# 6BM8/ Heathkkit S.88 Has only 3 and 15 ohm O/P..?

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#### Alastair E

Had a bit of luck, got hold of a complete Heathkit S.88 amplifier....

It has a P-P 6BM8/ECL82 output stage, and the O/P Tx is wired for 15 Ohm or 3 ohm.....

There is No 8 ohm tapping....

Any ideas as to how to get the best out of this without changing the O/P Tx....??

Connect your loudspeaker between the 3 and the 15 ohm taps. Would this not be about 9.8 ohms? Should work with an 8 ohm speaker.

V

#### Vek

If the OT has two secondaries, wired in parallel for 3 Ohms and wired in series for 15 Ohms, there will be no 3-15-tap.
Then you will have to take the 3 Ohms arrangement. You will loose some power, though ... but in general it would work this way!

Greets

What VEK says is true. But I think the OTs on this particular amplifier have three wires on the secondary side; Black - common, Yellow - 3 ohms, and Brown - 15 ohms. Try the speaker between the brown and yellow wires.

#### gingertube

You need to remember that with transformers the impedance ratio is the square of the turns ratio.

Talking in terms of 4 and 16 Ohms

2 off 4 Ohm Taps in parallel doesn't change the numberr of turns so it still 4 Ohms.

2 off 4 Ohm taps in series doubles the turns so X4 of the impedance that is it becomes a 16 Ohm output.

the 3 and 15 Ohms mentioned for your transforemer are nominal impedances. The 3 is probably about 3.5 Ohms. It is extremely likely that the number of turns between the 3 and 15 Ohm taps is the same as between the Common and 3 Ohm tap. That means connecting a load between teh 3 Ohm tap and the 15 Ohm tap will just be another 3 Ohm nominal output.

If you wish to connect an 8 Ohm load I'd just hook it to the 3 Ohm output.

I had one of these amps - with (I think) the same output trannies. Do yours have ultralinear taps. If so then they are the same as I had. The Raa was about 6K and the Ultralinear Taps were at 20%.
I used the trannies in the ECL86 (6GW8) prototype which led directly to the "Baby Huey" design. I ran 8 Ohm speakers of the 3.5 Ohm tap

Cheers,
Ian

#### Alastair E

Thanks for all your input guys, I havent picked up the amp yet, but I do know it needs quite some work, Loads of those nasty old 'Plessy' elect-o-lytics to go, plus who knows what else...!

Hows this for a mad idea....

Replace the current 6bm8/ECL82 with summit like a EL86, or even a PL508 that 'likes' O/P impedance of 2.5K or 5Ka-a, Add summit like a ECC83 to replace the triode sections of the ECL82, along the same lines as the original scheme for phase-split and gain stage, and run a 8 ohm speaker from the 15 ohm taps....

Just a mad thought...It'll never fly!