New Rocket build

[M Fowler]

12AX7 amplification is 100
5751 amplification is 70
12AT7 amplification is 60
12AU7 amplification 20

So it lowers the amplification. You can use any tube of the varieties 12AX7, 12AT7, 12AU7 to lower the V1, V2 and PI stages. Can't remember what the 12AY7 gain is maybe 40.


Mark

[rawnster]

12AX7 amplification is 100
5751 amplification is 70
12AT7 amplification is 60
12AU7 amplification 20

So it lowers the amplification. You can use any tube of the varieties 12AX7, 12AT7, 12AU7 to lower the V1, V2 and PI stages. Can't remember what the 12AY7 gain is maybe 40.


Mark

yeah, you're right. I use a 12AY7 in V1 in my Express all the time. It calms the beast a bit.

[angelodp]

Did you use any shielded runs in the amp.

Ange

[rawnster]

Did you use any shielded runs in the amp.

Ange

On the rocket build? Yes. just a short run from the input jack to the 33k resistor for pin 7 of V1. This build is pretty dead quiet. So there is no further need of any shielded runs.

On my express build, I place a shield wire from the input jack to pin 7 of V1, and on the wiper lug of the volume pot that runs to pin 2 of V1.

[azatplayer]

Rawnster, i dont see a ground lead on the bus. I see you have the no solder type of deal, does it connect to ground directly/only on the pots washers?
I just finished a rocket and its pretty great. Ive gone via the standard layout, but have had some difficulty with a little DC on the pots. Ive rechecked soldering and grounds, rerun the grounds variously, but still have this little noise in the pots. Kind of hits the mid point in the wipers and has like an off/on effect.
Also with the volume turned right off, i still get a tiny bit of signal thru.
Im using bournes pots. Its a terrific sounding amp and where it gets set i could leave it alone as its quiet enough, just HAVE to find out why!
I built a octal rocket pretty much the same grounding and had no issues at all. I keep thinking maybe its one of the orange drops. I replaced both mica caps, no diff. And the PI .047 cap too. Just leaves the .022's. BUT i feel its really a ground issue somewhere.
Cheers.

[M Fowler]

Rawnster's Rocket is using the amphenol type lugs bolted to the pots so it is grounded to the chassis and then the buss wire is soldered to the lugs rather then the way I did mine solder directly to the bourns pots.

I have no noise issues with my Rocket it is very stable and good sounding amp and has been used gigging with my Asteroid 60.

Mark

[angelodp]

So what is the skinny on grounding schemes. Gurus differ on this widely. Star ground, bus ground, chassis ground. Aiken seems to propose a different approach than Hoffman, and Dumble has yet another approach. Is there a definitive scheme or set of rules that all the schemes obey.

ange

[M Fowler]

Also, and if you go to other forums they all have their way of grounding. Some put ground tabs all over the place where ever they think they want to ground something.

I have seen photos of amps that should have been so noisey and the guy will write no issues with my amp. The funny thing is I followed a low watt build that had grounds in four different spots and that is my quietest amp I have built to date and my Rocket is my next quietest build. I fiddle fart around inside the amp and push here and make sure things are up to snuff and in the end it sounds the same.

I have my own opinion on grounding that doesn't follow the accepted ways, after all isn't shortest pathway to ground/earth the best electronically speaking? I would think that we should pay more attention to the filtering stages then if we use multiple grounding.

[rawnster]

Yes, Mark is correct about how I hooked up the ground buss on the rocket. I've got no noise or grounding issues at all with the rocket build. The pots are dead quiet too.

azatplayer, I'm not sure why you've got issues with noise. Perhaps someone with way more knowledge than myself could chime in here.

[M Fowler]

azatplayer,

Take very close look of the wiring to the pots and make sure a wire isn't touching somewhere there. Use a magnifying glass and light. Funny what you can see and may spot the problem I have before.

You may need to reflow your solder to make sure you do not have any cold solder joints on the pots, boards, caps and tube sockets.

Mark

[azatplayer]

Thanks Mark , will do just that. I bought a lit magnifying glass recently to help my poor old eyes.
This is my 6th build in as many months, so tho im hooked and have worked out some basics, im still pretty new this caper.
I must say, that the frustrating little things that halt you along the way, are great lessons in the making. Spose i should throw a pic up as is custom.
Cheers guys.


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[img:800:600]http://img42.imageshack.us/img42/131/img1845.jpg[/img]

[Colossal]

Azatplayer,

Wish I could help you with the grounding problem however just wish to say that is a very, very nice looking build. Very neat both inside and out and I love the green chassis. Did you spray and clear coat it yourself? Well done. Good luck sorting out the DC issue.

[rooster]

AZP - On that Rocket, I would ground the power tube cathode somewhere closer to the power tubes, in between the two pairs of EL84s, on its own lug - not on the GZ34 socket ground.

But this won't help with your main concern. Here I would suggest swapping the cathode cap on V1, pin 3, until you get an improvement. Truth be told there is a scratchiness to my Rocket build here, as well, as I have the gtr plugged in with the amp on - and I adjust the volume pot on my gtr. It sounds like a slightly lamo pot on my gtr - this is part of your issue, right? I have tried two different caps here with a slight improvement, FWIW. My AC30 build, using the TB channel, does not have this issue, again, FWIW. The physical difference here is that it uses nylon Cliff jacks and the cathode cap is not attached to the buss bar. See something? So I think this particular ground (pin 3) should be relocated on my Rocket but I haven't been too concerned with it. Eh, someday.

Moving on to another issue with the TB channel, and some here live in a cave perhaps or do not really have an ear for it, in either amp there is a potential for radio wave pickup. And here it would be more noticable when the gtr is potted down a bit or quite a bit - depends. Now, I live in a heavy radio freq area, facing a hill with all kinds of radio station sending towers so this is going to come up for me everytime if the amp is capable of it. Here you can use a ferrite bead, a device that sheilds the input wire from radio freqs, things above 30K hertz typically. And I have this in my AC30 where it works very well for this application. (Of course there is always the attitude from purists that you are f'ing up the gtr signal by using such devices but I am not one of them.)

Any, if we are speaking the same language, then I think we are talking about the same issues here. So I would start with altered ground path for pin 3 - just put a lead on it and move it around while somebody adjusts the volume on your gtr. Consider the ferrite bead solution if you have the radio problem, too. Lastly, change that power tube cathode ground - look at the Build Guide for an example. Great looking build, BTW.

[M Fowler]

I'm wondering if it isn't parasitic noise from those cap cans?

You could try shielded wire from the input to the board even if it is short as some have suggested that before. Otherwise I don't know.

You have a great looking amp there.

Mark

[azatplayer]

Thanks Rooster. Will give that a go.
I got the trannies from Chris at Toneslut, and he was a very GREAT help to me. Really good guy.
When i sent him these pics, he suggested a few changes, one included the power tubes cathode, thats been fixed. Also he picked up the power supply running from pin 2 on the rec rather than pin 8.
Couple other things. I also reran the ground from the PI on its own wire off the bus, as this is the noisiest spot. The wires, the cap, everything on the PI input side is pretty microphonic.
I had this issue on another amp i built, ended up being a bad tube, i found this after converting all the signal wires to shielded to fix it..
Ive replaced the PI tube with a few, some better than others actually.
Colossal, yeah thanks man, i paint cars for a living, so HAD to do something with the chassis! I candied it with a little yellow tint in the clear. Also gave it a beige interior, which turned out really clean looking in the end.
I have a candy purple amp and a candy green as well, the green one got a grinder on it kinda like a trussart, i like!
I did clean the ground spots and the pot mounts to ground as well.
Will keep on looking.. cheers guys.