Re-tubed my TAD-60: impressions

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Re-tubed my TAD-60: impressions

Postby hurdy_gurdyman » Tue Sep 18, 2007 11:43 am

I re-tubed my TAD-60 PP amp a couple of weeks ago and have some impressions now. First, read my review of Jerry's Road Spud, where I made some comparisons and discovered a weakness in the sound I'd been living with.

http://www.hawthorneaudio.com/forum/vie ... php?t=1263

My complaint had been a bit less than pristine clear mid-range. The bass was already powerful and taunt, and the highs were smooth and sweet as high as I can hear (around 10 kHz or so). The mids, though, sounded a bit veiled compared to the SEP Road Spud. This was the only weakness the TAD-60 seemed to have, and it wasn't great, but now that I latched unto it, I had to see if I could improve things.

I re-tubed the amp's power tubes about 6 months ago.

http://www.hawthorneaudio.com/forum/viewtopic.php?t=433

http://www.hawthorneaudio.com/forum/viewtopic.php?t=293

Heres what I've done in the last few weeks. I changed the 12AX7 voltage amp tube to a 12AT7 tube, which "brightened" things up noticeably. The designer of the amp, Paul Grysbeck, approved this mod. This alone helped to make things better. The two driver tubes are the same Mullard 12AU7 tubes I've been using for about a year now. I'll feel sad when these finally wear out. :cry:

I could have lived with these improvements. However, on the advice of both Paul Grysbeck and Jim McShane, I tried a set of 6CA7 output tubes in place of the EL-34 tubes I was using. The ones I bought were EH brand. This was even more in the direction I wanted to go. Very cool! I doubt if I'll ever go back to an EL-34 in a PP amp.

One final tweek was to change from triode mode with no feedback to ultra-linear mode with some feedback. The feedback control is at the 11:00 position now. This made a surprising change for the better. I hadn't played much with this feature before, as it's been pounded into our heads for several years that all triode mode is superior, being more musical sounding, than any type of pentode mode (which includes ultra-linear mode). However, the music just jumped to life in this mode! Now, switching to triode mode with little or no feedback just sounds lush, not exciting. Makes me wonder why I didn't seriously pursue this option before. I guess we truly are "programed" by the common wisdom that we read, both on the net and in paper magazines. I was so convinced of the superiority of triode mode that I only briefly listened to ultra-linear mode and didn't really give it a chance before. I'm very glad I gave it a second chance. :D

Anyway, I am now happier than ever with this amp. Detail, power and "magic" are all there in full now. The match to the Silver Iris speakers is better than ever. Someday, I may try some some KT-88's in this amp, but for now, I feel no need.

Dave :)
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Postby Mr Content » Wed Sep 19, 2007 12:19 am

Hi Dave, I agree with you, I prefer PPP with my 20w tube amp. In triode mode the soudstage is very flat as compared to a very 3D soundstage in PPP. Or maybe you and I have the same ears :D

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Postby hurdy_gurdyman » Wed Sep 19, 2007 7:35 am

Mr Content wrote:Hi Dave, I agree with you, I prefer PPP with my 20w tube amp. In triode mode the soudstage is very flat as compared to a very 3D soundstage in PPP. Or maybe you and I have the same ears :D

Mr C
Hey Mr C,

I suspect you ears are much better than mine these days.

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Re: Re-tubed my TAD-60: impressions

Postby Eddie Vaughn » Thu Sep 20, 2007 12:54 am

hurdy_gurdyman wrote:I hadn't played much with this feature before, as it's been pounded into our heads for several years that all triode mode is superior, being more musical sounding, than any type of pentode mode (which includes ultra-linear mode). However, the music just jumped to life in this mode! Now, switching to triode mode with little or no feedback just sounds lush, not exciting. Makes me wonder why I didn't seriously pursue this option before. I guess we truly are "programed" by the common wisdom that we read, both on the net and in paper magazines. I was so convinced of the superiority of triode mode that I only briefly listened to ultra-linear mode and didn't really give it a chance before. I'm very glad I gave it a second chance. :D


Hi Dave,

You're exactly right. There are plenty of "gurus" who diss ultralinear operation, and their minions (most of whom couldn't identify triode, ultralinear, or pentode operation on a schematic) shout "Right on!" and give them a high five. They dismiss it as a cute parlor trick that looks good on paper but is inferior to both triode and pentode operation. I sharply digress, and have always liked ultralinear operation.

No, it's not as creamy as triode, nor as powerful as pentode, but it never claimed to be. It's an "in-between" mode that gives you a nice blend of the characteristics of each extreme, while proportionally reducing the associated drawbacks of each. It has much lower output Z and distortion than pentode operation, and requires no screen grid power supply. Compared to triode operation, it has much higher power and is easy to drive thanks to relative freedom from Miller Effect capacitance.

One of the major things that gave ultralinear operation such a bad rap was some of the really bad vintage amps using it, that had 50 gain stages and 200 coupling caps encompassed in the global NFB loop. They have more phase shifts than the moon has went through in the past 5000 years, and as a result the sound is dead, flat, and homogenized.

But, when ultralinear operation is applied to a simple, two stage PP amp (especially one with a short global NFB loop applied back to the LTP phase inverter), or a SE amp, it can sound very good with the right speakers. People who power their Hornshoppe Horns with the Carina universally prefer its Ultralinear Mode. Likewise, I prefer Ultralinear Mode with my little Planet 10 Fonkens, which have a similar driver.

The same thing happened in the guitar amp realm. Some of the early '70s Fenders had ultralinear output stages, in an attempt by the tin-eared CBS engineers to get lower distortion from the amp (in a day when most players WANTED distortion). They sounded so awful that they forever turned guitar players off to ultralinear operation, and (among many other things caused by CBS's mismanagement) almost caused Fender to go out of business around that time.

Today, several Dr. Z amplifiers have ultralinear output stages, including the incredible sounding Route 66 model. It'll ridiculously blow away any of the mass-produced, big name brand garbage you find in your local music store.

In the end, it's all about the music, but so many people forget that and get caught up in "audiophile politics."

Eddie :D
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Postby hurdy_gurdyman » Thu Sep 20, 2007 12:27 pm

Hey Eddie,

Good to hear I'm not loosing my mind. :lol:

Dave :)
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Postby dantheman » Wed Sep 26, 2007 6:27 pm

Today, several Dr. Z amplifiers have ultralinear output stages, including the incredible sounding Route 66 model. It'll ridiculously blow away any of the mass-produced, big name brand garbage you find in your local music store.



I couldn't agree more. I just got to use this amp 2 days ago. There's a guitar geek at my new job. He's got a lot of nice toys.
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Postby hurdy_gurdyman » Fri Sep 28, 2007 3:05 pm

Been doing a bit more thinking (not good for me, I'm sure). I suspect that one of the reasons triode mode is so much hailed might be because small fullrange speakers are frequently used with them, as well as multi-way horn speakers. Both type tend to be very thin sounding compared to a typical two or three way speaker. The lush sound of triodes seem to perfectly match the thin balance of these speakers. The SI's have a very well balanced sound to begin with and just seem to sound a to lush with triode mode. At least, it's something to think on... :?

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Postby hurdy_gurdyman » Wed Oct 24, 2007 11:37 am

Not sure what happened, but last night, just as I shut my amp off, one of the new power tubes flashed me! After that, when I tried to get it turned on, it just glowed red at me and got brighter and brighter red. :( These tubes were just over two months old! I usually get at least siz months out of them. I had to put my old Shuguang EL-34's back in. They still sound good, but lack some of the sparkle the EH 6CA7's have. :( The Shuguangs have about 7 months on them so far. This does say something about their quality of build.

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Postby Bob in St. Louis » Wed Oct 24, 2007 1:18 pm

:(
Sorry to hear that Dave. I'm the last one to give tube advise, but it seems you're overdue for a transistor infusion on your rig.
Tell you what, I'll trade you my transistors for your tubes. :wink:

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Postby hurdy_gurdyman » Wed Oct 24, 2007 1:47 pm

Bob in St. Louis wrote::(
Sorry to hear that Dave. I'm the last one to give tube advise, but it seems you're overdue for a transistor infusion on your rig.
Tell you what, I'll trade you my transistors for your tubes. :wink:

Bob
Bob,

If you'd come up with a transistor amp that sounds as good as my tube amp, I'd swap in an instant.

Dave :)
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Postby Bob in St. Louis » Wed Oct 24, 2007 3:06 pm

hurdy_gurdyman wrote:If you'd come up with a transistor amp that sounds as good as my tube amp, I'd swap in an instant.

Let's say, for the sake of argument, that a H/K AVR-645 IS.... :wink:
Although I have a feeling I'd have a hard time finding enough optical inputs on yours. :lol:

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Postby hurdy_gurdyman » Wed Oct 24, 2007 3:17 pm

Bob in St. Louis wrote:
hurdy_gurdyman wrote:If you'd come up with a transistor amp that sounds as good as my tube amp, I'd swap in an instant.

Let's say, for the sake of argument, that a H/K AVR-645 IS.... :wink:
Although I have a feeling I'd have a hard time finding enough optical inputs on yours. :lol:

Bob
That would take a lot of arguing... :lol:

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Postby Bob in St. Louis » Wed Oct 24, 2007 3:21 pm

:lol: :lol: :lol: :wink: Well THAT just shut me up. :P
I'll leave your thread alone now Dave.

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Postby hurdy_gurdyman » Sat Oct 27, 2007 12:57 pm

The saga continues:

I've been listening to my old Shuguang's for a few days now. Other than the slight mellowness in the higher range, they are still an excellent sounding tube. On advise of a couple of different people, I decided to play with the voltage amplifier tube again. Remember, before I had switched out my 12AX7 for a 12AT7. This brightened things up noticeably, but not quite enough with the EL-34 tubes (was perfect with the 6CA7's). Today I replaced the 12AT7 with a 12BZ7. This went one more step brighter. It's almost as good as the 12TA7 with 6CA7 output tubes. I can live with this, I think. I'll give it a few more days to be sure. This could save me money in the long run. I can continue to buy Shuguang EL-34's for under $60 a quad, including shipping. They certainly seem to hold up well, as the ones I have have already lasted longer than the JJ's I had before, as well as sounding better.

So, very happy with this. :D 8) Now, I just need to find a couple more 12BZ7's for spares...

Dave :)
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Postby hurdy_gurdyman » Sun Oct 28, 2007 5:27 am

Drat it all. About an hour or so after installing the 12BZ7, I noticed a slight "ping" on certain notes on some instruments that I know doesn't belong there. The dang tube is microphonic! Just my luck to have the only one I have turn out to be bad. :roll: Back to the 12AT7 for now. Tubes! You can't live with 'em, you can't live without 'em. Almost as bad as women! :roll: :lol:

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