Building a Rocket - Layout Check for group build

[Fischerman]

Sven,
I don't know which schematic is more correct or what but there are some differences in yours and the one RJ posted (and the one I posted as well). Some things I noticed right off:

You're using a 47uF for the first B+ node and 47uF for the screen node
RJ's shows 80uF for the first and 40uF for the second

You show a 250K treble pot but RJs layout doesn't show the pot...I've seen some schemos with a 1M treble pot. I dunno which is more correct or what.

You show a 100K plate and 3.3K cathode resistor on the first gain stage; RJs shows 220K/1.5K. Interestingly, usually you'd see the 1.5K with a 100K plate and 3.3K with a 220K plate(at least in Dumbles and some others). Again I dunno what's more correct however IIRC one of the many Vox reissues used the 100k plate where another reissue used the 220k plate and people that know AC30s say the 220k sounds more 'right'.

You show a 1000pF coupler after the first stage; RJs shows 500pF. But then the plate/cathode pair on the preceeding stage are different too so...maybe it's a push?

You show .1uF caps at four places: the PI main input, the PI second input grid, and the couplers between the PI and power tubes (2).
RJs shows .047uF. I read in one of Aiken's papers (I think) that ideally that second PI input grid cap should be at least 10x the main input cap (I have no idea why) but that's often not the case in guitar amps. Still, you usually see a .1uF at the second input grid. What I'm getting at is that I always just put a .1uF there and will probably do so here...then I might adjust the main input cap.

Then there is the power tube cathode resistors, your schemo shows 2x130ohm where RJ's shows 2x100ohm (when seperate) and 1x250ohm when shared. I think that 250ohm value is supposed to be 50ohm when all four power tubes share the same Rk. If it's 50ohm when shared then they should be 100ohm when split...right? And the capacitance should stay the same when split (i.e. if shared uses 220uF then split should use 2x220uF)...right?

I don't know which values are correct and to be honest it doesn't matter that much to me since I'm gonna build mine taking what I perceive to be the 'best' of all of them (including the ole AC30). By the time we build these things we'll all know 'our' schematic like the back of our hand.

[RJ Guitars]

AmpGarage Guru's - Does anyone want to shed further light on the Rocket power supply? We've had some work going on behind the scenes on this topic. I'd like to bring the discussion out into the forum for the benefit of everyone.

One of the final frontiers in Trainwreck re-creation seems to be the Rocket Power Supply. There are numerous iterations of the Rocket mainboard and I've seen some authentic looking images of everything but the Power Supply.

Many of the "Amp Masters" have posted input and others have quietly provided info directly to me on "how it is in a real rocket". As you might expect, these do not all agree. In all cases I find the intent is to help us get it right... whatever that is.

The one area that I have yet to see any digital image of or even an authentic drawing of is - the Rocket power supply. When I go through the old archives I see that exact same scenario played itself out without consensus or closure previously.

There are however a few pieces pieces of information that pop up regularly and allowed me to come up with a list of the most popular assumptions and assertions as to the layout of the Rocket power supply.

#1 - The Rocket power supply is identical to the Liverpool power supply. Several heavy hitters believe this idea, or at least similar iterations of it. "Stack O' Caps" and no Power Supply board. The location of the cathode bias components varies. There is at least one AmpGarage post quoting conversations with Ken Fisher where he confirms the Rocket uses the 80uF cap like the Liverpool power supply.

#2 - The Rocket power supply used can caps with only the dropping string resistors on a PS board - then various iterations of mounting the cathode bias components. Again this info comes from noteworthy sources and I wouldn't quickly dismiss it.

(In #1 & #2 there is consensual agreement that the first cap is an 80uF)

#3 - It doesn't matter because the mojo is not in the power supply and several iterations have been proven to work well.


We have created our Rocket Group Build with the options wide open for power supply layout including: using a PS board, putting some components on a board, or no board at all.

I have my own ideas about how I'll build my amp but I'd like to bring as much information as we can get into the open so each builder can use it.

thanks,

rj

[Allynmey]

The Rocket uses no power board. The caps are stacked like an Express or Liverpool. They use the same dropping string resistor values and they are soldered to the front of the caps. It uses a 15H 75mA Choke. It uses a 50 Ohm Cathode resistor and 220uF bypass cap that is chassis mounted on the preamp side of the power tubes. Almost all the layouts and schematics I've seen have some parts that are wrong. The screen resistors are 5W 100 Ohm Dales.

[HeeBGB]

The Rocket uses no power board. The caps are stacked like an Express or Liverpool. They use the same dropping string resistor values and they are soldered to the front of the caps. It uses a 15H 75mA Choke. It uses a 50 Ohm Cathode resistor and 220uF bypass cap that is chassis mounted on the preamp side of the power tubes. Almost all the layouts and schematics I've seen have some parts that are wrong. The screen resistors are 5W 100 Ohm Dales.

And there ya have it!

[UR12]

The Rocket uses no power board. The caps are stacked like an Express or Liverpool. They use the same dropping string resistor values and they are soldered to the front of the caps. It uses a 15H 75mA Choke. It uses a 50 Ohm Cathode resistor and 220uF bypass cap that is chassis mounted on the preamp side of the power tubes. Almost all the layouts and schematics I've seen have some parts that are wrong. The screen resistors are 5W 100 Ohm Dales.

And there ya have it!

But how could that be? That doesn't sound anything like the Two Rock Clone that was a "direct copy" of a Rocket.

[RJ Guitars]

The Rocket uses no power board. The caps are stacked like an Express or Liverpool. They use the same dropping string resistor values and they are soldered to the front of the caps. It uses a 15H 75mA Choke. It uses a 50 Ohm Cathode resistor and 220uF bypass cap that is chassis mounted on the preamp side of the power tubes. Almost all the layouts and schematics I've seen have some parts that are wrong. The screen resistors are 5W 100 Ohm Dales.

Thank you Allyn, not much ambiguity about it. I am greatly appreciative of your help on this project and your work is certainly part of the driving influence to build these amps.

rj

[Sven]

deleted (look at page 23 for the best layout)

[Sven]

deleted

[Fischerman]

Sven your layout/schematic look great. Some things I noticed and I will need some confirmation on this from others please:

Your tube sockets are 'backwards'. Start at the gap and the first clockwise pin is pin 1. Also, the heaters on the EL84s are pins 4 and 5.

RJ are you sure the tone pots are both 1M-A...some schemos say linear some say audio. In my experience linear usually works better at the Treble pot and audio usually works better at the Bass pot (then linear for the mid pot if there is one). But I've never used this tone stack so I dunno.

Tha cathode resistor for the power tubes should be 50ohms.

That's all I noticed but I'm sedated today (medical) so I may be all wrong.

[Allynmey]

Audio pots on the Volume and tone controls. 100 Ohm screen resistors 50 Ohm cathode resistor. Move the power resistors to the other side of the power tubes. CF is mounted on the board as is the 33K grid resistor on the input. No mid pot. 10K resistor to ground for mids. The CF spans V1 and V2 on a real Rocket.

There is no 80uF cap, just (2) 40's in parallel like all the other wrecks.

Dana....

[Fischerman]

The CF spans V1 and V2 on a real Rocket.

Thanks Allyn, so it's wired like other 'Wrecks where the third stage uses V2 and half of V2 goes unused?

[Ron Worley]

Allyn-

I will pool my ignorance... what do you mean by "CF"

You do not mention the cut control- is it Audio or linear???

You mention 50 Ohm Cathode resistors- what wattage?

Just checking- 100 ohm screen resistors, not 1K??

Muchos Gracias!!

Ron

[Ron Worley]

OK, I took 2 seconds to think about it... CF- Cathode Follower....V2a following V1a....

I still have sooo much to learn...

RLW

[guitarsnguns04]

man...this is great that some of the people who actually know are contributing to the build. I sure appreciate Allyn chiming in with the facts. Thanks to all who have contributed and are contributing. It should make for a great build.

[Fischerman]

Another thought: Anybody know what preamp voltages to expect? Running it with the second stage on V1 (like a 'Wreck) or V2 (like a Vox) will definitely affect the voltages and, just as a wild guess here, it looks like our first stage plate voltage is going to be very low, especially if wired like a 'Wreck. Should we be surprised if our first stage plate voltage is, say 90vdc?

EDIT: Did some 'Wrecks use a single 9.1k first dropping resistor instead of 18k? Is that sometimes the case on these lower voltage amps?