Noise in a (somewhat of a) Rocket build

[mauiboy81]

I am finishing up a build of a rocket type amp and have some noise issues.

It has:
Low:Hi voltage switch
Solid state rectifier with 100ohm sag resistor
500ohm resistor instead of choke
Input for single triode and and input for parallel triodes.
Three way bright 100pf-0-250pf
Three way switch for cathode bypass cap on second stage 1uf-0-10uf
25kL mid pot
Ppimv with 2.2m resistors
470ohm screen resistors

The voltages are not quite right yet but I will get to fixing that... They are a little low because of the parallel triode first stage.

There is quite a bit of hiss when I turn up the volume which is only boosted by the bright and cathode bypass cap switches. When I turn the master all the way up I get a hum that pretty much goes away when I back it off a couple of notches. There is a hum that goes away when I touch the chassis right above the tone controls but not anywhere else. Chopsticking around I find that from the input grid to the pi back to the treble pot is super sensitive. Especially with the master up. Tapping the wire,cap,resistor makes quite a bit noise. Holding them hums a lot.

There are a couple spots that I need to redo because I just tacked them together quickly so I could hear it... The input being one of them.
Here are some pics from my phone sorry if they are big.

[mauiboy81]

Couple more

[Richie]

First i would do some tube swapping, tubes can be causing the hum,or added hiss.
or pull the first tube, and listen to see if the hum is still there, do this all the way through the PI.
If you pull the PI tube, and the MV hum can still be heard then...

Untwist the signal wires going to the output,spread them apart so you connect on each end for each set pair of tubes.
I know all the info on that MV says to twist them, but this always isn't "the best" way, and can cause the hum problem.

And the CF resistor, i always thought that was a bit weird, why not have that resistor on the tubes pins like all the other amps. That way you only have the one wire. And can do away with the other wire.

You may need to check grounds or move them or try different locations.
Ground buss etc.
Is the cathode wire on the preamp sensitive on the CF? Might sound crazy, but sometimes like in MV marshalls a piece of shielded wire cures that.

For the touching the amp, noise thing, that may go away if you install a bottom shield. Or lay a shield across the amp and see if it changes.
Some tubes are a little leaky and can cause static ground noises around sections of the amp, and may be worse on lower voltage of the tube.

Amp look very neat.

[mauiboy81]

Thanks!

I had noticed that the hum went away when I held my hand over the preamp without even touching the chassis so I laid another chassis over it like a shield and the hum went away.

As for the wires to the power tube grids I don't like how they are crossing the power supply to get to the tubes.

The hiss is still there especially when the cathode bypass cap is switched on the second stage.

I will swap places for the cathode cap switch and the bright switch.

I'll look in to those other things as well.

[mauiboy81]

The cathode cap switch pops despit having resistors to ground. I have a 4.7meg resistor from the hot lug to ground for each.

[Reeltarded]

Is it setup to swap caps, or to parallel them? I get a little click from a dimed 100 watt amp but mine are just to add one of two cap choices over the already bypassed stage.

I thought most people only added maybe 10k or even 4k7 at the switch to swap values?

[M Fowler]

Looks good just follow the good advice you received and keep at it I think you'll get everything worked out, probably poor solder joints.

Mark

[mauiboy81]

Thanks guys.

Reeltard: I had some small 4.7meg resistors left over from a dumble build for mid boost so I thought they should work for this. I'll go smaller when I move the switch and see how it goes.

Mark: I thought about poor solder joints... This is my first time using turrets instead of eyelets so maybe I am not getting it. I never touch the solder to the iron to melt it only to the part so I thought they wouldn't be cold joints. The solder tends to blob around where the wires wrap around the turret and when it does that it doesn't look nice and shiny. When soldering turrets do you just fill the very top with solder or do you fill the whole thing. I have been filling the whole thing so the solder is flush on the bottom. is that a problem?The b+to plate resistor wires come up through the turret from the bottom. I worry about the wire coming out if reheated so I bring them through the top and wrap over the top.

[mauiboy81]

Oh yeah... I had an old RCA 7025 in v1 that was microphonic. If I tapped the chassis it rang like crazy. I swapped all the preamp tubes for new one and its a bit better.

Mark, I know you have built a lot of these, what have been your go to tubes for the preamp?

[M Fowler]

Mark: I thought about poor solder joints... This is my first time using turrets instead of eyelets so maybe I am not getting it. I never touch the solder to the iron to melt it only to the part so I thought they wouldn't be cold joints. The solder tends to blob around where the wires wrap around the turret and when it does that it doesn't look nice and shiny. When soldering turrets do you just fill the very top with solder or do you fill the whole thing. I have been filling the whole thing so the solder is flush on the bottom. is that a problem?The b+to plate resistor wires come up through the turret from the bottom. I worry about the wire coming out if reheated so I bring them through the top and wrap over the top.

I get the iron hot and get a shiny solder joint. If there is no wire in the turret top hole then that is where i place the solder iron so the whole turret heats up. Good wire must be used other PVC would melt with high heat.

Mark, I know you have built a lot of these, what have been your go to tubes for the preamp?

I used to use JJ's ECC83's then I started using JJ ECC803 gold pin then I started buying EI and Sino-Chinese. Also tried Sunrise but they are large bottles so tube shield don't fit, some old tube shields do fit.

I tube roll starting with JJ's ECC83 and work from there. Rockets are pretty easy to get a great tone from with low noise.

Mark

[Richie]

Also tried Sunrise

I did too, and sent them all back..

[mauiboy81]

So how much noise is normal from about 12 o clock on up to full volume? I get white noise in that range.

[mauiboy81]

Here it is now. Went through and changed a bunch and resoldered etc etc etc

[dartanion]

Is it me, or do you only have 2 of the grids connected on the output tubes? Also, why change to terminal strips over the flying resistors? Unless there is a lead connecting the terminals that we can't see in the photo (latest post), only 2 output tubes are getting signal.

I will look a little closer and see if there is anything else that might be causing your issues.

[M Fowler]

That is a very nice look build. So no more problems?