Hi, cos I'm not using my LD as a preamp I haven't really looked at any of this before... but it's interesting so I'll have a read on stuff over the weekend and see if we can work it out (hopefully other people will also chime in).  I wasn't sure if an amplifier would become damaged or not by DC...

Hi yep I think they included a DC protection circuit in the later amps.  If someone wanted I would think you could do this yourself + add it to the chain.  Probably there would be 2 ways of doing it, either after the DC coupled power amp with something like this...

It's probably a good plan :).  The problem with taking the amp apart - as you probably found - is that it's pretty shoehorned in there.  I should've said that if you do that then you have to be really careful cos you could break connections just because it's such a hassle to pull it out enough...

Hi, the easiest thing to check first are the tubes.  You can swap the tubes from one side to another, and wiggle them a bit while you have the buzz to see if it is a dodgy connection with the tubes.  If it's that then cleaning the pins/changing the tubes will probably fix it.  After that it'll...

Um.... I just smashed it.  The 6080 I had has a metal base anyway (Thomson) so that stayed together... and then I just cut off the main body of the tube from the rest... and could solder wires to the wires coming off the pins.  Really it's just cos I had a broken tube and I wanted the octal base...

Yep I was thinking of something similar (to be able to try them).  I've got a 6080 tube that had stopped working, and so I smashed it and reused the base - soldering in wires to the wires going to the 8 pins (including the heaters).  As I replaced the 7pins with a single octal socket, I can then...

Agreed :)... tldr it's not that much of a risk to run 6AS7s... but still a little bit of a risk.  And I don't have a horse in this race any more as I bought a cheap 165v HT transformer, and so am now running the 6080s I have at over 90mA, with a 6SN7 for about 100ma per transformer (the stock...

Hmm I'm learning this stuff as I go, so I needed to check this a bit more carefully.  The VA rating above is correct for the entire transformer, so the transformer can handle that amount of power and the resultant heat, but obviously the question is whether the winding itself can manage...

Hi, I was reading about transformers and because I kinda created some worry over the 6AS7 tubes, I thought I'd put some minds at rest....  We're actually running the transformer under it's rating (I think) with the 6AS7 tubes.  I wasn't sure before how it worked if you weren't using all of the...

Hi because it's interesting and it helps me to learn this stuff as well.. I drew some load lines on the valve curves to try and show what's happening:   6AS7:   6n6p:     I've only really learnt all of this stuff in the last month, but I *think* this is right.  So basically the load...

Hmm from the sounds of it it isn't the transformer hypnos (it just wouldn't get any power I would've thought if it was).  I'd still say it's probably the resistors in some part of the amp.  Before uprating some I had resistors being run over spec, and they didn't stop working, but kinda melted a...

You've caught me, I'm a risk taker at heart !  Or well that's a little bit of it.  The transformer has that as a rating, but it is self wound by LD (I think) so I'm not sure how accurate it would be (they didn't even really need 100mA for stock configs so they might have put a conservative...

Hmm it's an interesting question as to whether there's a difference.  I've only got a single pair of 6080WAs (Thomson) so I can't do any testing to find a difference between tubes.  With this tube I found they match the 6AS7 curve very closely (so at least with this 6080WA they appear to pull...

Hi, I'm not really sure if there's much of a relationship between the heater currents + the likelihood of problems (obviously so long as you are using an external PSU).  The 6AS7 is just known as a very current hungry tube, if you look at the curves for them in comparison to 6SN7 you can see...

Sad to hear that it was your amp hypnos :/.  I remember reading about you finding the c3gs + tbh they're probably the first tubes I'll roll in once I've finished faffing around with the mods to the actual amp.  I'm pretty amazed that an amp has actually died really, I've made plenty of mistakes...

Hi gibosi.  I've modded my mkIII pretty extensively at this point, and I have wondered how well the transformer would hold up with the current the 6AS7s draw.  I found with a config ish close to stock mkIII the 6AS7s would pull over 80mA per tube....  The mk IV I'd guess would be similar but...

I'd definitely recommend the CCS's (but not with the LM317/TL783 - see below), they seem to sound a lot better, are really simple/cheap and don't take much space.  Just remember about the voltage difference between input/output though - only 37v for the LM317 and 125v for the TL783 - on mine the...

Hi, sorry not been watching posts so late reply... It looks like on the schematic TrollDragon has drawn he has the same config as I had on the MK III, he has the power led whereas as I don't as I took it out.  They both seem to use AC... I have seen where people have had voltage regulators on a...

It sounds like you've probably tried some of the simpler stuff... testing the different tubes, different RCAs etc just to be certain that it is a problem with the amp.  You could also try moving the amp if you haven't already, they're really susceptible to interference.  As well make sure you've...

Just an update after installing 2 x Thomson 6080s (6SA7 type) instead of the 6n6ps.  The current draw from my old config went from less than 50mA with the 6n6ps to over 170mA with the 6080s (over 80mA per 6080)... so I wanted to reduce that.  And the increased current also meant the 6SN7 tube...

Hmmm mine is a bit different... I wouldn't mind if the voltage was just changing a bit, but it jumps around at less than a volt when first turned on (+LED blinks on the regulator) until I rebias it .  I'm wondering if it might be cos the tubes probably pull more power initially so maybe it's...

Hi, mine was the v2.  I think the only difference was the plate resistor for the 6n6p was 68 in the old version (Rs 5+6 in the diagram).   Edit:  Actually thinking about it maybe the 2 180 resistors in the power section were less than 5W on some of the mkIIIs (I remember seeing some burnt...

Hi I've got a pair of Thomson 6080s installed now, with a 6SN7.  They sound good and hopefully will improve with breaking in.   I was pretty shocked how much current the 6080s pull when I was near stock, ie over 150mA total for amp compared to 50mA or so with 6n6ps.  The increased current draw...

It's not ready for public viewing - I need a new top plate - but I kinda did the same thing as with the Bottlehead Crack.  So a simple open base of wood with a top plate (currently just 5mm acrylic).  I'm expecting if I like the 6AS7s I'll probably then take the 6n6p sockets out too... the...

I've got the mk III version, which I use with a pair of HD650s, and have made quite a few changes since I first bought it (a couple of years ago).  I started with trying to change the caps - basically following this thread - but found that the case really was pretty bad to work in.  I ended up...