Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: foghornleghorn on September 11, 2011, 10:22:36 am
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I'm planning a 5E8A tweed low power Twin build. I have the hookup wire from a '67 AB165 Bassman head I deconstructed to build a '70s ODS Dumble 50W. It is solid, 20 ga for the heaters and 22 ga everywhere else. I would like to use it in the 5E8A for cosmetic reasons.
Anyone know if the tweed gauges are the same or heavier? I would normally use 18 ga on the heaters and 20 ga everywhere else in a 50W build. If the tweeds were heavier I'll use new cloth covered wire.
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IMO they are same gauge
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18 gauge on heaters and 22 gauge everywhere else is common. Honestly, you only need the 18 gauge for the power tubes and could run the rest of the heater string with 22 gauge in most amps (unless there are a lot of preamp tubes).
Cheers,
Chip
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I can understand the cosmetics, but remember that solid core wire only takes so many bends before you induce a break in it.
- Chasing an electrical gremlin like a broken wire is not fun.
For cloth wire, buy some of the cloth wire from Doug, as it is awesome and looks great.
http://www.hoffmanamps.com/MyStore/catalog/parts18.htm (http://www.hoffmanamps.com/MyStore/catalog/parts18.htm)
(http://www.hoffmanamps.com/MyStore/catalog/images/IMG_2330.jpg)
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For chassis wiring:
18 ga. is rated 16 amps
20 ga. is rated 11 amps
22 ga. is rated 7 amps
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I think that's wrong.
House wiring (copper) is 12 ga. @ 20 A, 14 ga. @ 15A. So 18 ga. can't be rated @ 16A. :think1:
I believe these #'s are right: 18 ga. @ 6A
20 ga. @ 3.7A
22 ga. @ 2.4A
24 ga. @ 1.5A
Brad :icon_biggrin:
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I will agree with topbrent in that I reworked an early-60's Bassman a while back. I had some cloth covered wire from another source which stood out like a sore thumb in the amp- it was "improved" with a teflon inner cover which made it look physically larger than the original wire of the same guage. I ordered some yellow wire from Mr. Hoffman and after aging its cloth, it matched the original wire beautifully.
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I think that's wrong.
House wiring (copper) is 12 ga. @ 20 A, 14 ga. @ 15A. So 18 ga. can't be rated @ 16A. :think1:
I believe these #'s are right: 18 ga. @ 6A
20 ga. @ 3.7A
22 ga. @ 2.4A
24 ga. @ 1.5A
Brad :icon_biggrin:
You are both right.
Inside a chassis or an electrical box Labb is correct.
Inside walls in your house you are correct.
I believe the reason to be the length of the run.
Ray
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I believe the reason to be the length of the run.
Ray
Good point Ray. :think1: Hmmm, R of wire in inches instead of X's of feet?
Brad :dontknow:
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The ratings I gave are specific for in chassis wiring and are from 1978 ARRL Radio Amateur's Handbook. Power transmission and in house wiring is something completely different and the amp ratings per wire size go way down for those services.
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Labb,
My mistake, good to know the info. It's gotta be the wires resistance over distance?
Thanks, Brad :lipsrsealed:
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Probably, If my feeble memory is correct, for lines the equation is R=r L/D where r is the resistivity coefficient for the material, L is the length and D is the diameter, but that is really testing my memory. The thing with wiring that I am most concerned with in the amps that we build is the rating of the insulation of the wires. I just use 600 volt for everything and not worry about it.
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I like Doug's wire cloth wire a lot. I always liked solid wire, I know it only takes so many bends, but I tend to bend it once and it stays there. :dontknow:
Regards,
Don
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> wires resistance over distance?
No, that's a separate issue.
In-wall house wire uses a large factor-of-safety. It could burn your house down, maybe someone gets hurt.
House-wire also has nearly infinite short-term short-circuit current available.
In-chassis, wire can run much hotter. The fire should be confined to the chassis. Probably nobody gets hurt. The short-circuit current is less because of line-cord and particularly if you are behind a power transformer.
BTW, #12 is a special case. The ampacity should be 25A, but NEC limits it to 20A fuse. NEC also has the 80% rule, a long-running load should only suck 16A.
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> wires resistance over distance?BTW, #12 is a special case. The ampacity should be 25A, but NEC limits it to 20A fuse. NEC also has the 80% rule, a long-running load should only suck 16A.
How long?
Thanks, Brad
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My guess is anything over 100 feet (?) I know out in the barn, I run 12 (uf rated) for everything, even if it's nothing more than some lightbulbs (and soldering iron) since everything is so far away from the box, but use 15A breakers. Mostly just following the way everything else was done 40 years back.
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> How long?
Long TIME.
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:embarrassed: :laugh: