This is fascinating. I personally think the weirdest most telling thing here is that Ken actually cloned an AC30, or wanted to. Here's a guy who created the Liverpool and the Express - and then started producing and selling AC30TB clones.
In a way, it makes sense, because all AC30s are not created equal, and it's obvious with Ken's amp repair service that he could have run into one or two that were remarkable. I can easily see him being fascinated with the build and wanting to sort it out. Which I think he did to a good degree. However I also think the Rocket was - in a way - a work in progress. I personally think that he had some revelations here, while working with the Rocket, and hence the various Rocket version seen. One thing here that stays with me is the story by 2tone regarding the idea of the switchable 220K load resistor - that Ken contacted him after the completion of the sale and said that this would more correctly duplicate the AC30 layout (the added Normal channel load in an AC30). I mean, what? Here he was selling the Rocket amp and yet it occurs to him that the tone and feel of the AC30 could be better duplicated by adding a load resistor. This shows an appreciation of the AC30, yes, but it also says to me, work in progress.
2tone, if I misrepresented this story feel free to enlighten me.
Most people stall out when fixing a mistake that they've made. Why?
rooster wrote:This is fascinating. I personally think the weirdest most telling thing here is that Ken actually cloned an AC30, or wanted to. Here's a guy who created the Liverpool and the Express - and then started producing and selling AC30TB clones.
In a way, it makes sense, because all AC30s are not created equal, and it's obvious with Ken's amp repair service that he could have run into one or two that were remarkable. I can easily see him being fascinated with the build and wanting to sort it out. Which I think he did to a good degree. However I also think the Rocket was - in a way - a work in progress. I personally think that he had some revelations here, while working with the Rocket, and hence the various Rocket version seen. One thing here that stays with me is the story by 2tone regarding the idea of the switchable 220K load resistor - that Ken contacted him after the completion of the sale and said that this would more correctly duplicate the AC30 layout (the added Normal channel load in an AC30). I mean, what? Here he was selling the Rocket amp and yet it occurs to him that the tone and feel of the AC30 could be better duplicated by adding a load resistor. This shows an appreciation of the AC30, yes, but it also says to me, work in progress.
2tone, if I misrepresented this story feel free to enlighten me.
The 220k and 25 uf mod wasn't actually recommended as an improvement. It was more a curio, to get a little more of an AC 30 grit to the sound by duplicating that part of the schematic. The Rocket stock has a more pure sound and lots tighter bottom than an AC30(80 uf filters). I installed the mod, but never use it, as I prefer the straight Rocket sound, as did Ken of course.
It's funny that for a lot of people here the rocket is an AC30 clone and in my honest opinion it's NOT that!!
The basic architecture of the AC30 is totally diferent. The schematic may be close but having 1 input Vs. 4 , diferent transformers, diferent chassis, and as 2tone said diferent tweaks to the circuit in the places that it really counts makes it a totally diferent amp which to me represents Ken's genious to the max.
The Liverpool which was his first design by the way wanted to emulate Brian May's sound but only with the amp. So Brian May' AC30's plus the germanium transistor treble booster= Liverpool straight. How cool is that?
Then the Express came and it was meant to be a brown sound (Eddie VH) on steroids and with 2 goals in mind: clean with guitar or go to infinite sustain even not dimed.
That is what I've heard from people close to him or read in interviews but still his favorite out of those 3 was the rocket. I think Ken described it in a brochure like an AC30 that died and went to heaven.
One day someone told me that the rocket was the most dynamic of the 3 amps and @ that moment I didn't understand dynamic as touch responsiveness but range from clean to mean.
Now I finally got it, with single coils, strat or tele if the rocket is not dimed but a generous 1pm on the volume you can still have lots of dynamics even with the guitar on 10, and all controlled by your touch.
That to me makes all the sense in the world.
Last edited by redshark on Mon May 19, 2014 2:46 am, edited 1 time in total.
rooster wrote:This is fascinating. I personally think the weirdest most telling thing here is that Ken actually cloned an AC30, or wanted to. Here's a guy who created the Liverpool and the Express - and then started producing and selling AC30TB clones.
In a way, it makes sense, because all AC30s are not created equal, and it's obvious with Ken's amp repair service that he could have run into one or two that were remarkable. I can easily see him being fascinated with the build and wanting to sort it out. Which I think he did to a good degree. However I also think the Rocket was - in a way - a work in progress. I personally think that he had some revelations here, while working with the Rocket, and hence the various Rocket version seen. One thing here that stays with me is the story by 2tone regarding the idea of the switchable 220K load resistor - that Ken contacted him after the completion of the sale and said that this would more correctly duplicate the AC30 layout (the added Normal channel load in an AC30). I mean, what? Here he was selling the Rocket amp and yet it occurs to him that the tone and feel of the AC30 could be better duplicated by adding a load resistor. This shows an appreciation of the AC30, yes, but it also says to me, work in progress.
2tone, if I misrepresented this story feel free to enlighten me.
The 220k and 25 uf mod wasn't actually recommended as an improvement. It was more a curio, to get a little more of an AC 30 grit to the sound by duplicating that part of the schematic. The Rocket stock has a more pure sound and lots tighter bottom than an AC30(80 uf filters). I installed the mod, but never use it, as I prefer the straight Rocket sound, as did Ken of course.
Sorry 2tone, if I may be so bold, what is this mod?
redshark wrote:I wish you could show us a pic of how the switch is wired.
can't show chassis pic, but it's the 25 uf from the v2 cathode to ground. This is omitted in regular Rocket for clarity sake. Also an extra 220k from the 220k post tone stack(join to the existing 220k and then thru switch to ground) both the components can be grounded by one switch..
Had a bit of extra time today so I swapped my Stancor 8356 out of my Rocket and installed a MM TW-PT in there to compare voltages.
My wall voltage was a little high today at 122v.
I ended up using the 260v taps on the PT and was happy with the voltages it produced.
I reverted back to the 50 ohm bias resistor and when I fired up I had 297v on the plates and 10v on the bias. Quick math tells me that this is 14w and 48ma and spot on with vintage AC30 specs.
I watched the tubes and I had no red plating so I will leave as is for now.
Sound of amp did change a bit and breaks up a little easier. I think the tone is smoother and not as stiff if that makes sense.
The higher voltage of the Stancor did keep things tighter and cleaner at higher volume so might be useful for some.
Just my 0.02 but I think the MM was a better choice for this application over the Stancor 8356.
Drew.12345 wrote:Had a bit of extra time today so I swapped my Stancor 8356 out of my Rocket and installed a MM TW-PT in there to compare voltages.
My wall voltage was a little high today at 122v.
I ended up using the 260v taps on the PT and was happy with the voltages it produced.
I reverted back to the 50 ohm bias resistor and when I fired up I had 297v on the plates and 10v on the bias. Quick math tells me that this is 14w and 48ma and spot on with vintage AC30 specs.
I watched the tubes and I had no red plating so I will leave as is for now.
Sound of amp did change a bit and breaks up a little easier. I think the tone is smoother and not as stiff if that makes sense.
The higher voltage of the Stancor did keep things tighter and cleaner at higher volume so might be useful for some.
Just my 0.02 but I think the MM was a better choice for this application over the Stancor 8356.
How high were your voltages with the Stancor? I'm guessing you just crossed the Class AB to Class A threshold with that swap.
Zippy,
I posted my Voltages of the stancor on the first page of the thread but it ended up at about 325 on the plates.
Either way I think it sounds a whole lot better now with the lower voltage.
Next up I need to order a 250-0-250 and hear how that sounds to really make my mind up on these Rocket PT choices.
Drew.12345 wrote:Zippy,
I posted my Voltages of the stancor on the first page of the thread but it ended up at about 325 on the plates.
Either way I think it sounds a whole lot better now with the lower voltage.
Next up I need to order a 250-0-250 and hear how that sounds to really make my mind up on these Rocket PT choices.
Thank you, Drew.
While trying to sort apples and ducks with voltages, it may also be interesting to adjust the dropping string such that preamp/PI voltages stay the same while changing the operating point of the outputs.
Zippy is right here. My AC30 is 325VDC and I had to change the power supply resistors to get it sounding in the park with my Rockets. (And I don't use a cathode cap on V2, identical to the Rocket.)
Most people stall out when fixing a mistake that they've made. Why?
Another Poster here, Dave G., sent me this about that 220K resistor to ground mod:
"...adding that extra 220k to ground at the PI entrance cuts the signal going into the power section by -6dB, giving the 2nd preamp stage much more of a chance to clip before the power tubes go into hard clipping. Giving that stage a chance to clip more not only prevents the power section from clipping too hard, but also means that the signal going in to the power stage is now asymmetrically clipped, so a lot more even order harmonics are preserved."
Now that on a switch I'd like to hear.
In theory, theory is the same as practice. In practice it's different.
