Building a Rocket - Layout Check for group build

[RJ Guitars]

hey rj, what is that white keeper you are using on the PT wires...

The white keepers are from the local hardware store... there are actually two of them. They are white plastic loops with a set of screw holes in them. I'll get you a close up.

Any thoughts about a bias circuit for this amp....

The Rocket is a self biasing amp, so the bias circuit is pretty simple. a 50 ohm resistor in parallel with a 220 uF cap from pins 3 to ground on the output tubes. Where you locate those components depends on your choices between a hybrid build or a traditional one, but electronically they are fundamentally the same... let me know if that is what you meant.

Is the BOM and layout locked in.

In this case I am building a hybrid, although trying not to stray from the original circuit values... so maybe with a few small exceptions, I have finished the layout and BOM I'll use. I need to make a couple updates to the layout file and then I'll send it to you. I'll also post it here if there are others interested in it...

At this point in my picture, this amp could become either traditional or hybrid. The layout and BOM differ slightly between those two, but as I said, electronically the intention is to keep the circuit exactly the same. I don't want to dictate to anyone what they should build, but rather offer to assist and provide support for whatever choice they make. I will give you all the intimate details and closeup pictures of my build you want.... and you can copy me exactly if you want.

We have also secured a really good set of images and plans for a traditional Rocket so that a person can build it exactly like the original if they choose to... either way, let me know what you need and I'll make it available. I'm considering building both so I can actually hear for myself the differences between the two and undoubtedly learn something in the process.

What is that bare wire below the fuse?? Can you send another close-up please

It's kinda of an optical illusion in the picture... I think what you are seeing is the tabs on the fuse holder that I soldered the leads to... they are not actually below the fuse holder... I'll definitely give you close ups from other angles. I prefer to wait until daylight hours to photograph so I can get good natural light... it will be tomorrow evening before I get that done.

I'll be in touch,

rj

[RJ Guitars]

RJ, connect the plates of V4 and V5 together and V6 and V7 together. You have them mis wired in that pic.

Allyn, you are right. I had not appreciated this wouldn't be correct for the traditional way of wiring it....

Let me make sure I understand - we are talking about pin #7 and the "normal wiring on a Rocket" makes pairs of V4-V5 & V6-V7. The way I have it makes pairs of V4-V6 & V5-V7.


If you can indulge my hybrid notion of the half power option, I think the way I have it makes it simpler to pull two tubes or switch them off... fully recognizing that it's not traditionally correct, but it should be fundamentally the same circuit.

I won't try to argue that it's better or even good, but am I correct to believe that it would be functional as wired?

rj

[Allynmey]

Let me make sure I understand - we are talking about pin #7 and the "normal wiring on a Rocket" makes pairs of V4-V5 & V6-V7. The way I have it makes pairs of V4-V6 & V5-V7.

correct.

Wire the cathodes inner and out pairs. 1/2 power switch doesn't give half power in amp volume though. try it you'll see.

[angelodp]

If that is true then why bother with the 1/2 power switch

ange

[Fischerman]

That's why I didn't install one...IMLE it doesn't affect volume that much but the amp will sound better in full power mode. I've tried 1/2 power switches in the past and they always stay on full power. There was post by '67Plexi (the Carol-Ann guy) about "Just finished servicing Ginger" and he said it had a 1/2 power switch and said a similar thing. But these are different amps so maybe 1/2 power works. I can tell you this much...they aren't bonecrushingly loud to begin with...not compared to a 50W Marshall or an Express.

RJ, if you wire the grids right it will be electrically the same...but different than most other 4-tube amps. I would do it to be consistent with other amps...who knows what rock star will be playing your 'vintage homebrew Rocket' in the year 2108?

And hell no RJ...I hate heater wiring MORE than you do!

Oh yea; the Matchless Chieftain circuit uses a reverse-audio bass pot.

[RJ Guitars]

... 1/2 power switch doesn't give half power in amp volume though. try it you'll see.

Yea I'm aware of the half power vs half volume thing... For the sake of those that haven't seen the theory written elsewhere or in other terms - The rule of thumb is you'll have to be 10X higher in watts to achieve 2X in volume... it's that non-linear component of audio.

If that is true then why bother with the 1/2 power switch

The half power switch will change the character of the amp in many ways... kinda like switching to a different amp. My understanding of this mod is that among the other things it does, is it allows the amp to break-up a little earlier but may sound awful when you crank it all the way up.

It's that earlier breakup that I want... and yet I'm inclined to believe that Fisch is right... 1/2 power switches usually stay on full power.

Historically, the majority of my build history has to do with small output amps from 1/2 to 4 watts... big amps are just learning tools to help me find the Grail.

rj

[Allynmey]

1/2 power switches don't significantly reduce power. They do however screw up your OT impedance. Say the Rocket OT has an input impedance of 4.3K. In half power mode the tubes are now looking for 8.6K to keep the correct balance. You will have to adjust your speaker selector to correct the impedance if you want the sound to be similar.

[angelodp]

well this disconcerting to hear. I do not want to build in the 1/2 power unless its safe and clearly works.

[DocJames]

yeah, I know for myself on this build. If I want to be able to decrease volume, I'll be looking at power scaling the whole amp. Txbluesboy, how has the VVR worked so far in your build? Any change in tonal properties from loud to soft? Does it break up nicely at lower volumes?

James

[Abstract]

well this disconcerting to hear. I do not want to build in the 1/2 power unless its safe and clearly works.

Will it "work"? Absolutely.

Now, will it work as you expect it it should? Maybe, maybe not.




The wattage will be halved (or an approximation thereof)...the "issue" is that wattage is linear...and humans hear on a logarithmic scale. We perceive a doubling of wattage as a 3db volume increase (just barely perceptable) not a doubling of volume. FYI doubling volume is an increase of 6db.

It works the same way backwards.

You halve the power and just barely drop the volume.


If you want to halve the volume...multiply wattage by .1 (divide by 10....a 10w amp is 1/2 as loud as a 100w amp)

[Lonely Raven]

well this disconcerting to hear. I do not want to build in the 1/2 power unless its safe and clearly works.

Will it "work"? Absolutely.

Now, will it work as you expect it it should? Maybe, maybe not.

If you want to halve the volume...multiply wattage by .1 (divide by 10....a 10w amp is 1/2 as loud as a 100w amp)

Which is why it cracks me up when people are like "Oh, that's only 40 watts".

[UR12]

I'll be looking at power scaling the whole amp. Txbluesboy, how has the VVR worked so far in your build? Any change in tonal properties from loud to soft? Does it break up nicely at lower volumes?

James

I have the VVR installed in an Express and I am regulating the whole amp and it is working great. You do loose a some of the quality at extremely low volumes but it doesn't matter how you go about dropping the volume your speakers will reach a point where they aren't moving enough air and at that point you will loose tone. Anything above the extremely low volumes (Think 1/2 volume instead of 1/2 power) you get very nice tone, breakup, harmonics and sustain.

[Allynmey]

Use the VVR. They work great. I've been installing them in my Concorde Clones and they work great! Dana's a genius

[angelodp]

What about a layout for the newbies

ange

[tubedogsmith]

Here's another possible option. It's a variation on an old master volume a guy on the Metro amps forum posted. I've pulled the power scaling thing out of a couple Marshall clones/replicas, what have you, amps and put this in for a large, large improvement. I was really suprised how good it sounded. I haven't tried this in a wreck type amp and probably won't but here it is if somebody wants to try it.