OT transformer question

[angelodp]

Hi, I have an OT out of an old single ended amp. It reads

24119 352513 those are the only codes I find. I see that it may be an

Essex from the code, but not certain.

Anyone know what this is and specs.

The amp is champ like with

2- 12ax7
1- 6v6
1 - 5y3

[Phil_S]

Finding specs on old transformers that were not listed in a catalog is a near impossible task. I got lucky in one case, an old Heathkit PT that was made by Foster. I emailed them. Someone must have had nothing to do on that day because I received a schematic for an item made 40 years ago. Next time I tried for another one of their products, it was as if I'd never contacted them.

What you have is likely a typical 5W 5K primary OT. I suggest checking the turns ratio, read here: http://www.radioremembered.org/outimp.htm and that will tell you most of what you need to know.

If you post a picture along with measurements, we can make an educated guess about the rest. Measure the outer dimensions of the lams and the dimensions of the core, as best you can.

[angelodp]

[IMG:768:1024]http://i260.photobucket.com/albums/ii9/angelodp1/IMG_5710_zps30de64d7.jpg[/img]

[IMG768]http://i260.photobucket.com/albums/ii9/angelodp1/IMG_5711_zps98a6a052.jpg[/img]

Hi Phil, thanks for the reply, I will get those measurements.

Outer jacket 2.25"
Inner core - 1.5"

[Phil_S]

I'm no kind of expert at this, but based on what I see, that one should be good for 5W no problem. I'd say, given the tube compliment, you can use it for just about any lower power tube SE design. I am guessing the bigger tubes like 6L6 will put out ~10W SE and that will be too much.

You should still run some low AC voltage on it to determine the impedance ratio. I see terminals 3, 4, 5, and 6 and assume these are secondary connections. Primary is on the other side I can't see and should be 2 wires for a SE transformer. I am going to guess you've got 4-8-16 ohms on the secondary and the turns ratios you find from the low voltage test will confirm this. If you do have 3 secondary taps, it makes that OT quite the score, IMO.

I usually take the low voltage supply from the PT filament winding for input to the secondary. 5 or 6V in will generate ~100-200V out. You must meter the low voltage input under the load of the OT to get an accurate denominator for the turns calculation.

Your power section is almost certainly SE cathode biased. If you want to try a 6L6, you can always step down to a 6V6 and change the cathode resistor.

[Firestorm]

Looks like 3 and 6 are jumpered. I'd start by disconnecting the leads and seeing what has continuity.

[rdjones]

Looks like 3 and 6 are jumpered. I'd start by disconnecting the leads and seeing what has continuity.

This makes me think maybe it's a "universal" output transformer, where different impedances can be selected by jumpering and/or selecting various taps.
If so, the primary may also have one or more taps if it's SE or pairs of taps if push-pull.

Stancor has several universal OTs with terminals that were marked with a similar "4-5-6-7-8".

If this is the case it would really help if you had the spec sheet to decode the terminals. ;->

rd

[angelodp]

Yes, I have been trying to locate the spec sheet. I believe that Essex was taken over by Stancor…. but so far I do not see this specific code in the Stancor catalogue. I will try my hand at the 1v test to determine the impedance ratio.

I have the schematic for this amp and will post it, that might be helpful to th more experienced eyes.

Thanks for the input.

[angelodp]

Here is the schematic for this amp. I am converting it to an guitar amp. I will post anew, looking for suggestions on what can be deleted from this circuit.

http://i260.photobucket.com/albums/ii9/ ... g~original

[angelodp]

Ok so here is the skinny.

Terminals 3 to 4 are connected with 3 common ground

5 to 6 are connected

Turns ratio of 5 to 6 = 34/1
Turns ratio of 3 to 4 = 4.4/1


34sq = 1156 x 8 ohm load = 9248 ohms

ELR with 310 volts or more is 8000 with a 6V6 so good match

I am using terminal 4 for neg feedback via a 50k linear pot.