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Ok, I wasn’t clear whether you meant the HT power supply, or the amp’s max audio power output, or something else. The lower ripple, potentially stiffer HT provided by a choke is only really going to affect the screen grid’s HT supply node, and is only really going to make much difference at...

That could have several meanings, could you rephrase it?

As the front panel and back panel are both from a 2203 then, it’s reasonable to say that’s what the amp was originally.

It may be worth considering a protection diode for V3, the DCCF, see http://www.valvewizard.co.uk/dccf.html Or use a GZ34 rectifier, so that the HT has a nice slow ramp up, that doesn’t happen until after the other valves have warmed up some :)

The volume controls are labelled ‘master’ and ‘preamp’, the inputs (left hand side pair of the array of 4 front panel holes by the preamp volume) are labelled ‘high’ and ‘low’ ‘sensitivity’. Those things would be different on a model #1959 super lead.

Thanks, it’s just that I inferred from post #6 that you had access to IEC standards, and I was interested in checking the one mentioned, but not so interested that was prepared to pay hundreds of ££ for the privilege :rolleyes:

Just to note that from the front panel, I suspect it may have been a 2203 originally.

Using the low input? How about if it's turned up to the onset of power amp clipping? Turn gain up, treble, presence and bass to min, mid up full (for flattest freq response).

Someone’s gone to town implementing the ‘WTF’ mod :) It seems there’s an fx loop, and perhaps a second channel with its own gain and master vol? And relay switching for them, with an additional power supply. I’d think there was a footswitch jack somewhere? Otherwise the relay switching would be...

What does the wave look like at the master volume? With presence at min, what does the max sine wave output look like, at the onset of power amp clipping? Consider injecting the sine input at the power amp input (eg as if there was an fx loop), to avoid the preamp confusing things.

A HT can cap is falling out and and circuit board looks to have a lot of carbon deposits around the bias supply, probably from a valve shorting and taking out its screen grid resistor. I suggest to take it to a competent tech for appraisal. Just to note it’s a 50W 1986 bass model, not a 100W...

Thanks! Do you have a copy of / access to, IEC60335-1? I’d very much appreciate a scan of it :)

As per post #2

DC is more demanding on a switch than AC, as arcs with the latter tend to self extinguish. Whichever, the switches used for standby are being subjected to voltage far beyond their rating. Dunno how that works with UL, CE etc approval?

Yes, that’s possible. Maybe try a higher value anode load resistor if you want a couple of dB more gain, eg 470k. Due to the big 1nF bright cap, that’s to be expected. The tone should get a bit fatter as the gain is turned above 5 though.

Oh, and some sort of anti vibration fastener for the safety earthing screw, eg an additional locknut / nylock etc.

Happy days indeed when these could be bought. Such a shame that Ingo isn’t making stuff anymore. Perhaps he should have charged twice as much, that may have kept the workload manageable, and it would still have been good value.

It looks nice, good job :thumb: Is there a star / toothed washer between the green earth crimped lug and the chassis? Unless it was crimped with an industrial grade tool, I suggest to crimp AND solder that earthing lug to the wire.

Without knowing which specific model it applies to, that chart is of limited utility. Note that the other 50W chart there has rather different V1 voltages. I don’t think that ‘ampchart’ is an official Marshall thing, rather it seems most likely to have been cobbled together from various...

It seems as if that would wire the fuse between live and neutral? Neutral should be wired directly to one primary leg, with a layer or 2 of heatshrink over the joint. Incoming live to the back of the fuseholder, out of the side of the fuseholder to the switch, out of the switch to the other...