Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mike_J on December 04, 2020, 10:17:43 am
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I have looked at articles concerning grounding techniques. Some of them suggest soldering a bus bar across all potentiometers and grounding the bus bar at the input jacks. The chassis then acts as the source to ground. The speaker jacks are also grounded at the respective spots on the chassis where the chassis acts as the source to ground. These are techniques I used when I originally made the 5f6a 22 years ago,
This is what I want to do now and ask for any input you can offer regarding same.
1. Lift the speaker ground and send the ground via wire to a turret at the same point the 100r balance resistors are grounded on the circuit board. The power ecaps will also be grounded at this same location. A wire from this point will be sent to the same lug on the power transformer bolt used to ground the speaker.
2. Lift the input jacks and ground them to the end of a bare bus wire. The bare bus wire continues to the ground points for potentiometers as indicated on the schematic (each volume, the middle and presence pots). A wire from the presence pot end of the bare bus wire is then sent to the same turret used to ground the 100r balance resistors, speaker and power ecaps. These all get terminated at the power transformer bolt. The only other connection to the power transformer bolt lug is the PT center tap. By using the balance resistors the center tap for the heater supply will be taped off and isolated.
3. Individual power ecaps for V1 and V2 will be installed on the circuit board close to the cathode caps feeding their associated stages. Grounds for negative leads on the power ecaps and cathode caps are sent by wire to be grounded to the bare bus wire near the potentiometer ground point for that stage.
The reason I started this topic is somewhere I read it is best to have grounds proceed in the same order they appear on the schematic. By using the input jacks as their own grounds and tying all the pots to that grounding point you are essentially grounding backwards through the preamp and PI stages as I see it.
Soldering a bus wire to the back of each pot makes a mess and makes it hard to replace potentiometers. I don't see why it is needed but am willing to be corrected concerning this matter.
Thank you for helping. Best to talking things out before soldering or setting turrets as I see it.
Mike
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This is tried and true
https://el34world.com/charts/grounds.htm
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This is tried and true
https://el34world.com/charts/grounds.htm (https://el34world.com/charts/grounds.htm)
Thank you so much for the explanation. I need to modify my plan by grounding the node C ecap where the presence pot is grounded to the ground buss versus with the main and screen ecaps to the main ground point. Also don't need to lift the ground for the input jacks but instead use them as the preamp ground point. This is contrary to what I read before regarding having all grounds follow the ground path from beginning to end on the schematic. It is consistent however with another article I read that says it is very important to ground the preamp grounds at the input jacks. Your comment that it is tried and true makes me confident the latter is the method I should use. With the former version the input jacks must be lifted in order to run a wire from the presence pot end of the ground bus to the main ground point or else I am pretty sure a ground loop situation would be created. I have used the lift the input jack method before with inconsistent results. Sometimes great sometimes lacking. Again thank you for your help.
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I just finished a 5F6A build, using the grounding concept referenced by EL34, with good results.
You say: "I have used the lift the input jack method before with inconsistent results" ... I found isolation washers (also referenced here https://el34world.com/Forum/index.php?topic=18825.0) to work very consistently well, including after many dis-assemblies and re-assemblies of the input jack area.
Good luck!
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I just finished a 5F6A build, using the grounding concept referenced by EL34, with good results.
You say: "I have used the lift the input jack method before with inconsistent results" ... I found isolation washers (also referenced here https://el34world.com/Forum/index.php?topic=18825.0 (https://el34world.com/Forum/index.php?topic=18825.0)) to work very consistently well, including after many dis-assemblies and re-assemblies of the input jack area.
Good luck!
Thank you. I am going to try to use the jacks as the ground location for the preamp. Will also try to ground the speaker jack at the speaker jack instead of lifting it and running the ground to the PT. Easy enough to change if I am not satisfied with the result.
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I don't use isolated input jacks. But I also don't rely on them for my preamp ground. Sure, the input jacks are connected to chassis but I've seen too many input jacks that have become loose. I bolt a dedicated ground lug very close to the input jacks, secured with a kep nut. All my preamp grounds connect to this ground lug, including the input jack. I trust this lug to never come loose. Like this...
http://sluckeyamps.com/supro/s-10.jpg
http://sluckeyamps.com/supro/supro_02_big.jpg
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I don't use isolated input jacks. But I also don't rely on them for my preamp ground. Sure, the input jacks are connected to chassis but I've seen too many input jacks that have become loose. I bolt a dedicated ground lug very close to the input jacks, secured with a kep nut. All my preamp grounds connect to this ground lug, including the input jack. I trust this lug to never come loose. Like this...
http://sluckeyamps.com/supro/s-10.jpg (http://sluckeyamps.com/supro/s-10.jpg)
http://sluckeyamps.com/supro/supro_02_big.jpg (http://sluckeyamps.com/supro/supro_02_big.jpg)
Thanks sluckey. Great advice as always.
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I never had problems with loose input jacks.
If you use a Switchcraft jack and put a star washer in the inside, they will never come loose. You got to screw the nut with a box, not long nose pliers, though. All the pots and ground of the preamp sectipn are tied to this jack via a 14AWG naked ground copper wire, as a grnd bus. ( in my builds).
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In a lot of old tube amps of various kinds, such as radios and PA system amplifiers, you'll find that where they have a ground lug to the chassis, they have it soldered to the chassis. No worries about the connectivity of that ground point.
I use a mini torch to tin the spot on the steel chassis where I'm going to put a ground lug. That way, when I mount the lug, it's a lot easier to solder it to the chassis. This obviously won't work with an aluminum chassis...unless you know of a way to get solder to stick to aluminum that I'm not aware of...
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In a lot of old tube amps of various kinds, such as radios and PA system amplifiers, you'll find that where they have a ground lug to the chassis, they have it soldered to the chassis. No worries about the connectivity of that ground point.
I use a mini torch to tin the spot on the steel chassis where I'm going to put a ground lug. That way, when I mount the lug, it's a lot easier to solder it to the chassis. This obviously won't work with an aluminum chassis...unless you know of a way to get solder to stick to aluminum that I'm not aware of...
I have seen many of those solder blobs pop off the chassis
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I never had problems with loose input jacks.
If you use a Switchcraft jack and put a star washer in the inside, they will never come loose. You got to screw the nut with a box, not long nose pliers, though. All the pots and ground of the preamp sectipn are tied to this jack via a 14AWG naked ground copper wire, as a grnd bus. ( in my builds).
Good suggestions and easy enough to do. Do you use the star washers on the inside of the potentiometers? Not sure why that would be necessary although maybe it is. Something I wonder about every time I do a build.
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IF I'm not to use the indexing tab on the pots, yes I do always use them. Otherwise, over time, the pots often loosen.
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I have seen many of those solder blobs pop off the chassis
Yes, that's why I use a screw and kep nut to hold the ground lug in place, just in case I didn't get the solder to stick to the chassis well enough.
Some of the PA amps that I've converted have several of the tag strips riveted to the chassis and then soldered. They can be a pain in the butt to remove if you don't want it there, or want one with more tag mounts on the strip...
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I always put a star washer to whatever is bolted to the chassis. Pots, jacks and others