Oh, 1 more thing missing on the Rocket..(+ KF flyer & cl

[Clyde]

I used a MM AC30 power transformer.
P3- 9.46
P7- 335
P9- 326
I have the cathode cap also, liking it.

[angelodp]

Any thoughts on making this optional on a switch??

A

[rooster]

Well, OK, about that switch. The slick way is using a transistor circuit so that the cap can be switched in silently. But in the world of brutal beauty, you can just use a SPST mini switch. Add the cap, attaching the positive side of the cap to the resistor leg that attaches to pin 3. Next attach the ground leg of the cap to one leg of the switch, the other leg of the switch to ground. When you complete the circuit by throwing the switch, the cap is installed. Flip the switch the other way and it is removed.

If you have audio, if the amp is up and running, expect a popping sound as the cap is engaged, and a popping sound as it is removed from the circuit. This doesn't hurt anything but it will be quite audible. OK?

Alrighty then, back to the biasing of the EL84s.....

First off, let me correct what I said earlier. That was wrong when I said. "I think I am looking at a lot of COLD amps" as I looked at the voltage charts. What I should have said is that, "I AM LOOKING AT A LOT OF HOT AMPS". Which really makes more sense to me as to why all these builders are not adding the cap on pin 3 of V1. The power tubes are overbiased and already saturating.

How I realized my error is from a meeting with rawnster and comparing amps. He had posted that his voltage at the power tube cathode was 8.?? VDC. We measured it again this afternoon and it was actually 8.46 VDC. Next we checked his ma current on his power tubes. He has a well matched quad and they all measured at 42 ma. And here is where I realized my earlier mistake. The LOWER the voltage here, the higher the current draw form the power tubes. (So plainly, if you've ordered those tubes - WOAH BOY!! - you need to go the other way: instead of going UP to a HIGHER number, you need to choose instead, a LOWER number.)

Eh, my very bad. .....But it does explain why then all these guys are so happy with their amps with the V1 cap pulled: the power tubes are overbiased. Duh!

Any, the solution is to keep it like it is and keep buying power tubes - because they will burn out sooner. Or buy colder tubes from the gate. Or lastly, change the power tube cathode resistor to a higher value. And here, stock being 50 ohms, try 75 ohms like I run. (The side benefit to the last option might be that you can finally add the cap on V1.)

Now, I am hearing that all of you that are in the 8-9 VDC range are happy with your amps. Cool, your call. And rawnster also pointed out that someone here had seen a REAL ROCKET and this V1 cap was missing? Can somebody back this up? If you can, I am seriously confused about the origins of the posted schematic then and its otherwise identical cloning of an AC30TB Brilliant Channel. In other words, did somebody move away from something Ken actually did? I would like to know if this is the case, actually.

OK, longwinded, I'll follow up later. Again, sorry for the misdirection on the voltage vs. biasing current!!!!!!!!!

[RJ Guitars]

...First off, let me correct what I said earlier. That was wrong when I said. "I think I am looking at a lot of COLD amps" as I looked at the voltage charts. What I should have said is that, "I AM LOOKING AT A LOT OF HOT AMPS".

...And rawnster also pointed out that someone here had seen a REAL ROCKET and this V1 cap was missing? Can somebody back this up? If you can, I am seriously confused about the origins of the posted schematic then and its otherwise identical cloning of an AC30TB Brilliant Channel. In other words, did somebody move away from something Ken actually did? I would like to know if this is the case, actually.

Rooster, glad to see that correction of the hot/cold direction... these rascals are definitely pushing the tubes. I was kinda scratching my head wondering if I had everything wrong there.

I don't know if anyone has dramatically changed the bias and posted the results or not. These amps seems to be easy to push over the edge and most folks report tales of early breakup. With only 90 volts on that first gain stage and running hot biased EL84s in combination with all the other design aspects of the Rocket, limited headroom seems predictable. However, there are also reports of pristine cleans even when they are cranked.

There is enough known about the real Rocket that I believe that 2nd gain stage bypass does not exist on the original. If I recall correctly, the option of adding it was noted in an old document by Mark Abbott (one of the earliest of us to build a Rocket amp) and that is where I found my info that lead me to label it as "Optional". What is interesting about that is that almost everyone who built the amp has tried adding the cap and most liked it better without... there is probably some sound explanation for that but for myself I've only gotten as far as "it sounds better" that way.

As far as asking Derek Ferwerda about component values or voltage measurements, that has never happened. He promised Ken Fischer years ago that he wouldn't provide anyone the technical details on his amp and he remains faithful to that promise. He really enjoys helping others make better amps and when we talk about amps he talks about what he listens for and how he listens... His encouragement is always more about the pursuit of Ken Fischers ideals than repeating his successes.

rj

[rooster]

RJ - Hey, that's good info. So you are saying that Mark Abbott added the option of the bypass cap - but that the Rocket he saw DID NOT HAVE IT? Well, if I have this correct, and if it can be assumed that this was true for all Rockets (?), then this is interesting to know. It means then that Ken altered the AC30 TB Brilliant Channel slightly, and did not cop it exactly. Hm. Go Ken, I guess.

Well, then I will mess around with this cap a bit I think. I like how mine ramps up right now, but maybe the bass can stand to be lessened a bit. So tomorrow I will try a 1uf cap there, just to see if this is better to my ear. ......And I will try it without it, as well. Obviously my power tubes are not as saturated as some others here, so my amp is behaving differently. Playing rawnster's amp today was a good thing for the sake of comparison, and we both agreed, the amps were brothers from the same family.

Also I would like to add that the host of this forum is reported to have seen more than 3 Rockets. Is Allyn willing to share any insights on this subject of the cap/no cap on the second gain stage? That would be nice - and helpful at this point, too. As to Derek's position, OK, I get that. And since he's not building any amps it make perfect sense that he would not even know or care about it. Yeah, cool, play gtr is what I say to that, of course, it is a better past time.

OK, I'm done for the day on this. Happy Easter everyone. Rawnster, have a good event tomorrow and thanks for sharing your time. I learned much.

[CapnCrunch]

Hey Rooster:

This thread intrigues me. I am curious if you or RJ or Ron, or anyone else for that matter, has any thoughts into Ken's design philosophy in losing the second Cathode cap and working with lower voltages, thus pushing the output tubes to their limit. I know that one of Ken's driving philosophies was to push an amp to the edge of out of control. Hence the Express and the Liverpool.

What I'm curious about, is what is the noticeable difference between the Rocket and the AC30? I know that Ron's amp is not a KF made Rocket, but it's pretty close to Allyn's clone, and the clips I've heard sound fantastic. You've said his amp is definitely from the same family as your AC30. Can you tell us how the two amps are different? In other words I'm interested in how they are different, but I'd also like to try to understand "why they were designed to be different". Do you think that it was Ken's intent to alter the AC30 to make a better clean amp? Or do you think that his alterations of the circuit were intended to create a more "out of control" amp? Or maybe neither. Curious about your thoughts.

I am anxious to start my own Rocket (parts are on their way) and I'm enjoying reading everything I can about the various Rocket builds that have happened through this forum over the past couple of years. A lot of good info. and good folks here at the ampgarage.

[rooster]

captain - Well, here's the short answer. Except for that single cap, or lack of, and the beefed up power supply - the two circuits are identical. (This is refering to the AC30TB model, not all three channels, but only the Brilliant Channel.) And frankly, this should surprise some here, what with Ken's basic philosophy of being original and even dissing circuit copiests. ? Its kind of odd to consider. And when you read Derek's (from RJ's post) account of when Ken introduced him to the Rocket, it seems pretty clear that Ken thought it was quite a circuit.... And if Ken ever thanked Dick Denny I never heard about it. But its very clear he liked the AC30, and yes, adding the bigger filtering (bigger caps) in the power supply really helped the circuit. Mark Sampson (Matchless) did this exact thing in his AC30 clone, as well.

So maybe it was a sign o' the times, reinventing something that was unique and good, the AC30. At the time, who would have thought that the VOX amp would ever come back from a company named VOX? And it has, but certainly it is not as good. Wasn't it around 1990 when this happened? Clearly after Ken and Mark did their things

And that's what I have to say about it. The only sticky point for me is that Ken didn't acknowledge Dick Denny in word somewhere. Oh, I am sure he talked about him to people around him, he had to. But oh well. Of note, as well, there is a schematic in the Groovetubes book that has been drawn by Ken (Trainwreck Circuits) that pretty much clones the entire AC30 with the exception of the exact tremolo circuit (he alters it slightly), a beefed up power supply with a silicone rectifier (?), AND the cap missing on the top boost mod (just like on the Rocket, BTW) - that was drawn at least before 1990. I am not clear if he built a few of these amps or what, but I have to assume he did. Anybody seen one? In point of fact, if he did, and I will add that just mapping the schematic is a feat in itself, Ken clearly knew his shite. To this day there are no 'sissy' build guides for AC30s, this is a job for a man with an understanding of circuits and very complex circuit paths. Building a Fender or Marshall relative to a complete AC30 is like a stop by the 7/11 for a slurpy vs. making your own grain alcohol - very different things indeed.

OK, too much talk, brain needs coffee. Over and out and I hope this is helpful.

[rooster]

Clyde - OK, Buddy, it looks like you and I need to capitulate. No, we are not going to have sex. But I think we need to back up on the cap on pin 3. In my last post I revisited the only authentic Trainwreck schematic I know of - and truth be told, I forgot about it until I started writing my response to the captain. Clearly, in Ken's own drawing, he cops the AC30TB Brilliant Channel - and he omits the cap. (!!!)

So this is good enough for me as to documentation of of 'proper' Rocket circuit. Coupled with what seems to be the other versions from Mark Abbott, etc., I concede now that this was Ken's decision.

But, moving on to the rest of your build, I see that you are using a PT like mine, with 330VDC or so on the plates. Brother, you need to change that cathode resistor to something like 75 ohms. This will at least assure that you can find some power tubes that will work in your amp. Clearly, the quad you have in there now is too hot. You need to run a colder set in the very least. Eh, I know you say you like it like it is, but have you tried it another way? You might like that better. If you are familiar with eurotubes and want to try a colder quad, go with something like a number '24' or '26'. This would put you in the park. Thanks for sharing your voltages, BTW, this was helpful.

[RJ Guitars]

I'll attach a pretty good read on the Trainwreck line of amps. This is one of many documents that I collected in researching the Rocket amp before I actually built my first one. The attached catalog will tell you directly, the Trainwreck Rocket was intended to be the best you could get from an AC-30 top boost, without any of the bad... It is interesting that one person in ten actually preferred the VOX over the Trainwreck... imagine that, a factory amp that sounds better than a Trainwreck?

Now, if we give credit to Dick Denny, then we also should consider a debt to Jim Marshall, Leo Fender, and possibly some other un-named engineers from RCA that wrote the tube manual way back in 1947 or so.

The tube lineup, (Gain Stage-Gain Stage-Cathode Follower-Phase Inverter-Output section) is extremely similar in these amps. Take a 59' Bassman and look at the preamp schematic... a few subtle differences in the preamp component values and depending on your choice of output tubes, you've got a Rocket or AC-30 or JTM-45 - etc...

Happy reading

rj

[rooster]

RJ - Ha, good read. I also have a few flyers that Ken sent me years ago, and one on the Rocket. My scanner is on another computer but I will scan it and get it to you. Of particular note are the prices of the 3 amps. Drum role please...........

Express - $1995
Liverpool - $2095

Wait for it..........

Rocket - $2295

I for one, find it incredibly interesting that the single amp that smacks of clone should go for the highest price. Even today a NOS Mullard and a tube socket will go for less than $300. Eh, sign o' the times I suppose. Clearly, Ken was proud of the Rocket. Take care.

[CapnCrunch]

Hey Rooster:

There's a recent post comparing clips of an AC30 and a Rocket but they're both actually AC30's. Do you think it would be possible to do a blind taste test with your AC30 and Rawnster's Rocket. You know get a clip of each through the same speaker cab?

[Clyde]

Rooster, sorry bud, I've got a horrible headache and I'm happily married to boot. Unfortunately the amp in question is gone, my customer picked it up last night and he really liked the extra gain even after I explained the situation. It's sister amp, the AC30, whose clips I posted on the other thread, was on the road for over 2 years with nary a problem and the exact same circuit and voltages. The output tubes showed some wear so they were replaced a year ago-JJ's replaced the EL84M's, still going strong and this amp is gigged regularly.

[rooster]

Captain - Yes, I can do that. I recorded our little get together the past weekend, actually. Give me a day? I will add that the comparison is what it is, and this was before I pulled the V1 cap.

Clyde, man, did you at least tell the wife about me? Any, I did hear your sound clips. They are AAC files and need to be converted to MP3 for most folks, Mac vs PC thing. To me they sounded pretty compressed, just like an quad of hot EL84s should/would sound. I get that you like it that way and that it will survive the road. Here I am only wondering out loud if you would still like it if it were biased a little on the colder side? Since the amp has a fair amount of gain in the preamp, I suspect you would. Eh, but its not my call. Now, what would be interesting would be KF's biasing numbers on his Rockets and Liverpools. I am very sure he had an opinion here.

Nice job posting the clips, BTW, they were a great break and helpful.

[Clyde]

Hey, what happens on the amp board stays on the amp board. It's all good.
Seriously though, the fellow who owns the AC30 prefers his amp to the Rocket. He was in a hughly popular band when I first built the amp for him and I'll bet they did 200 gigs the first two years. In fact they all burnt out and had to shut it down for a year or so. I did try a 56R cathode resistor in place of the 50 and we both preferred the 50 in the Rocket. You can get away with running the tubes hotter in cathode-biased amps so I say "Run 'em hot". Sorry about the clips, I didn't do them and don't know beans about digital audio.

[Zippy]

Of note, as well, there is a schematic in the Groovetubes book that has been drawn by Ken (Trainwreck Circuits) that pretty much clones the entire AC30 with the exception of the exact tremolo circuit (he alters it slightly), a beefed up power supply with a silicone rectifier (?), AND the cap missing on the top boost mod (just like on the Rocket, BTW) - that was drawn at least before 1990.

Didn't want that to get lost in all the verbiage.