Hi Proddy. You will most likely find the "socks and pieces of string" are really unnecessary. The valves just need the clips which are fitted over them lifted off. I've never had a problem just pulling them upwards a touch and off to the side by hand. Once the clip is off they are really easy to remove by just pulling up out of their sockets with a little gentle side to side wiggling at the same time. They are pretty robust despite being made of glass and looking fragile.
You got it right with the warranty issue, the bottom screws only need enough loosening for the end cheeks to fall outwards a cm or two so the lid can be slipped out. It only takes me two or three turns. And you don't need to touch the front screw of the handles, it only holds the handle onto the end cheek. It's perfectly safe to run the amp with the lid off for short periods as you test as long as you keep small children and the cat out of the way. You don't need the clips on the valves either of course to just run it up for testing. You need to take care with the LED strip when you refit the lid but it isn't difficult once you know it is there.
As to what you will find in playing around with the valves, I would take a lot of what you will read online with a pinch of salt, especially in forums. On the internet everyone is an expert in their own lunchtime because their mother's next door neighbour's postman's girlfriend's manicurist told them things were so so it must be. Experts or not, there is only one criteria to use when you judge things like which type of valves to choose and aspects like microphony and the valves' "gain" (which doesn't exist!). That is, does my amp sound good to me with this set of valves in it? I know of people who actually love the sound of their original cheap Chinese ones which we all know are crap and prefer them to the usual suspects recommended as "the ones to go for" when rolling. These people are not willing to wade into the mire that is "reasonable discussion" because they just get mockery and grief from the "experts" who have golden ears and the ultimate "common knowledge" of the subject. They are happy with what they have and just enjoy it. They are the sensible lucky ones!
I can tell you that the valve manufacturer makes only a minor difference to an amp if any at all. There are those who would passionately differ with me on that but the answer is in blind listening tests, not in swapping them and remembering what it sounded like a few minutes ago. If there is a perceptible difference audibly then there must be a difference electronically to cause that. If that is so it must be possible to identify it on the bench. No one ever can! My own experience, (and I have a lot of experience listening to and assessing hifi tweaks and mods for many many years as well as guitar gear), is that changing from the stock Chinese valves can remove some of the hardness that you may perceive in the top end of the H&K amps. If you love that brashness then fine, (the designers at H&K Grosse Hauptquartier do), but if you don't you will want to swap out at some time. There is no rush to do that. I tried valves like Electro Harmonix and Marshall originals which I had around as well as the usual JJs and I came to the conclusion that the JJs were as good as any of them and anything I could hear elsewhere. In fact there is only a whisker of a suggestion there may just be any difference at all between the 3 "better quality" ones I checked out if the listening conditions were just right. There is absolutely no benefit to paying out huge sums of money for the latest NOS sensation of the month with the "flowery recessed mid range" and "velveteen mahogany bottom end" when you are going to be cranking the volume against a bass, keyboards and, God's own comedy hunchback torturer, the drummer. That hint of "pink tinged lemon flavoured frothiness around 1kHz" you can perceive in the Clean channel in a quiet room late at night with the gain and volume down honestly vanishes when you get out in a pub brawling with the rest of the band, dimed and playing "Don't Fear The Reaper". And if you play hearing only your irritating lack of Tinkerbell like sparkle at 4kHz then you aren't cut out to be a musician.
You need to do some assessment work first on this. Check out the settings you end up using when you use your amp in real life with other musicians. Are you constantly striving to tame too much gain? Is that so acute you could consider 5751s to get lower amounts of gain on tap which opens up the bottom end of the Gain control? Are you unhappy with the general tone in terms of raggedness or harshness in the upper registers? That could point to a different valve make possibly helping you but.... Have you tried different speaker setups first? That is
MUCH more important and can genuinely make a huge difference to your sound.
Yes, valve sets are much cheaper than new speakers but not if they end up making only a tiny difference if any at all, that way they are just more wasted money to no benefit. And no one wants to admit they have been a dumbass and forked out cash unnecessarily once they have realised they have done it. Hence most of the advice, "changing your valves out for a set of "NOS Yamatoshi Ninja Platinum Grid Super Large Anodes" will make your GM40 sound like Eddie Van Halen's Variac fed Marshall rig". Once you have willingly made the same mistake would you be able to "out" the guy who advised you to go down that path?
And there is always the desire to be one of the guru group. "A guru told me, so if I tell others that must make me a guru too!" These are some of the reasons why all guitar gear myths are so easily propagated on the internet. People basically want to believe and then don't want to own up to their own gullibility.
On different models, my advice is very clear and based on understanding something of the ramifications of circuitry changes. Do not go for 12AT7/12AU7/12AY7 type swaps, those valves are NOT anything like equivalents and everything the designer sets out to make reliable in a stage can change. They make drastic changes in the setup of a stage designed for a 12AX7. They may work happily and they may give you a sound you temporarily like but the result of putting them in there is not predictable and the circuit design may well become very susceptible to effects like ageing of components in a way it was not with its original design valve, a 12AX7. The now well known 5751
IS a good close equivalent in all its parameters with the Amplification Factor μ (mu) dropped from about 100 to about 70. The name Amplification Factor is what most people mistake for Gain. It is not gain at all. It does
NOT mean the gain of the stage will drop from 100 to 70 or even by a factor of x0.7, life is more complicated than that. You do get some relief in the GM36 when you swap out for 5751s. It isn't so much tonally but the range of Gain (of the amp) becomes a little less overall but opens up at the bottom end of the control. In other works it is like saying that with 5751s in place a lower portion of the Gain control's range spreads across the whole control to become 0-10 losing the upper end. Some of us classic rock fogeys who don't do ultra high gain like that.
Take this whole concept slowly, there is always time to get to grips with it and mistakes can be costly, especially if you find you didn't really need them after all.
The Valve Wizard - from his book - Designing Valve Preamps for Guitar and Bass wrote:Some versions [of valves] are reputed to have a particular tonal character, and much has been written about the apparent superiority of, say, the Mullard ‘long plate’ ECC83, or the RCA ‘black plate’ 12AX7. These subjective differences are not a consideration for the circuit designer and will not be mentioned here again. So-called ‘tube rolling’ and ‘cork sniffing’ is fun, but is left to the discretion of the reader. Real tonal control comes from the choice of topology, manipulation of overdrive characteristics, voicing, and from a complete understanding of the circuit’s functionality, not from the particular manufacturer or vintage of the components used. This book will furnish the reader with this essential understanding, and the author will do his best to make it a painless experience.
The Prosecution rests m'lud!
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