6550C

[Julia]

Well, since you all know I'm in paranoid mode on tubes I thought I'd give an update on these.

They are sounding better, but I've noticed something and just want to ask. I know some changes are normal. Is this normal?

Here are my initial bias settings on 9/1/09 (V1-V4 left to right): Note line voltage = 116 VAC

V1 = 40.4
V2 = 41.4
V3 = 40.8
V4 = 40.8

Here are my bias readings today 9/11/09: Note line voltage = 116 VAC

V1 = 37.8
V2 = 37.3
V3 = 37.3
V4 = 37.7

On 9/17 Line voltage was at 116 VAC:

V1 = 36.4 fine adjusted to 39.8
V2 = 37.1 fine adjusted to 39.6
V3 = 36.2 fine adjusted to 39.4
V4 = 35.3 fine adjusted to 40.1

Okay so today marks 4 weeks. No AC running today. (9/29) Line voltage = 120 VAC

V1 = 42.7
V2 = 41.9
V3 = 42.4
V4 = 42.8

So apparently there's a little jump with the line voltage going up only 4 volts. This is interesting because if I'd biased hot at 70% with the line voltage at a low point, when it returned to it's "normal" level, the bias could actually drift to 75 to 80% which would mean a shorter tube life especially if there is a weak tube in the quad. Right now they're at around 64%.

Interesting.

 

[Jaded Faith]

Totally normal results. I typically bias my KT88's @ 49 for example. Typical voltage in my house is 120-121. With AC and the dishwasher running during practice (3 amps and a PA running) I have seen it hit as low as 115-116 mid-summer. After 10PM here I can see it go between 124-126 on any given night. My bias will drift accordingly. I tend to bias the 88's @ 49 because the average voltage when we play out at any given venue is 115-116, which sits my tubes right between 42-46.

 

[Rod]

Interesting stuff folks!!

 

[Julia]

Totally normal results. I typically bias my KT88's @ 49 for example. Typical voltage in my house is 120-121. With AC and the dishwasher running during practice (3 amps and a PA running) I have seen it hit as low as 115-116 mid-summer. After 10PM here I can see it go between 124-126 on any given night. My bias will drift accordingly. I tend to bias the 88's @ 49 because the average voltage when we play out at any given venue is 115-116, which sits my tubes right between 42-46.

Funny thing is that I couldn't find anything about how line voltage affects tube bias, and it seems to be a trade secret among amp techs. It may have been contained in a bunch of formulas but it wasn't written in plain English.

 

[kylendm]

Just got my 6550s today. Just letting them warm up on a 35-37 bias so far. Gonna see where this goes .

 

[Rod]

Totally normal results. I typically bias my KT88's @ 49 for example. Typical voltage in my house is 120-121. With AC and the dishwasher running during practice (3 amps and a PA running) I have seen it hit as low as 115-116 mid-summer. After 10PM here I can see it go between 124-126 on any given night. My bias will drift accordingly. I tend to bias the 88's @ 49 because the average voltage when we play out at any given venue is 115-116, which sits my tubes right between 42-46.

Funny thing is that I couldn't find anything about how line voltage affects tube bias, and it seems to be a trade secret among amp techs. It may have been contained in a bunch of formulas but it wasn't written in plain English.

I personally think that a lot of techs aren't as fussy as some of are with our tube amps..They seem to have just a general knowledge of bias ect

 

[Julia]

I won't go that far. I just have this need to understand things.

 

[kylendm]

Hey I was just wondering how the results turned out. Did you get the tubes where they needed to be with out them drifting?

 

[Julia]

They seem to be sitting at 42 mV right now. My line voltage has gone up a couple points since summer. It's also at 121 VAC. The tone is good. I just hope these last longer than 3.5 months. I'm back to using my Hot Plate but set at 0 dB attenuation -- I've been using the line out. It's given me the ability to record two tracks at once -- one from the amp, and one clean direct from my JDI in case I need to re-amp.

 

[kylendm]

Very nice .

I was just wondering. How do you check you line voltage?

 

[Julia]

Very nice .

I was just wondering. How do you check you line voltage?

My power conditioner has an LED meter on it.

 

[eyeball987]

Marked for later. My 6550's should be here this week. I think I might also try a 5751 in the PI.

 

[jdr94]

man, now i wanna try some 6550's or kt88's. i've always used 6l6 amps and this is my first rm100 so i'm eager to try it all out anyone know how a 6v6 stands against the 6550? i know the wattage would be lower but tone wise.....

 

[kc2eeb]

JJ 6V6s and KT88/6550's are at the opposite sides of the stage. If you're a player who likes to push the whole amp, if you like SRV, Albert,B.B.,
even Keith or Jeff, if you're going to turn the master level all the way up, 6V6s will give you GREAT tone.
But, masters up, and use the gain like the volume control of an old, no master volume amp.
KT88/6550s were designed from the beginning to produce linear, high headroom POWER. Think Sunn amps (saw The Who with them) Loud and clean. If you like to form your tone in the preamp, or use a lot of pedals, and then want to take that sound and raise it, nothing better.
I'm not saying this as the only possibilities, just as a way to think about it.

 

[jdr94]

ah i see. think i'll be tryin the 6550's first. thanks for the enlightenment.

 

[supercharged 350]

Clips!

 

[m0jo]

Can you use KT90's in the MTS amps?

A set of KT88 / 6550's and a set of KT90's seems like a nice combo of hugeness..

Also what are these EL34L's I read about? They seem KT90-ish?

 

[Shinozoku]

Can you use KT90's in the MTS amps?

A set of KT88 / 6550's and a set of KT90's seems like a nice combo of hugeness..

Also what are these EL34L's I read about? They seem KT90-ish?

From what I've heard, the EL34L is more like a KT77 but without the perks of being super hi-fi. Basically an EL34 with more bottom end.

 

[m0jo]

Can you use KT90's in the MTS amps?

A set of KT88 / 6550's and a set of KT90's seems like a nice combo of hugeness..

Also what are these EL34L's I read about? They seem KT90-ish?

From what I've heard, the EL34L is more like a KT77 but without the perks of being super hi-fi. Basically an EL34 with more bottom end.

Aah okay, thanks!

I don't know how much I really need more low end with a bassplayer and rythmguitarist .. I guess it's a matter of trying it out