Hints for Checking Used 5AR4?

[The New Steve H]

I'm about to open up a Vox AC30CC to see if it's okay. It blew a fuse, so I was asked to check it out. It has a history of blowing rectifier tubes.

I wanted to look over the rectifier to make sure it's all right. I was afraid that if I replaced the fuse and turned the amp on, a shorted rectifier could damage the rest of the amp. Logical?

I can only think of two ways to check the rectifier. One is to use an ohmmeter to see if there are any shorts between the pins. The other is to stick it in my 5F6A with a current limiter and see if it works. Brilliant ideas, or stupid? I guess I could also put my own 5AR4 in the Vox and check it that way, but I don't know what a shorted rectifier might have done to the Vox, and I am not looking to blow up my own tube.

[Cliff Schecht]

Did you stop using that standby switch? This is a known problem on those amps and if you just leave the standby on all of the time it's easier on the rectifier.


I think I mentioned it before that I fixed an AC30CC2 that had literally melted solder off of one of the rectifier socket pins causing a short. Don't know if this is your issue but one thing I can say is that amp was a nightmare to work on and cheaply/poorly built in a lot of ways.

[The New Steve H]

Planning to bypass the standby switch.

I checked resistance between the filament/cathode and the plates, and it was an open circuit in both cases. Guess I'll cram it in my 5F6A and pray.

Edit: the rectifier works. The socket on the AC30CC is very loose, however. Guess I can try to tighten up the pins.

[The New Steve H]

I bypassed the standby switch and retensioned the rectifier pins. In order to retension the other pins, I believe I would have to take the chassis apart, so I let it go.

No offense to Vox fans, but I did an A/B with this thing and the 5F6A clone I built, and the Vox sounded horrible in comparison. Muddy, dark, no pick sensitivity, and sort of sour.

The construction is appalling. The cabinet is solid, but once you get to the chassis, you start to see rivets instead of screws, everything is kind of flimsy, and there are ribbon cables.

[Zippy]

Another opportunity for a new circuit board.

Gut it and rebuild it!

[Weathered]

I bypassed the standby switch and retensioned the rectifier pins. In order to retension the other pins, I believe I would have to take the chassis apart, so I let it go.

No offense to Vox fans, but I did an A/B with this thing and the 5F6A clone I built, and the Vox sounded horrible in comparison. Muddy, dark, no pick sensitivity, and sort of sour.

Did you run it wide open? Voxes sound super anemic until they are running on the verge of exploding. Loud through a pair of Blues is the only way to hear an AC30......

I had a CC that I replaced the coupling caps in and swapped the speakers to Greenbacks, and it was the best recording amp I've ever used. Too loud for live use though....

[NickC]

I saw Bob Dylan a few years ago. Both his guitarists were playing through what looked like brand-spanking-new blonde AC30s. I don't know if the amps had been modded, but they were loud as hell and sounded heavenly.

[The New Steve H]

I turned the volume knobs up halfway. That's about all I can take in my garage.

[Lonely Raven]

Earplugs and sound absorption.

I'm building some studio grade sound absorbers this weekend for my guitar room.

[Bob S]

The things I remember about AC30's back in the early 70's :--
Lead guitar players loved them.
They played them cranked wide open.
Often smoke came out of them, then they went silent.
This was quite a common occurance - the attitude was - just wheel in another one.