Bias on 6550 Orange amps......

[Steve Conner]

In my limited experimentation an El34 can produce almost the output of a bigger bottle but the waveform never looks as pretty or clean with the El34's as it does with the KT88's or 6550's. This probably explains why guitarists love El34's so much and why KT88's and 6550's are such a popular choice in hifi and bass amps.

Well, it's only a subjective data point, but I'm pretty sure my hi-fi amp sounds better with KT88s than with EL34s. The EL34s were kind of harsh at higher volumes, but the KT88s are just super sweet. They look nicer too.

[Bernardduur]

Well, it's only a subjective data point, but I'm pretty sure my hi-fi amp sounds better with KT88s than with EL34s. The EL34s were kind of harsh at higher volumes, but the KT88s are just super sweet. They look nicer too.

+1!!!!!

I use a 8x EL34 amp that now runs 6x 6550 pretty sweeter!

[spy]

Wow! I set the bias at 55% and the sound is totally different! Finally there is headroom! It sounded so thin before!

Bernardduur, does your PT get any hot? Mine is getting a little bit but it stays constant. At 45% becomes cooler and I feel it safer. But I was wondering what is happening with yours. By the way, thanks for your help! I replaced the 68K with a 33K and the bias setting starts from 25%.

[Bernardduur]

No heat here....... if you don't trust it get a fan!

[spy]

Haha! No fan! I hate fans!

The amp was upside down and all the heat remained below the chassis! Now I placed it as it must be and ...no heat!

Now, I'm testing various preamp tubes...

[Wilder Amplification]

As for the 'unstable' comment, I noticed an effect on sound when playing that could be close related to the resistance of the fuses.

Whether you did or didn't is subject to debate, but if there is in fact a tone difference, this doesn't make anything "unstable". When something is "unstable", this is a term that is used to describe a certain exhibited electrical characteristic that is outside of the design spec of the appliance under test, not a tone difference. That's why the logic didn't make any sense.

[Bernardduur]

Whether you did or didn't is subject to debate, but if there is in fact a tone difference, this doesn't make anything "unstable". When something is "unstable", this is a term that is used to describe a certain exhibited electrical characteristic that is outside of the design spec of the appliance under test, not a tone difference. That's why the logic didn't make any sense.

Woops; I didn't meant that..... and again, I did. The bias would make the unit fluctuate a bit between 50 and 60% (rough margin) on the amount of heat / load it had...... So I would call it both tonewise fluctuating as unstable.

Removing it made my unit more 'stable'; it kept the bias set at one point