6 ohm speaker on 4,8 ohm ST35.

A couple of years ago I built a Dynaco ST35 out of various parts. I think that it is the sweetest sounding amp that I own. I had been using it with a pair of old Technics SB6oooA 6 ohm speakers. I think that I was using the 8 ohm tap. The ST35 also has a 4 ohm tap.

After about a year of use. one of the Mullard "reissue" EL84 tubes started making popping sounds. EICO tube tester verified a bad tube.

I have tried other EL84s and the Mullard reissues sound best to me. I'd love to have some NOS Mullards but...

Should I have been using the 4 ohm tap, or should I try to squeeze in a pair of 6 ohm Edcore output transformers. I have a pair of Edcores with 4, 8, and 16 ohm taps, for a different ST35, using a chassis and board from Triode. The are much larger and heavier and the 6 ohm version uses the same core and end bells. The only difference is a slightly lower input impedance than it's 4, 8 and 16 ohm brother.

Should I order a 6 ohm pair of transformers? I can use the 4 ohm taps on the Triode ST35s and just chalk it up as a bad tube. No damage was done to the amp, as it powers a pair of Rectilinier Mini IIIs just fine with a set of JJs. I'd like to order another set of Mullards but don't want to damage that wonderful little amp.

Thanks so much.

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As for tubes, any EL84 would do just fine. ST35 are pressing the tubes, installing EFB will
decrease the tube loading AND in addition give more power AND less distorsion.

Installing EFB is way cheaper and with much better result that switching transformers.

Source for EFB :
http://tronola.com/html/daves_store.html
scroll down to "ST-35 EFB Power Supply Board"

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I think that it was just a bad tube. I installed a matched quad of Sovtek EL-84Ms (7189 equlivent), balanced everything with the amps bias control, moved it into the living-room setup with a pair of Rectilinear III Highboys and basked in a wide-open glorious sound.

Granted, the Rectilinears normally ask for a more powerful amp, but they haven't yet complained.

also keep in mind that speaker "impedance" such as a rating of 6 or 8 ohms is a "nominal" value, not even an average value.
99% of all speakers have their lowest impedance below 300Hz, and it raises gradually at all higher frequencies.
Also 99% of all speakers have a very large bump in the low end, usually somewhere between 30 to 70Hz where the impedance is typically around 25 to 45 ohms.
Here's an example . . .

Thanks, tubesforhifi. I'm presently studying two, fairly recent basic tube design books. I now regret dropping my junior college basic electronics class. Of course, that was 48 years ago but who's counting.

I should probably order a couple more books from you.

Regards, Steve