tubeswell wrote:If its 60 cycle hum, then you probably need better filtering. Look at the 5e1 schematic for what I mean, and think about adding a small 50mA 150R HT choke between the rectifier and the OT primary filter cap. You will need 450V 10uF-20uF input cap in front of the choke (like what is in the 5e1). The rest of the circuit would be the same as the bog standard 5F1 (i.e. only you'd have 4 x filter caps).
i understand what u are saying but i dont see the extra cap in the 5e3
again i cant see how this is how the amp sounds stock and everything is okay? i just need to add filtering? it doesn't make sense to me at all... so all 5f1 do this?
No they don't all make noise but some where in your amp there is some component, solder or grounding that is causing the problem or its your supply from the wall making problems. Lighting or other equipment or appliances on the main line?
M Fowler wrote:No they don't all make noise but some where in your amp there is some component, solder or grounding that is causing the problem or its your supply from the wall making problems. Lighting or other equipment or appliances on the main line?
Mark
the ac outlet is fine. my plexi and valve junior sound fine using this outlet.
yes by all means try redoing the grounding. It is possible to get SE amps fairly quiet with the 'right' grounding, lead dress, elevated heaters, shielded signal cables etc, but they tend to be naturally a bit more hum prone than PP amps.
Remember the champs were the cheapest practice amps made by Fender and were made on a shoestring. This mean't saving parts as time went by, hence the 5e1 had a choke but this got eliminated in the 5F1. Same 'evolution' happened in the tweed princetons.
The tendency for some more mains-cycle hum is usual in amps that don't have a choke filter. In a PP OT the hum is virtually all cancelled out because the primaries balance each other out, but that doesn't happen in an SE OT. So whilst some inductive filtering happens in the primary of the OT, it is still not as completely removed as it could be, which is where adding a choke makes a difference in SE amps if you want them real quiet. In this regard, I wasn't meaning the the 5E1 had 4 filter caps, what I meant earlier was if you add a choke the filter system would be like:
rectifier - 10-20uF reservoir cap - choke - 10uF cap for OT Pri - screen dropper resistor - 10uF screen node cap - pre-amp dropper resistor - pre-amp cap (hence 4 caps)
But it might not be solely, or even just, inadequate filtering. So try re-doing the grounding first. Then tackle the other aspects. (There might be hum-contributing factors from different sources). It is important to note that a split ground system works best if each ground return point has its own separate wire directly to one of the 2 common return points on the chassis. This makes for more wires in the chassis, but it is possible to do this and still have it neat looking.
In my 5F2-A I used a buss grounding scheme with all grounds connected to the buss and the buss grounded on a grounding lug right at the input jack..Go over to AX84 site and take a look at the P1 or HO layout for an example of buss grounding.
tubeswell wrote:If its 60 cycle hum, then you probably need better filtering. ........
Filters filter 120 cycle power supply ripple (hum.) I would try grounding the grid of the 6v6. If the hum remains, it's probably a bad 6v6. Probably the hum will go away during this test which would mean the 6v6 is not the source of the hum.
I built this circuit as my 1st project about 12 years ago. It hummed big time and took about 6mos for me to realize what I did wrong. Many said to check for a ground loop but I didn't understand what that really meant. I had the CT of the HV winding for the rectifier grounded way on the far side of the chassis. Most of the other grounds, including the filters, were on the other side. Moving it to the ground point of the filters fixed it and it has roared ever since.
The red heater wire on the 12ax7 is somewhat parallel with the plate wire on the same socket. Probably not the cause but worth pushing to make it more perpendicular.
Well yeah - 60hz, 120hz (I took the '60' to read '120' anyway). And yes it could be grounding as already said, but it could also be filtering, unwanted coupling, heaters, bad tube(s) you name it. My main point (made earlier) was that sometimes you have to persist with a range of various possible fixes, one at a time.
