Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

25A6G + speaker match
#5

(08-10-2015, 06:09 PM)Bob Andersen Wrote:  Yes, but you can have two coils with different static (DC) resistance that have the same impedance.  For example one may use a larger gauge wire which would result in lower DC resistance but have the same impedance.

Ok Bob, let me see if I can flush this out...

The 25A6G pentode  impedance at 400hz is 4000 ohms 
The original speaker matching transformer with a 1 ohm voice coil primary is 200 ohms (per Philco)
Divide 4000/1.25 and get 3200 or 3200:1
Take the sq rt of 3200= 56.6 and the output transformer for the original speaker should have a transformer with a 60:1 turns ratio
Since Philco calls out 200ohms  200/60 =approx 3-4ohms Or the original transformer would be 4ohms / 200 ohms

If I wanted to use an 8ohm speaker

4000/8.25 =484 sqrt= 22  or  a transformer with  about a 20:1 ratio  10/200

Does this seem right?

The speaker the chassis is connected  to now has a voice coil of about 1.2 ohms and a 500 ohm primary with a secondary of 1/2 ohm
So for the impedance to be right the secondary  should be more like 10 ohms?
So this speaker they connected seems to be not the right choice.

I have no idea how to calculate the needed choke value to replace the field coil.

To make this a whole lot easier I'm hoping to find the real speaker.


Messages In This Thread
25A6G + speaker match - by thinktreasure - 08-10-2015, 12:46 PM
RE: 25A6G + speaker match - by Bob Andersen - 08-10-2015, 02:05 PM
RE: 25A6G + speaker match - by thinktreasure - 08-10-2015, 03:44 PM
RE: 25A6G + speaker match - by Bob Andersen - 08-10-2015, 06:09 PM
RE: 25A6G + speaker match - by thinktreasure - 08-12-2015, 05:19 PM
RE: 25A6G + speaker match - by codefox1 - 08-17-2015, 05:03 PM
RE: 25A6G + speaker match - by Radioroslyn - 08-17-2015, 05:56 PM



Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Philco 91 Speaker Replacement
The spider is glued on the cone and so is the voice coil. I think you can use a cotton swab dipped in acetone and carefu...RodB — 02:42 PM
Restoring Philco 37-604C
Yes I saw that. If I knew, I'd probably try to arrange for getting it myself. But I have just got one. Which does not m...morzh — 01:44 PM
Philco 38-2 Automatic Tuning
When you push the lever, you are supposed to rotate the disk to the desired station. Then the magnetic tuning will acqu...morzh — 01:42 PM
Philco 38-2 Automatic Tuning
I figure out the muting from another picture that helped. Now I need to know how the automatic tuning works. When I push...dconant — 12:11 PM
Philco 91 Speaker Replacement
How would I go about removing the spider from the cone?dconant — 12:04 PM
Philco 38-2 Automatic Tuning
Hello, I am having trouble getting my automatic tuning to stay unmuted. If I play with the tuning handle I can get it to...dconant — 10:51 AM
Does anyone make photofinish replacements?
Here’s the link to the DIY photofinish section of our site: klondike98 — 09:46 AM
Delco car radio Peko vibrator converstion issues
Hi Richard, Thx for posting the schematic.  As I remember as a kid, these were great performers for the time, likely...MrFixr55 — 08:56 AM
Delco car radio Peko vibrator converstion issues
hello mr Fixr, The Electro  Powersupply that I am powering the radio with has a huge choke plus a 10,000ufd electrolyti...radiorich — 10:58 PM
Delco car radio Peko vibrator converstion issues
How about putting a choke in the power supply? The big cap was likely an attempt to stabilize the DC. Kids who cre...MrFixr55 — 09:19 PM

[-]
Who's Online
There are currently no members online.

>