Original AC30

[lowell]

Anyone know of any kits that are true to the original 60s amps with the pitch vibrato? I recently fixed one....and then listened to some Daniel Lanois...and now I'm completely set on building one....or buying one. But...I don't have the bread for that kind of purchase.

This is incredible...check it out
https://youtu.be/S7OoV96Ih3k

[Gingertube]

THis may help.
JMI era VOX AC30/6 ? circa 1964 replica layout ? turretboard.org


Click on the Rev7.pdf toward bottom of the page.

Cheers,
Ian

[Rob's Radio-Active]

The phase shift vibrato? I didn't know the AC30s had that. Pretty cool. I don't know of any kits though, unfortunately.
cheers
Rob

[lowell]

Yes! The 60s one...at least the one I repaired had pitch vibrato. And the sound overall really was better than the new reissues. That Daniel Lanois video says it all.

This is also the first circuit I've seen where there is pitch shift vibrato without any special LDRs. If you view this schematic you can see what I mean.

https://goo.gl/images/OXtvsW

[Gingertube]

One thing I consider an essential change is to ditch the 50 Ohm cathode bias resistor bypassed by 220uF which is common to all 4 output tubes.

I did a restoration of a copper front panel AC30 (1963?) which came to me with multiple problems the worst of which was a totally blown output stage.

When I rebuiolt teh power amp I put 235 Ohms (2 x 470 Ohm 2W resistors in parallel) bypassed by 47uF/50V on each of the output tube cathodes. That is bias each of the 4 output tubes separately. That runs the tubes just marginally cooler and obviates the need for tightly matched tubes. Also significantly improves the output stage reliability as one tube cannot hog all the current and thus expire.

The owner of that AC30 said that he could not tell the difference sonically with this change.

I have an interest in this as I have on my "donor amps" shelf and old AWA PA Amp which ran a quad of EL84 (6BQ5) and a 5AR4 rectifier tube. So chassis and trannies are suitable for an AC30 clone.

Cheers,
Ian

[lowell]

Somehow I overlooked Weber's kit. Has the pitch vibrato!

http://www.tedweber.com/media/kits/6v30_schem.jpg

[loudthud]

Weber sells a kit for the AC30. It's not cheap. Link to schematic: http://www.tedweber.com/media/kits/6v30_schem.jpg

Is that the one you are looking for? It has the Trem/Vib switch.

[Gingertube]

Now that you mention it I recall seeing that Weber Kit. I had a minor concern at that time - V4 of the Weber Kit is specified as 12AT7. This aligns with V8 on the original VOX schemo which is specified as a 12AU7. The U7 has a lot more grunt than a T7.
Still - its easy to change a tube.

Cheers,
Ian

[lowell]

Simulpost!

[Chuck H]

A little but the original AC30 was a 1x12 combo's with a pair of EL34 tubes!!! I only mention it because the thread title says "Original AC30"

I though maybe someone had seen one or even had one on a bench!?!

[lowell]

Right on Chuck! I did not know that.

[lowell]

Also found that the AC30TB has the vibrato channel. So not a bad price.

The VOX Showroom - The Vox AC30TB and AC30TBX Amplifiers

[Malcolm Irving]

A little but the original AC30 was a 1x12 combo's with a pair of EL34 tubes!!!

Nice website here with a picture of one:
http://www.lchr.org/a/5/gw/topboost.html

I'm working on a 1960s AC15 right now. Chassis only, box and speakers long gone, lived in a loft for 30 years. I keep finding problems and fixing them, but so far I've only got the normal channel working. The vib./trem. channel is a pig! With all new components, I'm sure it would be fine. It has an ECC82 (12AU7) for the 'modulator'.

[Chuck H]

Nice site. So I was wrong. It was a 1X15" and not a 1x12" But look at the size of the thing!?! That was a big amp. I've outlined the speaker opening for scale:


EDIT: Looks to be about 30x30

[loudthud]

Info I have from Jim Elyea's book says it was a 12 inch speaker. They actually used the cabinet and chassis from an AC15 but added a separate chassis in the bottom of the cabinet for the power transformer, choke, rectifier and filter cap. No info on cabinet dimensions.