I'm working on an old crusty dusty Howard 220-270
http://www.nostalgiaair.org/PagesByModel/218/M0009218.pdf

The output transformer primary is open. ( tried to fix it ..tiny hair wires no luck)
So I need a new one.
This radio uses a 41 for output tube.

How can I determine the correct primary impedance?

I went to www.Oldradioparts.com and scrolled down the output transformer list to find some in the proper dimensions for my mount... but I can't determine which of the four listed below is best?

#1 does not indicae the output tube
#2) shows a 42 output tube
(#3) shows a 41 tube... so I thought that would be best.
#4 shows 50L6 tube

So does this mean I should ONLY use # 2 or #3 since a 42 is very similar to a 41?

or can I use any of these with little noticible difference?

Right now fopr test purposes I'm using a big clunky old thing with about 500 ohms DCR on the primary..temporarly jumpered in and it seems to work great.
I tried another one with it's own speaker too...that only has about 150 ohms DCR on the primary and that works too but not as good.. but maybe it is not as good a speaker?

Norm or someone... can you shed some light here please?

I don't know how to find the correct specs for the bad part.

A little help please?.. thank you.

1.) SP TO V.C., 140 OHMS PRI, Z=?, 1 WATT,

2.) SP (6F6/42/ETC) TO VC, 3-5 WATTS,

3.) SP (10K Z - 3V4, 41) TO V.C., 3-5 WATTS

4.) SP TO 3.2 V.C., 2.5K Z (50L6, 50C5), 1-3 WATTS

:I'm working on an old crusty dusty Howard 220-270
:http://www.nostalgiaair.org/PagesByModel/218/M0009218.pdf
:
:The output transformer primary is open. ( tried to fix it ..tiny hair wires no luck)
:So I need a new one.
:This radio uses a 41 for output tube.
:
:How can I determine the correct primary impedance?
:
:I went to www.Oldradioparts.com and scrolled down the output transformer list to find some in the proper dimensions for my mount... but I can't determine which of the four listed below is best?
:
:#1 does not indicae the output tube
:#2) shows a 42 output tube
:(#3) shows a 41 tube... so I thought that would be best.
:#4 shows 50L6 tube
:
:
:So does this mean I should ONLY use # 2 or #3 since a 42 is very similar to a 41?
:
:or can I use any of these with little noticible difference?
:
:Right now fopr test purposes I'm using a big clunky old thing with about 500 ohms DCR on the primary..temporarly jumpered in and it seems to work great.
:I tried another one with it's own speaker too...that only has about 150 ohms DCR on the primary and that works too but not as good.. but maybe it is not as good a speaker?
:
:Norm or someone... can you shed some light here please?
:
:I don't know how to find the correct specs for the bad part.
:
:A little help please?.. thank you.
:
:
:
:
:
:
:
:
:1.) SP TO V.C., 140 OHMS PRI, Z=?, 1 WATT,
:
:2.) SP (6F6/42/ETC) TO VC, 3-5 WATTS,
:
:3.) SP (10K Z - 3V4, 41) TO V.C., 3-5 WATTS
:
:4.) SP TO 3.2 V.C., 2.5K Z (50L6, 50C5), 1-3 WATTS

Hi Peter,
The input impedance is 10K ohm. A transformer used for a 6G6, 19, or 49 output tube will be an exact match.
I got that from a web site that had a wonderful write up on this subject. The web site is now gone, but I have a copy. I could email a copy if I had your eamil address. You may email me at bill@avorex.com.

All the Best,

Bill Grimm

To determine the primary impedance of a audio output transformer look in the tube manual for the load resistance value given for the output tube. The 41 tube in my old tattered RCA manual refers you to the 6K6 that is electrically the same. The three tables for the 6K6 are broken down by plate voltages, 100V, 250V and 315V. Plate voltage from the schematic is 180V, so 10,000 ohm primary should be very close. It's not that critical that it be exact.

Richard

Rich:
Thanks.. I went to the same 6k6 page but didn't realize that the plate load resistance meant the same thing... (I think was looking for it to be expressed as transformer-impedance I guess) but sure of course that makes sense.

So I see that generally those older output tubes required from 9-12k ohms load ( impedance ) and the newer 50L6 or 50C5 requires a much lower 2-4k ohms load.

Hi, all. Theoretically, the load impedance = output tube plate resistance will result in maximum power to the load (speaker). I can prove this mathematically!

But because of distortion and maybe other factors, the preferred load impedance is less, maybe half or a third of the output plate resistance. I sort of understand this, but not enough to deliver a lecture ;>)

:Rich:
:Thanks.. I went to the same 6k6 page but didn't realize that the plate load resistance meant the same thing... (I think was looking for it to be expressed as transformer-impedance I guess) but sure of course that makes sense.
:
:So I see that generally those older output tubes required from 9-12k ohms load ( impedance ) and the newer 50L6 or 50C5 requires a much lower 2-4k ohms load.

it would be really nice if these audio output transformes were more simply classified... like type "a" or type "b" etc... y'know?