by bordonbert Fri May 05, 2017 9:47 am
Yes, the first steps most people take in getting to grips with the H&Ks is to swap out the valves and play with speaker choices. I would guess you've already seen some of the comments here (mine I mean) about this aspect. My advice, don't get too wrapped up in valve choices, it's an "Emperor's New Clothes" topic! It doesn't make anywhere near as much difference as most people convince themselves it does. That said, there are slight differences to be had and the level of importance of a slight difference is subjective, but you won't make a Peavey into a Fender with different valves. Most of us here tend to just go with something generic and reliable. JJs are a common choice, I use them myself. And as you may have read I also strongly advise you reject the idea of going with 12AT7/12AU7/12AY7 type swaps, they are NOT equivalent valves to a 12AX7 in any way. If you really wanted to drop the gain in some of your stages then a 5751 is the only valve to go for as it has very similar characteristics in the invisible areas which no one really knows about but which are crucial to the circuit design.
The speaker choice is the more important one, that really does make a lot of difference and it isn't surprising. Every aspect of a valve's characteristics can be measured highly accurately and that electrical data is what would give each valve a different sound, magic mojo does not exist, it is only a way to describe something the person does not really understand. Engineers understand a lot more in many areas than mojo magicians! Other than reliability, there are precious small differences to be found between different manufacturers in measurement as they are all trying to stay within a well defined set of parameters, so there can only be tiny differences to be found in sound. To call a valve a 12AX7 it must meet well defined values in a lot of parameters. Cheap Chinese valves still meet those parameters or they could not be labelled 12AX7. If you could genuinely hear a difference then we could measure it! If the difference in sound was huge then the difference in some parameters would also be. In speakers, there is both the driver and the cabinet to consider and both these can genuinely be measured and shown to have really significant differences. In my own experience V30s will give you a more modern "in your face" type of sound, while something smoother like G12M Greenbacks offer a smoother more classic sound. It depends on your music and your taste as to what you decide on but I really advise you to spend time trying out the amp with speakers before you buy them. The H&K amps tend to have a characteristic sound of their own and are a bit unforgiving, so testing speakers with a different amp and expecting that to give you an idea of what they will sound like with your TM36 does not work in any reliable way.
My advice, start with a set of JJs which will keep you going for a few years until you decide whether the TM36 is the amp for you. Otherwise you are just spending money to no benefit except to the person you hand it on to. Putting in a new set of valves will give you the Chinese originals as a set of backups and will tell you whether it is a valve which is at fault with your noise. I strongly lean towards a transformer issue here and I don't mean a fault, I just mean a vibration which is natural in magnetic components. I have a Marshall JVM205 which can physically hum strongly, not through the speakers just coming out of the case. That hum changes in character with the day and location as the mains differs in its cleanness. In my home on a Sunday with no industrial use around me it is a smooth soft hum, in other dirtier locations it can become a strong buzz. It still performs perfectly anywhere.