Thanks Pete!

Yes I didn;t show it on the video but I made myself a couple of nice pieces of toast....

Hi John. One side of the fuse had all the valve heaters in parallel, so quite a low resistance. The other returned via the 6.3V secondary heater winding. Again low resistance. Quite surpirsed it was half an ohm though, Would have expected maybe a few ohms.

@@stuartukguitarampguy5830 , Having gone down this particular rabbit hole in the past and learned the hard way, I no longer test fuses in circuit. If they're hard to get to for complete removal I simply pull one end of the fuse up out of the clip with dental pick or spring-hook tool, and then put the meter on it.

@@goodun2974 Yes I usuall do that too but had a brain fade on this amp for some reason.

The tube heaters have a positive temperature coefficient, like most metallic materials, which means that they have a very low resistance when they're cold but the resistance increases as they heat up, in other words, they are non-linear resistors. Incandescent light bulbs behave the same way, as a very low resistance, almost a dead short, when they are cold but with much higher resistance when heated up. This is why bench technicians use an incandescent light bulb in series with the power cord to amplifiers and other devices under test, because the light bulb will heat up and limit current if the device tries to draw too much juice due to a circuit fault or the tech making a mistake, slipping with the meter probes, or whatever. You should look up the definition of of a thermister: a nonlinear resistor with a negative thermal coefficient that actually has a fairly high resistance when it's cold but decreases in resistance when it is hot. They are often used to prevent inrush current from damaging devices or blowing fuses, and as they heat up they take themselves mostly out of the circuit because the resistance decreases and becomes minimal.

Hi Monty. Tes oddly enough when I tried the overdrive on this amp I didn;t like it much.

Thanks Ed!

Thanks. It's been 3 months now since the amp went back and it seems ok, so fingers crossed it was a one off.

@@stuartukguitarampguy5830 Of course the designer should have made this an owner serviceable rear panel fuse , because it's bound to blow sooner or later .

The parallel tube-heater string could be viewed similarly to a "dim bulb" current limiter in line with the power cord, as seen on many technicians" benches. Like a light bulb, the filaments of the heaters have very low resistance *until you you pull some actual current and voltage through them, and then their resistance increases significantly as they heat up. Light bulbs, and vacuum tube heaters, are non-linear resistors with a positive temperature coefficient; as opposed to thermistors, which have a higher resistance when cold but decrease in resistance as they heat up (negative temperature coefficient).

@@faultlessguitarsandamps1116 But... but... that would have cost 20c more and made it EASY for the user. Why on earth would they want to do that...

Exactly! Hence it was a dumb mistake.

@@stuartukguitarampguy5830 , comedienne Erma Bombeck said that if she could sell all her mistakes for what they cost her she'd be a wealthy woman!

@@goodun2974 I like that!

Thanks Alex. I did this amp about 3 months ago now and it hasn;t come back, so all seems well.

Thanks Shiloh

@@stuartukguitarampguy5830 your very welcome sir.

Hi Michael. My own view is that there is aboslutely no difference between the SOUND of a pcb amp and a hand wired, if the amp design was the same. This is, of course, impossible to test! (Even two pcb amps straight off the production line would not be identical in terms of parameters).

Hi The part is SCK15105MSY I hope that helps

Thank you so very much. Very much appreciated!@@stuartukguitarampguy5830

Nice! These things are sent to test us!

@@stuartukguitarampguy5830 Indeed. Such a simple thing like that can send you down any number of rabbit holes and waste hours or days of time chasing ghosts.

I have seen an overheated power cord become a resistor, 30 to 70 ohms !

@@goodun2974 Never seen that. One to look out for. I have, in the distant past, made the error of using a fan heater with a reel extension cable not fully unreeled....

@@stuartukguitarampguy5830 , yup, I did that with a small heater in my garage in wintertime; plugged it into the drop-light outlet which was mostly still wound up inside the spring loaded reel. It got quite hot!

Hi. It's SO difficult to try and diagnose an amp over email. Probabyl best to find a tech near you and get them to take a look.

Obviously check the guitar lead is good. It may be soldering on the input jack (does waggling it cause the sound to come and go?) Also if the amp has FX send and return jacks, clean those. Otherwise.... tech time.

Ok thank you so much. I really apreciate the feedback. I opened the amplifier and there was alot of water inside from being outside . The previous owner had other outside as trash so i grabbed it.

The VOX AC30 does not require biasing.

EVERY tube and needs correct biasing. What you probably mean is, that there is no adjustment provided for adjusting the bias of the tubes. I consider this a bad design eventually burning out the tubes faster than necessary, because they run too hot .... I would still measure the standby current and (depending on the bias type used) adjust eventually a resistor to make sure that the power tubes are biased within their specification.

There is a well known saying "A little knowledge is a dangerous thing." Please go and look up 'cathode biasing'. @@Andreas_Straub

Well, ok. If this amp is one of the low power ones that use cathode biasing, it will need no adjustments, of course.@@stuartukguitarampguy5830

Yes? That is an amp which requires biasing. The VOX AC30 does not.

Not sure. isn;t it marked?

​@@stuartukguitarampguy5830 It appears I need a 6.3 Time delay

​@@stuartukguitarampguy5830that still didn't fix it however

@@therusseljournal Ok easily obtainable on eBay. T6.3A is what to put in.