Trouble with Fender Champ 5F1 clone.

[jimmy74]

I tied all 3 hanging wires together and noise and hum is minimal, no squealing, but I did notice that the hum increases gradually up untill around 3/4 of the volume then going up to max it decreases again... is this normal? I think I'll have to wait untill the new jack arrives and see what happens.

[jimmy74]

Well resoldering the wire to pin 8 fixed up the squeal, but I'm getting an even stranger problem now. My lab doesn't have grounding atm and the amp seems to be much quieter, just giving that classic noise when turning up the volume. If I try the amp in out recording studio where ground is present, the amp is very noisy with low frequency hum that gets louder when turning up the volume and when reaching max volume the hum seems to sweep out into a different frequency. What's going on here? Could it be the heaters? There's no centre tap on this amp for the heaters so I soldered the heater wirings to two 100r resistors which follow through to pin 8 on the 6L6 socket.

Any help would be great.

[Structo]

Try grounding the heater artificial center tap (2x 100R resistors) on it's own ground lug near the power tube.

If it still hums you might benefit from a humdinger pot.

(500R pot with the heater connected to the outside lugs and the center lug going to ground)
Then adjust for lowest hum.

Most likely your hum is a lead dress issue.

[jimmy74]

I've noticed that the original champ schematic has pins 1 and 2 on the power tube joined together and grounded, should I do that too? here some photos of the kit:

[Structo]

Are we talking 6L6GC?

If so, pin 1 is not connected to anything internal in the tube.
So it is frequently used as a tie point for mounting grid or screen resistors.

If you plan on running a EL34 as well, then you will want to connect pins 1 & 8 as pin 1 is connected to the suppressor grid, G3, in the EL34.

Fender did some weird stuff in the early days like grounding half of the heater supply and the like.
But safety dictates that we don't do that anymore.

I would use two, one watt 100R (ohm) resistors, preferably flame proof, and connect one to pin 2 and the other to pin 7.
Then connect the free ends to a ground lug.

It almost looks from your picture that you have both 100R resistors connected to the same pin?

Just to be clear, one 100R resistor is soldered to pin 2.

The other 100R resistor gets soldered to pin 7.

Then you can either join the two ends of the resistor or take each one to a ground lug, which can be mounted on the socket screw.
Be sure to scrape the paint off under the solder lug.

Also, single ended amps such as this Champ, tend to hum a bit more than a push/ pull amp so be aware of that.

[jimmy74]

Those 2 100r resistors are soldered together on pin 8 of the 6L6 tube. I have wired both directly to the heater terminals on the power transfomer. It's more or less the same thing (following your instructions) if I just unsolder them from pin 8 and solder them to a common ground point making sure the chassis is completely free of paint. My other question maybe silly, but is there a usual scheme to follow when wiring the heaters from a power tube to a pre amp tube? Does it matter if I wire from pin 7 of the power tube and follow though to pins 4 & 5 of the preamp tube?

[Structo]

I see what you did there with the heater resistors, that should be fine.

I don't think the heater phasing will cause any problems on this single ended amp.
On a push/pull amp it is desirable to run the same wire to the same pin on each preamp tube.

Just try to do it the simplest way that uses the least amount of wire.
Twist the wires tightly together but not so tight you stress the wires.

A cordless drill works great for that.

[jimmy74]

Well all this doesn't really answer my doubts, if I use the amp in a non grounded plug, it's quieter and doesn't give out that low frequency hum... similar to when you touch the tip of the guitar lead.
If I use the amp in a grounded plug... that hum is present... I only have used 2 ground points - 1 for the mains and HT center tap and 1 for the PTP, pots and jacks.
I wonder if moving the junction of those 2 100r resistors to a ground point would fix the problem!

thanks
J.

[jimmy74]

Well I tried moving those 2 resistors to a ground point, and tried the amp in a grounded plug and sure enough there was that noise, as I turn the volume up it gets louder and after 3/4 seems to sweep into another frequency.
When assembling the amp I did cut down the 4 and 16ohm secondary wires to around 5cm, as the owner will be using only an 8 ohm speaker. I tied these 2 wires to the other wires coming from the OT on the top side of the chassis, could there be interferences between the OT primaries and secondaries being tied together?
The thing that really gets me puzzled is that when I use the amp in a non grounded plug... there no noise and the amp works splendidly... could it very well be out of phase heater wiring from the power tube to the pre amp tube?
Also all three jacks are switched mono and I've noticed that the switch terminal doesn't touch the tip terminal when there's no lead connected. But even if I connect a guitar to the amp, the hum is still present.

thanks

[Reeltarded]

Tying the OT pri and sec together is a no do. Undo that part and tuck the spares away in the other direction..

[jimmy74]

I separated the primary wires from the secondary, but that didn't change anything, however I did notice that if I turn the mains plug around, the swooping phase effect on the volume disappears, even though the backround noise is still there, atleast the volume pot seems to work properly.
What could this be caused by?
I'll try resolding those 2 resistors back to pin 8 on the power tube, I feel there was less noise that way.

thanks

[bluesfendermanblues]

I separated the primary wires from the secondary, but that didn't change anything, however I did notice that if I turn the mains plug around, the swooping phase effect on the volume disappears, even though the backround noise is still there, atleast the volume pot seems to work properly.
What could this be caused by?
I'll try resolding those 2 resistors back to pin 8 on the power tube, I feel there was less noise that way.

thanks

Sorry for joining in this late...

A single ended Amp like the champ, doesn't cancel out hum like a push/pull amp like any 12-100w fender amp.

BTW, after having build 3 dumble amp clones, I decided on building a 5F1 champ. Getting a great sound out of that simple circuit turned out to be really tedious. Probably because in a simple circuit the fewer parts are the more important.

My Champ also hums, but when the music plays nobody notice.

In my particular build, which was build in order to get is as close to the original sounds as I could get, I ended up using Orange drop capacitors, NOS tubes and a weber signature S speaker. Its a great sounding amp. I usually run the volume at 2-2:30 o'clock (7-8 on the scale ....goes to 12) AND it didnt sound very good until it was played in after a couple of month. I don't use any pedals with this amp. The guitars volume control and pick attack gives every thing from AC/DC to Albert King.

[martin manning]

...AND it didnt sound very good until it was played in after a couple of month.

Pretty standard for a student's practice amp, no?