Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dbishopbliss on February 04, 2019, 10:39:07 pm
-
Continuing this in a new thread to make it easier to find in case someone else has a similar question:
I will leave the heater supply for now.
On second thought I won't leave it alone. I swapped the power cord the other night and played around a little more. This time one of the light switches with a dimmer attached was on and I could hear more buzz so I think I will re-wire the heaters. Not to mention, the location of my new filter caps is directly over where the old can cap used to be. I removed the cap and mounted two terminal strips in the holes where the rivets were holding it in place. This is significant because the heater wires are sort of in the way of the filter caps and resistors. Not to mention the routing of a bunch of the other wires is just awkward now.
I plan on using Belden 8450, shielded twisted pair wire, for the heaters. Here's my question, should I run the wire to the tube, then back to the corner, then back to the next tube, then back to the corner, etc. Or because the wire is shielded can I just run from tube to tube?
Character mode artwork:
corner of chassis corner of chassis corner of chassis
---------+ +---------+ +---------+ +----- continue doing the same down and back for each tube
| | | | | |
| | | | | |
| | | | | |
+ V1 + + V2 + + V3 +
Or should I just do:
========== V1 ========== V2 ========== V3 ===== continue going is a line to each tube
If I go in a line from tube to tube should I run along the chassis or have the heater wires hover over the tubes sort of like Fender heater wiring?
Any thoughts?
-
Belden 8450 has two 22ga wires. I just read that is good for 2.4A. The tubes in the 1484 are two 12AX7, two 6V6, one 6AU6 and one 6X4. According to the data sheets the total current for the heaters will be 2.5A.
Should I use something else?
-
You don't need STP for filaments in that amp.
-
You don't need STP for filaments in that amp.
Need vs have... I have the cable and its pre-twisted for me and it is two colors so its easy to be sure I'm wiring all the heaters the same. That said, if the 22ga is too small then I will have to twist up some other wires.
Please comment on how I should route the heater wires. In the past I have routed them so the twisted wire is tucked in the corner of the amp (learned that from sluckey). However, the 1482 doesn't really have a corner close to the tube sockets. The corner is around 4 inches away from the socket whereas they are around 2 inches between them. Seems like traveling an extra 8 inches without being in a corner might defeat the purpose of tucking the wire in the corner.
As always, thanks for your help.
-
Belden 8450 has two 22ga wires. I just read that is good for 2.4A. The tubes in the 1484 are two 12AX7, two 6V6, one 6AU6 and one 6X4. According to the data sheets the total current for the heaters will be 2.5A.
Should I use something else?
I am seeing it as 2.9A per conductor.... ? Did you get 2.4A from a spec sheet or just rule of thumb for 22AWG?
https://catalog.belden.com/techdata/EN/8450_techdata.pdf
Not to say it would work or not, just a difference in Max A.
-
From the tube charts: I too total 2.4A total current draw for all tubes. Therefore, 1 series filament string should be rated for 5A.
You need to verify the specific current handling for your particular wire. Twisted pair inside a shield won't dissipate heat as well as a single wire in the open, so you can't rely on generic info.
You can use your Belkin wire if you make multiple separate parallel runs to various tubes; e.g., one run to both preamp tubes. The current in each run should be no more than 1/2 of what your specific wire is rated for. It would be best to keep each run: i) near the chassis; ii) as far away as possible form other leads; and iii) crossing other leads at right angles.
-
Different layouts call for different wiring schemes. On the stuff I build that has all the tubes in a straight line along the back edge of the chassis I like to run the wires like this...
(http://sluckeyamps.com/VAC15/11.jpg)
But other layouts may call for different strings. Looking at the layout on the 1482 schematic I would probably connect the PT wires directly to the 6X4, then 6AU6, then 6V6, 6V6, 12AX7, 12AX7. Seeing a gut shot of the actual amp might make me alter that slightly. Show us a pic of the inside of your chassis for some better suggestions.
I would not use 22AWG unless that was all I had. I like 20AWG. And again, I would not use STP even if it was 20AWG. You will not see a benefit of shielded wires in that amp.
-
FWIW, my 1482. Note the green twisted heater wires.
-
Here's the best gut shot I have. Sort of hard to see, but the yellow and white wires are the heater wires (mostly some yellow wire is used for other connections). You can see that there was no attempt at all to twist them.
The chassis is made from a bent piece of aluminum. The bend at the top of the photo is around 4 inches from the sockets and around 45 degrees so it would provide good shielding. On the other hand, the wires are closer to the volume and tone controls (not sure if that matters).
The bend at the bottom of the photo is around 2 inches from the socket and an obtuse angle... pretty flat really. The run from the socket to the corner is shorter, but the wires would be close to the input jacks.
(http://blissamps.weebly.com/uploads/7/2/4/8/72487915/img-4538_orig.jpg)
-
Don't run the filaments near the front panel pots! Don't run the filaments near the input jacks! If I was gonna redo the filaments I would twist the wires and follow the same path they are running in that pic. But, I don't recommend redoing the filaments unless your just bored.
BTW, the buzz caused by the light dimmer switch has nothing to do with how the filaments are run.
-
Don't run the filaments near the front panel pots! Don't run the filaments near the input jacks!
What about the filaments running untwisted near the filter caps? That is how they would be run if I don't change them. Maybe just twist those wires.
-
What about the filaments running untwisted near the filter caps?
No problem. The filter caps operate at AC ground.