#124 Questions

[martin manning]

If you wire up the relays and DIN foot switch jack as shown in the D-amp layout (without the standard power supply arrangement) the coil circuit is isolated from the chassis. Then you can run a test with filament derived power with the rectifier/regulator breadboarded and/or clipped in to see if there is any unwanted noise. I would make a small purpose-built eyelet board for this rather than trying to adapt the Hoffman turret board.

[Bombacaototal]

If you wire up the relays and DIN foot switch jack as shown in the D-amp layout (without the standard power supply arrangement) the coil circuit is isolated from the chassis. Then you can run a test with filament derived power with the rectifier/regulator breadboarded and/or clipped in to see if there is any unwanted noise. I would make a small purpose-built eyelet board for this rather than trying to adapt the Hoffman turret board.

Thanks Martin, just to be clear should I leave the manual switch, the 3rd PIN of the footswitch jack and the relay board ungrounded as well?

Thanks for the suggestion on making a small board for rectifier/regulator. I will try to get something together.

[Bombacaototal]

One more question, this time about the PAB. I am doing it without the Rock/Jazz switch.

Do I just add a lead to the 22M that feeds the 3rd lug of the treble pot (green line)? What do I do with the other 22M (circled in red)

[norburybrook]

Here you go.

Del_RJ.png

M

[Bombacaototal]

Awesome Marcus! Many thanks

[Bombacaototal]

A bit of a sidetrack here but I didn’t want to start a new thread just for this.

I am planning a new amp and I am very keen to try the scattered tube layout for the first time. Is there any guideline regarding the distance of a pre amp tube to the OT? As per my initial assessment/planning I might have one very close (pic attached) but given HAD always seemed to have them further from the OT I am thinking this might be a No No

[erwin_ve]

A bit of a sidetrack here but I didn’t want to start a new thread just for this.

I am planning a new amp and I am very keen to try the scattered tube layout for the first time. Is there any guideline regarding the distance of a pre amp tube to the OT? As per my initial assessment/planning I might have one very close (pic attached) but given HAD always seemed to have them further from the OT I am thinking this might be a No No

A big nono: pt and ot are high voltage and current. That means big magnetic fields which are likely to induce in the lower voltage/current preamp tube wiring.

[Bombacaototal]

A bit of a sidetrack here but I didn’t want to start a new thread just for this.

I am planning a new amp and I am very keen to try the scattered tube layout for the first time. Is there any guideline regarding the distance of a pre amp tube to the OT? As per my initial assessment/planning I might have one very close (pic attached) but given HAD always seemed to have them further from the OT I am thinking this might be a No No

A big nono: pt and ot are high voltage and current. That means big magnetic fields which are likely to induce in the lower voltage/current preamp tube wiring.

Thanks a lot for the help Erwin. Back to the drawing board. Is there a safety distance to keep in mind? Maybe 10cm?

[erwin_ve]

The position of the tube in relation to the ot matters. Look at the position of the PT in relation to the OT.
The ot is fairly close to the pi tube in a ods, BUT the ot is positioned in such a way the magnetic field isnt a big factor. It would if it was angled at a 90 degree positioning.
Sorry im no native english speaking, so I have a hard time explaining.

[Bombacaototal]

The position of the tube in relation to the ot matters. Look at the position of the PT in relation to the OT.
The ot is fairly close to the pi tube in a ods, BUT the ot is positioned in such a way the magnetic field isnt a big factor. It would if it was angled at a 90 degree positioning.
Sorry im no native english speaking, so I have a hard time explaining.

Thanks Erwin, it does make sense and very helpful indeed

[Bombacaototal]

Hi Erwin, I was browsing through some of HAD amps and found that the Hoyt Axton ODS has a tube (OD) as close to the OT as my original plan. I am screatching my head wether I should take a risk as this seems to be the only way I can fit all I want on the small enclosure chassis.

[erwin_ve]

Well then: theres only one way to find out.
Make sure you have the shield on the tube, and the screws holding the tube socket can touch the bare metal of the chassis.

[talbany]

Erwin is right
As a general rule and the collective wisdom say's not to put high-level signals (either line or output stage) near sensitive input stages (Choke included). However, there are some production amps out there that ignore this practice (Sunn, Boogie being a few) and place their preamp tubes within a 1/2 inch. My experience has been transformers can very widely in how much fringe field they disperse (especially with E-I Laminations). End bells, copper straps, and lamination construction and size might also determine the size of the field (The bigger the better). The placement also matters in relation to the flux line angle, all of these can play a role in the amount of noise picked up from the EMF they generate. So IMO if you are not using the same OPT that Dumble is using there is no guarantee that your OPT will radiate the same field. My guess would be you should be OK (@90 degree's) but there is no way to know for sure so I cannot say for 100% certainty that you will be OK.
BTW. An aluminum shield won't do much and a steel one might help (a little)

"May the force be with you"

Tony

[Bombacaototal]

Thanks Tony and Erwin. In the end I will follow the advices and not attempt the tube so close to the OT. I appreciate the help and the inputs

[pompeiisneaks]

I would also add that tube is likley the PI that's near the OT. It's the preamp tube with the most signal and least susceptible to noise injection. Doesn't mean it's 'safe' but it's less risky at that point.

~Phil