#124 Build Questions

[lgehrig4]

Actually, I was wrong. Both rear switches are working in reverse so I will just rewire them.

If anyone sees anything in the photos that I should changes, esepcially related to lead dress, please let me know. I was thinking of going back through the amp and shortening any leads that I could. My initial intention was to do the best I could at keep the wires from the preamp board to the preamp sockets from touching and I have a few looping wires as a result. My chassis seems more crowded than some of the other photos I've seen. Not sure if its my wiring or that the wire is just thicker. I uses 20G solid PVC for most and 18G solid PVC for the power board and heaters.

To do:
Change mid switch to correct on-on type
Rewire PAB and Overdrive switches
Change the power and standby switches. The ones I uses are large and clunky and I cannot stand the way they look or how they crowd up that section.

I'll post some photos when I'm done for reference.

p.s. so far I really like this amp with a Scumcack H55/H75 mix (4x12 cab)

[GAStan]

When I did my #124 I went by these pictures and emulated HAD's lead dress as best I could.

[pottedplant]

When I did my #124 I went by these pictures and emulated HAD's lead dress as best I could.

I too am doing this, some of his wiring choices are so strange especially some of the grounding conventions. One particularly perplexing thing to me is his bias grounding. The negative side of the cap (the positive marked side) goes to the ground lug by the transformer that also has the grounds for the copper shield and center tap reference (ground point4) BUT the pot case ground goes to the ground wings by the last 2 power tubes (ground point 3). Wouldn't it make sense to take that pot case ground wire and bring it back to where the bias cap connects (ground point 4)? I assume this is about current flow or something along those lines. Of course I am not suggesting I know the best way to do it but rather asking because I'd love to know why I'm wrong and to better understand the potential theory behind this choice. Lead dress is probably going to kill me when I get this amp together. lol

[ijedouglas]

When I did my #124 I went by these pictures and emulated HAD's lead dress as best I could.

I too am doing this, some of his wiring choices are so strange especially some of the grounding conventions. One particularly perplexing thing to me is his bias grounding. The negative side of the cap (the positive marked side) goes to the ground lug by the transformer that also has the grounds for the copper shield and center tap reference (ground point4) BUT the pot case ground goes to the ground wings by the last 2 power tubes (ground point 3). Wouldn't it make sense to take that pot case ground wire and bring it back to where the bias cap connects (ground point 4)? I assume this is about current flow or something along those lines. Of course I am not suggesting I know the best way to do it but rather asking because I'd love to know why I'm wrong and to better understand the potential theory behind this choice. Lead dress is probably going to kill me when I get this amp together. lol

The pot actually grounds at the chassis (insertion point) but I'm guessing he just added the ground connection to ground 3 as a safety. In other amps he runs the pot tail resistor directly to ground 3 and in this case the pot connection would just be purely for shielding (no dedicated ground wire but insertion point). It probably makes more sense to run the pot ground to the bias supply ground if you run your pot tail directly to ground and not via the pot casing but the amps sound pretty good like this Perhaps a good experiment to try?

[pottedplant]

When I did my #124 I went by these pictures and emulated HAD's lead dress as best I could.

I too am doing this, some of his wiring choices are so strange especially some of the grounding conventions. One particularly perplexing thing to me is his bias grounding. The negative side of the cap (the positive marked side) goes to the ground lug by the transformer that also has the grounds for the copper shield and center tap reference (ground point4) BUT the pot case ground goes to the ground wings by the last 2 power tubes (ground point 3). Wouldn't it make sense to take that pot case ground wire and bring it back to where the bias cap connects (ground point 4)? I assume this is about current flow or something along those lines. Of course I am not suggesting I know the best way to do it but rather asking because I'd love to know why I'm wrong and to better understand the potential theory behind this choice. Lead dress is probably going to kill me when I get this amp together. lol

The pot actually grounds at the chassis (insertion point) but I'm guessing he just added the ground connection to ground 3 as a safety. In other amps he runs the pot tail resistor directly to ground 3 and in this case the pot connection would just be purely for shielding (no dedicated ground wire but insertion point). It probably makes more sense to run the pot ground to the bias supply ground if you run your pot tail directly to ground and not via the pot casing but the amps sound pretty good like this Perhaps a good experiment to try?

Oh right, it's not isolated from the chassis so it would ground from being mounted. I see now. The case of the pot is a shield when it's placed in the chassis. A very illuminating perspective that I hadn't thought about but it's logical after being pointed out. Is this similar to the FET jack's ground wire perhaps? A backup?

Another interesting wire choice was the ground for the reservoir. It just pops out the side of the power supply board to make its run to ground point 4 instead of coming off the front where the caps terminate since they're axially terminated. I would have just ran the wire from that negative but he tucked it inside the PS board assembly and then drilled a hole for it to exit out the side.

[ijedouglas]

Is this similar to the FET jack's ground wire perhaps? A backup?

The FET jack is only grounded via it's ground wire. The kobiconn jack used is isolated (as is the NOR jack)

[ijedouglas]

Another interesting wire choice was the ground for the reservoir. It just pops out the side of the power supply board to make its run to ground point 4 instead of coming off the front where the caps terminate since they're axially terminated. I would have just ran the wire from that negative but he tucked it inside the PS board assembly and then drilled a hole for it to exit out the side.

The reservoir caps are radial. The board was probably designed for axial and he just modified it (I'm guessing)

[pottedplant]

Another interesting wire choice was the ground for the reservoir. It just pops out the side of the power supply board to make its run to ground point 4 instead of coming off the front where the caps terminate since they're axially terminated. I would have just ran the wire from that negative but he tucked it inside the PS board assembly and then drilled a hole for it to exit out the side.

The reservoir caps are radial. The board was probably designed for axial and he just modified it (I'm guessing)

The FET jack is only grounded via it's ground wire. The kobiconn jack used is isolated (as is the NOR jack

Woops I definitely meant radial. I have axial on the brain I guess since that's how all these old amps are laid out. The inputs are isolated though? I need to make sure to do that. Hmm.. Good point about the board stock. he probably just made it work which is quite resourceful. Thanks for explaining, especially about the inputs because I had no idea.

[ijedouglas]

The inputs are isolated though? I need to make sure to do that. Hmm.. Good point about the board stock. he probably just made it work which is quite resourceful. Thanks for explaining, especially about the inputs because I had no idea.

Yup, FET (Kobiconn isolated jack) and NOR (isolation washers) are both isolated as well as the EFX send and return (isolation washers) (in the amps I have seen). He ran a dedicated ground to each send and return jack. The speaker jacks are not isolated though and are chassis ground (insertion point).

[pottedplant]

looks like i got more shit to buy

I"ve examined the photos quite a bit and have noticed the washers behind the jacks but I assumed those were to space out the bushing for a cleaner look on the front and to time the fasteners. Guess I should do a search hah Thanks for the tips as always!

[martin manning]

Don't overthink the jack treatment too much. My ODS, which is going on 15 years old now, has no isolated jacks and is still very quiet. All pots and jacks have toothed washers on their bushings to insure good electrical contact.

[pottedplant]

Don't overthink the jack treatment too much. My ODS, which is going on 15 years old now, has no isolated jacks and is still very quiet. All pots and jacks have toothed washers on their bushings to insure good electrical contact.

i read up on it a little tiny bit and it seems people do either or and things seem to be okay so i'll try em both out and see how it goes

do you happen to know why dumble would create grounds points when there were readily available posts nearby? IE the one by the voltage regulator is millimeters away from the power transformer mounting stud, as is the one by the LED terminal strip but he made dedicated holes for just the ground tabs. i'd love to hear a proposed reasoning why. i'm open to all ideas tbh. esoteric or otherwise really. i enjoy a good quirk haha

[ijedouglas]

Don't overthink the jack treatment too much. My ODS, which is going on 15 years old now, has no isolated jacks and is still very quiet. All pots and jacks have toothed washers on their bushings to insure good electrical contact.

i read up on it a little tiny bit and it seems people do either or and things seem to be okay so i'll try em both out and see how it goes

do you happen to know why dumble would create grounds points when there were readily available posts nearby? IE the one by the voltage regulator is millimeters away from the power transformer mounting stud, as is the one by the LED terminal strip but he made dedicated holes for just the ground tabs. i'd love to hear a proposed reasoning why. i'm open to all ideas tbh. esoteric or otherwise really. i enjoy a good quirk haha

HAD was building amps for touring musicians and they had to be bomb-proof. Dedicated grounds gave him the ability to ensure that the best possible ground was made and it wasn't going anywhere. The other reason may be aligning ground points with the ground return of the chassis so that they do not cross or interfere with each other and introduce noise.

I prefer doing it the same way that HAD did it. He obviously felt it was important and you can see this in his attention to detail on ground connections.

[martin manning]

do you happen to know why dumble would create grounds points when there were readily available posts nearby? IE the one by the voltage regulator is millimeters away from the power transformer mounting stud, as is the one by the LED terminal strip but he made dedicated holes for just the ground tabs. i'd love to hear a proposed reasoning why. i'm open to all ideas tbh. esoteric or otherwise really. i enjoy a good quirk haha

Transformer bolts are not a good place to make grounds. They have a tendency to loosen over time due to vibration.

[pottedplant]

thanks for explaining ian and martin! i value this information so much. thank you guys. i may have to start my own thread now