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Old 10th May 2007, 12:47 PM   #1
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Default Matched tubes required?

Hi all-
I'm working on a nice Zenith radio that has a push pull output stage, and had a question. This output stage does not have a phase inverter tube, instead phase inversion is accomplished by a transformer. My question is, do the output tubes have to be matched for current draw in this type of output stage? I've never seen this type of output before, so I'm not sure about tube matching.
Thanks
Glenn


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Old 10th May 2007, 02:08 PM   #2
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It just a normal output stage with an interstage phase splitting transformer (should sound nice). The output transformer should have a slight gap to allow for slight current mismatch. This is standard for almost all PP output stages. The interstage transformer is designed like a SE output transformer ie with a suitable airgap.

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Old 10th May 2007, 03:38 PM   #3
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Thanks Shoog.
The only reason I ask is that this set has one original 6L6 with the "ST" shape, and the other is a newer (still a vintage '70's tube) 6L6GC with the small cylindrical round top envelope. I guess this doesn't matter as long as the current draw is close. I just didn't want to ruin the set by running it with possibly mis-matched tubes. I'm still looking for a vintage "ST" shaped 6L6, as the newer looking units don't look right in this radio.
Glenn

The two upper left tubes are the 6L6's. Guess which one is not original



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Old 10th May 2007, 08:11 PM   #4
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Looks lovely - good luck with it.

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