Thank's for your comment, genthry.

I think you're right, that it's better to use isolated input jacks. I used those.

Basic knowledge about star grounding: http://www.aikenamps.com/StarGround.html
I followed those instructions.
Star 1: PT center tap, 1. filter cap, OT secondary ground
Star 2: 2. filter cap, preamp stage
Connected star 1 and star 2 at one point.
AC mains ground remains separated from all this.

But maybe I shouldn't give you any advice, because my amp is not that silent. 

Today I finished the amp.

- rewired preamp stage
- new socket for V1
- new input jacks
- new grid stoppers and V1 cathode resistor (2w metal film)
- cleaned up the star grounding a bit

--> No difference at all. Probably this is the tonal character of a 5e3.
However I am very happy with it.

Thank's for reading!

Thank you very much for your reply, wyatt!

Yes, I use nothing but the single coils of my Fender Mustang. But there is no noise, when the volume of the guitar is muted or when no instrument is plugged in. So I think it is not the guitar that is hissing.

In the next few weeks I will rewire everything before V2 with new parts. I'am going to report of course.

Thanks again for reading.

Maybe I should emphasize the 2 questions, that are most important to me.

1. Did you experience hiss, when you crank the tone pot of your 5e3? And when does it start?

2. When I pull V1, the hiss is completely gone. Does that really mean, that the source of the hiss has to be in front of the grid of V1? Or is it just very likely?

Thank's for reading!

Hi,

The instrument/bright channel of my ceriatone 5e3 hisses. The hiss becomes louder, as you turn the instrument volume pot and/or the tone pot. Hiss starts at about 2 (instrument volume) and 6 (tone pot). The amp sounds great, but i would not record the amp with a cranked tone pot, even at lower volumes because of the hiss. If you pull either V1 or V2, the hiss is gone.

I built the kit according to the ceriatone layout with few exceptions:
- I used another PT, which had no filament CT.
- did not ground the first filter cap to the input/tone-section, but near the PT.

What i tried:
- installed artificial filament CT (two parallel 100 ohm resistors to ground) --> got rid of some hum, but not the hiss
- changed all resistors in the preamp section and the B+ supply to 2W metal film resistors
- changed bypass and decoupling caps in the preaamp stage
- swapped V1 and rectifier tube with tubes that do not hiss
- shielded the wires which go to the grids of V1 and V2
- changed the two tone caps
- changed potentiometers

All this had no effect.

The only thing that killed the hiss was a second 5 nF cap bridging the complete tone pot (between the 2 already existing tone caps). But then the amp had a lack of highs of course.

Do you have any idea?
Or is a hissing 5e3 normal, if you crank the tone pot?

I would be deeply grateful, if you will tell me your opinion.