Replace 20 ohm full range speakers (Heath GR-36 FM Table)?
 

I have a great Heathkit GR-36 FM only table radio. The speakers are very light thin 5" full ranges without whizzer cones.

I'd like to replace these with 5-1/4" Fostex drivers I recently picked up. Unfortunately there is a big difference in measured direct current resistance, with the originals showing 20 ohms(!). (Fostex are 8 ohm rated)

The radio is very loud already, so the only thing that comes to mind is to add 12 ohms of wirewound resistor in series with the new drivers. Kind of afraid any fidelity might suffer. Any clues on other options, or if the 8 ohm speakers might be OK directly if using only very low volumes?

(Alternately, would like to get a T-amp's board in there and bypass the resident amp (which would fit easily) but also wondering about listening to the onboard radio Tuner with such a revealing amplifier and speakers.)
Thnx for all opinions, -sf

Better to get 16 Ohm speakers - these early solid state amps are touchy about speaker loads... series resistor will eat 2/3 of thepower and will give no speaker damping.

Were the speakers in parallel? Hook the two 8 Ohm ones in series... if they WERE in series, 16 Ohm ones would be your best bet.

T., Thanks for the view. There was just one 20 ohm speaker on each channel (L & R). I'm not likely to find another pair of quality 5" full range drivers for this anytime soon at 16 ohms. I sure won't need much power. Maybe some second 8 ohm speakers (pair) like tweeters can go entirely inside the cabinet in series just to give an appropriate dynamic load...?????. -sf

Well seeing that you already have the replacement speakers, I vote you try them with 8 or 10 ohm resistors in series and see how they sound. If you are pleased with the sound and they play load enough for you applications then don't worry about the theory, just enjoy them.

They sound like a much better speaker then the original ones so you might come out with better sound even with the series resistors. What have you got to lose?

Lefty

I did put the Fostex/Fisher full ranges in the Heath with 10 ohm resistors in parallel. There is plenty of volume, in fact I am only using about 10% of the volume dial before it is too loud for my office. :)

The sounds is quite pleasing as a very early stereo table radio -it also doesn't command all of your attention as it is still just a radio. Great for NPR. I'd say its not as good as a JVC Executive mini-system (the FS-x00s) in sound quality after the driver upgrade. (But far more novel and attractive, I'm still toying with the idea of getting a T-amp board in there.) -sf

You meant to say "in series", yes? If you did parallel, take the resistors out.

remember dc resistance is not the same as impedance, i would try two 16 ohm speakers in series because i bet the impedance is close to 32 ohms if the voice coil resistance is 20 ohms

:) Oh yah, thanks for checking the math. Keyboard fatigue perhaps, but they are inline (series) with the positive leads giving a direct current resistance of 18 ohms where the originals showed 20 ohms.

I am left to wonder what improvment would be seen if I used another speaker (~8 ohms) as the series resistor, as a small one would fit entirely inside the cabinet (cannot handle 4 speakers without serious and unpleasant modification). -sf