Substitute higher secondary a.c. voltages
Posts: 816
Threads: 25
Joined: Mar 2014
City: Louisville, KY
Has anyone ever used a power transformer as a substitute in a radio, that had a little higher high voltage secondary than the original, and replaced a few key resistors to bring the d.c. supply voltages back in line to what they're supposed to be?
I'm curious about doing this with the 39-6 C I, and replace resistors, (part numbers) 19, 23 and 24. Also maybe insert some resistance in the output transformer / output plate connections for the 41 tube? Has anyone done this successfully?
Jake
Posts: 7,301
Threads: 269
Joined: Dec 2009
City: Roslyn Pa
There's a couple of ways to lower the dc output of the power supply. One way is to lower the value of #26 and increase the value of #25. Or you could add a series resistor to the field coil.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 16,507
Threads: 572
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
...or use a small (it's a small radio) bucking transformer.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 184
Threads: 3
Joined: Feb 2018
City: Chesapeake VA
OR use a rectifier that has greater voltage drop. Sometimes takes a bit of experimentation.
Tom
Posts: 16,507
Threads: 572
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Tom
A rectifier that has greater voltage drop is what Terry just suggested - increasing the FC resistance (placing a resistor in series).
Not many other options: using a tube with higher plate resistance won't do much plus it will run hotter. Using a selenium rectifier - like peeing against the wind as everyone is doing the opposite  - they are getting bad.
Inserting diodes with resistors - see Terry's suggestion again.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 184
Threads: 3
Joined: Feb 2018
City: Chesapeake VA
Voltage drop between tube rectifiers vary between different tubes.
I replaced a transformer in a zenith amp that B+ was 360v using a 5V4. With replacement transformer voltage was approx 20v high. Subbing a 5Y3 brought voltage within a couple volts of original.
Tom
Posts: 7,301
Threads: 269
Joined: Dec 2009
City: Roslyn Pa
Tom,
If you need more of a drop use a 5R4. Has a 2a filament but it's the same size as a 5U4G or there is a mil spec version. [Image: https://proxy.duckduckgo.com/iu/?u=https...nt.jpg&f=1]
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 04-05-2019, 06:12 PM by Radioroslyn.)
Posts: 16,507
Threads: 572
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Yes. Again, they run hotter.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 816
Threads: 25
Joined: Mar 2014
City: Louisville, KY
Terry ,
The adjusting filter capacitance change is most-interesting. I didn't know anything about that.
I suppose the simplest route is the added resistance in the dc supply. The filter caps I've bought will handle the extra voltage, ( 450 volts), so I don't think changing them for fear of them being underrated is necessary. I would assume it best to add the resistance after the field coil.
Not sure it will be necessary...... I'm trying to buy another transformer from someone on here. He may have one more-like the original. there's one on Ebay that's a little high. I'm not rushing into either choice yet.
I appreciate the help. 
morzh ,
An additional transformer sounds expensive, and a little complicated. I'll probably stick with resistance if I have to do it at all . I'm hoping to get a better replacement from someone I came across after I posted my original post. Thanks for the suggestion. 
Tom,
Your suggestion of a different rectifier sounds wonderfully the easiest to implement, ( as long as the pin arrangement is the same...not that I'm not capable of re-wiring it). This thing has an 84 rectifier though, and I'm feeling any newer rectifier ( like the 5Y3), may go in the other direction. I don't know things like plate resistances, so I need to study that more in the online tube manuals. 
Jake
(This post was last modified: 04-05-2019, 08:34 PM by Jake Blake.)
Posts: 16,507
Threads: 572
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
An additional small transformer (I recently bought 2 larger ones, 3A 12V, for $6 each) is electrically ideal way: there is no power dropout, except for parasitics. All other ways result in power dissipation.
Expensive it is not, if bought on eBay.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 184
Threads: 3
Joined: Feb 2018
City: Chesapeake VA
(04-05-2019, 06:08 PM)Radioroslyn Wrote: Tom,
If you need more of a drop use a 5R4. Has a 2a filament but it's the same size as a 5U4G or there is a mil spec version. [Image: https://proxy.duckduckgo.com/iu/?u=https...nt.jpg&f=1]
The 5R4 has 67v drop at 250ma, meaning in real world, it drops approx half voltage of the 5Y3 that's rated 60v drop at 125ma. In said amp, that draws roughly 80ma, the 5R4 & 5V4 gave similar B+. A 5V4 is rated 25v drop at 175 ma.
As far as heat, will be similar in any 5v, 2A filmant that handling same amount of current.
The 84 has a 20v drop at 60 ma. Being a big pin and 6.3v tube vs 5v, are less choices for substitutes. Almost any workable choice will increase voltage.
Tom
(This post was last modified: 04-05-2019, 09:49 PM by 35Z5.)
Posts: 7,301
Threads: 269
Joined: Dec 2009
City: Roslyn Pa
Not sure abt how all the math works out but my recollection is that the 5R4 is able to rectify much higher voltage (1800vac) but the max current is abt 150ma. Swapped out a pair of 5U4's w/5R4's in a transmitter I had and there was some drop in the hv by comparison. Maybe 50v or so. I wasn't suggesting that the 5R4 would be a suitable replacement for the 84 I only mentioned it to illustrate that that some have a higher voltage drop than others.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 04-05-2019, 10:57 PM by Radioroslyn.)
Posts: 816
Threads: 25
Joined: Mar 2014
City: Louisville, KY
Radioroslyn
An excellent point, well-taken bud. Thanks.
Jake
Posts: 184
Threads: 3
Joined: Feb 2018
City: Chesapeake VA
The 5R4 has a maximum current rating of 250ma, generally make dandy subs for 5U4, but watch current as 5U4GB can handle 275ma. Probably not a issue, most any equipment that draws over 200-225ma likely uses two rectifiers. The 5U4GA is rated 250ma, orig 5U4G only 225ma.
Tom
Posts: 16,507
Threads: 572
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
As it is with solid state devices, same size type with higher collector/drain voltage has lower current limits and higher resistance in the fully open state.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Users browsing this thread:
|
|
Recent Posts
|
|
Philco 42-345 Restoration/Repair
|
| Yes, 57 is an electrolytic cap that should be 12 mfd 400 volts according to the parts list from the Phorum library schem...RodB — 06:01 PM |
|
Philco 42-345 Restoration/Repair
|
| Looks like if I am reading it correctly it looks like the silver capacitor#57 that appears to be a replacement is of a l...osanders0311 — 05:09 PM |
|
Philco model 38 code 121 not receiving signal.
|
| Thanks Arran. Yeah this plastic is pretty thin. It's a little thinner than the original stuff. It kinda reminds me of p...Stormlord5500 — 04:37 PM |
|
Testing a speaker and output transformer Trutone A2-G
|
| The equivalent of one short turn is basically the same as that of a shorted load.
If it is the primary's turn, then the ...morzh — 03:53 PM |
|
Testing a speaker and output transformer Trutone A2-G
|
| I've never had an output transformer become shorted, the failure mode is usually an open primary, or in a center tapped ...Arran — 03:52 PM |
|
Philco model 38 code 121 not receiving signal.
|
| As long as the plastic sheeting isn't too thick, I think that the thickness of photographic film would be just about rig...Arran — 03:19 PM |
|
Philco model 38 code 121 not receiving signal.
|
| Well why not! :lol:Stormlord5500 — 03:14 PM |
|
Philco model 38 code 121 not receiving signal.
|
| Good luck next thing you know you will be winding coils just for the fun of it. DavidDavid — 11:29 AM |
|
Testing a speaker and output transformer Trutone A2-G
|
| morzh
Short-circuited turns can be considered as a half-dead transformer.
But on this case transformer will hot and s...Vlad95 — 11:01 AM |
|
Testing a speaker and output transformer Trutone A2-G
|
| I am not sure how a transformer could be weak. It could be inadequate, but only when you replace the original with somet...morzh — 09:56 AM |
|
Who's Online
|
There are currently 2175 online users. [Complete List]
» 2 Member(s) | 2173 Guest(s)
|
|
|
|
 
|
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
