38-116 Input Transformer Info - Printable Version
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38-116 output transformer - bm071 - 02-13-2015
Hello Everyone!
It's been a couple of years since I've posted. I decided to re-visit my 38-116 since I've got it playing. I knew it did not have the correct output transformer but never paid much attention. I finally checked the specs on the Hammond hx 126 series and it is only 4 watts. I've read some posts here and see many go with the hx-125e or the hx1650f. I chose the Edcor gxpp15-4-8k. Looking at the specs of the original transformer the primary resistance is 7600 ohms. The Edcor is 8K. My question is will the extra 400 ohms cause any major changes in tone or clarity? With the current transformer the radio sounds just ok, not much fidelity, volume up almost 1/2 way....just doesn't bark so anything would be an improvement but I'd like it to rattle the windows!!
Thanks!!
RE: 38-116 output transformer - morzh - 02-13-2015
(02-13-2015, 02:03 PM)bm071 Wrote: Hello Everyone!
Looking at the specs of the original transformer the primary resistance is 7600 ohms. The Edcor is 8K. My question is will the extra 400 ohms cause any major changes in tone or clarity?
No it won't.
However, do make sure that this 8000 Ohms ARE at the Voice coil impedance of the speaker.
I do not remember wht the VC impedance but if say 8000 Ohm is at the VC=8 Ohm and you have VC=4 Ohm your input impedance will be 4000 Ohms then.
RE: 38-116 output transformer - Ron Ramirez - 02-13-2015
The voice coil impedance of the 38-116 speaker is 3.9 ohms.
RE: 38-116 output transformer - Ron Ramirez - 02-13-2015
Additionally:
The original audio output transformer is rated at 8000 ohms primary impedance.
The Edcor GXPP15-4-8K is a near perfect replacement - 8000 ohms to 4 ohms.
https://www.edcorusa.com/gxpp15-4-8k
Great price, too, compared to a Hammond equivalent. The only problem I see is mounting it to your speaker, since the Edcor does not mount in the same way as the original transformer. But I'm sure you can figure something out.
RE: 38-116 output transformer - morzh - 02-13-2015
The single problem that kept me fom ordering Edcor is they ave no stock, they build to order when they have enough.
Otherwise great looking good transformers with great price.
RE: 38-116 output transformer - bm071 - 02-13-2015
(02-13-2015, 05:44 PM)morzh Wrote: The single problem that kept me fom ordering Edcor is they ave no stock, they build to order when they have enough.
Otherwise great looking good transformers with great price.
Oh boy,, am I thinking wrong or totally screwed up? I am replacing the so called output transformer on the radio chassis. It's between the 6l6 and the 6j5 tube right behind the tuning condenser. Am I confused with the input transformer? My transformer on my 15 in speaker is Philco #32-7717N. I was/am teaching myself how to read schematics and such and from what I could conclude part # 32-7751 located on the back of the chassis. I purchased this radio at an estate auction and the Hammond 124E(sorry I thought it wa sa 126 series) was a replacement located on the chassis as I described. I don't mind being wrong and thanks in advance for the correct info, I just would like to have the correct replacement parts.
RE: 38-116 output transformer - Ron Ramirez - 02-13-2015
No, no, that is the audio interstage transformer. The audio output transformer mounts on the speaker.
The interstage transformer is a totally different monster. And if it requires replacement, you will have to have one custom made or else find one from a junk 38-116 chassis. This transformer has two separate secondaries, not a center tap. The split secondaries are necessary because of the radio's design; a center-tapped secondary won't work without some modifications to the set's original design. And it is a step-down transformer.
RE: 38-116 output transformer - morzh - 02-13-2015
Ron
Hammond interstages do not work for 38-116? I mean, they do make those. I used one in my 111.
RE: 38-116 output transformer - Ron Ramirez - 02-13-2015
Unless they make a step-down interstage with split secondaries (two separate secondaries, no center tap), then no.
The secondary of the 111's interstage has a center tap.
I recall someone had Heyboer make one of those for them. I don't remember if it was someone on the Phorum or elsewhere, but as I recall, the finished product was identical to the original and fit in the original shell.
RE: 38-116 output transformer - bm071 - 02-13-2015
ok???? I guess the 124e is not the correct replacement for that however it plays with that transformer installed. Please tell me what I need to do to. If I need to have one buitl I think edcor will build to my specs. Unfortunately now I am in over my head. Would you be able to provide me with specific/original build specs to have one made? Or any leads to a used one?
Thank you Ron for your time and trouble!!
RE: 38-116 output transformer - morzh - 02-13-2015
Yes, mine was with split secondaries, I connected them in series.
http://www.hammondmfg.com/pdf/5C_124_126.pdf
RE: 38-116 output transformer - Ron Ramirez - 02-13-2015
The 124E won't work as it is a step-up transformer. The 38-116 wants a step-down transformer.
I do not have the impedances, but the primary DC resistance is 400 ohms. Secondary #1 is 175 ohms; secondary #2 is 150 ohms.
RE: 38-116 output transformer - morzh - 02-13-2015
Can you take 124E and invert it? It would become a centertapped stepdown, as I remember, 3:1
RE: 38-116 output transformer - bm071 - 02-13-2015
(02-13-2015, 11:26 PM)Ron Ramirez Wrote: The 124E won't work as it is a step-up transformer. The 38-116 wants a step-down transformer.
I do not have the impedances, but the primary DC resistance is 400 ohms. Secondary #1 is 175 ohms; secondary #2 is 150 ohms.
Thanks Ron...I may post on the board for a used one. Hopefully someone has a junk chassis. Guesss I could have ordered the Edcor xpp style transformer instead of the gxpp. My fault for not doing research. I tend to take the easiest path right or wrong!!
RE: 38-116 output transformer - Ron Ramirez - 02-13-2015
http://www.nostalgiaair.org/Resources/235/M0013235.htm
Notice that each secondary has a 10K resistor in series with the two (separate) windings, and then each end of these resistors connect together and to B-.
Mike (morzh), I would bet that you could come up with an alternative method of biasing those 6L6G tubes while allowing the use of a center-tapped secondary. I'm not an engineer so I freely admit such reverse engineering is above my pay grade.