actually the old amps have the bright cap, tis actually the coupling caps that are lower values making the rest of the am brighter, but the bright cap mod is popular. You could also check the cathode resistors on the power tubes against vintage, I bet they are a non-vintage value making the amp colder and more brittle in the treble frequencies. Vox has actually been running the cathode bias cooler and cooler since always. My 62? you can fry an egg on it. It once caught fire and needed extensive restoration.

There is extensive info online about measuring the voltage drop off the cathode resistor and finding a safe but musical value for an ac30. Or if you wanna play it real safe and still sound killer look at the matchless schematic or the schematic for the fawn handwired AC30HW2, both have a sweet balance of reliability versus unfatiguing treble and I think are both rpetty close to a alte 60s ac30. I would tell you to look a old schematics but they often don't match what's in the amps. Vox was tweaking the bias all the time.

or is C26 not on the input?

instead of a switch for the V15 why not install a pot to vary the amount of feedback, I am not sure how to implement this but I know I've seen it done on 6V6 fenders with NFB like the tweed tremolux and the non-tweed princetons... I think its called the "soul knob' mod.

the soul knob is kinda like a full bandwidth presence control in practice, where a presence takes NFB off the high frequencies only

Hello Jimmarchi1 Good news according to the bad microphonic auxillary valve noise I was having in one of my V15`eens. In the V1 position, i exchanged the sitting ECC81 with a ECC82, which has a much lower gain factor, and puff - away is the noise...completely ! I am very happy with the result, and it even sounds a little more creamy when turning up the power, So I am a very happy Dane these days :O)

I have been lucky by purchasing 2 Vox v15. I played them for just a few month before cutting the brown negative feedback lead, going to the 820 Ohm resistor. The result was quite astonishing, as the Amp suddenly started to play at least twice as loud as before, and next that especially one of the amps started to sound very microphonic when turning up the volume. I managed one of them to play all way up volumw wise, by dampening the baltic birch chassic with divided cloth pins, for leaving out unwanted resonance, which immediatly would start the tubes to go microphonic, and it really helped on the one of them, but I am almost giving up on the other one - at least for now. As already being mentioned ... they do sound very much like Marshall, and perhaps not that weird, as the Marshal factory did build the Vox amps in a period, where Rose Morris were the owner of the brand. Still the V15 sounds terrific, aand I am truly happy about having them, though they do not have quite the chime as my Vox Ac15 ccx1.

I know, if you look at the circuit it needs a reduction in the amount of NFB to be more like a high gain marshall 18 or 20 watt in my opinion, taking the NFB out may not be the best thing for an amp with extra gain that's not laid out internally to prevent oscilaltions and microphonics without feedback to surpress it... its interesting to know that you had this problem cutting the feedback loop everyone like everyone talks about because I always suspected it would be a potential problem, especially if any parts have drifted over the years. But anyway I suspect you should just retube and then add the feedback back but in a smaller dose so change that resistor value before running the NFB elad. You will probably be very pleased with what you get then. Surpressed squealing, nice tight bass, amrshally midrange.... go take a look at the values in marshall's 18 watt and 20 watt treble/bass amps, the so-called miniplexis that were the hot homebrew amps 10 years ago.

just a heads up, I own a couple vintage ac30s (JMI, arbiter) and the custom classics are chimier than them.... they are chimier than the current handwired fawn ones.... they are chimier than my matchless, they are chimier than the marhsall-made 90s reissues... and all those amps chime it up. Vox got carried away revoicing the custom classic to sound like a Beatles recording forgetting that the Beatles mainly sued other amps. AC50s, AC100s, those vox hybrid amps, vox solid state amps, blonde and blackface fenders, selmers... ac30s and 15s are only on the earliest recordings and I think they traded their fawn ones in for a couple of factory top-boosted 30s in black by the time they did meet the beatles. I would have to dig up Babiuk's book to be sure. But seriously, the CC1X is going to outchime any amp so its not a great reference. Its got some really screwy value caps shaping the abss and treble on both channels to be extra bright. Its not bad, I think they sound rather good, but they don't have the mids of the old voxes to be sure, nor do they have the bass.

instead of switch on the NFB you could put a pot too... make it variable

You are so absolutely right about the brightness of the ccx1, and as a result of annoyance by this screaming treble, I did cut the capacitor on the pcb board - placed at position c26. And it has become a very different beast by now...more sweet sounding, more bass...I had to re position the treble and bass chicken knobs to more normal positions, and I am so delighted by the result. To go back to my troubled v15...I will try buy some tubes/valves less agressive to what I have now, and try damp the vibration of the chassis with yet more split clothespins, and also perhaps take up your fine idea about a pot, instead of the nfb switch I have at present....or else I dont know what to do...the other v15 I have do not make any trouble anymore...but gawd how I love the sound of them - a mix between Marshall and chimey Vox