The AM Forum

I recently picked up a Hammarlund SP600. The audio output jack on the rear panel is for 600 ohms impedance. I am trying to figger out the best way to hook up an 8 ohm speaker. I came up with five ideas and I'd like to hear what you all think is the best way to do this. The SP600 has a single ended 6V6 audio output tube. I think it has about 3 watt audio power.

1. hook up the 8 ohm speaker to the 600 ohm jack and put up with crappy audio.
2. Replace the audio output transformer with a new one - 5000 ohm primary:8ohm secondary
3. Attach a 600ohm:8ohm transformer to the output jack
4. Find a 600 ohm speaker
5. Take the audio off the IF - This one sounds good to me but I forget how to do it.  :-\

Thanks,

Ron W8ACR

Ron,

Its been many years since I even looked at an SP600 but way back
in the memory I seem to recall that 600 ohm output was made for
feeding the AF to a 0dbm line.

However, if it is the only load on the output of the 6V6, acquire a standard
500 ohm to voice coil transformer (radio shack used to carry them) or
if you have a small 115 volt to 6 volt (1 amp or so, not critical) filament
transformer handy, it's a great substitute...

A 70.7v line to voice coil transformer would be a close enough match for the 600 ohm output, I believe.

I use method #3. It works FB.  ;D ;D

It really isn't a big deal, at least to me.  Hammond makes a high quality 600 ohm to voice coil transformer model P-T119DA.  It's a quality transformer - you only need to buy it once.  I can't count the times I've heard work-around solutions to this question.  Be nice to your great receiver (I have one of those too)  Get the transformer -- it will outlive you

73 es GL

Al

Correct, you need one that has a 10watt tap.  When you connect to the 10watt tap that is about 500ohms off a 70.7 constant voltage speaker system.  Some xfmrs only have up to 5 watt taps.  If you connect a 4 ohm speaker to the 8 ohm tap and then use the 5 watt tap you will be at the same 500 ohm load on the 70.7 volt line.

Fred

I did a search on this website and found the thread started by KE7TRP regarding HI FI audio from an SP-600 by taking the audio off the diode load circuit point using a 470K resistor and a 10uf nonpolarized cap. Can someone draw for me a simple schematic of this circuit?

Thanks, Ron

Hi!

I only have one 600 Ohms speaker, so I had to find a way of matching the SP-600 (and oter BA's) to a speaker of 4-8 ohms. In the junkbox I found a small (20 VA) transformer, 230 V primary and 24 V secondary.
The BA to the primary side and the speaker to the secondary, and as far as I'm concerned, the problem was solved...

I now use the 600 ohm to 8 ohm transformers sold on Ebay. They are alot cheaper then the hammond and seem to work ok. I have no complaints about the hammond other then the price.

The audio amp hookup is best.  Just use a 22UF cap from the diode load and then to an RCA cable center.  The SHield of the RCA goes to nearby ground screw.  I used the resistor as the level was a bit high.   I got this from R390a.com but its dead. It works perfectly.

C

Hi Clark,

Thanks for the post. Is there a paricular reason you stopped using the diode load output method? In your previous thread you seemed so amazed by the quality of the audio using that method.

73, Ron

I use the diode load on my SP600 with a small vac tube amp to an R46 hallicrafters speaker. Its Hi FI audio all the way. 

On my other rigs, I use the 600 ohm to 4 ohm transformers.  I see no drawback using the Diode load.

C