Review: Tube Audio Design TAD-60 Tube amp

Category: Amplifiers

I'll start by saying that I've been into higher-end audio for a few decades now, and quite a lot of equipment has been through my hands to this point (half the fun of this hobby). Somewhere around 12 years ago, I'd come to realize that I preferred tube amplification over solid state in terms of an overall involving presentation of the music, and ever since then have owned tube stuff (brief flirtations with various solid state devices only helped to enforce this notion).

Which brings me to the discovery of Tube Audio Design, the provider of components conceived by Paul Grzybek (of Bizzy Bee Audio fame), built to his specifications by a very reputable Chinese manufacturer, and then hand-finished by Paul in his shop located in Wheaton, IL. (His offerings are available exclusively online; detailed product info is found at

The TAD-60 amplifier is built like the proverbial tank; overall appearance and heft (not to mention its specifications) in my experience indeed belie the modest asking price. With its stainless steel chassis and almost 1/2"-thick black anodized face, the relatively compact package portrays a masculine but elegant stance (also included is a lift-off stainless steel tube cage). All function controls are easily accessible from the chassis top, as are the tube bias test-points and adjustment pots (a digital voltmeter is included too).

EL34-based, the TAD-60 is rated at 60wpc in UL-mode, and 30wpc in switchable-on-the-fly triode-mode. Other standard features include adjustable input sensitivity and adjustable global feedback, adding flexibility to a host of possible preamp and speaker combinations (the input sensitivity control may also be used as a volume pot in a single-source direct input configuration).

Listening to the TAD-60 after the recommended 30 hour break-in period and beyond, the music really began to open up, and along with the TAD-150 preamp, I was experiencing just about every CD I spun in a whole new manner - I'm particular to small-ensemble jazz and female vocals - there was an in-the-room conveyence of the music that I found startling at times - present is deep, tight bass, a glorious midrange, detail, depth, and an overall natural presentation that allows hour after hour of enjoyable listening. I've found that the feedback adjustment permits a fine-tuning of balance between dynamics and warmth, and was able to "lock in" the amp to my speakers for what sounds to be a perfect sonic match (just a tad of feedback along with the triode-mode setting seems to be the magic spot in my case).

Without attempting to describe every sonic attribute I'm hearing (though I'm happy to answer any particular inquiries), suffice it to say that the TAD-60/TAD-150 combination strikes a synergy and glow that is especially musical, and is among the finest I've had the pleasure of owning. The TAD-150 has already been highly praised in at least a few user and online reviews, and I bet the TAD-60 will soon be recognized as a similar standout. If you happen to be in the market for high quality, reasonably priced, excellent-sounding gear, just take a listen for yourself, and you will hear what these components can do for music. (Paul also offers a 15-day in-home trail period.)

Note: I have no financial interest or business relationship with Paul Grzybek or Tube Audio Design.

Associated gear
Magnepan 1.6QR, California Audio Labs CL-10, Music Hall MMF-5/Goldring G1012

Similar products
Conrad Johnson MV55
Sonic Frontiers SFS-40
VTL 50/50
Golden Tube SE-40
ASL AQ-1004
Sound Quest SQ-88
Thanks for the review. Just curious if you ever compared the Golden Tube SE-40 to the TAD-60. BTW, Your speakers would seeem to be a rather tough load for all the above mentioned amps. Which amp has driven them the best?
Jig, I no longer own the two SE-40 amps I'd used with the 1.6QR's (each in mono configuration produced 80 watts into 4 ohms), so no opportunity for a direct comparision, but I can say that the TAD-60's resolution and low end response is superior in my setup (at the time I had the SE-40's I was also using the TAD-150 preamp). There are 4-ohm taps on the TAD-60, so the 4-ohm load of the 1.6QR's is not a problem. I listen at low-to-medium volumes, so available power hasn't ever been an issue, but still it's tough to answer which amp does best with driving the Magnepans - all did fine, my favorite at this point being the TAD-60. -gg
How do you compare the performance (detail, tone, dynamics, noise level, etc.) of TAD combo with the similarly priced Sound Quest SQ-88 that you listed.

Which of the mentioned amps is your favorite?I have always wondered if I'd like the Sonic Frontiers SF 40.I have had some tube gear like Mesa wish I wish I had tried the tube mod to EL34/KT88since I didn't like the 6L6.MY Conrad Johnson MV50 was the warmest amp I have had but like my EAR intergrated since it is less noisy.It's to bad Sonic Frontiers went down the tubes (a definite pun in english!)but it is nice that they still service or do modest upgrades.I like that the pre-amps had a phase reverse.But again which of those amps was best?
Saisunil: I still own the SQ-88, which is indeed a very musical and engaging integrated amp, but prefer the TAD combo in my main system due to a higher overall level of resolution and dynamics, plus a more solid low end response.

Chazzbo: Each of these amps through my MG 1.6QR speakers has certainly yielded pleasing results, but I can say with some level of confidence that the TAD-150/TAD-60 setup has been my favorite thus far in terms of how effectively it conveys the soul of the musical experience.
Why would they make two items that were intented to be used as a pair different colors and widths? I hope it sounds better then it looks, Paul if you ever read this, please consider the esthetics as well as the sound, even the lettering is different. I hope the next version has matching faceplates, and get rid of that gold hue, it should be black or silver, people other equipment to match you know!
Perkadin: I believe the two models are each provided by a different manufacturer, so there's one explanation. Paul had mentioned a while back that he could get ahold of an optional black faceplate for the TAD-150, but I think the setup looks just fine the way it is - I wondered about a visual match as well before actually seeing the two pieces together, and as it turns out, in person the setup really does come off very nicely. In any event, what matters most to me is the glorious sound that this pair produces.
I own the TAD-60 and TAD-150 Signature combo and I agree with the review. These are wonderful sounding pieces. They are also very well made made and I like the look. Highly recommended!!
Has anyone made any direct comparisons with the cayin Ta-30 which I have paired with the Tad-150 I would imagine the Tad-160 would have better dynamics due to the increased pwr rating but just wondering if there any other differences to note.

Having owned both the TAD 60 and TAD 150 for about a month, I'd like to chime in about these wonderful tube beauties. I've been in high end audio for thirty years and have owned lots of both tube and transistor units, What the Tube Audio Design pieces remind me of are the early Conrad-Johnson classics of the mid 70's. Back then the PV-2 and MV-45 combo was a warm musical experience that was pleasing to both your ears and your wallet. These TAD creations from Paul Grzybek are detailed, tight, warm and smooth. They offer some great features for the money as well, like a remote(150) amd variable negative feedback(60). As previous fans mentioned, they are built like tanks and have the fit and finish of "Salon" equipment. So what you get ultimatly are, new classic tube gear that give you the C-J type sound but are faster, quieter and affordable.
As Finrok points out, the sound is very much like the CJ offerings, which I surmised and instead of purchasing the CJ CAV-60 ($1500 used), I went with the TAD-60. I couldn't be happier.

I've only run mine for about 20 hrs, so commenting is a bit premature, but the sound is detailed, tight, warm and smooth as previously mentioned. I'm running it with a Bottlehead Foreplay III and the sound is simply exquisite and this combination can drive even inefficient speakes.
Had my set up about four weeks. it has about 30-40 hours on it. At first I had it hooked up to an outlet through a surge protector and getting a hum or buzz but, I moved the hook up to an adjacent wall and it went away. Now for the sound. Without having another amplifier inn house to compare I will only be able to give my impressions and not a comparison.

Rest of system: TAD-150 (non-signature), Vandersteen 2CE sigs, Eastern Electric Minimax Cd

The amp appears to be broken in as of about ten hours ago. I play classic rock through it so not all the recordings are good. However, When the volume knob is at 915AM(approx), the sound really comes alive. I was listening to CCR greatest hits which has always sounded compressed through my other amps in the past. Not with the TAD-60. The soundstage and separation on that old CD was incredible. Could almost visualize John Fogerty in one spot, Guitar to the right and drums to the left. Totally unexpected result. Image does not appear to come directly from the speaker even on this old remake. Same result with Bob Seeger, Jimi Hendrix, Lynard Skynard, etc. This impression again is not a comparison but, an actual listening experience. Better recordings were even more spaced out.

Since this is my first tube amp experience, I could not characterize the sound as like CJ, Cary, or any other manufacturer. Since I went from a McCormack DNA-1 to the TAD-60, I can detect an increased richness and roundness to the sound. It basically just jumps out at you. Bass is strong, tight, and well controlled, Midrange is something that I never experienced before. Highs when the volume is sufficient has no evidence of shine or brightness. I listened about an hour at a time and at no time did I have the urge to turn up the volume to see if anything was missing.

This amp is defintely a fit for the equipment described above. Power appears to be more than adequate for the Vandersteens which are somewhat inefficient.
I cannot say whether or not it compares to amps more pricey as price is sometimes not a good indicator but, of the amps that I have had in this price range, the TAD-60 is in a totally different league. Not even a fair comparison.
The TAD-60 has a negative feedback control and a switch on the fly that moves the amp from Ultra linear to Triode. Biasing was simple and with Paul's instructions took about 15 minutes...

If you are considering a tube amp in the 60 W range need to give the TAD-60 a try.
I bought a Cayin TA 30 from Paul 2 years ago and have enjoyed it very much so I'm going to give the TAD 60 to myself for Christmas.

I have a Transcendent Sound Ground Grid tube preamp and tried a JUicymusic Merlin tube preamp but I stayed with my 2004 Luxman L505f int amp that I use as a preamp. I tried all 3 preamps with the Cayin, the amp section in the Luxman(100 watts), and a pair of Monarchy Audio SM 70 pros(80 watts) and for my taste I like the SS luxman with a tube amp.

I am thinking about a Super Tjoeb tube cd player with upsampler. I have a NAD C542 with a Musical Fidelity X10v3 tube buffer stage that works very well together but I want to try a true tube cd player.

I purchased my TAD-150/TAD-60 combo after researching tube gear on the web for 6 weeks. This is my first tube purchase, and Paul was very helpful and approachable when it came to answering questions and assisting me with my setup: mains - Rocket/Onix Reference 3; sub - Rocket UFW12. I was using an Outlaw 7125 amp, and a Denon 3805 as a pre, and couldn't help but feel that something was missing in the mids and highs. Most of my listening is classic & alt rock, and the guitar parts (especially those with overdrive) were not as punchy or dynamic as I knew they could be. At first I thought it was the speakers, but a fellow Ref 3 owner talked about how adding a tube pre really helped to open up the soundstage, especially in the mids, so I decided an upgrade to the "tube side" was in order. Must admit, I was skeptical at first. I mean, how much of a difference was this 60watt amp, and tube pre combo going to offer over my "state of the art" Denon, and 190 watt (bi-amped) Outlaw? Well, let me tell you, the difference is night & day. Don't let the 60watt rating fool you, the TAD-60 is plenty powerful and punchy, yet very musical and detailed. I like it best in Tri-mode which actually drops the wattage to 30, yet still there's plenty of power to drive my floor standing Ref 3s. In fact, I find myself turning down the sub, and setting it's crossover to 60, that's how good the bass response is. One of the nicest perks of this setup has been that even less than stellar cds and mp3s sound great, and offer details and nuances I've never heard before.
I've been playing guitar for 20yrs, and typically you can "feel" when the harmonics and overdrive are just right, and that's what the TAD-60 & TAD-150 do, they get it right. The rolling decay, and growl, with much added slam and punch, simply awesome. I love this gear so much, that for the past 3-4 weeks I listen to random Stones, Zep, Who, GD, etc 2-3 hours every night - yes, it drives my wife nuts, but I'm happy. Btw, the bias procedure is super easy, and takes only a few minutes. And I never thought I say this, but I'm actually looking forward to tweaking the sound with different tubes :)
I'm ordering a TAD-60 from Paul later this week.

Onotu2 I switched out my Svetlana EL34s tubes for electro-Harmonix 6CA7s tubes in my Cayin TA 30 with very good results. The EH 6CA7s have better bass and to me have a overal smoother sound than the Sevt EL34s. However I think my EL34s were ready to be replaced.

Once I get the TAD-60 and let the amp and EL34 tubes break in I'll do some tube rolling with the 6CA7s and see which I like better. Paul said to bias them like EL34s 350-370. I also want to try some KT88 and KT90s.

Well enjoy your new toys let us know how the tube rolling goes.

Well mailed off a money order to Paul for the TAD-60 so Merry Christmas to me!! I'll post reviews between the Cayin TA 30 and TAD-60.

Jbsljbsl - I've no doubt that you'll enjoy the TAD-60 very much. And thanks for the tube recommendation. I just emailed Paul for some additional info on tube setups as it will be a first for me and I don't really know the different characteristics of the various tubes available, but I was thinking KT88s to start with (as they are mentioned so often), but you never know...
The KT 88 and KT 90 are also the next tubes I want to try also. The EH 6CA7s have better bass than the Svetlana EL34s do and I like the midrange better also. Once I get the TAD-60 I'll let the Svet EL34s break in and then compare them to the EH 6CA7s. Then whichever I like best compare to the KT 88 and KT 90.

Enjoy and I'll post once I get the amp.

The TAD-60 does look like a beautifully constructed amp. There are alot of folks on this thread that have excellent tastes. This review & thread has sparked my interest into purchasing one. I especially like the ability to switch between ultra linear & triode mode. I'm sure this will match up perfectly to my speakers which have a sensitivity of 105db. Tube Audio Design products are a tremendous value!
I got the amp today and there is NO HISS with a pair of 2004 Klipsch La Scalas 104db. The only way I could barely hear some hiss is with my ear right up against the midrange horn. Phd what speakers do you have? Sounds like some big ole horns to me. What kind of preamp?

I know the amp and new Svetlana EL34s have not burned in yet but I think the sound from EL34 tubes just does not work for me. I know the 6CA7s work very good for me so now I'm curious about the others.

Another thing I'm going to try with this amp that you could also do with the Cayin is to take out tubes 2 and 4 and rebias between 500-600 is what Paul said and it runs as a SET amp. The Cayin would run at 4 watts and sounded good but the bass was not as good and if you turned up the volume to rock it sounded like it was starting to clip.

So now that I have the Cayin 35 watt amp and this TAD 60 triode 30 watt amp I'm going to biamp my La Scalas. Put the 35 watt Cayin on my bass speaker connections and the TAD 60 on the high freq connections and let em rip. Might also put the TAD 60 into SET mode with 2 tubes and see how it sounds.

Has anyone taken the tube casings off the driver tubes and then put them back on to see if there is any difference? I like the look of the amp without them so unless I can hear a difference they are staying off.

Jbslibsl, I have four large Klipsch CF4s. For a tube preamp I am currently using an ARC MKII Reference II and I intend on pairing this expensive preamp with a TAD 60. I had a TAD 150 & regretably let it go thinking I would pick up the Signature later but the ARC preamp-purchase put a hold on this. I still consider the TAD 150 an excellent preamp!
Well I've had my TAD-60 for about four days now and I'm still going to wait till I've had it for a week.

Can anyone suggest some KT 88, KT 90, and 6550 tubes to roll in the TAD? I never really liked the SVetlana EL34 tubes in my Cayin TA 30 and I'm waiting till the amp and EL34 tubes have a chance to burn before I make a decision on the EL34s. I was using EH 6CA7s in the Cayin with very good results but tried them in the TAD -60 last night and was not impressed.

So Feb I'll try some other tubes.

First my name is Pete and I've owned this amp for at least 6 weeks. I've played it everyday for several hours since buying it and I swear it just keeps sounding better with evry passing day. I'm using all stock tubes currently and like what I'm hearing. My question to you is what about the Svet EL-34 do you not like? I too will try some different tubes in the future but am enjoying the current lineup. Outside the of the EL-34's what 12u-7 and 12-ax7 tubes did yours come with? Thanks.
I have had the 60 for close to two months and I agree that it just keeps on getting better with every listen. Today, I rolled in a quad of Valve Art KT88s and I have to say that I like these better than the stock Svets right out of the box. The KT88s have more authoritive bass and are better in the highs. The midrange is very good too and is almost as good as the Svet EL34s so, you are not losing much there. IMO, this tube is better than the stock tubes.

I also ran a pair of Tung-Sol reissue 6550s in V1 & V3 only - single ended. This tube is very neutral sounding top to bottom and also gives you a little more bass than the Svet EL34s. I changed them out because I needed more power to get to the listening levels I need for rock music. I should have bought a quad instead of a pair. Oh well.

I also have the TAD-150 pre and I changed out the stock 12AT7s (couldn't tell which brand) for a pair of Telefunken 12AX7s. These tubes expanded the width of the soundstage which was more to my liking. The 12AT7s seemed to image everthing between the speakers.

I am really enjoying this TAD combo and definetly feel that I got my money's worth in spades. Well worth the wait!
I am geting my first tube set-up also. I got the TAD 60 and plan to mate it with the TAD 150. I will be using the set primarily for vinyl listening. What speakers are sutiable for staters like me? My room is ratively small, about 12'x12'.
I am using Vandersteen 2CE signatures. Excellent combo..

I am using KEF C75 speakers. They are 4 ohm speakers with a sensativity rating of 91db. No problem driving these speakers in PP UL or triode mode. In single ended mode (using only two power tubes instead of four) the amp couldn't drive these speakers at all. It had no problem with Klipsch Heresy though in single ended mode. The Heresy has a sensativity rating of 97db. I think the amp could drive most speakers with a moderate sensativity rating if used in PP mode. That leaves you a lot of speakers to audition. Happy hunting.
Interesting that you use MG 1.6 do I. Some time ago I investigated whether I could use 60watt tube amps for my three MG1.6. In spite of the fact that my Maggies are crossed over from subwoofers, usually at about 80 Hz, voltage measurements at the speaker terminals revealed peaks that could only be achieved by a much more powerful amp. Mine are 600 watts into 4 ohms, and they just barely make it without clipping. Admittedly this was with very loud and challenging organ music, but that is sometimes what I listen to.

This TAD amp, and the model 1000 which would interest me appear to be excellent products at a very reasonable price. They remind me of the tube amps that I knew many years ago. However, the thought of the care and feeding of a dozen output tubes (for three TAD1000) puts me off! If I had a small system played softly these TAD amps would be in it.
I also wonder how the upcoming TAD 803 speakers would fare with the TAD 60/TAD 150 setup. From the info listed on Paul's site, it sounds pretty impressive for $499. I just can't get that B&W image out of my head for a long time. Maybe I wait a few more weeks and see if any new 803 owners will chime in as the shippments are being filled this month.

Thanks for the suggestions anyways.
Just rolled in a set of Electro-Harmonix KT-88s this weekend and the difference IMO was an overall improvement. The most noticeable difference was in increased headroom and a tighter more controlled bass. There was also a nice seperation of instruments in the highs and mids, a welcomed plus, because I love the sweet tone of the EL-34s but the KT-88s were right there as well. In general, I thought the EL-34 could muddy the bass a little when volume levels were cranked, where the KT-88 really held things together at high volumes. You know you've found a good thing when new things jump at you (in a good way) on familiar tunes that you couldn't zone in on before. Always brings a smile to my face. I was running the TAD-60 in tri-mode with the EL34s because I liked the warmth in the mid-range over the UL setting. However, I did like the extra power and dynamics UL provided, but I was constantly adjusting feedback to find that elusive level of warmth. With the KT-88s I have the TAD-60 set to UL mode now, with the feedback knob set at 2:30 and haven't felt the need to touch it once; its a perfect blend of warmth & dynamics that I couldn't achieve with the EL-34's. Tubes were purchased from the Tubedepot, they arrived in 2 days and were very helpful on the phone. However, 2 of them were running a little hot (715-720 range), so I freaked and called Paul, who was very good about walking me thru the setup, tubology 101, and assuring me that they would run fine. As you can probably tell, I'm new at this stuff, so it's nice to have a real pro to call when you need help.
Metslp, how did you choose the Shuguang tubes? I just rolled in a quad of Tung Sol reissues with excellent results. More punchy music, stronger bottom end...

Metslp, do your Shuguang KT88 plates have holes in them or are they solid? I replaced my Svet EL34 with Shuguang (Valve Art) KT88's and think it's a real improvement over the stock EL34s. I agree exactly with your assessment of the KT-88's I got the one with holes but there is a lot of buzz on the net that the solid plate Shuguang (Penta) are the ones to buy, so I was wondering which ones you have?
Strongly agree with Metslp, the TAD-60 is a great piece of equipment. I too switched out the EL-34s for some KT-88s (Electro Harmonix) and I couldn't be happier. The 88s displayed an overall improvement right away, but sounded so much better after settling in - bass is totally on a different level now. However, Metslp has me curious, so I think I'll be trying a quad of Shuguangs soon. I'm new to the tube scene, but I love that you can improve or change the sound with a modest investment.
This is somewhat unrelated, but I would appreciate hearing from other TAD-60 owners as to what CD player or turntable they currently use or would like to purchase. I'm new to vinyl, but I was leaning towards a Rega P5 or VPI Scoutmaster; for the Cd player, a Jolida JD-100 or Shanling 100. I currently have no true cd player, I'm using an X-box - pls don't laugh - and Apple's Airport to stream my mp3s to my TAD-150 preamp.

I have that set up and using an Eastern Electric Minimax CD with Amperex Navy Nos tubes. Check out the reviews. Will only set you back $900. I rolled in a quad of Tung Sol 6550 reissues. Definitely more punch and extention but, I may go after those Shuguangs...

Thanks Eagleman. Found quite a few reviews and they all sound good. The folks at Underwood Hifi offer 2 mods, but they seem really expensive. I'm sure rolling in different tubes will probably do the trick. Thanks again.
For those of you that have rolled the TAD-60 with KT88's what did you set your bias at? Paul's site states 600-625. Just wondering if this is the same with all mfg's. Just thought I'd give Paul a break and ask the forum. I imagine he spends a lot of time replying to customers. I'll post my thoughts on the Penta KT88's once they burn in a bit. Thanks!
I biased my VA KT88s at 610. I think it is the same for all KT88s & 6550s regardless of who manufactures it. If you were looking for a less romantic sound with more bass - I am sure you will be pleased.

I just rolled a pair of NOS Sylvania triple mica gray plate 5751s into my TAD-150. Sounds real good right out of the box. Also the volume control has more play now because the 5751s have only 70% of the gain that a 12AX7 has.
Thanks. I thought that was the case. I'm having a problem with my bias pots at this time so I'm kinda stuck at the moment. Left channel won't cooperate and is excessively hot. Not the tubes to my knowledge as I've rolled several with the same result. Any way to calibrate the bias pot? I did email Paul, hopefully not a painful remedy.
I also have the TAD-150. I'd like to try other tubes in that unit. Thanks.
Meerp1: regarding the bias pots I can't get KT88s or 6550s to go much below 525. I noticed Paul changed the bias instructions on his website for the TAD-60. He used to want you to start at 200 (like the EL34) but that is not possible on my amp. I am no expert, but the remedy is probabaly to change the resistors on the bias pots. I'm interested in Paul's answer so keep us posted and good luck.
I got the Penta 88's up and running but it took a little tweaking. I normally would Bias with the Feedback fully right but that was not possible. Actually the left channels, V1 & V2 run quite a bit hotter than the other side. V1 has a reading of 635 at its lowest point so that's where the quad is Biased at. If i turn the feedback all the way up the left channels will oscillate, run excessively hot, and shut the amp down. I had one happy fuse "blown". So I tested a lot, being more careful and finally dialed it in. Paul was helpful. I still may send it in in the future to get a bigger range with the Bias while using 88's or 6550's. Currently breaking in the new tubes and it sounds very good. Thanks for the reply. let me know if you have questions. I'm sure I'll have some.

New Finding on my oscillating problem. With speakers connected my Feedback knob will function full range with no problems. I read where it's best to have speakers connected on tube amps. Here's what I read, "An output transformer stores inductive energy, and a speaker load prevents this energy from being returned to the tubes in the form of high-voltage transients."


Thanks for the reply. I am glad that you got the KT88s running. They are my favotite so far for this amp. I had never thought of adjusting the feedback before biasing the tubes. I used to keep my feedback at 10 o'clock but lately I have it at 1 o'clock. I just biased the tubes at what ever the feedback knob was adjusted to at the time. I really like the KT88's so I don't think I will be rolling in any different tubes for a while. I might start rolling the 12AX7s and 12AU7 tubes in the amp to see if it makes any difference.
I've recently installed the Penta KT88s in my TAD 60 and had a similar experience with high bias readings. The V1, V2 & V4 sockets all rose quickly to the 580 range while the V3 went all the way up to 620. After about 15 minutes at idle, the V1,2 & 3 settled in at approx. 525, while the V3 settled at 585. I'm new to tube power amps so this was pretty scary since I couldn't get down to that recommended 200 starting point but I emailed Paul and he said not to be too concerned unless the readings hit the 700 mark. They never did and all seems well after a couple days.

Paul has some new bias settings on his site that should be worth trying. The new settings will provide Single Ended Class A for the first 10 watts and Class A/B for 10-50 watts.
Dave, I'm using the Penta 88's also and find them to be a good sounding tube. What are your impressions?

I've got only about 15 hrs. on the Pentas but I really like what I'm hearing so far. From top to bottom they are an improvement over the EL34s with great balance and more articulate bass so I'm looking forward to what 50+ hrs. on them will bring. Do you know if Paul's single-ended class A bias is adaptable to the KT88s or is it just for the EL34s?

From the bias levels it would be used for the EL34's. I did try it with my stock tubes & it did sound nice. Especially in the mids. Worth a try. Nice to have alternatives.