Champ 5F1 wiring?

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M Fowler
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Re: Champ 5F1 wiring?

Post by M Fowler »

That is a very common to ground input jack to the cathode resistor ground of V1.
sluckey
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Re: Champ 5F1 wiring?

Post by sluckey »

That is a very common to ground input jack to the cathode resistor ground of V1.
Look at the layout. I'm not talking about V1. I'm talking about the output tube which is V2. That cathode resistor should not be grounded to the input jack.
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Re: Champ 5F1 wiring?

Post by Mark »

I agree Sluckey, it's not something we would consider doing now, perhaps it was the fastest way to build the Champ back in the day. :?:

I'll look at Blackface Champs and see what was changed there.

http://vintagefenderamprepair.com/wp-co ... layout.pdf
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Re: Champ 5F1 wiring?

Post by tubeswell »

Mark wrote: Sun Apr 30, 2017 12:11 amAs the heaters allow audio, I notice the hum gets louder, per the attached recording.

I notice if I rotate the volume control I hear a hum which gets louder and becomes a hiss at full volume per the attachment. It isn't overly annoying but I know it shouldn't be there. This noise was worse prior to the shielded cable going into the amp.

Any thoughts on removing the noise?
Tried changing your ground return scheme? (See fig 13.12b in the attached article)
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Firestorm
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Re: Champ 5F1 wiring?

Post by Firestorm »

There's something intuitively wrong with putting the power switch on the volume pot: hummy wall current right next to a grid wire -- and even with the lead shielded, the resistive element itself must still be basking in that 60 cycle glow (as would the bright cap, too). If you look at vintage Champs, the switch part of the on/off-volume pot is shielded and I wonder if it might also be internally better shielded than modern equivalents. In the day, Fender also put a "death cap" on one leg of the mains, which is a no-no today, but did put a polarized hum on the chassis itself. They also connected on side of the heater circuit to the chassis, which does the same thing. This may have been part of the "induce hum in one place to cancel opposite phase hum in another" thing that some people suggest Fender did quite deliberately. As an experiment, you might try hardwiring the hot mains lead away from the switch and see if it reduces the hum. If so, you'd then have to figure out where to put a separate power switch.

As to the lack of phase cancellation in SE outputs, in my SE builds, I have two filters with a 100R between them taking B+ from the second. I also DC bias the heaters by quite a bit. Because they're so simple, Champs can be unforgiving. Good luck.
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Re: Champ 5F1 wiring?

Post by Mark »

Thanks Firestorm, I agree that vintage Champs do have a lot of wiring errors, which have been mentioned in this thread.

I suspect having the heaters located near all the wiring is also bad news as the signal is smaller at the input and the heaters are a lot closer to the wiring than the mains being near the volume controls wiring.

I noticed Blackburn's build had the heater away from the wiring. This is probably the best first move with the amp as is makes good sense.

Getting back to the wiper wire, it was more than just the noise issue that was the problem, this wire effected the tone of the amp which I found more important than the noise. I can't get over what a difference this made to MY AMP. I'm not sure if this happens to all 5F1 Champs though.

Thanks for the link Tubeswell, I am familiar with Merlin Blenecowes books. One of the tragedies with these amps is that we can't see what the earth paths are doing and how they are interacting.
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Re: Champ 5F1 wiring?

Post by tubeswell »

Mark wrote: Wed May 03, 2017 9:18 am ... One of the tragedies with these amps is that we can't see what the earth paths are doing and how they are interacting.
Yep. That's why he recommends using a ground buss wire, with the ground returns arranged 'galactically' :D

Maybe something else you might want to consider (besides an HT choke in a CLC filter between the rectifier and the 6V6 plate supply) is tweaking the PT-OT core/lamination alignment.
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Re: Champ 5F1 wiring?

Post by Mark »

Tweaking the PT-OT core/lamination alignment.
So I assume you mean experimenting with the orientation of the output transformer. The power transformer is a "Z" mount so that isn't an option.

The output transformer is quite a distance away from the power transformer. It is located near the preamp valve and is bolted across the chassis.

I'll have to find a photo of the transformer mounting.
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Re: Champ 5F1 wiring?

Post by Mark »

I decided to get back on the Champ today. I pulled all the valves out and listened to the transformer hum. It was there but not that loud. I then put the 6V6 valve and listened. The hum became a lot louder, I decided to put a switch on the heaters to see what impact they had upon the hum. In short, none whatsoever. The hum is from the power supply.

There is noise in the pre-amp but it pales in comparison to the power supply hum.
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Re: Champ 5F1 wiring?

Post by martin manning »

Mark wrote: Fri Jun 09, 2017 5:56 am...I then put the 6V6 valve and listened. The hum became a lot louder, I decided to put a switch on the heaters to see what impact they had upon the hum. In short, none whatsoever. The hum is from the power supply.
There is noise in the pre-amp but it pales in comparison to the power supply hum.
Do you have another filter cap and a Deluxe Reverb power supply choke handy? Make a CLC filter in front of the OT.
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Re: Champ 5F1 wiring?

Post by Colossal »

martin manning wrote: Fri Jun 09, 2017 10:51 amDo you have another filter cap and a Deluxe Reverb power supply choke handy? Make a CLC filter in front of the OT.
I do this for SE builds and it really knocks the ripple WAY down. Way more than just a single C (to OT) or a CRC. And as Firestorm suggested, elevate the heaters. The simplest way is just to run the heater center tap (or virtual 100R/100R center tap) to the output tube cathode cap. I prefer to tap off the B+ supply with a divider and dedicated cap for a +50-70V offset, depending on the amp. I have made some very quiet SE builds this way.
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Re: Champ 5F1 wiring?

Post by pompeiisneaks »

You may also want to make sure the nuts/bolts on the transformer laminations are super tight, if they get loose they can cause hum as well.

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Re: Champ 5F1 wiring?

Post by Mark »

Thanks for the replies, the filaments isn't the issue (yet) as I have switched the filament supply off with the amp going, there is no change in noise levels. Once the heaters cool and stop the valve conducting the amp is quieter but that is due to the output valve not working.

I'll try an extra stage of filtering but wondered if there is a superior way of handling the earths to minimise hum?
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Most likely useless, but in doubt...

Post by ChopSauce »

According to the litterature, the way to go seems to minimize the length of the small signal grounds. The rest seems far less consensual - notably HAD's reported champ layout - see http://ampgarage.com/forum/viewtopic.php?f=5&t=25599

Image

does not separate amp and pre-amp filter cap grounds, which is a major sin, according to common theory.
(& I wish I could read some comments about that)
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Re: Champ 5F1 wiring?

Post by Mark »

Thanks for posting the picture.

I saw a picture of the HAD Champ where the filaments were modified (possibly not by HAD) so they were at the other side of the chassis and not near the wiring.

I'm surprised HAD didn't do anything with the wiper wire, as that effects the tone of the amp.
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