A British guy named Grusvenor has published a complete guide to servicing Vox amps, containing never-available-before diagrams, layouts and schematics.

"All amplifiers are oscillators and all oscillators are amplifiers"!

Makes you wonder what happened to quality control at the manufacturing stage. Great fault finding Stuart, as always. Thoroughly enjoyed that one, thank you.

Stuart, A fine example of why I so enjoy your videos. The way you talk through the troubleshooting process is wonderful. The use of the schematic to explain the process is enlightening. The way you do this has taught me much. Thanks, Mike

Young Stuart! The man!

Splendid as usual 🎉

The AC-30 is my favorite Vox model. It is a shame that the factory Q.C. was horribly irresponsible. Great job getting it sorted, Stuart. I admire your sense of saving the customer a possible 75 quid for a full exploratory. The mod worked well. Thanks for posting. Cheers!

Hey Stuart, a bit of pest that one..Love the way you get around these nasty little faults..Great job as usual..Interesting video..Ed..UK..😀

Great work Stuart.. I think Vibrato & Tremolo are great effects to have built into an amp and I'm sure the customer will have been delighted that you managed to fix them at a sensible cost. You can get a very adequate trem pedal for £20 theses days so I completely see your point of accounting for the time/cost/value equation her. It works now.. Job done !

Jolly good!

You must fill that amp with helium first. Then it's easier to lift. 😂 BTW, don't do it like Zeppelin did. They filled those airships with hydrogen and everybody knows what happens if hydrogen catches fire... And because of the quite low working frq of the tremelodramatic oscillator, I usually use larger (50-200uF) cathode bypass cap value than that standard 25uF because it at least theoretically gives higher gain to that osc triode at those very low frequencies.

Valve Wizard/Merlin Blencowe---> "A visual frequency / rate indicator: There is one useful modification that can be made to this otherwise ancient circuit- LED biasing. By replacing the cathode resistor with an LED we eliminate the need for the large bypass capacitor, and obtain maximum gain and minimum output impedance at all frequencies in one fell swoop. A red LED will be suitable in most cases, providing about 1.6V bias, although other colours can be experimented with of course. Additionally, because the oscillations extend to cut-off, the LED will flash in time with the trem' signal giving a novel and useful visual indication of the frequency, and that the circuit is actually working! The circuit [right] shows this, using an ECC81 this time."

I only have a VERY Basic understanding of this stuff, so pardon me for asking........... What was that "Hum" trim pot adjusting..... Heater voltage.? Some kind of feed-back loop.? Phase inverter output.? I really have no idea. Not even sure if i have seen that before 🙂 Thank Yiou

Why did they use a 6 positions rotary switch for 3 speeds available ? Maybe (if it would have been connected) would it make different configs of resistors to achieve 6 speeds ? We’ll never know. Good job anyway 👍

Odd, as you say, that all three tracks were going nowhere. PCB board to board fingers never soldered properly from new, perhaps (and a design accident waiting to happen).

STUART, Why does reversing the output transformers Primary winding will fix power amplifier oscillation problems?

Not to split hairs but it’s actually a tremolo, not vibrato 😉

Please correct the tremolo to tremolo ....