My Liverpool Experiment

Express, Liverpool, Rocket, Dirty Little Monster, etc.

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jferris5
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Joined: Thu May 15, 2008 2:05 pm

My Liverpool Experiment

Post by jferris5 »

I wanted to share this build and progress so far. I was going to build a straight up Liverpool but decided to experiment some. This build has the Liverpool power section along with another Ken Fischer inspired preamp,the one with the split plate resistors.

So far i'm pretty happy the way it came out but I'm having 1 issue. This thing is running HOT with the 130 ohm bias resistors. If I did my math and measurements correctly its running 25 Watts dissipation!!!

I have a 160, 180, and 200 on the way to try out in hopes it will settle things down.



I'd love to hear your feedback and suggestions!

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Mark
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Re: My Liverpool Experiment

Post by Mark »

I'd imagine with the higher rail voltage that the valves would exceed their 12 watt rating. I don't think the 130 ohm resistors will do much to lower the current. The 1K resistors on the screen grids should help the valves once the signal is applied.

How did you come to the figure of 25 watts dissipation?
Yours Sincerely

Mark Abbott
jferris5
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Re: My Liverpool Experiment

Post by jferris5 »

These are the numbers and math I used. Its very possible I messed this up:

V4
Resistance CT to Plate = 47.5 ohms
Voltage Drop = 3.6
Plate Current V/R = 3.6/47.5 = 0.0757
Plate Voltage 328
Plate Voltage * Plate Current = 328 x 0.0757 = 24.8296

On the links above the "bias" one is my calculations for v4, v5, v6, and v7.
sluckey
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Re: My Liverpool Experiment

Post by sluckey »

The voltage you should use is the voltage between plate and cathode (328-11.1=316.9) And 316.1 x 0.0757 = 24 watts. That's a little lower. But that power is shared by V4 and V5, so if you assume the power splits equally then each tube is idling at 12 watts. That means the tubes are biased at 100% max plate dissipation and that's quite normal for a cathode biased amp. I'd say you are right on target.

I personally like to use 150Ω cathode resistors just to run the tubes a bit cooler. Doesn't really make much difference but it just gives me a better feeling. :D
jferris5
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Re: My Liverpool Experiment

Post by jferris5 »

Ah thanks...I knew i was forgetting something. I''m still going to bump the cathode resistor up some to cool them off a bit.

Here is a quick demo, dont mind the crappy playing.

https://youtu.be/4aKgYKpJ50I


[youtube]https://youtu.be/4aKgYKpJ50I[/youtube]
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pompeiisneaks
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Re: My Liverpool Experiment

Post by pompeiisneaks »

Sounds great! To use the youtube button here, you need to just use the part after the / or the = depending on the url type, yours is:

4aKgYKpJ50I

So I'd wrap that with those tags to get:




Removing some spaces to make it 'not' work gets teh same idea:

[ youtube ]4aKgYKpJ50I [/ youtube ]

You'd want to remove those spaces and have none, just aded them so it's more obvious what I did.

~Phil
tUber Nerd!
jferris5
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Re: My Liverpool Experiment

Post by jferris5 »

Thanks Phil. As you can see I was struggling with the youtube tag...lol
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Vince
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Re: My Liverpool Experiment

Post by Vince »

With your voltages try 180R - 220R cathode resistor. You can it biased at about 85% at idle. EDITED: 180R - 220R cathode resistor PER PAIR.
And you will like what you hear :)
Last edited by Vince on Mon Nov 13, 2017 6:00 am, edited 1 time in total.
Mark
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Re: My Liverpool Experiment

Post by Mark »

This is pretty much the same thing I found with my Rocket. A single 100 ohm resistor would put it in class A/B, there are AC-30's out there that use 80 ohm resistors. So I wouldn't get too hung up on resistor values.
Yours Sincerely

Mark Abbott
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Vince
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Re: My Liverpool Experiment

Post by Vince »

No more class A EL84 with B+ voltages over 280-300V.
AC30, TW, all DR Z, Matchless, BadCat amps all are class AB amps with silly overbiased EL84.
"Class A" marketing hype on these tube eaters ;)
jferris5
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Re: My Liverpool Experiment

Post by jferris5 »

Thanks guys. At higher gain settings it can be fizzy sounding. Someone on a different described the sound i'm hearing perfect, it sounds like the fizz is sitting "on top" of the notes. Do you guys think bringing it down to 70-80% idle will help? It could be the speakers too, I'm currently running it through a 2x12 closed back Mesa Boogie Rectifier cab loaded with vintage 30's. I'm looking to get an avatar single 12 so i can play around with some different speaker too.
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Vince
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Re: My Liverpool Experiment

Post by Vince »

Yes, higher cathode resistor get out some "shattered glass" from tone.
Sound will be warmer and rounder - simply try it.
I edit my previous post:
EDITED: 180R - 220R cathode resistor PER PAIR
jferris5
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Re: My Liverpool Experiment

Post by jferris5 »

I already have some different values on the way to play around with...lol I'm hoping they will be here early this week.
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norburybrook
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Re: My Liverpool Experiment

Post by norburybrook »

try it through a pair of Alnico speakers.

For me it's the perfect choice for a rocket, it sort of smooth's out the high end and also gives some speaker break up too. think of the original AC30...2x12 blue alnico speakers.


the Z wreck matching cab is a 2x12 gold and blue celestion alnico.


for me they soften the sound very nicely.


MC
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