A birthday present of a new set of valves in a 2009 PV classic 30 and after a few weeks of use , copious magic smoke and then nothing. V7 has a near to short varies [cold] 3 to 6 ohms or so cathode to G3, p2 to p9 of EL84 mechanical failure inside, burning out the HT1 to HT2 dropper R58, 400R. Anything that could externally precipitate such failure to check, before a new valve/s ?
er
p2 to
ck,
With the tube/valve removed, is the grid negative with respect to the cathode by several volts????
after
to
check,
With the tube/valve removed, is the grid negative with respect to the cathode by several volts????
++++I have to replace the dropper first, ridiculous mechanical design of 3 "wrap around" boards with something like 2 sets of 27 short link single filament conductors. Presumably copper and with age and work hardening , what is the probability of one of those links failing in the unwrapping/working on/ rewrapping process, then the probabiliy of another such link failing in sorting out the first failure. Replacement dropper will be wrapped around the stand off pillars, I think.
p2
dropper
So what is the metal of those 50 or so short curved links, that you have to bend all of them to unwrap the boards? something specially formulated that does not age and work harden? I doubt it , probably deliberately designed like that to make repair as awkward as possible. Could easily have been soldered eyelets on one edge of each run. Perhaps you have never come across ribbon connectors that fail at a solder point , only because you've had to flex the ribbon to gain access . Or moving the discrete wires to the wire-wrap terminal boards of 60s kit? Anyway heatsinked the pcb ends of the pillars and 2x1K 2W plus 2K2 2W in there now, could not find a 400R,5W of the required dimensions to otherwise go in the available space
meaning artery forceps clamped around while soldering
For a valve/tube amp why does it say minimum load 30 ohm on the back or is minimum actually maximum in USA useage?
Might it be because 30 ohms is less of a load than say 8 ohms?
Ron
So its a two nations divided by a common language sort of thing
No! it's simple elecronics. Ron
Anyone any experience of reducing the hum in these. Mainly due to a monster reverb tank that would normally be in a 2x12 cab, lost in the bottom, but in here only a couple of inches from the mains Tx Testing amp outside the cab then normal sort of , no input, output hum level. That hum trebled when reassembled. Found some salvaged mu-metal , so bent to extract and to wrap partly round this Tx, but hum level now only double, an audible improvement, not just by meter. As not a bass amp, how much performance reduction in the reverb if a tiddler tank was put in here instead. ?
I wonder where you get new mu-metal from. And, where to learn how to handle salveaged mumetal from oscilloscopes/ reform its cloaking character, if lost. Would mu-metal only around the reverb tank coils be enough? Tx nearest (in tank terms) the transmit end but as the hum is straight , not reverberrant, I assume its geting in at the far , receiving, end
The hum is definitely coming from the output side no matter what. However, just how are you saying that it is not induced on the input side ? It is a continuous wave, an echo would be inaudible.
However, since some shielding does help it is obviously not induced at the input side.
I find it hard to believe that the unit was sold like that and you are upgr ading a faulty original design. I wonder if the big copper strap around the transformer (can be internal) has cut loose. They are soldered and if this thing is new enough to use lead free solder I think that a viable suspect.
Can you see the salesman in the store saying "Yes it has a reverb but you c an't use it because of an annoying hum caused by a design defect" ?
Anyway, I would have a good look at the reverb unit itself. If this thing i sn't junk, it has to have some sort of shielding from OTHER sources of EMI no ? What, you have to keep the thing three meters away from anything with a power transformer ? I tend to doubt it. I think inspection of the reverb unit might reveal a fault there.
However, since some shielding does help it is obviously not induced at the input side.
I find it hard to believe that the unit was sold like that and you are upgrading a faulty original design. I wonder if the big copper strap around the transformer (can be internal) has cut loose. They are soldered and if this thing is new enough to use lead free solder I think that a viable suspect.
Can you see the salesman in the store saying "Yes it has a reverb but you can't use it because of an annoying hum caused by a design defect" ?
Anyway, I would have a good look at the reverb unit itself. If this thing isn't junk, it has to have some sort of shielding from OTHER sources of EMI no ? What, you have to keep the thing three meters away from anything with a power transformer ? I tend to doubt it. I think inspection of the reverb unit might reveal a fault there.
+++++It is a regular complaint by owners of these amps. May be not so obvious when they are used in 60Hz countries, 50Hz here. The next time I came across one I might explore with small pieces of mu-metal around the coils in the tank, and put a scope on the thing. Reading around mu-metal it seems that to restore its invisibility cloak effect then you just need a hydrogen furnace to re-anneal, I'll knock one up from my pile of scrap
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