I guess the lesson is: for fuses on low voltage parts of the board, always remove and test fuse out of the holder. Low voltage suggests low impedance load, and therefore it can easily make your meter beep even if fuse is open. Thanks for showing all of this. Very informative.

This amp is very electrically similar to the Fender Blues Deluxe. Both often have heat-related problems from the position of the valves. I don't know if this could have been the case. However, it is perfectly noticeable when a good technician has experience repairing amplifiers. It was another great video. Cheers

Thanks for being honest and teaching a valuable lesson on fuses!

I have run into that myself. I saved that fuse because I was putting on electronic traing at a company I worked for. I sure give those guys a go with that fuse. I would chatch them 9 out of 10 times. So much fun with it.

As always... very informative Stuart! Thank you.

Great video Stuart, shows your process of fault finding and what can be missed. So informative. Thanks for sharing..Ed..uk..😀

Great job! And you fixed two separate problems.

Hugely entertaining as ever Stuart. It's great that you don't edit much content out so it feels like we're there looking over your shoulder as you talk us through each repair job. No trying to spook you though 😂

Hi Stuart, thanks for the video. Sometimes fuse and fuse sockets develop some oxidation, so should clean those before changing. By the way, the push in connectors could also develop some oxidation. I have seen that a lot. Again, good cleaning is often the cure. Have a nice day and thanks again for the video.

A lesson for us all to learn, Stuart. It nevertheless was still an intriguing episode. It had occurred to me that I haven't seen you perform a service on a Hiwatt amp, unless I missed a past episode. Please stay safe. This ever-mutating scourge is another reason to be vigilant in the UK. Cheers!

I repaired a few of this ... and you have confirmed that it is a nightmare to remove the main board.

That is why I like your videos.

Great video looking forward to more.

thanks man had the same problem you turned it into a quick fix

Having been fooled by the exact same thing on more than one occasion, to test fuses and switches I always try test for voltage across them with the circuit live. If a fuse is good or a switch is closed there is no voltage across it. If the fuse is blown or the switch is open you have full circuit voltage across it. This gets around the issue of testing continuity in a circuit where you may get continuity (or at least low resistance) from other components in the circuit. Anyway, I love your videos and have learned a lot from watching. Keep up the good work!

Great job!

worth watching just to see you wrastle that board out. :p Another one lives to play again.

At 25:40, Stuart says, " There are two different kinds of jacks, god knows why"; Well, I am no deity, and neither is Stuart, but I know "why", and if Stuart thinks about it for a minute he would know why as well: the main output jack is designed to short to ground if there's no speaker-cable plug inserted into it, in order to protect the output transformer from damage caused by operating it without a load. This is and has pretty much always been standard for Fender amplifiers since the 1960s. I'm not sure if the extension speaker jack is wired so that an extension cabinet would work in parallel with the speaker in the amplifier's combo cabinet ---- note that lowering the overall impedance could cause problems for the output tranny ---- or in series so that the impedance increases rather than decreases, or if plugging in an extention cabinet shuts off the combo speaker and the audio only runs through the extension cabinet; but almost certainly there will be some type of built-in switching to minimize the chance of output transformer damage. Note that the Main jack makes metallic contact to the amp chassis,, but the Ext jack is insulated plastic and isolated from the chassis.. PS, the audio signal from the output transformer secondary *needs a chassis ground reference*, otherwise you can't use negative feedback from the output to lower distortion elsewhere in the preamp or phase invertor.

Hats off to you Young Stuart!! HATE those damn Circus boards! (Do they shrink them in, in the Factory!!?)

Hate is a strong word, but I hate those glass fuses. Especially the ones sitting in that kind of holder. Have had numerous of them fooled me over the years :)

Hello Stuart When calculating dissipation of the output tubes on a cathode biased amp which is the correct plate voltage reading to use? i.e. I’ve seen techs measuring from plate to ground and plate to cathode Thanks

I’ve got the same issue with my blues jr but all the tubes go on except one of the power tubes, I replaced the tubes but same issue, going to try the fuse next, if that doesn’t work I’ll try checking the tube socket like you did.

Brilliant mate.. how did you get started? Really honest insightful videos. 👍

Considering the amount of force it requires to pull the spade connectors off of those spade lugs mounted on the board, it's generally a good idea to automatically resolder them, simply because as we all know leadfree solder doesn't bond well to larger metal parts such as board-mounted fuse holder clips and spade lug terminals. I suspect that the metallic mass of those larger parts is sufficient that they conduct the heat away a little too quickly as the circuit boards are passed over the wave-soldering machines, and therefore the parts never quite get up to a sufficient temperature for the solder to bond to them. The same thing applies to the potentiometers and especially the input jacks. While you have the board up it's best to just reflow those connections.

Unrelated question: what brand is your magnifying visor? I need a new one and I can't find anything that suits me, but it looks like the one you have is just what I"m looking for. Not that my eyes are getting old or anything... it's just poor lighting... yeah, that's it... poor lighting.... Oddly, I've encountered many intermittent fuses. I usually take them out and give them a little twist and tug just to be sure. It's rare, but it happens. Only takes a second to check.

STUART UK, how does the output transformer block high voltage DC 350vdc to 600vdc because inductors PASS DC?

My Blues Junior has worn out grommets in the aluminium U-profile. Where can I buy new one? Is that rubber or silicone grommets?

Referencing the spark at 3:40, for discharging caps I use an old Heathkit resistor-substitution box with a rotary selector switch; I can begin at 1K ohms or higher and rotate down to 4 ohms in incremental steps. The original resistors were all 1 watt size, but I increased the lowest ohms-value resistors to 2 W, or 5 W if I had them and they would physically fit.

Hi Stuart. Do you need the service manual to this amp?

What is a "dry joint"? Is it the same as what we call a "cold solder joint" here in the States?

Your touching valves!!! I new a twitchy guy who wore lint free cotton gloves, like a snooker ref, to handle valves. He stated the oil in your fingers would cause the valve to explode. He wore them to handle L.P's as well His wife ran of with a plasterer working on their house

Stuart drives the wrong way up a diagnostic blind alley, so that the rest of us won't have to! [Edit: Now that I'm thinking about it, you British already drive the wrong way anway, so perhaps its just your natural default position for everything else! 🤣]

So you had to take out the whole board to change a fuse that has no real purpose......and it's prob under rated as there would be a surge even using the stand by.......SHM

An ADJUSTABLE WRENCH, held VERTICAL, to remove the input nut? ARE YOU KIDDING ME? This is just proves that a little knowledge can be FAR more dangerous than none. I wouldn't let you sweep the floor of my shop, as you're unqualified to even HOLD A WRENCH, let alone select the proper tool, to not mark up a CHROME control panel. The rest of your 'work' would require a novel to point out and correct.