Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Sat 24, 2020 4:03 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 15 posts ] 
Author Message
 Post subject: Any disadvantage in relocating output transformer?
PostPosted: Mar Sun 19, 2017 3:59 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5911
Location: Beautiful Downtown Burbank CA
I'm building a 12AU7/50C5 amp/antique speaker box and running out of space on the chassis. Knowing AA5s routinely mounted their OTs on the speaker, is there any disadvantage in mounting the speaker combo this way? How about farther say 50 feet away? More susceptible to hum/QRM?

Or are we talking about such a small output it doesn't matter? :roll:


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Sun 19, 2017 4:15 am 
Member
User avatar

Joined: Jan Fri 06, 2012 8:47 pm
Posts: 6795
Mike Toon wrote:
Knowing AA5s routinely mounted their OTs on the speaker, is there any disadvantage in mounting the speaker combo this way? How about farther say 50 feet away? More susceptible to hum/QRM?
The major disadvantage I see is running high voltage DC with appropriately specified high voltage wiring to where the speaker is instead of just a long run of low impedance speaker wire.

Curtis Eickerman

_________________
http://curtiseickerman.weebly.com


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Sun 19, 2017 8:37 am 
Member
User avatar

Joined: Sep Sat 27, 2014 4:24 am
Posts: 1876
Location: Oxford, MI
If the speaker is external the problem of having B+ on the speaker terminals also presents a problem.

_________________
Hunter

Caretaker of Portable Tube Radios


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Sun 19, 2017 3:00 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11652
Properly insulated/protected I don't see a issue... Current is like what?? Fifty ma at most??? You could run #24 wire for several hundred feet... Now whether it picks up hum or not is another issue,,,

If you want to be sure there is no voltage drop use some double naught cable.. :wink:

Per this chart, #24 wire has less than 26 ohms per 1000ft... Or 1.3 ohm in 50ft, non issue...

https://www.tedpella.com/company_html/w ... vs-dia.htm


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Sun 19, 2017 3:10 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30665
Location: Livermore, CA
Shouldn't be a problem. If speaker wires are near the input may be feedback, oscillation.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Sun 19, 2017 8:20 pm 
Member

Joined: May Tue 30, 2006 4:46 pm
Posts: 10196
Location: Santa Rosa, CA
Quote:
Properly insulated/protected I don't see a issue... Current is like what?? Fifty ma at most???


But 120V DC at 50 mA is more than enough knock some unwary person on to his butt! No one expects 120V at a speaker box!

Rich


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Mon 20, 2017 1:05 am 
Member
User avatar

Joined: Sep Mon 16, 2013 2:42 am
Posts: 4231
Location: Tucson, Arizona U.S.A.
If the speaker gets disconnected while the amplifier is turned on, the plate connection to the 50C5 will be interrupted. Then all the cathode current will go to the screen grid which will overheat and probably melt. Then you will need a new 50C5. You could wire it with a 3 wire cable so that the screen voltage is also cut off if the speaker is disconnected.

_________________
Jim Mueller


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Mon 20, 2017 1:35 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11652
Rich, W3HWJ wrote:
Quote:
Properly insulated/protected I don't see a issue... Current is like what?? Fifty ma at most???


But 120V DC at 50 mA is more than enough knock some unwary person on to his butt! No one expects 120V at a speaker box!

Rich


I did say properly insulated/protected... :| Anyway 50ma is tube draw, assuming a 1N4007 rectifier in P/S, if one really tried could probably draw a amp or more... Ka-pow!!!


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Mon 20, 2017 5:06 am 
Member

Joined: Sep Thu 23, 2010 6:37 am
Posts: 12437
Location: Powell River BC Canada
Bottom line. You are extended a circuit out of a radio approved for being self contained.
50 feet away, it might meet up with another appliance, which is plugged into the other side
of the 120/240 split. Now the shock can be 240 volts, and the whole thing needing switch off
at two separate circuit breakers, maybe in two meter loops.

You have to think like a butt-covering electrician. We see stuff that would turn your AC to DC. :D

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Mon 20, 2017 2:26 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11652
Hey Mike, with all this gloom & doom you better run the wires through conduit... No not from Lowes or Home Deport, go to a real electrical supplier and get the thickest wall, outdoor grade you can find... Also be sure to ground it in at least 12-15 places(19 would be better)...


Tom


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Mon 20, 2017 5:46 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5911
Location: Beautiful Downtown Burbank CA
The distance thing was just hypothetical. I was thinking a foot max, and about static or hum problems.
I do appreciate the warnings. :roll:


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Tue 21, 2017 2:19 am 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21951
Location: Somers, CT
Well, I squared R losses will lower using a higher voltage (impedance) feed between the radio and speaker. LOL.
Instead of 50 feet of 12 gauge wire, number 22, well insulated, would work better.

Pete

_________________
Just because it can be done doesn't mean it should be done.


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Wed 22, 2017 11:24 pm 
Member

Joined: May Tue 30, 2006 4:46 pm
Posts: 10196
Location: Santa Rosa, CA
Quote:
Well, I squared R losses will lower using a higher voltage (impedance) feed between the radio and speaker. LOL.
Instead of 50 feet of 12 gauge wire, number 22, well insulated, would work better.


Which is one of the reasons they invented the 70.7 volt Public Address distribution system!

http://www.belden.com/blog/broadcastav/ ... ystems.cfm

Rich


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Mar Thu 23, 2017 1:08 am 
Member

Joined: Sep Thu 23, 2010 6:37 am
Posts: 12437
Location: Powell River BC Canada
The 70 volt system is recognized by electrical wiring standards.

The over current protection is adjusted to 100 / (e.g.) 70.7 , or 1.4 amps. The voltage
of this group of class 2 wiring lies between 60 and 150 volts.

DC Class 2 circuits can also be powered by batteries.

There are also *many* other rules as to how and where wires these circuits can be
installed, and by whom.

The favorite joke of sound system installers, was about the drive in theater
owner who complained, that after buying a new speaker to connect the line from
his amplifier, it was the only one he could hear.

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


Top
 Profile  
 
 Post subject: Re: Any disadvantage in relocating output transformer?
PostPosted: Apr Fri 14, 2017 3:20 am 
Member
User avatar

Joined: Dec Sat 24, 2011 9:17 pm
Posts: 6661
Location: Vancouver Island, Canada
It is not too unusual to see an old console radio with the OT down on the speaker.

But when you're done building, if you amp has a hum, you won't know if it's internal or external. :lol:

_________________
Watch the doughnut, not the hole.
Burl Ives, RIP, oldtimer.
[:l>)


Top
 Profile  
 
Post New Topic Post Reply  [ 15 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: BobWeaver and 8 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB