While trying to determine if the speaker for my model 90 cathedral is just not that good sounding (it is a model 20 speaker with an Hammond 125C transformer) 2- 45 push pull output tubes.
I hooked up my model 20 speaker from a restored 20 radio. I was able to just set it next to the 90 chassis and plug it in. It sounded a whole lot better.
What I did notice was the amperage draw when using the speaker with the Hammond transformer was 825mA
with the speaker in the 20 radio that has an original output trans. the amps. were 625mA.
Whew, my question is :
Is the difference in the amp. readings anything to be worried about or is it just the difference btwn. the original OPT and the Hammond OPT?
Extra 20W...doubt it is the xfmr. Unless hooked really wrong. But even then....
How's your field coil, the resistance?
What's your Hammond hookup to tubes and field coil? Also show exactly how you have your speaker plug connected yo FC and xfmr prinary.
I'll try to explain it. I hope its not too confusing.
OPT- red wire to green & white speaker wire and also field coil wire which is D pin
OPT- blue wire to BLK/white speaker wire which is P pin
OPT- brown wire to solid white speaker wire which is second P pin
Green speaker wire to other field coil wire - which is E on schematic
(07-31-2016, 04:14 PM)KCMike Wrote: [ -> ]I'll try to explain it. I hope its not too confusing.
It is
I mean, your speaker colors don't mean much. I need to know the functions. Which you gave, we need to make sure you are sure the "white speaker wire" is a P.
But we also need to
1) the connections to the plug (make sure your pkug and socket pinouts agree) and
2) voice coil to xfmr output connection (numbers).
Okay the white speaker wire which is connected to brn. wire of the OPT. is one of the plates of output tube, it is also correct at the plug pin and socket hole.
the blk/wht speaker wire is connected to blue wire of OPT and is the other tube plate. It also is correct at the plug pin and socket hole.
The red center tap wire of OPT is connected to the other field coil wire and speaker plug pin that goes to D socket and is correct.
The other speaker wire, green, connects to the field coil wire and its pin out goes to correct socket hole E that has the primary of AF transformer attached to socket inside the chassis
The voice coil wires are connected to secondary # 5 & 6 of OPT. which on the series connection chart on the Hammond box shows that at 1.5 VC impedance would be 8500. I did try 1-3 connection that's 5400 it didn't sound as good.
You need to try 3 and 4 pins. They give 1:100 ratio which is what 20 xfmr is.
Don't go by impedance - go by ratio.
Thanks Mike I'll give that a try tomorrow. Time for a brew and bed.
I went ahead and did as you said Mike went with pins 3&4. It does sound better but still has some distortion.
I let it play for about 2 hours and all seems okay as for as anything getting hot. Transformer was just medium warm to touch.
I think I'm going to leave it alone and finish the cabinet, getting close to putting the grill cloth in and reinstall the chassis & speaker.
This was the ugly painted green cabinet that I have been working on.
Thanks for your advice.
Mike
Tere also could be a problem with the speaker itself.
Good test, take this same transformer, and attach the output to a good PM speaker, using proper taps to match impedance. See if the speaker sounds better.