AD 50, after bias and attenuator

[kars0747]

My custom shop AD50 has just been to the amp doctor, apparently a very good amp doctor who services several big bands in my country. He was really impressed with the amp which he has now biased. He especially seemed to like it with an old marhall cab loaded with greenbacks. However, I just tried it on my orange 212 ob loaded with a greenback and a g12h 30. After having the amp biased I must admit I prefer the 50watt setting. It has more clarity and punch which suits a les paul I guess. I tried to go back to closed back (I have made a seperate piece of wood) but it´s just so much sweeter as an open back.

Also I have bought a Palmer pdi06 mkII to keep the volume down a bit. I found out that the sweet spot on the volume knob was from two o´clock and up. Now I keep it on 3 o´clock and the attenuator set on 50% (which is not half volume but half the wattage). Since going back to the 50 watt I have finally started to bring the presence up a bit. I now keep it around two o´clock. Treble around 11 and bass around one. The gain I keep around 10.30. No need for overdrive pedals. If I want to clean it up a bit I just turn the volume knob down on the guitar. Also I have found that it improves the sound from my les paul if I take just the edge of the treble on the guitar. I think for now my quest for good tone with this amp has come to an end. Glad to finally be pleased and concentrate on the essential, which is to play. The audience probably won´t notice much difference anyway, and maybe the band won´t comment either. But I notice the difference and that makes me stand up a bit more tall and proud when playing.

[Boy_Narf]

Cool!

I re-biased the tubes in my RV100 right before I sold it. I set them a bit hotter and like you noticed a slight improvement. Bit more raw and felt better to play. Still sold it haha, but it is interesting none the less. I wonder how many folks fall out of love with their amps simply because the bias has drifted to far over to the cold side. I did some live testing while adjusting and couldn't believe the difference between the colder, and hotter settings. Really does make a difference.

I'm only using baby amps these days, so the bias is done automatically.

[MojoBlaster]

As the owner of an un-biased AD 50, I'd be curious as to how hot or cold your amp was biased.
I have searched high and low for some information on biasing and I'm hoping you might be able to provide me with a starting point.
Thanks,

[Boy_Narf]

Bias info should be in the manual.

[Jondog]

70% is a good starting point. I usually start there because it's about as hot as I would go. I liked my Rockerverb around 60-65%.

[Ade]

Bias info should be in the manual.

That was a joke right?

viewtopic.php?t=2148

I had a similar experience after getting my AD50 biased following a repair. Really seemed to wake it up.

This is a noob question, but what causes an amp to "drift" out of its optimal point of bias?

[kars0747]

I don´t know how he biased the amp - I just know it sounds good. I will ask the shop owner if he remembers anything from when the amp guru worked on my amp

[Les Paul Lover]

Bias info should be in the manual.

Only if there were bias access point and pot on the back of the head.

Biasing the amp with open chassis is pretty dangerous for the amateur.

[a.hun]

This is a noob question, but what causes an amp to "drift" out of its optimal point of bias?

Power valve wear. The current they'll output for a given bias will likely change a bit with use. It isn't the amp drifting, it is the valves.

Biasing isn't an exact science. There is generally a reasonable working range and biasing anywhere within that range is fine. Helps of course if all power valves are reasonably close to each other in performance and all doing a fair share of the work!

Best tech I know biases by ear, then checks the current to make sure it is a safe and reasonable setting. Makes sense really, if you know what you are doing...

He also generally favours a cooler bias for most fixed bias amps. (Not too cool obviously!) This is what he usually finds works best in terms of tone, punch, and actual power output.

70% idling dissipation isn't a target, it is an absolute maximum for many amps, and way too high for some.


Andy.

[Ade]

^ Thanks so much Andy.

Ade