean on both surfaces to make a good contact. A good test is to stand the guitar away from all electrical kit and yourself. Does it hum? Then pick it up and put it on and don't touch anything metal. Has the hum increased? It should! Touch the strings and the hum should drop noticeably. That is all normal. You yourself reradiate noise which your body picks up when you are surrounding your guitar with your body and the guitar picks it up. When you touch the strings the guitar grounds you and you stop radiating. That is a sign all is well with your guitar grounds.
Really poor noise levels usually comes from the preamp valves and in particular the first input stage. That is the ECC83/12AX7 on the right as you look into the front which should be covered by the aluminium can. That can is important as it is there to prevent pickup in the first sensitive stage which is then amplified by every following stage in the amp. It has by far the most effect on noise levels. Is the can there? If not then get one pdq. Assuming it is then try the following.
If you have access to a spare 12AX7 which you know to be good then swap it for V1, the covered right hand valve. Even if you don't have a spare you can swap V1 with V2, that's the covered 12AX7 on the right with the middle one. (If you swap V1 and V2 remember to swap them back afterwards as it is better to keep valves in the slots they were originally chosen for. Sometimes a valve can be chosen for specific characteristics such as lowest noise for an input valve or balanced action for a Phase Inverter.) If your first valve is noisy then the noise level should drop noticeably when you swap it for a better one. In the case of the V1 and V2 swap the noise has not gone away, it is simply not going through as many gain stages now in the V2 slot so should be quieter.
Failing that, if you don't know the history of the valves then it may just be the right time for a swap of the preamp 12AX7s anyway. Guitarists frequently dump their oldest rattiest valves into an amp they are selling, particularly if the sale is online. Preamp valves in well designed stages last a ridiculously long length of time but do gradually fade and need replaced someday. Replacing preamp valves every 18 months or earlier as a matter of course is STUPID and wastes money! It's the equivalent of changing your car's clutch every 20,000 miles just in case it is wearing. If it 'aint broke don't fix it dummy! They should give you many years of use as they are not stressed in any way in use. They all work with low bias currents and signal currents which are even lower, and their anode voltages are well inside their design capabilities (in good amps). They do not "wear out" in use. They are killed by such things as incorrectly designed Standby circuits or by use in circuitry which was not designed for that particular valve.
Here's a handy hint from an old engineer: Swapping for 12AT7, 12AU7, 12AW7 or 12AY7 is dumb! The whole stage design goes up the swanny and every parameter changes unpredictably, sometimes even dangerously. There is no "family" of 12A*7 valves which are all equivalents, they are all totally different and have been designed to perform totally different jobs. It's like saying your Porsche Boxer and your Honda Civic only differ in their top speed, just like these valves only differ to the layman's mind in their "gain" which doesn't exist as a concept for valves anyway. The only valve to consider if you must valve roll is a 5751 which has a lower Amplification Factor, (definitely NOT the same thing as gain), but is so close in its other parameters to the 12AX7 that they actually can be considered as high and low gain equivalents. Many valve stages are designed so the external components, the resistors and capacitors, control the stage gain and response anyway and the valves' parameter differences are actually nullified by the stage design.
The H&K Standby is special and doesn't exhibit any problems but others in some mainstream amps like some Marshalls and Fenders should not really be used, at least for extended times. They actually kill the valves they control, usually just the output valves and maybe the PI, by cathode poisoning (Google it) if they remove the HT but leave the valve heated with no way to remove the electrons emitted. I do not understand why just turning down the Master Volume is not acceptable, it achieves the same effect with no detriment to the valves. No, remember, I said they don't "wear out" in normal use, as in when they are idling with no signal. The H&K Standby works by controlling the output valves' standing current via semiconductors in the cathode circuit. These play no part in the signal amplification. The Standby cuts these down to a low steady current which prevents the problem of cathode poisoning. It does leave the amp with a very low just audible signal level when played and this irritates some guitarists. But why the heck are they trying to play the damned guitar when the amp is on Standby?
I also recommend you do not spend loads of time researching the valves which gurus reckon will give you the best tone. In truth the whole idea that valves of the same type from different manufacturers have different tones is a laughable one and can easily be demonstrated to be incorrect despite what most guitarists insist on believing. That concept defeats the whole electronics industry's aim of producing components to fit within the same quoted spec from all manufacturers. They all have exactly the same frequency response through the audio spectrum and up into radio frequencies and that is flat. When they are used outside of that design spec area, as in when they are overdriven by us, they can overload differently so the character of distortion can be a little different but this is at best a subtle thing. It is the cork sniffers who will tell you there is a world of difference between a JJ and a Mullard NOS. There is, but it's only the price and bragging rights! In the years I have been on this site I can tell you there have been and still are a few valve aficionados hanging around but the vast majority of people buy simple JJs or similar, or they simply put in what they have to hand. They then make no noise about it so stay quietly satisfied with their amps. If you have £70 NOS types then by all means use them but please don't shout out to everyone you are getting "a couple of tantric levels above the normal" sound because your valves are old and ridiculously pricey. The guys who work in electronics at anything like a high level laugh up their sleeves when they see stuff like that. The guys who sell those valves piss themselves all the way to the bank.
Ok, recap. Is your guitar and cable up to spec? Is there a can fitted on V1? Is it fitted properly so it is correctly earthed to the chassis? Can you swap out V1 for a known good spare? If not, can you swap V1 with V2 using the proper procedure for opening up the amp, (if you don't know it let me know and I'll post it here)? Give us the answer to those questions and you may find your noise level drops to sensible levels.