Mmmm interesting especially the last bit anyway, thought it worth a punt / set my limit fired up my sniping software and waited. I won it for a good price (considering these are priced new at around £900-£1000) , and decided to pick it up. Anyone who doesn't pick a unit like this up themselves is asking for trouble in my opinion !!
Got it home and then left it for several weeks - work etc.
I have some very simple rules when testing any equipment I buy - unless I know (and trust!) the person i've brought it from - I never plug it in without a very careful internal examination and safety check - old(er) equipment gets extra special treatment - when I write up one of those I will detail what I do.
Anywhere here it is on the bench (forgive the mess!!) -
As you (hopefully!) can see its in pretty good nick really, looks hardly used, all the knobs works really smoothly with quite a satisfying 'clunk' on the band switch.....
So obeying my rules (however tempting!) I opened it up and ...... boy was I glad, in fact I was amazed that the seller didn't damage himself permanently (perhaps fatally!).
However have a closer look (there are no valves these were removed by the seller as the anode's of the valves had 'fallen' off) the white 'things' hanging down are the ceramic caps that should connect to them (there are 4 valves in total) the other two are just to the right of the centre of the picture. If you look closely the board that these connect to (actually the parasitic board) looks a dark colour - perhaps a clue here ? and the coil below looks a little odd as well doesn't it ?
Here is a picture (Right) that shows a close up of the board (with the coil below it) as you can see the board has been badly overheated (and I mean badly!!) . If you look really closely the coil below is also very dark, and if you look really carefully you will see that the coil has got so hot that it has actually melted the coil winding making it open circuit !!! - you can also see the braid connecting from the parasitic board to the anode ceramic cap had also been blackened very badly. Wow !! now you can see why I'm glad I have my checking routine as without it I am not entirely sure what would have happened, probably (as per the seller) nothing too bad, HV (1.7Kv) would have been generated but wouldn't have gone anywhere as the coil is open circuit (and of course no valves !!).Anyway here's a close up of the coil you can see the damage that has been caused by the overheating. One can only speculate what has caused this overheating.
I've worked on many valve amplifiers with many / varied faults but I've never seen one this badly damaged by heat / overloading. It doesn't look like a result of bad tuning (there are no signs of arcing anywhere) it simply looks like one of its previous owners has loaded it up in a mode with a high duty cycle - Digital / PSK or RTTY perhaps, maybe CW in a contest - at the maximum output power and gone for it !!!
And then done it again and again and again (maybe !!) - either way it needed some work - urgently !!! - I decide to give it a more detail electrical and electronic check, and with the exception of one capacitor in the meter circuit, all were good, no signs of any damage or arcing in any of the usual places (plate / load capacitors). inductors etc.
From the date stickers looks like a early 2009 example, so not too old at all.
So time to do some digging on the net and see what I can find, these are popular amplifiers in the US, with quite a good following, reviews vary but treated well will do well over the UK legal limit without breaking sweat. Looks like I will need to get / make a new parasitic PCB and anode coil at least, I also plan to add some of my standard upgrades such as a glitch resistor and upgrade the HV Caps if I can find some decent examples.
More on this one to come :)
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