EL34 vs 6L6 tubes

[rickaddict]

Hi there! I apologize if this has been covered somewhere before. I tried to do a search, but I found nothing.

My Ampeg B-15R has a switch in back that allows it to run on either EL34 tubes or 6L6 tubes. It sounds great with the 6L6 tubes that came in it stock, but I wonder what it would sound like with the EL34's. Would there be a difference?

[scott_s]

It depends a lot on how much you distort the amp when playing. Below the clipping point, the negative feedback in the output section will correct for uneven frequency response and harmonic distortion. So it will likely sound the same if you play clean, and the tubes will only reveal their character when it's distorting.

(NFB is what allowed them to make great hi-fi amps out of every output tube under the sun. )

HTH,
- Scott

[rickaddict]

It depends a lot on how much you distort the amp when playing. Below the clipping point, the negative feedback in the output section will correct for uneven frequency response and harmonic distortion. So it will likely sound the same if you play clean, and the tubes will only reveal their character when it's distorting.

(NFB is what allowed them to make great hi-fi amps out of every output tube under the sun. )

HTH,
- Scott

Thanks Scott. So how would the amp sound different when it distorts?

Would it distort earlier, distort more, distort more harmonically?

[scott_s]

I'm not familiar enough with that amp to say. I think in general, EL34's can put out more power given the same plate voltages, but whether that would translate into a noticeable headroom bump is another thing.

It's worth trying!

- Scott

[soundmasterg]

EL34's typically have a balanced frequency response, with soft overdrive characteristics. They compress easily but sound sweet and harmonically rich throughout their frequency range. They work well for guitar overdrive and rock sounds, and work well for bass until you overdrive them a lot, when they get a little loose on the bottom end.

6L6's tend to have lots of bass, a bit of a mid scoop, and some clear and often somewhat brittle highs. They have harder overdrive characteristics as compared to an EL34, and their frequency emphasis towards the lows and highs maintains itself as they overdrive. They work great for guitar and bass and are used in a ton of stuff.

Overall there would be a difference between the sound of the power that you would notice more and more as the amp was turned up. If you play bass with it, then the 6L6's are probably a better choice. If you play guitar, either one should be fine, though the amp was designed around the 6L6.

Greg

[rickaddict]

Thanks, Greg. I do play bass through it, and IMO it is possibly/probably the best sounding amp I've ever played through so maybe I should just leave well enough alone and keep the 6L6's. Here's a quick pic for your amusement:

[ken_j]

Originally the Ampeg Portaflex amps used 7027A tubes. I understand that these are tonally somewhere between a 6L6 and an EL34. I read somewhere that the larger the plate area the more bass a tube will have. So it makes sense that a 6L6 has more bass.

[johnallg]

Very interesting discussion.

[scott_s]

Originally the Ampeg Portaflex amps used 7027A tubes. I understand that these are tonally somewhere between a 6L6 and an EL34. I read somewhere that the larger the plate area the more bass a tube will have. So it makes sense that a 6L6 has more bass.

Well, a 7027(A) is basically an uprated 6L6GC with a slightly different pinout. Tube manufacturers actually stuffed the same guts into both bottles at times.

- Scott

[soundmasterg]

The Portaflex didn't use the 7027A until later models. They used the 6L6GC from the beginning. The first amps were cathode biased, lower power, sounded very nice, and then later became fixed biased, still sounded good, and the cabinet design changed numerous times. The B15N can actually comprise over 7 different models that all sound good.

The 7027A is a harder vacuum 6L6GC with a different pinout. You can use a good 6L6GC in place of it in any amp. The 7027A can not be used in any 6L6GC amp without making sure the socket is wired appropriately.

Greg