Variac a Super Lead instead of attenuating

[dirtycooter]

Try 8 into 16 and that should knock it down a few more dB. Tightens it up too a little more. Adds a little brightness also.
I didn't try 16 to 16 on mine yet. Will have to see when I am not so mezmerized by it all what I get there that way.

[vh junkie]

I notice that when you first turn down the variac, it is still pretty loud... but over time it gets quieter and quieter. Some of this could be explained by all the filter caps discharging slowly, but it seems too exaggerated for that. Something else is going on. Might try setting the variac at 60 before turning the amp on?

[dirtycooter]

Someone else said that too. That the variac adjustment didn't just poof! Do its thing and took a while to roll to a stop. Mine is like a 5 sec lag then it settles in to the voltage.
On start up do you guys fire up on full wall then after its ready to come off stand by then dial down??

[Krinkle]

Yeah DC, I noticed you were running 8 into 16. I should go ahead and do that, it will knock some volume off.

I set it the variac to 60VAC a week ago and my meter is connected and letting me know what my voltage is. That's what it's at when I turn it on.

I'll check the voltages today, B+ bias etc, and see what I have, that way anybody with their amp opened up can compare, and at least we'll have some numbers on record.

[Krinkle]

Figured it out, I'm an idiot with terrible eyesight. While I am a tech and have enough sense to figure out how to wire my new multi-tap 120/220 VAC variac, I'm too stupid to put my meter leads where I have my wires connected.

I had one meter lead on the next tap above the neutral wire (grounds are connected but are hanging off to the side, I still need to connect them to the variac frame, I know, don't ask!).

With it sitting on the floor it looked like it was in the right spot. When I put the meter lead in the right spot, I get 80VAC instead of the 60VAC I was previously measuring. I'm guessing that 20 volts is going to make a difference with the volume To quote my little nephew, "Hurrrr Durrrr!"

Anyways, teenagers are still sleeping, so when they get up soon I will let er rip again and see where I am. Now I'm really excited, it was sounding great at 80VAC, can't wait to try it at 60VAC!

Thanks for the comments guys, this is such a great place to hang out.

[Sean_McFly]

Dude this sounds so spot on for VH II
Great job! It's so open and clear! The presence and treble is there but not in your face, which is a wonderful tonal quality to have in a brown sound! Question: what mic did you mic your cab with, and what type of MXR 6 band is yours? Vintage blue or new black? Also, just because I'm a production nut, where do you keep your amp cab in accordance with your wall (angled, in a corner)? That makes a huge difference in recorded tone. Keep up the stellar tone

[Krinkle]

Okay, now that I'm at bedroom level because I'm finally at 60VAC, it's time to look at the next step.

At 60VAC I don't have the same distortion as I do when I have 120VAC and my LarMar turned down. Granted the LarMar will add distortion as you turn it lower due to the negative feedback frequencies not getting cancelled out, but I suspect that the amp is biased cold.

So I just set the variac to 90VAC so we can talk in terms of what we already know. DF says that the bias for Ed's amp is 50mA at 90VAC. Given that the general bias formula is;

I bias = EL34 power dissipation in Watts/Plate voltage

where;

EL34 PDW = 17.5W
Plate Voltage = 353VDC (just measured in my amp)

then;

I bias = 17.5W/353VDC
I bias = 49.5mA

It seems to me that Ed's amp is biased exactly as it should be, not cranked to near fire burning levels as I was imagining.

So what does my amp bias measure at 90VAC? The range for all four EL34's? Between 15 and 17mA!!!!! C'mon, that's too low! So, I'm headed down to the basement to see if I have enough bias voltage range to jack it to 50mA at 90VAC, then I'll run it at 60VAC and see how it sounds. Is this a risk, will the amp fry? I really don't think so. But I'm doing it anyway, you know what they say, no pain no gain......

[jnew]

The only pain will be if you get shocked. You're not going to hurt the amp Darren.

[Krinkle]

Okay, so that was fast. I can only get my bias up to 21.5mA at 90VAC!

Does/did Ed's amp have a resistor change to get enough negative voltage range to bias it to 50mA? It's never easy, is it?

Does anybody know what the spec is for Marshall PT's regarding the bias tap? How much power/current is available?

Where's Larry when you need him

[Krinkle]

The only pain will be if you get shocked. You're not going to hurt the amp Darren.

Last week I snipped my ground bus to put a 25k resistor between the 25k mid pot and ground to get the equivalent of Ed's 50k mid pot.

The end of the bus towards the input jack wasn't soldered well enough and came apart. The sound fizzled out and I got a pretty nasty zap when touched the standby switch to begin to turn the amp off!

[jnew]

I had to lower my bias resistor to get in range even at 90VAC. But I run my stuff at 90VAC. No doubt you would would really have to lower that resistor to get it to bias at 60VAC. I don't know that guys are re biasing at 60VAC though. Yeah, I think it's real cold down there if no re-biasing is being done but listen to the tones they're getting. Just have to play with it and see what sings to you.

[dirtycooter]

I thought Dave said bias up at wall voltage then drop down to 90 and the bias lays where it lays?
This I think is what he stated.
Which kinda makes sense if everything runs fine at normal and is tuned then dropping voltage should just scale down everything together.
All I know is I got my variac, unboxed, and without fear went directly to my amp. I referemce checked the output meter on the variac with my furman and found common readings. Plugged it in set at 110. Fired it up-actually sounded better than the 123v normal at the wall, played a bit, and just started dropping it.
The pilot light began to fizzle some and the tubes brightness dimmed down from a nice bright light to a warm less intense same color, volume really started to drop off about the same time my pilot light said "seeya" but the tubes still glowed dim and it sounded fine-just really quiet. Played like a mofo for an hour straight-sound never changed ir got goofy noises or erratic things goin on. Shut it offf for about an hour then went back in and powered up exactly as I left it lastly set, jammed another 20min and then shut it down again and went to work.
I stopped at 70 because that was more than comfortable volume level and nothing sounded like it was misbehaving or gonna go up in smoke. Less hiss and normal operating noise and not much heat from the tubes and trannies. Only thing I noticed about the sound was some sag and the distortion texture smoothed out and had this brown velvety texture to it and thats it. Sounded like my normal amp but just way sweeter. I am not freaked out or think its abusing the amp no where near as bad as running it wide open normally or into a load resistor that always makes practically instant scary heat conditions begin.
I think its fine. Everything is just scaled down and thats it. I really think if your sensible with the dial on the variac and listen its just less power and everything else is remaining the same.
No one else is flipped out reporting they smoked anything down yet.... and hey.... everybody is doin it

[Krinkle]

Had to check to make sure - from the spill the beans thread;

"The screen voltage measurement was taken with a bias of 30ma to 32ma. At full output power the sag was around 80 volts. Biased to 50 ma while the variac was at 90 volt I believe it was around 354 v on the screens. Now I am not looking at the paper with the specs so this is not exact but close.. The heaters were around 5 volts with the variac at 90. No change on the input circuit."

[dirtycooter]

I ain't scared of fuckin my amp up. This thing has sat unused for many years because its such a bear to manage volume and work it hard to get the tone I want with out a bunch if b.s. loads or what not. So...its stock.
Whats happening next is the power dampening is getting yanked completely outta the circuit, 6C's are goin in, and until then I am gonna ride these tubes at under 90v to 70v all day long like a cheap whore.
Something happens it happens. We been around and around this thing six ways from Sunday.
If this thing blows up it blows up. Big f'n deal. Its totally fixable. Yeah it would cost money but how much have we all spent buyin and tryin everything under the sun? Think about it.
I will take one for the team I guess and then I will have an excuse to visit George for some parts
Just how damn bad can it get? Really?
I am gettin cranked tone with no MV or attenuator bastardization to the final sonic outcome-my greenbacks are safe from blowing up. And all I wanna do is bang the front input of my amp like no tomorrow.
Life is good I am havin fun! Bein a pussy ain't gonna get me anything.

[dirtycooter]

Remember what Ed said in his 5153 creation video?

He drags on his cancer stick, looks at his cigarette in his hand, looks up and says

"You gotta take chances" with a smirk on his face