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I'm debating upgrading my James OPT from the 6113 (10 watts) to the 6133 (30 watts). My 300B SET is run conservatively at 5 wpc (370V / 65mA). I wouldn't change those settings. I'm curious: what benefits if any would I get from going to a larger OPT aside from bass?
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Anything that looks more powerful, is more powerful and better from a psychoacoustic standpoint. But in reality, 5 watts is 5 watts and your OPT is already overrated for the current. You want impactful bass, build a good sub-woofer.
GregI would get the 6133 and
use it for the choke load
and then parafeed the 6113.
The inductance of the 6133
and the finesse of the 6113.
A Win-WinDanL
EDIT: Better yet get the 6135 !
Edits: 10/20/14
Primary inductance may be one aspect but what about copper losses and all those other lovely caveats which apply to audio transformers ? Do you really need a 30 watt transformer anyway ? I would do some research based on the published numbers such as primary/secondary DCR , number of sections , primary inductance and core material . My own recommendation would be to find a transformer with at least 20H per 1k of Ra (for triodes) and a single secondary which ideally suits your speakers rather than 16/8/4 ohm taps etc...
Al
"...find a transformer with at least 20H per 1k of Ra..."[edited Oct 20 2014: I misinterpreted Ra so the following comment is not relevant - see retraction below.]
Good luck with that! The biggest I know of is the Magnequest FS-030 which gets 35 henries at 60mA max, with a 3000 ohm primary.
Edits: 10/20/14
I was talking Ra nor Rl . Should be easily do-able :)
Al
Yes, that much is quite reasonable - 15 henries more or less for 2A3 and 300B.
No one can even guess at the answer to this unless you know the in-circuit performance of the transformer you have now. What makes you think a larger transformer will deliver more bass?
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Buy Chinese. Bury freedom.
Even the bass is questionable without more information. Bass relates to inductance as much as to saturation. A 30-watt transformer might easily have the same inductance as a 10-watt transformer, hence the same bass extension limit but a greater power capability before saturation. In that case, the extra size likely does not affect the bass of a 5-watt circuit.
Incidentally, my analyses suggest to me that the better treble of small transformers is more related to their (usually) smaller inductance than to their smaller size per se.
Long ago I participated in a listening comparison of three SE transformers, all with the same turns ratio but of different sizes. This was of course a single experiment, so regard it as anecdotal rather than generalizable! The largest had 40 henries inductance and the best bass; the smallest 10 henries and the best treble, and middle one 20 henries and was in the middle on all measures. I thought the middle one was the best balanced, but there were advocates for each among the listening group.
Are you running them at 3.5K or 5K?
A bigger OPT gives you the opportunity for more inductance, but there is certainly the possibility of other issues.
Personally, I'd take the inductance, and you're moving up in quality in the same transformer lineup, so one would hope for similar frequency response up top.
Without looking at the specs of the two transformers, just relying on the size and wattage rating, I would say there would be no advantage (other than the bass) and there might be a dis-advantage.
The larger transformer might not have the high frequency extension of the smaller transformer.
Tre'
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