Vox AC30 speakers and load box

spark240

So I just notice some selling a Two notes  8 Ohm load thingy and I thought  it might be useful for my AC30 TB6 .

So I just checked the Vox speaker output and its 8 Ohms....great !.....then I notice the speakers are 2 x 16Ohm Vintage 30,s ...wired in parallel.

Now the amp works ok....never used it in combat...I guess I really should put 2 x 8Ohms in it ?

ICBM

If the speakers are 16 ohms each wired in parallel then the total load is 8 ohms, which is fine as long as the amp is set for that.

Stock AC30s are fitted with two 8 ohm speakers wired in series with the amp set to 16 ohms.

spark240

ICBM said:

If the speakers are 16 ohms each wired in parallel then the total load is 8 ohms, which is fine as long as the amp is set for that.

Stock AC30s are fitted with two 8 ohm speakers wired in series with the amp set to 16 ohms.

So the 8ohm two notes captur for sale here would be ok ?

ICBM

spark240 said:

So the 8ohm two notes captur for sale here would be ok ?

Yes, perfect.

Is it an old AC30 with a screw terminal connector or a modern one with a jack and a selector switch?

spark240

ICBM said:

spark240 said:

So the 8ohm two notes captur for sale here would be ok ?

Yes, perfect.

Is it an old AC30 with a screw terminal connector or a modern one with a jack and a selector switch?

Erm....its an AC30 6TB, it has. single jack in the rear of the cab labelled speaker 8Ohms.no selector.

ICBM

spark240 said:

Erm....its an AC30 6TB, it has. single jack in the rear of the cab labelled speaker 8Ohms.no selector.

An AC30/6TB could be anything from the 1960s onwards. How old is it?

Sorry, many questions!

Is the jack in the back panel or on the bottom of the chassis? Does plugging into it turn off the internal speakers, or are the speakers plugged into it? Is there an impedance selector on the inside?

Just curious... the V30s won't be original, and as far as I know all AC30s have been 16-ohm output with the stock speakers.

It doesn't matter for what you want to do with it though. If the output is definitely 8 ohms then it's fine with the load.

spark240

I reckon its mid 1980's...the jack is in the underside of the chassis, so inside the upper part of the cab and push ups into the jack...there is no impedance selector visible.

It came without sneakers so I had a couple of V30,s so they went it....ironically a couple of years ago I sold a pair of 1964 Vox Blues ...

ICBM

spark240 said:

I reckon its mid 1980's...the jack is in the underside of the chassis, so inside the upper part of the cab and push ups into the jack...there is no impedance selector visible.

It came without sneakers so I had a couple of V30,s so they went it....ironically a couple of years ago I sold a pair of 1964 Vox Blues ...

Sounds likely to be early-mid 80s to me as well. If it doesn't have a 16-ohm output they would have been no use anyway...

There may be a switch on the inside if you take the back panel off though - I think they have a mains voltage selector like that, if it's from the same general era as the V125.

spark240

No jack picks...but just for info,...

https://flic.kr/s/aHsmHXtA53

ICBM

spark240 said:

No jack picks...but just for info,...

https://flic.kr/s/aHsmHXtA53

That's a Marshall-made Korg reissue one, made in 2003.

Maybe I'm wrong and the non-X version - which came with Greenbacks originally, the TBX had Blues - was factory wired for 8 ohms... 

Dodge

ICBM said:

spark240 said:

No jack picks...but just for info,...

https://flic.kr/s/aHsmHXtA53

That's a Marshall-made Korg reissue one, made in 2003.

Maybe I'm wrong and the non-X version - which came with Greenbacks originally, the TBX had Blues - was factory wired for 8 ohms... 

I'd exercise caution @spark240 ;

My old TBX was definitely 2 X 8 ohm in series. That was a 2003 too.

I don't recall ever seeing 16 ohm speakers in an AC30TB, and this scan of the manual says it should be 2 x 8 ohm in series for a 16 ohm load, for both Blues and Greenbacks:

http://www.voxshowroom.com/uk/amp/ac30tbx_manual_p4.html

Not the clearest pic, but the jack on mine was like this, definitely 16 ohm:

spark240

Oh...Sh*t.....Ive made a grave error ;-(

  It is indeed 16Ohm,....Ive no idea why I thought it was 8...I even looked at it !.... 

  But...it does have the 2 V30 16Ohm in it....in parallel.....problem?

Dodge

I'll let @ICBM answer how well an AC30 tolerates an impedance mismatch, but the simple solution would be to only use one 16 ohm V30, which will present the designed load to the amp.  The V30 is pretty robust and it'll take whatever the AC30 puts out.

I'd be inclined to change the speakers though - the upper mid / lower treble spike the V30 has might not compliment the AC30 Top Boost sound.  I know Matchless / Bad Cat use modified V30's in their Top Boost-a-like amps, but they don't do the classic Vox sound (IMHO, having owned them).

Blues are the obvious choice, decent alnico alternatives such as the Fane A60 (excellent), Eminence Red Fang (very good, although I'm not sure they're still being made), and perhaps a Gold (ok, but more modern rock sounding).  Greenbacks also sound very good in Top Boost amps.

ICBM

spark240 said:

Oh...Sh*t.....Ive made a grave error ;-(

  It is indeed 16Ohm,....Ive no idea why I thought it was 8...I even looked at it !.... 

  But...it does have the 2 V30 16Ohm in it....in parallel.....problem?

Not if you’re not cranking it right up. It’s not ideal, but impedance matching is not that critical if the power stage isn’t overdriven. As Dodge said, the easiest temporary solution is to disconnect one speaker - a V30 is rated for 60W so this is completely safe.

However, if you’re planning to use it with the 8-ohm load so you can overdrive it, that is a problem. You do need a 16-ohm one.

In the longer term you’re definitely better with a pair of 8-ohm speakers as well. Blues are very expensive, and very loud... there are some other alternatives which sound good, are quieter, and lighter. Some of my favourites are actually 1970s G12S-20s - they have a voicing quite like the Blues, but are about 5dB less sensitive, which is a lot! It makes it possible to crank the amp up at a fairly tolerable volume.