Transformer Shootout- Hammond vs Magnequest vs Dynaco vs HW

for the DIY ST35, the Dynakit and every other PP EL84

Transformer Shootout- Hammond vs Magnequest vs Dynaco vs HW

Postby Shannon Parks » Sun Dec 28, 2003 1:34 pm

Happy Holidays, folks! I've been quite busy the last month putting together a 'super deluxe' testing rig. Diytube has been lucky enough to get a HP 8903 Audio Analyzer from the northern Illinois Motorola diaspora - still NIST certified, too. I've made a pretty decent GPIB controller out of an old PC and have written some custom diytube software. Sweeping these tube amps now is a breeze. The speedy, volumous data permits many tweaks to see gain, distortion and frequency response changes.

To put the rig through the paces I figured a transformer shootout would be just the ticket. Plus it answered some questions I had in my mind - maybe it will answer some of yours, too.

Important Note: Now this is not an ultimate test of these transformers - rather it is a test of these transformers plunked into a stock diytube ST35 circuit. I didn't tweak the circuit for any of these.

The test setup was as follows for each:
- 400mVRMS input was used for tests at normal output levels (green data)
- 850mVRMS input was used for ~1% distortion output levels (red data)
- Hammond 272HX power transformer with B+ at 391VDC
- bias set at 35mA per tube
- 19.2K negative feedback from the 8ohm tap

I tested these output transformers (all purchased by me, except the MQ which is on loan from a customer):
- Hammond 1620
- Hammond 1650F
- Magnequest MQ-565
- Dynaco Z-565 (dated 1965, cloth leads)
- Handwound 7.6K PP 25W

The data columns are: frequency tested, output VRMS, gain, percentage of distortion & noise, and finally power into an 8ohm load.



Dynaco Z-565

020Hz 5.25V +22.1dB .1778%THD+N 3.458W @ 8ohm
050Hz 5.28V +22.2dB .0979%THD+N 3.551W @ 8ohm
100Hz 5.32V +22.2dB .0893%THD+N 3.538W @ 8ohm
200Hz 5.32V +22.2dB .0737%THD+N 3.525W @ 8ohm
500Hz 5.34V +22.2dB .0704%THD+N 3.564W @ 8ohm
01kHz 5.32V +22.2dB .0747%THD+N 3.525W @ 8ohm
02kHz 5.34V +22.2dB .0891%THD+N 3.564W @ 8ohm
05kHz 5.29V +22.1dB .1513%THD+N 3.498W @ 8ohm
10kHz 5.24V +22.0dB .2760%THD+N 3.432W @ 8ohm
20kHz 5.16V +21.8dB .3050%THD+N 3.315W @ 8ohm
30kHz 4.92V +21.5dB .5300%THD+N 3.014W @ 8ohm
40kHz 4.29V +20.4dB .9850%THD+N 2.279W @ 8ohm


020Hz 10.50V +21.7dB 3.43%THD+N 13.81W @ 8ohm
050Hz 10.65V +21.8dB .841%THD+N 14.18W @ 8ohm
100Hz 10.68V +21.9dB .786%THD+N 14.23W @ 8ohm
200Hz 10.69V +21.9dB .792%THD+N 14.26W @ 8ohm
500Hz 10.68V +21.9dB .783%THD+N 14.26W @ 8ohm
01kHz 10.68V +21.9dB .840%THD+N 14.23W @ 8ohm
02kHz 10.68V +21.8dB 1.07%THD+N 14.23W @ 8ohm
05kHz 10.63V +21.7dB 1.94%THD+N 14.10W @ 8ohm
10kHz 10.54V +21.5dB 3.04%THD+N 13.86W @ 8ohm
20kHz 10.27V +21.1dB 3.77%THD+N 13.13W @ 8ohm
30kHz 09.60V +20.2dB 2.67%THD+N 11.47W @ 8ohm
40kHz 07.86V +18.2dB 3.14%THD+N 7.683W @ 8ohm



Magnequest MQ-565

020Hz 5.34V +22.5dB .2685%THD+N 3.498W @ 8ohm
050Hz 5.32V +22.5dB .1384%THD+N 3.538W @ 8ohm
100Hz 5.34V +22.5dB .1096%THD+N 3.551W @ 8ohm
200Hz 5.34V +22.5dB .0856%THD+N 3.578W @ 8ohm
500Hz 5.38V +22.5dB .0799%THD+N 3.605W @ 8ohm
01kHz 5.38V +22.5dB .0820%THD+N 3.605W @ 8ohm
02kHz 5.38V +22.5dB .0970%THD+N 3.605W @ 8ohm
05kHz 5.41V +22.5dB .1460%THD+N 3.645W @ 8ohm
10kHz 5.38V +22.4dB .2355%THD+N 3.605W @ 8ohm
20kHz 5.16V +22.0dB .3350%THD+N 3.315W @ 8ohm
30kHz 4.80V +21.5dB .4640%THD+N 2.868W @ 8ohm
40kHz 4.05V +20.0dB 1.139%THD+N 2.040W @ 8ohm


020Hz 10.58V +21.8dB 3.570%THD+N 13.97W @ 8ohm
050Hz 10.74V +22.0dB 1.047%THD+N 14.47W @ 8ohm
100Hz 10.80V +22.0dB .9680%THD+N 14.55W @ 8ohm
200Hz 10.81V +22.0dB .9250%THD+N 14.61W @ 8ohm
500Hz 10.86V +22.0dB .9480%THD+N 14.72W @ 8ohm
01kHz 10.87V +22.0dB .9920%THD+N 14.77W @ 8ohm
02kHz 10.87V +22.0dB 1.241%THD+N 14.74W @ 8ohm
05kHz 10.85V +21.9dB 2.147%THD+N 14.72W @ 8ohm
10kHz 10.74V +21.7dB 3.110%THD+N 14.42W @ 8ohm
20kHz 10.24V +21.1dB 3.040%THD+N 13.08W @ 8ohm
30kHz 9.550V +20.2dB 2.088%THD+N 11.35W @ 8ohm
40kHz 7.410V +17.6dB 3.570%THD+N 6.845W @ 8ohm



Hammond 1650F


020Hz 5.27V +22.2dB .2742%THD+N 3.419W @ 8ohm
050Hz 5.25V +22.2dB .1219%THD+N 3.445W @ 8ohm
100Hz 5.26V +22.3dB .0980%THD+N 3.458W @ 8ohm
200Hz 5.27V +22.3dB .0768%THD+N 3.485W @ 8ohm
500Hz 5.31V +22.3dB .0745%THD+N 3.525W @ 8ohm
01kHz 5.31V +22.3dB .0764%THD+N 3.525W @ 8ohm
02kHz 5.30V +22.3dB .0913%THD+N 3.498W @ 8ohm
05kHz 5.26V +22.1dB .1563%THD+N 3.458W @ 8ohm
10kHz 5.06V +21.8dB .3180%THD+N 3.188W @ 8ohm
20kHz 4.52V +20.8dB 1.139%THD+N 2.543W @ 8ohm
30kHz 3.91V +19.6dB 2.830%THD+N 1.901W @ 8ohm
40kHz 3.07V +17.6dB 5.570%THD+N 1.170W @ 8ohm


020Hz 9.910V +21.2dB 10.08%THD+N 12.20W @ 8ohm
050Hz 10.58V +21.8dB .7360%THD+N 14.07W @ 8ohm
100Hz 10.65V +21.9dB .6800%THD+N 14.15W @ 8ohm
200Hz 10.66V +21.9dB .6690%THD+N 14.15W @ 8ohm
500Hz 10.69V +21.9dB .6950%THD+N 14.28W @ 8ohm
01kHz 10.70V +21.9dB .7210%THD+N 14.28W @ 8ohm
02kHz 10.68V +21.9dB .8840%THD+N 14.23W @ 8ohm
05kHz 10.58V +21.7dB 1.500%THD+N 13.97W @ 8ohm
10kHz 10.27V +21.4dB 2.061%THD+N 13.16W @ 8ohm
20kHz 9.290V +20.3dB 3.070%THD+N 10.76W @ 8ohm
30kHz 8.120V +18.8dB 8.520%THD+N 8.222W @ 8ohm
40kHz 6.370V +16.3dB 18.05%THD+N 5.040W @ 8ohm



Hammond 1620

020Hz 5.20V +22.2dB .3350%THD+N 3.354W @ 8ohm
050Hz 5.23V +22.2dB .1172%THD+N 3.406W @ 8ohm
100Hz 5.24V +22.2dB .0983%THD+N 3.432W @ 8ohm
200Hz 5.24V +22.2dB .0764%THD+N 3.432W @ 8ohm
500Hz 5.24V +22.2dB .0731%THD+N 3.419W @ 8ohm
01kHz 5.24V +22.2dB .0773%THD+N 3.419W @ 8ohm
02kHz 5.23V +22.2dB .0930%THD+N 3.406W @ 8ohm
05kHz 5.17V +22.0dB .1501%THD+N 3.341W @ 8ohm
10kHz 5.00V +21.7dB .2470%THD+N 3.125W @ 8ohm
20kHz 4.49V +20.8dB .3950%THD+N 2.509W @ 8ohm
30kHz 3.91V +19.6dB .7880%THD+N 1.901W @ 8ohm
40kHz 3.13V +17.8dB 4.340%THD+N 1.217W @ 8ohm


020Hz 09.27V +20.6dB 16.18%THD+N 10.65W @ 8ohm
050Hz 10.48V +21.7dB 1.266%THD+N 13.83W @ 8ohm
100Hz 10.56V +21.8dB 1.183%THD+N 13.94W @ 8ohm
200Hz 10.57V +21.8dB 1.140%THD+N 13.97W @ 8ohm
500Hz 10.61V +21.8dB 1.183%THD+N 14.07W @ 8ohm
01kHz 10.62V +21.8dB 1.279%THD+N 14.10W @ 8ohm
02kHz 10.61V +21.8dB 1.560%THD+N 14.02W @ 8ohm
05kHz 10.50V +21.7dB 2.431%THD+N 13.76W @ 8ohm
10kHz 10.13V +21.2dB 2.909%THD+N 12.83W @ 8ohm
20kHz 08.98V +20.0dB 2.550%THD+N 10.06W @ 8ohm
30kHz 07.77V +18.4dB 2.828%THD+N 7.547W @ 8ohm
40kHz 05.87V +15.6dB 11.80%THD+N 4.278W @ 8ohm



Handwound 7.6K Push-Pull 25W

020Hz 5.12V +22.0dB .3610%THD+N 3.239W @ 8ohm
050Hz 5.17V +22.1dB .1563%THD+N 3.328W @ 8ohm
100Hz 5.18V +22.1dB .1190%THD+N 3.354W @ 8ohm
200Hz 5.19V +22.1dB .0882%THD+N 3.354W @ 8ohm
500Hz 5.19V +22.1dB .0809%THD+N 3.354W @ 8ohm
01kHz 5.19V +22.1dB .0834%THD+N 3.367W @ 8ohm
02kHz 5.19V +22.1dB .1654%THD+N 3.354W @ 8ohm
05kHz 5.19V +22.1dB .9550%THD+N 3.354W @ 8ohm
10kHz 5.14V +21.9dB 3.560%THD+N 3.290W @ 8ohm
20kHz 4.78V +21.3dB 6.660%THD+N 2.844W @ 8ohm
30kHz 3.97V +19.8dB 4.540%THD+N 1.960W @ 8ohm
40kHz 3.15V +17.8dB 2.325%THD+N 1.232W @ 8ohm


020Hz 09.76V +21.1dB 6.260%THD+N 11.83W @ 8ohm
050Hz 10.23V +21.5dB 1.881%THD+N 13.18W @ 8ohm
100Hz 10.32V +21.6dB 1.769%THD+N 13.31W @ 8ohm
200Hz 10.35V +21.6dB 1.677%THD+N 13.39W @ 8ohm
500Hz 10.37V +21.6dB 1.647%THD+N 13.44W @ 8ohm
01kHz 10.38V +21.6dB 1.757%THD+N 13.47W @ 8ohm
02kHz 10.40V +21.6dB 2.257%THD+N 13.52W @ 8ohm
05kHz 10.38V +21.5dB 4.710%THD+N 13.47W @ 8ohm
10kHz 10.15V +21.2dB 10.72%THD+N 12.90W @ 8ohm
20kHz 08.17V +19.1dB 25.39%THD+N 8.364W @ 8ohm
30kHz 08.00V +18.7dB 16.62%THD+N 7.920W @ 8ohm
40kHz 06.16V +16.0dB 7.950%THD+N 4.728W @ 8ohm





Epilogue

As one would expect, the Dynaco Z565 sets the bar. The Magnequest does meet or beat the Z565, which I would attribute to less losses in the wire - a fine transformer and the teflon coated wires really take the heat (yep, I tested!). The Hammonds really are quite a value. The bottom end performance isn't as spectacular as the 565s, but these Hammonds are still excellent performers to 30Hz. The Handwound transformer unfortunately underperforms at the higher frequencies in this stock circuit.

The screen feedback capacitor, a 20pF cap, does sharply drop the high frequency performance. Lowering its value (eg 15pF) may make the Hammond units even flatter at 20kHz. I'll do some twiddling with this in the near future, but that was not the purpose of these tests. Finally, I did remove this screen feedback cap during testing of the Handwound unit to see if I could achieve better distortion numbers, but while the 400mVRMS tests looked better, my 10kHz to 20kHz performance at 850mVRMS looked worse.

Do post your questions.

Shannon
Last edited by Shannon Parks on Tue Dec 30, 2003 7:33 am, edited 2 times in total.
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Nice work!

Postby EWBrown » Sun Dec 28, 2003 2:31 pm

This has confirmed some of my suspicions about the HWTs. They sound OK (to my less than fine tuned tin ears), but the fit and finish of the HWTs isn't the best. I suspect that they are "handwound" over in some sweat-shop in Asia, and not lovingly hand-crafted in Pennsylvania. The use of non-standard wire colors, and that the insulation is rather thin, especially on the HV AC power iron and the 10K SE trannies. They are supposedly hi-potted (1500VAC or 2121 VDC) but that insulation doesn't look like it would withstand that voltage level for a long time. When the HWTs were selling on E-bay they could be gotten at a rather low price, but then the wait was a l-o-n-g one.

Those Hammond 1620s look pretty good, I'll have to consider tehm for any future units.

/ed brown
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Hammond 1650F and notes

Postby Shannon Parks » Tue Dec 30, 2003 7:41 am

I edited the original post just now to add the Hammond 1650F 400mVRMS data.

I also did a bit of experimenting removing the positive feedback loop (lifted R44). My gain dropped 1dB and my distortion numbers quadrupled. Quite a neat trick indeed! I did try to get my new Tek's FFT looking into the source of the distortion but it looks like I'll have to read the manual (eek - my TDS1002 was bone simple). I'm wondering if this distortion might be even harmonic related.

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Distortion figures

Postby dhuebert » Tue Dec 30, 2003 3:43 pm

I have a question. I know from reading tube data sheets that load can play a part in tube performance. Distortion-wise, every tube has a sweet spot at a particular load impedance (resistance?). Do transformers have a distinct load impedance characteristic curve(sweet spot impedance versus frequency)? What I mean is, does the reflected impedance change with frequency?
Also, were the reflected impedances normalized in any way for this test? What I mean is, is there a way to correct for differences in distortion due to differences in reflected impedance for a given frequency?
Are these distortion data simply an evaluation of how well the mfg has matched the transformer impedance to the output tube for a range of frequencies?
It's my guess that Hammond is building a transformer for a variety of output tubes, whereas Dynaco built transformers strictly for 6BQ5. Perhaps if Hammond built a transformer that was dedicated to 6BQ5, it might be a fairer test, I dunno.
Would there be a way to compensate for reflected impedance mismatches by manipulating the load somehow?
Lastly, would it be worth doing to repeat these tests with a more complex load, such as a pair of speakers?
Ok, so thats more than one question...

BTW, If my thinking has gone into the weeds, please let me know.

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Re: Distortion figures

Postby Shannon Parks » Tue Dec 30, 2003 9:11 pm

dhuebert wrote:I have a question. I know from reading tube data sheets that load can play a part in tube performance. Distortion-wise, every tube has a sweet spot at a particular load impedance (resistance?). Do transformers have a distinct load impedance characteristic curve(sweet spot impedance versus frequency)? What I mean is, does the reflected impedance change with frequency?
Also, were the reflected impedances normalized in any way for this test? What I mean is, is there a way to correct for differences in distortion due to differences in reflected impedance for a given frequency?
Are these distortion data simply an evaluation of how well the mfg has matched the transformer impedance to the output tube for a range of frequencies?


Don, you've asked some meaty questions here that I can't begin to answer properly. Thermion told me of an old Glass Audio article explaining what to look for in a quality output transformer. We'll research this up and post the main points. I'll also look over the 'Sound Practices' LaFevre articles - I wish reprints were available.

The manufacturer has produced a transformer and they have given us a handful of data for application. We're given the power rating, the primary & secondary impedance (thus indirectly the impedance ratios), told it's PP with screens at such and such a %, and then given a frequency range we can expect in this application.

The Handwound and the Hammond 1650F are nearly indentical with respect to this data we've received from the manufacturers, so a fair comparison may be made between them, even if the circuit isn't tweaked for them.

dhuebert wrote:It's my guess that Hammond is building a transformer for a variety of output tubes, whereas Dynaco built transformers strictly for 6BQ5. Perhaps if Hammond built a transformer that was dedicated to 6BQ5, it might be a fairer test, I dunno.
Would there be a way to compensate for reflected impedance mismatches by manipulating the load somehow?
Lastly, would it be worth doing to repeat these tests with a more complex load, such as a pair of speakers?
Ok, so thats more than one question...

I think it is quite fair to say Hammond has made the 1650F for UL EL84s. The smaller 8K output they make would be welcome in these tests too, if I had one - but I would swag its sub-30Hz performance would be worse than the two Hammonds I tested (it's getting small). Once again, the differances are all pretty insignificant (except the Handwound).

Yes, a more complex load than a non-inductive resistive one would be handy. This brings up a huge point mentioned the other day, that speaker impedances are all over the ballpark - nominal 8 ohms doesn't tell us much. Trying to find this impedance data on a particular model, eg the Klipsch RF-7, let alone a frequency response chart, is a near impossible task. Do the DIY speaker guys have some nifty tests for this purpose? Anyhow, I think I'll buy some 5, 6, 7, 9 and 10 ohm power resistors just so I can do some testing with non-standard impedance ratios. This will give us a little insight.

dhuebert wrote:BTW, If my thinking has gone into the weeds, please let me know.

Don


Not at all.

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Impedance is futile

Postby EWBrown » Mon Jan 05, 2004 6:46 am

The corollary to "resistance is Futile"...

An 8 ohm nominal speaker is 8 ohms at only one frequency, add in a crossover and multple drivers, the impedance is anybody's guess.
Some crossover designs try to correct this by adding large power resistors, but all this does is make the speaker system less efficient.

The impedance is a function of the speaker voice coil inductance, and the back EMF generated by the coil moving through the magnetic field. Add in physical resonances, air resistance against the cone, etc, it gets very complex very rapidly.

Many years ago, I was lucky enough to find two very nicely made 8 ohm 150 watt power resistors, that had a sliding third contact. these are made in a heavy aluminum heatsink body and the wire resistance element is embedded in ceramic. These were at a local surplus electronics shop
(Eli Heffron's in Cambridge Mass) about 30 years ago. Well worth the dollar I paid for them. :D These are not "non-inductive" resistors, so thay aren't truly "perfect" but they do the job for me.

The old Heathkit audio analyzer I have has internal 25 watt load resistors of 4, 8, 16, and 600 Ohms resistance. I use the aforementioned resistors for the serious power testing, Only one time I got them really hot and that was both in parallel being fed by a 250 watt solid state car amp, I was repairing for a friend several years ago. (not 20 watts, D'OH :banghead: !!!!!!!!!) Proofreading is for wussies :jester:

/ed b in NH
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33 pf cap?

Postby EWBrown » Wed Jan 07, 2004 6:21 am

I had used 18 pF caps for the feedback caps on my first unit, though I didn't hear any discernable difference from the second unit on which I used 22 pf caps.

There is a 33 pF cap across the input, as there is in the original Dynao ST-35, removing this might help out in the freqs above 20 KC, the only real purpose it may have served is to eliminate broadcast station RFI from getting in.

Just an early morning fuzzy headed need-some-more-caffeine thought.

/ed B in NH
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Re: 33 pf cap?

Postby Shannon Parks » Wed Jan 07, 2004 7:30 am

EWBrown wrote:There is a 33 pF cap across the input, as there is in the original Dynao ST-35, removing this might help out in the freqs above 20 KC, the only real purpose it may have served is to eliminate broadcast station RFI from getting in.


Dang, Ed - I forgot about this low pass filter when I did open loop tests. Oh well - I probably didn't have all the open loop data anyway. I'll put this on my 'to do' list.

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Postby erichayes » Sat Feb 21, 2004 10:31 pm

Hi All,

I wonder if I could get a poll of what output transformers folks have used when they built their '35s. I'd like to duplicate as closely as possible what's out there for the first round of my tests, but I don't want to buy a transformer that only one or two people have used (I'm not talking about harvested Scott or Sansui iron, but new stock). Power transfomer info would be nice, too, but not essential at this point.

Thanks
Eric in the Jefferson State
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Re: ST35 IRON

Postby Shannon Parks » Sun Feb 22, 2004 6:04 pm

mg16 wrote:Hi,
OPT=Hammond 1650F's. Power = Hammond 272HX. Tubes = JJ Tesla power and input tubes, current production.
Theres probably better iron out there for it, but I don't have any desire to try others. Quite happy with the sound.
mg16


Thanks for the feedback, mg16. This definitely seems to be the most common setup.

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Postby nineno » Sun Feb 22, 2004 6:23 pm

I'm using the 1650E OTs and 276X PT.

Only a slight variation on the tried and true setup.

Using the 1650Es allows me to select between 4, 8, and 16 ohm operation without any re-patching (it has dedicated leads for each config).

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Postby erichayes » Wed Feb 25, 2004 9:53 pm

Hi All,

Thanks for the replies. I think I have at least one Z-565 at my shop in Santa Cruz, and I'll order a 1650F. Chassis should arrive sometime in the next few days, as should the small parts. I hope I'll have something to report by the end of March.

BTW, I was surfing around on another forum and discovered that Handwound is another offspring of David Lucas, he of DIY E'Stat subwoofer infamy. I never did business with him, but his full-page ads in Glass Audio used to make my neck hairs rise. Now it all makes sense.
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Postby Shannon Parks » Wed Feb 25, 2004 10:09 pm

erichayes wrote:BTW, I was surfing around on another forum and discovered that Handwound is another offspring of David Lucas, he of DIY E'Stat subwoofer infamy. I never did business with him, but his full-page ads in Glass Audio used to make my neck hairs rise. Now it all makes sense.


http://www.audiocircuit.com/9041-esl-circuit/Diy/Diypackages/Davidlucas-DAV/9041DDDAV.htm

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4 different combinations

Postby EWBrown » Thu Feb 26, 2004 6:55 am

So far I have built up 2 rev Bs and 2 rev Cs, the iron combinations are:

Rev B #1: Hammond 272FX and 1650Fs

Rev B #2: Uncle Ned PA774 and 2 original Z-565s

Rev C #1: Hammond 272FX and 2 HWT 25W OPTs

Rev C #2: Hammond 272FX and 2 Hammond 1620s

The "Handwound" story:

I have also used some HWTs in an ST-70 "Dynaclone" and 2 25W SE OPTs
for a futire project, these were bought on E-bay, delivery was very unreasonably slow, ( over 4 months) and I had to play "hardball" with Lucas. That indeed did get action and a half-hearted apology and a long list of weak excuses, but the iron did arrive. I found the quality of the OPTs to be satisfactory, though the power tranny for the ST-70 had a weird ringing resonance from the top bell, which I quieted by putting a 1" square piece of double sided tape on top, and then stuck a small copper plaque on that (mostly for looks). My own SWAG is that the HWTs were ordered from and made in sone "sweatshop" factory over in China, and not lovingly crafted by Pennsylvania artisans.

The only advantage getting them from E-bay was that the prices were substantially lower than on the HWT website.

/ed brown in NH
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