Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Champ_49 on June 26, 2020, 10:38:24 pm

Title: "Normal" Hiss or hum from a stock 5E3 build?
Post by: Champ_49 on June 26, 2020, 10:38:24 pm

Hi everyone.
I was just starting to think my grounding scheme was not exactly the best and thought of improving it. Was thinking of a ground buss wire going from the power stage to the preamp stage and connect one point to the chassis.
I used triode's layout and thought I could do better in terms of grounding layout.

I posted this video of what I have now and if this was "normal " hiss or hum for this, stock.  Although suggestive I wanted to know your thoughts. Because if it aint broke then dont fix it. But my ocd kicked in because i love the sound of this amp and ive been playing it alot. The hiss or hum doesnt really bother me per se but id like to improve it if i could.

There is no guitar connected to the amp. The tone knob is at max.

Would like to hear what you think.

The hiss sounds a bit louder in the video than in person but its still there.

Thanks in advance

Title: Re: "Normal" Hiss or hum from a stock 5E3 build?
Post by: tubeswell on June 27, 2020, 01:19:46 am

1st thing is to try changing the pre-amp tubes (just to see if you've got a hummy tube)


Otherwise, the hum could be a number of things - grounding, lead dress, PT EMF coupling into OT, lack of grid stoppers, lack of shielding on sensitive grid wires etc


Hiss is usually resistor noise. This can be related to:
1) Power handling of the resistors . Lower power rated resistors tend to hiss more.
2) Materials used in resistor construction. Some resistor types are 'hissier' than others (CC is worst, MF is best and CF is in between).
3) Resistor application/function in the circuit.  Plate resistors and grid load resistors in the pre-amp are where you get the most hiss because they are directly in the signal path.


So if the schematic calls for 1/4W or 1/2W CCs, then changing your plate resistors and grid stopper resistors to 1W or 2W will lower hiss. Also using MF resistors will lower hiss.

Title: Re: "Normal" Hiss or hum from a stock 5E3 build?
Post by: Champ_49 on June 27, 2020, 01:41:55 pm

Thank you for the informative reply. Yes i am using all carbon comp resistors.  I might try to build another one with metal film and proper grounding since I have an extra power transformer lying around.