'65 Vox AC-50

[Laurent Brondel]

I bought that amp not long ago and finally got to replace the electrolytics and clean up a bit. A bunch of replaced components, I used the vintage looking Mods caps to replace the poly replacements, so to speak, and left the replaced resistors in place.
It's super quiet and is a great sounding amp, the best clean tones on planet Earth on the Brilliant channel, the Normal channel is a perfect bass amp.

It's an overlooked piece of vintage gear IMHO, they can be had for better prices than new amps.

Behind the Siemens EL-34's you can get a pretty good 450VDC on the filter caps positive sides attachments if you touch them… Individual bias pots for the power tubes, which is pretty nice, and no Brimistor on mine, it seems totally fine without it. It has been replaced by 2 resistors in parallel, anybody knows what the purpose is, rather than a piece of solid wire?






Here's a demo for my trio I recorded recently, '65 Strat, AC-50 through The OX:
https://soundcloud.com/laurent-brondel/ ... -will-come

[ChopSauce]

Lovely!

Overlooked?

I can hardly believe it...

All the Vox amps I could see were always expensive.

Of course, you may have had some (lots of) luck when buying this one, but it isn't one of the overlooked amps I could think about at all...

[Stevem]

Beautiful amp!
I can’t comment on the two resistors without knowing there value or wattage, but a guess would be that the original item never really goes down to true zero resistance when it’s fully heated up so those resistors needlessly mimick that.

I bet that would make a killer recording bass amp with KT88s or KT90s in it!

15 years ago I picked up a badly beat up Ampeg B15n head and put a auxiliary transformer in just for the filaments and I now run KT88s in it and I have recorded with endlessly.
With some 28 watts it’s got the perfect combo of punch and light growl!

[Laurent Brondel]

Somebody suggested I replace the 2x resistors with a thermistor, anybody tried that?

[pdf64]

I seem to recall that Brimisters were a few hundred ohms when cold.
Perhaps they were fitted to protect the rectifier diodes from the initial switch on surge required to charge up the reservoir cap?
Consider something like a CL-90 NTC inrush current limiter, maybe even 2 in series.
What value are the resistors?

[Laurent Brondel]

I seem to recall that Brimisters were a few hundred ohms when cold.
Perhaps they were fitted to protect the rectifier diodes from the initial switch on surge required to charge up the reservoir cap?
Consider something like a CL-90 NTC inrush current limiter, maybe even 2 in series.
What value are the resistors?

They're each 100ohms, for a combined value of 61ohms between the 2 points. I mean everything is fine with the amp, there is no crazy surge when turning it on, but I'm intrigued by wiring a CL-90, what do you think?