Harman-Kardon TA5000X, A500 or A50K OPT - Quality?

[rongon]

Hi there

I'm trying to clean out the closets. Found a really dusty old Harman-Kardon TA5000X receiver with no tubes. I was thinking of cleaning it off and putting it up on that auction site, but then thought I'd find out if the output transformers are worth using in a new build.

So, does anyone have experience with the output transformers from a harman-kardon TA5000X receiver, or A500 or A50K integrated amplifiers?

The receiver used 7355 output tubes, which I gather is pretty much a 6L6GC in a smaller bottle. I'd expect the OPT's primary impedance to be about 6.6k. I figure if the h-k OPTs are better than Dyna A470 then they'd be worth using.

Thanks for any help.

[zoe]

Hello

I've built an amp with these transformers. I think it sounds great . It is my main amp.
I used 12AX7 driver to 12AU7 phase splitter gain type to Sovtek7591xyz output tubes (6.00per tube)

[rongon]

Thanks for your reply. I guess these trannies must be at least "good." I wonder how they compare to Dyna A470 (from Stereo 70)...

I was thinking of using these H-K OPTs in an amp with triode-wired EL34s, with about 390V plate-to-cathode and 60mA going thru each tube. In that situation, I don't know if any imbalance will immediately cause core saturation.

The output transformers I have in there now are from a junked Fisher 800B receiver. They sound very nice with good bass, but there is a definite ring on 10kHz square waves. The highs sound pleasant, but I think have a bit of extra "zing."

I previously tried a pair of Dyna Z565 OPTs from a junked ST35 chassis. They sounded nice but were very light in the bass, which surprised me, as the Z565 is rated at 1100H primary inductance. In that light, I assumed that the light bass was caused by saturation of the core due to imbalance in the output tubes. The Dyna OPTs do ring a little, but a lot less than the Fisher OPTs.

I wonder if those H-K OPTs will ring as much as the Fisher OPTs?

I have a pair of Tango XE-45-5 that don't ring *at all* in that amp. I'm using those in my other (PP 2A3) amp.

Mostly I'd like to see a pair of OPTs with less ring (open loop, before equalization).

Finally, does anyone know of a way to dampen OPT ring without a global feedback loop? Snubbers on the output tube grid resistors, as in MJones' Beavois Valley amp?

[mfaughn]

Did you ever try out this iron? I have a set of the same and was wondered how it stacked up against the z565 as I have those as well. Trying to decide which to work with next.

[rongon]

I've been kind of busy moving, so no hifi projects recently. I have done some reading, though. It seems it's not fair to compare various vintage transformers to those Tango XE-45-5. Vintage OPT's from mid-priced gear of the day will all have more noticeable limitations. The Dyna Z-565 is better than most. I just don't know about the HK OPT's from that receiver.

In the Baby Huey thread, there's mention of using zobel networks from plate to screen in an ultralinear wired output stage. But that poster also mentioned that the ringing was only observable in UL mode, but not when triode wired. Now, with my Fisher OPT's, the ringing was easily seen even when triode wired. So I think those Fisher OPT's have a definite ringing problem. Will the HK OPT's have a similar problem? I don't know.

I do know the Z565's are really good. I don't think they were designed to take more than about a steady 45mA per side. I was running them with triode-wired EL34's at about 55mA per side, and I'm not sure the OPT's were happy that way.