convert a bass mate to a 4x el-84 amp

Almost certainly not possible.

For starters, the extra 2 EL84s will pull at least an extra 1.5 amps (9W) for their heaters and then a *lot* more power for the output - maybe another 22W or so. That's just extra load for the the power transformer.

Then, the output transformer is *very* unlikely to be happy with twice the power running through it.

Suggest you make a Lightning/18W/AC-15/etc with it

 

You really need to know what the capacity of both transformers is. The power tranny needs to be able to produce the extra amperage needed to run 4 tubes, and the output tranny needs to be able to handle that much current.

You might be able to get that info from Traynor.

In any event I suggest you get a different amp.

 

I've been on the lookout for one of the 2 X EL84 Bassmates. Hopefully one will come up cheap on Ebay soon. I wouldn't try the conversion you're proposing - I agree that you should consider sticking with the current power tube configuration and mod the preamp. Do you really need that much power? 18 watts into an efficient speaker is plenty loud enough for a small venue, and you can just mike it if you need more.

 

I've got one of the Guitarmates with 2 EL84s and there's enough volume for blues/classic rock gigs with 2 guitars, bass and moderate drummer. You can take the performance up a notch by switching to a more efficient speaker (Weber blue, EV, G12H-30, Jensen Neo etc-I decided on the EV and I'm very happy with the tone and volume).

 

What for?

You will likely not get any more power out of it with four tubes, especially since the output impedance will now be mismatched, assuming you use the same speaker. The power output is more limited by the transformers than the tubes - even without the filament draw issue. You may even possibly get less audio power output, due to the mismatch and the extra load on the PT... not to mention potential reliability problems.

If you want more volume or a fuller tone, you need a different amp, or possibly (depending on what you're using now) a different speaker, as Bob said. For example, replacing a 97dB speaker with a 100dB one will gain you as much as doubling the power of the amp. Going to something like an EV or a Celestion Century will make an even bigger difference.

 

Is this true for all amps, or just this 15 watter being discussed here?

 

Any amp.

It sounds surprising, but it is true. The difference between any sound and one of twice the power (measured in watts) is 3dB. Speakers vary in sensitivity, or efficiency - some produce more acoustic energy for a given electrical power input. If you have one speaker which is 3dB more efficient than another, it will produce the same acoustic power output as the less efficient one would if being supplied with twice the electrical power.

12" guitar speakers vary roughly over the range of 94dB (the lowest I know of, a couple of Jensen models) to 102dB or possibly 103dB (Eminence Red Fang, I think). This is an amazing range of volume - a 15W amp going through a 103dB speaker will be as loud as:

A 30W amp through a 100dB speaker
A 60W amp through a 97dB speaker
A 120W amp through a 94dB speaker

Really.

Speaker efficiency is at least as important as amp power in determining volume.

This is also partly why your typical 100W hi-fi doesn't really sound all that loud, but a 100W guitar amp is REALLY loud! Hi-fi speakers are generally in the mid 80s to 90dB range - they sacrifice efficiency for a more linear response.

Increasing the number of speakers also improves efficiency, but there's no set formula for how much since it depends on cabinet design too - typically, doubling the number of speakers seems to gain around 2dB.

 

John P - That's amazing! I had no idea. I thought the volume increase I experienced going from a 2x12 with Celestion G12-75Ts (97dB) to a 4x12 with Vintage 30s (100dB) was simply because I had more speakers and a bigger cabinet, but now I know it was also the increased efficiency/sensitivty. Very cool info. Thank you!

 

If you want "amazing clean power" you're not gonna get it from a Traynor Bassmate. By drilling holes and replacing all the transformers you are basically tearing up an vintage amp to build a new one that may or may not give you what you want.

I just bought a Bassman 100 off ebay for $350. Thats the kind of thing you need for cheap clean power.