Measure the clean power of your TW?

[jaysg]

Has anyone measured their clean output for the TW amps with a scope & a load?

Over the weekend, I played a few of my amps up loud. I could tell that the Liverpool clone wasn't as loud as my 18Watt...clean power only. I have it on the bench and I'm seeing roughly 10W clean at 1KHz. It was running a 12at7 pull in the PI, so I swapped in a new 12ax7...worse. I did sweep a range of frequencies to be thorough.

Unlike most amps, the onset of output distortion is not the end of amplitude. The output signal gets larger as the input increases. I'm used to seeing more of a railing behavior. Interesting.

[Cliff Schecht]

Others have discussed Ken's designs thoroughly in regards to how he achieves his distortion. His designs start distorting at the power amp, then the PI, the the third, second and first stage (in that order). This is how he achieves the clean to mean sound so well, initially avoid preamp distortion allows you to roll off your guitar volume just to the point of slight or no power amp distortion and therefore achieve a clean sound. I love this design ideology myself, I think it's a big part of the trick to achieve a great sounding distortion AND a great clean sound without having to muck with the amps volume/tone controls. I would really love to see his design notes to see how much of his design was guess and check vs. actually calculating the gain and signal level of each stage and biasing/adjust these variables accordingly to achieve the sound he gets from these amps.

[jaysg]

...designs start distorting at the power amp, then the PI, the the third, second and first stage (in that order).

I'm seeing the PI output and output basically tracking, and no distortion from the V1 sections. (I'm not running 2Vrms into the input..lol) HP function generator into the input and into V2.

[dartanion]

I am not sure you will see much clipping in stages 1 and 2, but it is true that they clip PA > PI > Clipper. It also ramps up quickly and won't be super clean. I always tell folks to set the sweet spot on the amp distortion wise, with the guitar tone midway, guitar volume all the way up. This is max volume, max distortion. Then work it all from the guitar. You should be able to roll down the volume into nice cleans, then roll up for distortion. Then use the tone(s) and pup selector to vary the tone. It also helps to vary your attack on the strings to conjure the right mood.

[jaysg]

Bump...seriously, no one has looked at this? 1KHz sine wave, 8 ohm resistive load, oscilloscope?

[bigbeck]

I don't understand why you would do this. Unless you were troubleshooting a low volume or tone problem.

[Scumback Speakers]

Bump...seriously, no one has looked at this? 1KHz sine wave, 8 ohm resistive load, oscilloscope?

My amp designer did it for mine. At 2 on the volume knob my dual 6V6 Capt Crunch (single ended) amp puts out 10.8w RMS, 8 ohm, clean, 1khz signal. At 5 it's 16w, and around 19-20 on 8. He won't dime it to measure that (damage to oscilloscope?) power rating.

But the clean power ends at 2, and it gets more gain/distortion as you turn it up...pretty typical from what I know of amps.

[jaysg]

I don't understand why you would do this. Unless you were troubleshooting a low volume or tone problem.

I am. Read my first post again. I've got a 4x EL-84 amp with a 300mA PT, that's only good for 10W clean and 20W square waving. If that's all a Liverpool does with the Heyboer set, then I'd like to know that. It would also be good to know about the Express and Rocket. I'm using the Sarge's Russian tubes, fwiw. A clear improvement over the JJs.

btw, I take back the last observation in that post. The amplitude doesn't go up as much as I thought after the onset of clipping.

[rooster]

jaysg - http://www.hammondmfg.com/pdf/EDB290MX.pdf

This is 230ma and that's for a 6 12AX7, 4 EL84, recto, and two primary taps, 120 and 240. Without the 240 AC tap it looks like 220ma is enough to do the Rocket or Liverpool.

Why do you think 300ma is only good for 10 watts clean? Lord knows, if the AC30 style amp is working, it sounds like jumping into a bowl of rice crispys - a good thing - but where would anyone draw that line as to super clean (no distortion) vs. typical AC30 'clean'? Eh?

FWIW, you might want to consider changing the cathode resistor? I run 75 ohms in my AC30 and Rockets. This probably gets me a little more 'clean' power than the typical 50 ohms in the Rocket. Also, doesn't Ken use 60 ohms in the Liverpool? FWIW, he did offer two bias points for the same output tube compliment and I think that's important to note. (I mean here that this is perhaps an area to consider for fine tuning your particular amp and its power tubes.)

[rooster]

Oh, make the 65 ohms in the Liverpool.

All of which is to say mix it up. If you want more clean headroom, start there. There will be a point where you might say 'too clean' but then look at me, I run a 75 ohm resistor and I think it sounds great. If I remember right, I was seeing almost 12 VDC on the cathode and everybody else was at 9.5 or something. That's a pretty significant difference - and they all loved theirs where it was. ?? OK, to each his own.

One other thing to ask you, jaysg? What pots are you using?

[jaysg]

Oh, make the 65 ohms in the Liverpool. [clip] One other thing to ask you, jaysg? What pots are you using?

My point about the PT rating is that it is capable of 30 to 35W unto itself. It uses the 5200 ohm wiring. I expected to get something on the order of 20 to 30W clean, so I want to know what the deal is before tearing into it. I recall Glen saying that he can't really get 'clean' from his Liverpool in a band setting, whereas his Expresses do fine. That's possibly a telling observation. Dunno yet.

I set the cathodes up with twin 120 ohm cathode resistors and 220uF caps, so that's like 60 for all 4 -- pretty standard. I suppose I should make sure the bypass caps are good. The pots are RV4, standard values. I've been injecting a sine wave at the input jack and at the input to V2, with the same output levels. The amp is built with power scaling. Jumping around that yeilded a watt or two.

I don't have any larger value 10W resistors...the 36W uses 150s, iirc...total of 75. hmm...

[rooster]

OK, I was looking at a Liverpool schematic and it showed 130 X2? Something to look at maybe.

Yeah Glen is an experienced player. Too, the Liverpool is very different than the Rocket. I have only built the AC30 and the Rocket so I can't speak accurately about the Liverpool. That said, I did convert one of my Expresses into a cathode biased EL34 pair and was amazed at how much distortion and compression was there. Too much. It became clear to me at this point, comparing the Liverpool to the Rocket, that Ken really made an effort to accomodate the Express front end attached to a cathode biased EL84 quad. Was he happy with it? I dunno. I do know that the last thing he did was create the Rocket, his AC30TB spin, and he seemed pretty over the top about it. ?? Not sure if you see any significance in that but I do, and just speculation on my part.

To me, the Rocket is pretty cool. And can be very loud I might add. I have no problem keeping up with any band situation using my Rocket into a 2/12 cab - and yes, I use an OD pedal into it. The Express, in comparison, is 'fuller' sounding (more bass with less distortion?) and louder into the same cab. I like them both but run with my Express most of the time. One exception was an outdoor gig or two with a 4/10 open back box with Weber reconed Jensen C10Qs. And this speaks to what the Rocket does best maybe, putting out a beautiful throaty midrange and some sweet top end. Plenty loud.

OK, rambling but check your cathode voltage? Try to get it into the 11-12 VDC range and see what you think. Considering the tubes Ken liked - the Sovtek EL84M - he was probably seeing 12 volts. I say this because, compared to the J/Js, they are very very cold given the samples I have tried. For example, running the coldest J/J set I can get from Eurotubes, and running the 75 ohm cathode resistor, I am seeing about 12 volts. ?? Yeah, when you said you didn't like the J/Js in your amp I could see why. They probably had 9 volts on the cathode - again - something I think Ken was trying to avoid in the Liverpool.

Oh, your pots are a good choice, just asking. I have found that a lessor pot just ruins these TW amps.

[jaysg]

el-84 cathodes idle at a tad over 8V. B+ is about 325V.

[Jackie Treehorn]

Perhaps there's a lack of headroom in the third stage? I would stick a sine wave of 2-3 volts peak to peak at the phase inverter input and see what the power amp does on its own.

[rooster]

jaysg - OK, this explains everything to me. Either try some other tubes that are much colder or change your bias resistors. Easily, running that quad (@ 8volts!!), you can change you bias resistors to 150 X2 and still be under 11 volts. I would do this in a heartbeat, what have you got to lose?

As to the PT, you are not running the typical Heyboer I see - you have too much B+. Just another reason to get those tubes in a cooler range. Er, I assume that 300+ number was from an EL84 plate? OR was that your actual B+ at the standby switch? Either way, they tell me that 300 at the standby switch is the target and I tend to agree - so - anything higher needs to be compensated for at the cathode and even the preamp B+ supply. I had to do this to the AC30 build before it would even begin to get to the sounds I was getting from the Rockets.