Posts: 45
Threads: 8
Joined: Jan 2013
City: Toronto Ontario
Hello phellow Philco phreaks,
It's been a while since I've posted anything, my 3 year old has been keeping me plenty busy.
I had a quick question about Isolation transformers...
Up until now, I've been replacing caps and resistors, testing tubes and getting rather lucky. I'd like to start doing some real testing on some of my problem sets but want to buy an Isolation transformer first.
I've notice the ones linked below but I'm not sure if they'd be right for radio repair. Does there have to be a minimum output from these? Anything in particular I should be looking for?
P.S. - I don't want to spend a fortune.
Thanks.
http://www.ebay.ca/itm/271405793357?ssPa...1423.l2649
http://www.ebay.ca/itm/180750352646?ssPa...1423.l2649
Posts: 1,195
Threads: 83
Joined: Jan 2014
City: Annapolis, IL
State, Province, Country: USA
Mine is an older Isotap 400w, 4a transformer that I have powered about anything electronic you can immagine. I dont think a radio would even test the limits of either of those you are looking at. They are a pretty good idea, esp on those ac/dc sets where one side of the a/c line is connected to the chassis. In addition, you may want to also consider a variac transformer, but not as a substitute for an isolation transformer.
If I could find the place called "Somewhere", I could find "Anything" 
Tim
Jesus cried out and said, "Whoever believes in me , believes not in me but in him who sent me" John 12:44
Posts: 16,266
Threads: 566
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
1.25A for the B&K (and those are good for smaller things to test) could become a limit with a large radio.
300VA is a good size.
I have this exact type
http://www.ebay.ca/itm/Dale-IT400-Medica...5401ff07d0
If you decide to by Dale/FLuke let me know, there is one thing you have to do to it first (an easy thing - disconnecting a jumper inside).
Posts: 5,129
Threads: 271
Joined: Nov 2012
City: Wilsonville
State, Province, Country: OR
$29 plus shipping
https://www.valuetronics.com/detail/Used...wuznIW9KHY
They have a few other models as well.
Posts: 411
Threads: 42
Joined: Sep 2008
City: Ironton Ohio
I built my own with 2 radio transformers, you can wire both 6.3 (or what ever the filament voltage is as long as both trans. have the same fil. voltage) together. It takes 120v to 6.3v to 6.3v back up to 120v. Cheap easy isolation transformer that works just as well as something you buy.
Posts: 16,266
Threads: 566
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
This Valuetronics thing, is it used?
If it works, can't beat the price.
No picture though.
Posts: 239
Threads: 10
Joined: Dec 2013
City: Columbia, SC
Be careful using two filament transformers. A larger Philco pulling 90 watts will put a more than 15 amp draw on the two back to back secondary windings. I doubt most are made for more than a few amps.
If you could get matched high voltage windings together, that would be better. I would suspect the voltage might not be as stable though.
(This post was last modified: 02-24-2014, 06:04 PM by skyscraper.)
Posts: 16,266
Threads: 566
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Yes, I agree - the two transformers back-to-back at 6.3V winding might not be such a hot idea (well could become hot  ) as at 6.3V the current draw even for a medium 60W radio could be too much.
Posts: 411
Threads: 42
Joined: Sep 2008
City: Ironton Ohio
I built it after reading on the net to use the lowest voltage on the trans, something to due with the windings. I have used it for years. I have a 1 amp fuse on the line side and a 1.5 amp mini breaker on the load side, it has never blown either.
Posts: 239
Threads: 10
Joined: Dec 2013
City: Columbia, SC
They wouldn't blow. 1amp x 120v is 120 watts. 120 watts going through at 6v works out to 20 amps. Stepped back up, that's an amp out. I don't know of many transformers that can handle 20 amps on a secondary winding, and I would imagine yours is either getting very hot or you haven't powered a large radio with it.
Posts: 411
Threads: 42
Joined: Sep 2008
City: Ironton Ohio
So would the high volt winding be better?
Posts: 239
Threads: 10
Joined: Dec 2013
City: Columbia, SC
I don't know a whole lot about high voltage transformers, but I do know Ohm's law. You can experiment, just make sure you have two transformers with matched windings.
I would guess the higher resistance would cause the voltage to fluctuate somewhat with load, but that's easy enough to test.
In the end, it's about the ratings of the transformer and Ohm's law.
Posts: 411
Threads: 42
Joined: Sep 2008
City: Ironton Ohio
http://m.youtube.com/watch?v=QDSmv9E5VgQ
This is the trans. I built, I remember using the 5 volt 80 fil winding now that I watched it again.
Posts: 239
Threads: 10
Joined: Dec 2013
City: Columbia, SC
That's even worse... That's 25 amps possible flowing through those wires with the fuse you have. The 80 tube uses 2 amps, for comparison.
Can anyone else confirm?
Posts: 411
Threads: 42
Joined: Sep 2008
City: Ironton Ohio
I dont have a great understanding of electronic laws I just know it has ran many transformer-less radios for hours without getting hot or any other problems. Maybe I have just been lucky?
(This post was last modified: 02-24-2014, 07:12 PM by tab10672.)
Users browsing this thread: 3 Guest(s)
|
|
Recent Posts
|
|
An attempt to remove the Field Coil from a G speaker
|
| Mike;
I've only run into a speaker with an open filed coil twice, and they were on newer speakers from the 1940s. One ...Arran — 12:48 AM |
|
An attempt to remove the Field Coil from a G speaker
|
| Arran
Yes, this is my plan for now and what do I got to lose, this is not even the speaker from this radio, but one o...morzh — 10:44 PM |
|
An attempt to remove the Field Coil from a G speaker
|
| Mike;
I would unwrap the field coil, and see if maybe there a break near one of the ends, like where the coil wire att...Arran — 10:23 PM |
|
An attempt to remove the Field Coil from a G speaker
|
| ...and this is what I did. I fed a little LT into the screwholes with a small brush, and a little on the rim next to the...morzh — 09:52 PM |
|
Philco 40-120C Restoration
|
| I combined the two 40-120C threads together as we like to keep the discussion of the same radio together. It helps with...klondike98 — 09:36 PM |
|
Philco 40-120C Weak, Distorted Ouput
|
| Just checked were I buy tubes price is four dollars. So living in Florid we have a local source for tubes. David David — 09:14 PM |
|
Philco 40-120C Weak, Distorted Ouput
|
| The higher voltage may be due to higher mains voltage. My mains run 120-125AC when the set was new mains would be 110-11...David — 09:09 PM |
|
Philco 40-120C Weak, Distorted Ouput
|
| Thank you for your reply. I pulled a speaker from a Philco 41-221 and received the same result. I used a signal tracer t...bluecap — 08:45 PM |
|
Philco 40-120C Weak, Distorted Ouput
|
| Have you tried a different speaker?
How did you trace the distortion?
How do you know it is weak? What is the reference?...morzh — 08:33 PM |
|
Philco 46-480 Electronic Restoration
|
| Amen to that! Every time I think I’ve captured them all, I realize that there’s another error. My goal is to finish with...jrblasde — 07:00 PM |
|
Who's Online
|
There are currently 6196 online users. [Complete List]
» 1 Member(s) | 6195 Guest(s)
|
|
|
|
 
|
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
