When Celestion first introduced the greenback range in the mid 1960’s, the G12M was rated at 20w and the G12H was rated at 25w.
In late 1967 Celestion upgraded the voice coils across all speaker models, to allow for roughly 5w more power handling. This gave us the familiar 25w G12M and 30w G12H – and we can assume the alnicos also increased from 15w to 20w.
Difference in voice coils
The “5w less” speakers had a white coloured voice coil former. These speakers are known to struggle with their rated power handling.
The “5w more” speakers had a brown coloured voice coil former, made from a more heat resistant material.
There are subtle sonic differences between the two types of voice coil, and the white coil speakers are the most sought after by collectors and discerning tone hunters!
The transition from the white former to the brown former did not happen all at once. It was a gradual transition over several months.
Whilst repairing speakers I have seen the brown formers as early as June 1967, and I have seen the white formers as late as Jan 1968. However, most speakers do seem to have the brown former by Nov 1967, and a white former as late as Jan 68 is pretty rare – I have only seen one example.
Even more confusing, the labels did not change “with” the voice coils. Celestion only altered the labels several months later – around April 1968. So there was a long transition period when the speakers had the ‘5w more’ brown voice coil, but they still carried the older ‘5w less’ labels.
So when buying speakers just be careful of this. Dealers will always ask a premium if they have the ‘5w less’ label on them, but if they have the brown voice coil former they are really no different to the later, and less valuable, pre-rola’s except for the slightly different cork gasket.
To be 100% sure of a white voice coil, the speaker needs to have been made before June 1967. Early greenbacks from that period are particularly rare due to lower production numbers, and that is one of the reasons why they are more valuable to collectors.
Sonic differences aside, there are no visual clues on the G12M speakers to determine what type of voice coil it has, except perhaps the manufacture date. The only way to look is by removing the dust cap, or by lifting up the spider support. This is definitely not advisable unless the speaker needs repairing.
On G12H speakers look for doping on the reverse side of the cone. This is usually a good indication the speaker has the white voice coil former. A G12H without the reverse side doping is most likely a brown former speaker – a 30 watter.
The first greenback speakers made between mid 1965 and mid 1967, with the white coil formers are the best sounding greenbacks Celestion have ever made in my opinion. They sound clearer, have better note definition, feel more responsive, and have that ‘woody’ tone in spades.
If you are a ‘plug straight in’ kind of guy, then you will probably love the white former period greenbacks too. Just be careful with them. The key to getting the best tone from them is to give them plenty of power. It can be a fine line between ‘optimum tone’ and blowing the speaker!
The brown coil speakers will give a warmer and thicker sound at lower volume levels and do not need to be pushed as hard to sound at their best. However, they lose some of the magic of the earlier speakers in my opinion. If you use a lot of distortion or other effects then you will probably prefer these later speakers.
Ultimately, the type of greenback you prefer will come down to personal taste, your playing style, and the other elements of your rig. Use your ears and keep experimenting!