Champ 5F1 wiring?

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Mark
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Re: Champ 5F1 wiring?

Post by Mark »

Steve, I think there are still issues in the amp, however the shielded cable has restored the top end response which is great. I'll post more pictures of the amp for discussion a little later. I agree that the grid leads should be kept short, there is no getting around the grid lead from the wiper of the volume control. I'm actually quite amazed that it has had so much effect on the tone of the amp.

Blackburn your amp has a different layout to the typical Champ. The 68K input resistors aren't mounted on the circuit card. I could only see the mains earth on a transformer bolt, the output earth via the output jack, an earth on the input via the input jacks. Where are your other earth wires located?
I'll post pictures of the earthing layout of the Kendrick Roughneck.

I noticed you only used 10uF filter caps,what was the reason for that? I ask as Dumble used 22uF caps in his Champ rebuild.

Thanks for your assistance and replies. I appreciate your input.
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Mark Abbott
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xtian
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Re: Champ 5F1 wiring?

Post by xtian »

I love those HUGE JAN 5AR4s. Now THAT's a rectifier.
I build and repair tube amps. http://amps.monkeymatic.com
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Blackburn
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Re: Champ 5F1 wiring?

Post by Blackburn »

Mark, I don't care for the hi/lo input setup and just use the #1 input. Sometimes I put a switch in #2 that disconnects the nf and adds a bypass cap taking it to a whole other level. This one has an old dead jack for #2. As for the layout, I cut and drill my own boards to save space and do things just how I like. On the grounding side of things, I just go from high current to low and utilize as few ground connections as possible. The filaments are the exception as the Heyboer transformers have a ct. The board supports most of them. And my filtering.... this is just personal taste, as this is the circuit I've played with most (and my absolute favorite of all time) and have come to find that I love, love, love low filtering in these amps. I've played with higher values but do not prefer them. I buy those 10uF in bulk. :)

Xtian, that's actually a 5R4 from 1952. The POTATO MASHER! :mrgreen:
Mark
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More Kendrick Roughneck photos

Post by Mark »

IMG_0234.JPG
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Mark Abbott
Mark
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Re: Champ 5F1 wiring?

Post by Mark »

IMG_0236.JPG
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Mark Abbott
Mark
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Re: Champ 5F1 wiring?

Post by Mark »

I haven't mentioned the bright cap, it is 70pF and is there to add a bit more chime. Regarding other parts of the amp. The speaker is a Weber Silver Ten which doesn't sound Celestion like but does have a good bass response for a 10" speaker. The output transformer is a Mercury Magnetics fat stack transformer with a 8 ohm secondary, thus the different feedback resistor.

Looking at the pictures the layout is very tight. The amp does have a hum before heaters have done their magic and allow audio to come from the speaker. This hum is likely to be mechanical.

As 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?

Thanks for your assistance.
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Last edited by Mark on Sun Apr 30, 2017 12:34 am, edited 1 time in total.
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Mark Abbott
sluckey
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Re: Champ 5F1 wiring?

Post by sluckey »

Leo used a small cheap OT and a cheap 8" speaker in the 5F1. Both of those will decrease the hum level simply because their frequency response is limited. But your speaker and OT will both accentuate the power supply hum because they have a lower frequency response.

A single ended amp needs good power supply filtering to minimize hum because they do not benefit from the common mode rejection property of a push pull amp. Many people like to add another filter stage between the rectifier tube and the plate node. This will really help reduce the hum.
Mark
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Re: Champ 5F1 wiring?

Post by Mark »

Slucky I agree the mains hum is likely to be due to the mains ripple. I had thought of putting a little choke in to get rid of the hum. There appears to be enough room for an extra capacitor. I agree that the output transformer would reduce the hum present, however the hum was present from day one when the amp had a smaller output transformer.

http://www.mercurymagnetics.com/pages/mainframe.htm
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Blackburn
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Re: Champ 5F1 wiring?

Post by Blackburn »

Mark, the hum you hear before the tubes are operating is transformer coupling. It may be worse when using different output trannies as I found out the hard way when using a MM 4/8/16R Princeton OT that was a drop in sub. I actually measured around 130mV on the primary! It was so loud that even at full volume, the hum still overtook the guitar sound. I switched to a stock model OT and it was back down to a small amount of coupling. The steel chassis may be the cause, though I've not played with an aluminum chassis to hear the difference. The fully shielded 4/8R sec OT from Mojo is a great choice because it offers extra protection. Trojan Man!
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Blackburn
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Re: Champ 5F1 wiring?

Post by Blackburn »

And as for ripple in the PS.... even with my low filtering I don't have any issues with hum. Perhaps consider lead dress or component placement?
Mark
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Re: Champ 5F1 wiring?

Post by Mark »

The mechanical hum I can live with, the electrical hum has to go. I know it has to be before the volume control as the volume affects the hums volume.
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Mark Abbott
Mark
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Re: Champ 5F1 wiring?

Post by Mark »

The mechanical hum I can live with, the electrical hum has to go. I know it has to be before the volume control as the volume affects the hums volume.

Here is the layout and gut shots of vintage 5F1 Champs.

http://tubeamplifierparts.com/layouts/f ... layout.gif

https://myfenderchamp.files.wordpress.c ... 2/rear.jpg

https://myfenderchamp.files.wordpress.c ... 3/caps.jpg

It might take a few days but I'll try and come up with a diagram that shows the positions of the earthing. So far it appears that the output and screen grids are earthed on the left hand side of the chassis, while the preamp supply is earthed at the input jacks. The first stage is also earthed at the input jacks too.
Currently, I'm not sure where the output stage 470 ohm is earthed or the second triode stage.
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M Fowler
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Re: Champ 5F1 wiring?

Post by M Fowler »

On page 3 of this pdf is the layout showing separation of ground, preamp ground goes to the input jack not to where the main filter caps grounds to at the PT.
5F1 Tweed Champ TAD schematic and layout.pdf
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Mark
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Re: Champ 5F1 wiring?

Post by Mark »

Thanks for the attachment Mark, that does clarify things.
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Re: Champ 5F1 wiring?

Post by sluckey »

That TAD layout has the output tube cathode resistor grounded at the input jack! That really should be grounded at the power ground along with the first filter cap and PT CT.
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