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I'm looking at one of the VTA amps.
Output tube choices are from 6550 and include KT88 and KT120.
I have a couple questions.
First? Just choose by sonics?
Second? Given PS limits, I don't see more 'power' but perhaps higher headroom? I realize the bottleneck could be any number of places from PS to output tubes to transformers.....power or output......
I've done a little looking at this and realize that the PS capacitor compliment is where it's at.......As voltage rises the energy goes up much faster. The 500v I see for some circuits represents a LOT of energy even at modest capacitance values.
Too much is never enough
Follow Ups:
I've been told by a well known tube amp manufacturer that the KT-88 is a more linear tube than the KT-120 which is why he doesn't use the KT-120.
!
The Mind has No Firewall~ U.S. Army War College.
Everything is colored. This means you prefer KT150 colorations. But linearity is a defineable fundamental and the manufacturer I know says the KT88 is more linear. That just means overall you prefer the color of different tubes, understood.
!
The Mind has No Firewall~ U.S. Army War College.
Linearity of thee equipment comes first. Then you can play with the room acoustics which I agree are very significant. Unless you make your own gear you're stuck with the linearity of the equipment. You do have ability to improve room acoustics.
The room trumps {by magnitudes} any other consideration. I do make my own amplifiers, most people have never had the unalloyed joy of listening to a SET 801 or a push/pull 45 but that is small in comparison to my speakers and the room. Oh, and by the way, a 6AQ5 tube triode wired is markedly more linear than ANY KT88.
The Mind has No Firewall~ U.S. Army War College.
Edits: 07/13/21
"a 6AQ5 tube triode wired is markedly more linear than ANY KT88"
Almost any triode is more linear than a power pentode. If not for the invention of NFB, the latter would be only a laboratory curiosity.
In your experience, how do you feel about the sound of a triode-mode 6AQ5 compared to a 45?
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Buy Chinese. Bury freedom.
THAT, is about as close as I have heard to a 45 from a beam tetrode.
The Mind has No Firewall~ U.S. Army War College.
nada aqui
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Buy Chinese. Bury freedom.
"The linearity you speak is of IS NOTHING compared to room and speaker non linearity"
OK but does that give a circuit designer license to no longer care about the amount of harmonic distortion produced by the amplifying circuits?
I guess I missed your point.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
The point is, there is a myriad of audio gear out there and everyone hears differently. I still admire the sound of Infinity Epsilon speakers. Compression drivers have ten times less distortion than a cone or dome. On that criteria no one should listen to any other type of driver. The frequency response of Horn speakers is another matter altogether being highly erractic. This whole outlook is comical to me, am reminded of all these over 50 men DEMANDING 20 to 20K frequency response when most listeners HF drops like a stone past 12.5 K.
Ridiculous.
The Mind has No Firewall~ U.S. Army War College.
that diminished age related hearing also has an effect with consonance. That's the ability of the temporal lobe to discern and produce a pleasantness response by differencing cords. If you want to be complete on the subject.
So ultra high resolution really isn't as important as it was when you were 20. Any neuroanatomist will tell you that.
!
The Mind has No Firewall~ U.S. Army War College.
That's interesting because Ken Stevens of CAT says just the opposite.
When asked, they have to come up with a reason for the choices they make and they rarely share the REAL reason with their customers, so...
I have great respect for the source of my info. But then again all I've heard about Ken Stevens including people who knew him, makes me respect him also. It would be cool for the two men to discuss their conclusions.
I don't think there'd be too much disagreement between them. Ken's latest amps are optimized for the 120 because he believes the 120 sounds better, and the 120 is what ships with his amps. He is also quick to point out that his amps deliver excellent results with the 88 too. So, re-reading my OP, I did not intend to make it sound as though he has a dislike of the 88, just that he's found a tube he believes sounds superior.
If I were not locked into my Acoustats and servos setup, I'd be figuring out a way to raid the retirement account for one of his JL series amps ... except then I'd have to figure out what speaker to pair them with.
A look at the respective data sheets would show that to be the case. My feeling is the KT120 was developed after the EI KT90 went out of production as a knee jerk reaction in the "More's law" idiom. If a little More output is good than lots MORE is better.
It sucks to get old. It really sucks to get old and bitter.
Edits: 07/08/21
I have YET to hear a sustainable bad word about the KT88, even new production, though I'm sure exceptions exist. I think as long as you stick to a few 'known' tubes you should be 'golden'....so to speak.
Too much is never enough
In these amps, there is no difference between the KT88 and KT120. No more headroom either, just wasted money on the KT120.
You might do better though, if some changes are made to the inferior, and quite dangerous power inlet.
I see VTA still uses Dynacos old way of wiring the fuse and crappy power switch, and the two prong cheapo power cord.
I've seen two examples of these amps in a month, and both had very live chassis, and one had a burnt power switch.
Dan Santoni
I already communicated with BL about that power cord. I rewired my ancient (about as old as the original ST70? and used 16-2 and a simple strain relief. Had to 'hog out' the mount and to do so I isloated it with TAPE on inside and out. I vacuumed after than SLOWLY peeled the tape. I used a MAGNET at the same time and DID trap a few additional particles..
As for the ST70 / 120? New chassis is 16ga (= 55 thousandths) of an unspecified STAINLESS alloy.
They claim non-magnetic which, IMO, is a red herring since ANY metal conducting electricity will also have a magnetic field AND the reverse is true. I don't know if a standard 'nibbler' would work or if I'd need machine shop help with a proper chassis punch.......
Cost for such a punch is in the 100s of $$.
Is what you saw with a 'live chassis' the result of a Hot ? neutral swap? If so? What do the directions say about this wiring? Short (sorry!) of doing something VERY WRONG, how do you fry a power switch?
And yes, my take from limited reading is that the KT120 is overkill. the KT88 seems to be the sweet spot. It also has good availability. There is MORE CONCENSUS about the 'goodness' of the KT88 than any other tube almost without exception.
Too much is never enough
On one amp, a simple reversal of the plug did reduce the chassis voltage (120V down to about 26), the other was not so good. Both ended up getting three prong power cords.
The power switch, while I think is rated at 3A, is not really very good. The contacts started to arc when turned on and off. Eventually failing.
Place a snubber capacitor across the contacts will help.
Dan Santoni
Something WRONG there.
If such a device is plugged into a GFI (Ground Fault Interrupt) circuit, I think it'll trip, right?
A 3 amp switch and what I'm given to think is a 5 amp fuse? A NON-Starter.
Were these Kits or Factory assembled?
Too much is never enough
I'm not sure about the GFCI tripping. But possible.
The 5A fuse is not even in line with the switch directly. The switch is on the neutral, the fuse on the hot. Wired like the original Dynaco ST70 from days gone by.
Certainly doesn't meet UL.
Dan Santoni
I think the ground fault NEEDS ground. Any dsagreement in current between hot and neutral MUST be at ground......CLICK!
I'd need to see the direections for assembly. Some think AC is not what it IS......and might just wire the hot / neutral wherever and not care about fuse....it's in series, right? or the power switch, also in series.
I'd be very careful ......
Too much is never enough
Yes, you are right about the GFCI. Answered too late last night.
The fuse and the switch are in series. They need to be, but the fuse is on the live, and the switch is on the neutral, not directly in series with each other with the fuse first. Of course since the power cord is not polarized it can be flipped.
Dan Santoni
Even the CHEAP 16-2 cord I recently purchased was polarized.
ONE Wide blade and the other Narrow....And the cord is 'ribbed' on one of the 2 wires. So the orientation can be continued to the device being 'recorded'.......I had bought an EXTENSION cord and just clipped off the outlet knuckle (worthless, anyway) and used the cord......
So it'll only plug in ONE way, ragardless of 3rd wire ground. Or Not.
If / When I build this amp? I'll give thought to fuse / switch BOTH on the hot leg. NO REASON, IMO, for any voltage to appear between chassis and ground.
I think an error was made somewhere in the assembly. A blob of solder? A skinned bit of insulation? Lack of stand-off insulator somewhere?-
I can't believe that installing a 3-wire system (with ground as #3) and with voltage on that wire would NOT result in a tripped GFI. I'd personlly try the device in the bath or kitchen where the GFI outliet lives. If it trips (I give it 90%) than the device is UNSAFE and should not be used until the real problem is found.
But that's just ME.......
Too much is never enough
The AC never touches the chassis. At least in anything built after 1962. The AC circuit is entirely isolated from the chassis. So the argument of polarity and chassis grounding is wrong. FYI a power tranny does not require polarity. The AC wave being in one of two 180 degree phases make no difference in converting AC to DC.
Edits: 07/09/21
View YouTube Video
About 25 years ago, I asked one of our electrical technicians at work what the dots on the schematic of a power transformer meant, and he said "phase". Since none of my old tube equipment transformers were marked, I simply ignored it. Even the newer Hammond power transformer I bought has no polarity markings, at least not on their included schematic.
Your discussion with jedrider got me curious, and I found the above video this morning. Our Canadian friend in the video explained it in a way that not only could I understand (most of) transformer phase, but something more important. The video showed a simple way that I can test my unmarked transformers for phase, which I always thought would require a room full of expensive test gear.
Where I need to do some further research is regarding the benefit of proper phase. Is it simply higher or lower secondary voltage? Power supply efficiency?
My next thought was "Did the transformer winder wind in the same direction for all three secondary taps?" in a multiple tap PT, and does that matter, if I find proper phase for all three?
I haven't finished my coffee yet, and all this is making my head hurt. But I see I've got a lot more homework to do.
It's been my experience, at least with torroidals, that the capacitance to ground is different for each leg, as the circuits appear to pick up hum otherwise. Most torroidals are labeled such I believe and it should be followed.
AC is a 180 wave. Polarity is simply the point in the wave that is hitting the tranny. It's like a lightbulb.
So what you're saying is that if some inept electricians helper wired my socket wrong, which happens far more frequently that one would imagine, that your stereo is going to hum or not work?
Just because you can rewire a socket doesn't mean most other people can. So that would present a significant percentage of non working stereos.
"The AC circuit is entirely isolated from the chassis."
No, it's not. The schematic doesn't show the capacitance to the chassis from any of the primary components. Most power transformers that aren't hospital grade leak enough current to the chassis to kill a person who comes between the chassis and ground. It's unconscionable to build and sell a tube amp without a three-wire power cord.
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Buy Chinese. Bury freedom.
Keep up the honest discussion! SAFE
equipment MUST connect the service ground
to the chassis.
-Dennis-
> > "The AC circuit is entirely isolated from the chassis."> > No, it's not. The schematic doesn't show the capacitance to the
> > chassis from any of the primary components. Most power transformers that
> > aren't hospital grade leak enough current to the chassis to kill a person
> > who comes between the chassis and ground. It's unconscionable to build
> > and sell a tube amp without a three-wire power cord.False.
The power transformer has a few hundred pF at most from one end of the winding to ground, which can pass an AC current in the microamp range. Modern safety standards allow 0.7 mA (below the "startle" threshold of about 1 mA, which could cause someon to jump or drop something) and well below a hazardous current. GFIs trip at 4-6 mA, a level considered hazardous. A typical voltmeter is 10 megohms, a cheap one one megohm; can show a voltage even when a non-hazardous current is available.
However, a kitmaker does not build and sell an amplifer; and cannot get safety approval since he does not build it. It would require a 3-wire grounded cord to gain safety approvals (or to be double insulated, which is not practical for the power transformer or output transformers).
Edits: 07/10/21
Even if I was wrong (I'm not), what happens when the insulation deteriorates or there's an arc-over inside the power switch to the chassis? Only a third wire ground can protect the user from these and countless other hazardous conditions. Sure, you can trust your life to a Chinese interrupter. Not me.
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Buy Chinese. Bury freedom.
Your statement that transformer leakage could kill a person is false - it's minuscule. Yes, you can measure it with a voltmeter - but current is what's dangerous. This sort of design met safety standards for decades, though it would not today.
That said, I'm currently working on some amps from 1960 that have UL labels next to the (previous ) 2-wire cord. Now with grounded cords, like everything else I work on.
If you were interested in a retrofit?
Punching the IEC hole in the 16ga Stainless Steel chassis could be a problem. I don't thnk a regular 'nibbler' would work. Chassis punch is $$$ for a one time use.
MIght be easier to take a drawing to a machine shop and let THEM do it? This prior to any assembly.
Before any of that? make certain you have enough clearance behind connector......
Too much is never enough
I don't think a machine shop can punch that after the chassis is formed. Buy a Heyco strain relief to fit a 3-wire cord (16 or 18 gauge) and file the hole to fit. Incidentally, contrary to popular belief, many stainless alloys are no harder than mild steel.
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Buy Chinese. Bury freedom.
I would suspect a 300 series stainless.....Austentitic / non-magnetic......Available in the 16ga thickness and not expensive.
Still and all, 18% to 20% Chromium.......and a smattering of 'other'.....Including Nickel?
But I DO suspect it's pretty tough.....
I DO have a strain relief fit for CL2 wire.....I can't find the dimensions now, but it does work.
I used one on my KENWOOD Integrated when I re-corded it, up from 18ga to 16ga
i wonder what OTHER stainless alloy qualifies? I think 400 series is magnetic, mostly, while stuff like Invar and Monel are much more $$$......
Bob Latino himself answered my post about nibbling or punching the chassis....and he was not optimistic about the prospects...
Too much is never enough
"Bob Latino himself answered my post about nibbling or punching the chassis....and he was not optimistic about the prospects..."
And he's right. A small taper file (triangular) and small rat-tail file will take care of this. It's a half-hour job at most to carefully make it exactly right for the Heyco. Be sure to use calipers to measure the strain relief before filing the chassis. They aren't always the exact size specified in the data sheet. If you make the hole too large, there's no going back.
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Buy Chinese. Bury freedom.
As you noted, not ALL stainless is 'created equal'....though by definition, must start at about 18% Chromium content. Without getting 'exotic', VTA probably commissioned a 300 series alloy. Some other VERY exotic alloys exist, like H1 which SPYDERCO uses to make knives for the marine enviroment which essentially WILL NOT CORRODE.......And they are $$$......
I'm looking at both the DRAWING and the PHOTO of the complete amp and I'm not certain of the clearance between an IEC connector and the transformer. I do NOT know how far 'below' the 'deck' the transformer protrudes nto the lower part of the amp.....The image doesn't have the 'depth' I'd like to confirm and no mechanical drawings are offered.
There IS space if the connecter were mounted on the TOP of the amp, 'prongs down'.......You would not need the 3rd wire unless you measured voltage from chassis to neutral.......You could check this easily using a GFI circuit in-house.
IF you could trace such voltage to the power transformer....IMO the only 'real' possibility, could a shielf of MuMetal fix the issue?
The Fix would take 2 minutes.....TOPS.......
Too much is never enough
IMO, the IEC hole is way too much trouble to cut. The Heyco is simpler and much faster, especially in stainless. Plus, you already have a "starter" hole at that location in the chassis. Even if you don't measure voltage to earth ground (highly unlikely), faults can occur at any time. There's no substitute for the three-wire cord in any piece of equipment installed within an audio system. Ix-Nay on the mu-metal.
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Buy Chinese. Bury freedom.
We were rewiring the utility and other switched outlets (all 110) on an ION IMPLANTER. The IDIOT that did the work managed a hot / neutral swap and the ENTIRE CHASSIS was HOT. Of course, he worked nites and was GONE for the next 2 weeks on vacation.
I've been around a LOT of high voltage. In E-Beam metals evaporation, the voltage is around `13kv.
I'm linking the manual. You'll see a FULL POWER Triode in the circuit. This was a WATER COOLED device and required a certain water purity since it was part of the circuit. A lot of current, too.
Ion implaneters have a 20kv Extraction PS which gets the ball rolling and the ions into the acceleration tube. Which is up to 200kv. The Glassman Power Supplies were mostly AIR as an insulator.
Wafer Fab, where I worked as a process and maintenance technician (2 differetn 'careers') was a dangerous place to work. All sorts of nasty chemistry.
So you don't have to convince TOO hard for me to go 3-wire to an amp.
I have MANY horror stories. How about a wrench dropped on the inputs of a trasnformer the size of a coffee table? Wrench simply vaporized with a VERY loud noise. Or the guy who was reaching Uder the base plate of an evaporator and got ZAPPED by the power supply? Or the METER we turned to charcoal whey measuring high voltage......I think it ARCED arounnd the HV probe shield and that was IT.
Lot smore funs stuff.
So In short? I REALLY appreciate your safety bias. Only thing? I have small bits for a DREMEL and may be able to get that hole right. I need to get a cord / relief 'set' so the cord workss with the relief.
Too much is never enough
Here's a 16-3 strain relief. 0.55 ROUND hole.
I could drill to 1/2" and GENTLY expand to correct size.......
I'd have to check out cordage, first, though.....
Too much is never enough
It's not round. The hole is either a D shape or an oval with two flat sides. That's what keeps the cord and relief from rotating in the hole. Check the data sheet for Heyco strain reliefs, you'll see what I mean. Also, there's a special tool to install these that prevents damaging the plastic. It compresses the relief into the cord while you push everything into the panel. I think you can find the tool on eBay, made by Philmore.
Coincidentally, I just ordered reliefs and 16-3 cords from Antique Electronic Supply. The part numbers are below, in case you want to look at the full descriptions. These are going into the amps I'm currently building.
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Buy Chinese. Bury freedom.
Other styles exist.......at least one for a round hole.
But I agree.. INSTALL is important and hole size critical. The one I just did on my ancient Kenwood is IN THERE for good....Well, I could get it out, but it is a real press-fit.
As the amp is issued? I'm not really in love with the simple Grommet used. That can be improved for minimal effort.
Too much is never enough
It's RECTIFICATION that converts AC to DC, but otherwise I get your point.
Many power tools are what was called 'triple insulated'.......and NOT 3-wire system required.
However? Somewhere in this thread is someone talkng about a voltage on the chassis of the amp.
This is a BAD situation. And IF True? .....my reasons are on the 'possible' list.
The 3rd wire.....GREEN.....connected to chassis is intended to drain misapplied voltage FROM the chassis TO ground. I think a GFI in that case would shut that circuit OFF....
Too much is never enough
There is no voltage on the chassis. There should never EVER be voltage on the chassis.
AIRTIME::
I was right......
PLEASE look at the posts from BLACKDOG where he notes 'chassis voltage'.......which I 100% agree should NEVER BE.
So, I fall back to what I said at that time about some kind of assembly ERROR .......
Too much is never enough
Of COURSE......
But I thought I read somewhere in this thread where someone SAID their was voltage on the chassis....
That is what got me started.....
Too much is never enough
Link below:
I had somehow lost that link.
...-VTA 70 if you need 35 watts, VTA 120 if you need 60 watts and M 125 if you need 125 watts.I would not use a 5AR4 rectifier in either of the two larger amps, asking a single to rectify the B+ for four 6550/KT88/KT120 is, IMHO asking for trouble and I would just use the solid state plug in rectifier, unless having full output is not an issue. And if it's not, I would go with the VTA 70 as you can use EL34 and 6L6 in addition to the already mentioned tubes and the 5AR4 becomes a more viable option,IMHO and YMMV. I prefer the tube rectifier, but if the larger amps and Copper Cap is chosen, there is no need for the soft start circuit. There is no evidence of so called cathode stripping and additional circuit elements, even outside of the circuit path are just complications. Make the circuit as simple as possible and no simpler.
Edits: 07/07/21
An amplifiers power supply and the frequency response of the output transformers will probably have a more profound effect than the output tubes. See Rod M's revelation below.
Also take a look at Jim McShanes site to see the reasons he gives for the deserved reputation of the Citation II and V.
It sucks to get old. It really sucks to get old and bitter.
After hearing McIntosh MC-30s, I had to find a pair. Maybe it's the trannies or the tube, but it's got it all with bass authority that I couldn't get with the Dynaco for my Altecs.
-Rod
"6P3S-E in ST-70"
Did you try the 6L6 in the ST-70? Or are you only referring to the Mac VS the Dynaco?
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Buy Chinese. Bury freedom.
No, I never had any clue that 6L6s would work in the Dynaco ST-70.
Are the plug and pray or need a mod?
-Rod
Definitely not plug 'n play. The pinouts aren't even the same.
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Buy Chinese. Bury freedom.
The pin-outs are indeed different (no G3 on KT66) but the original ST-70 manual recommend them as emergency substitutions. I'd be comfortable at least suggesting Rod try a KT66 or 6P3S-E, perhaps both a bit more robust tubes than a standard 6L6.
Am I missing something?
Yeah, it looks like not a great idea. I've got a set of Westinghouse 6L6GB and GE 6L6GCs that I using now in the Mac. Given the cost of replacing these NOS tubes, it doesn't seem worth the risk.
-Rod
As posted in the original Dynaco ST-70 manual, KT-66 was an acceptable "emergency" substitute for the EL-34, but the KT-66 is a more robust tube, voltage wise, than the average 6L6.
If you're really curious, you might run the idea by Jim McShane. He handles the Gold Lion KT-66, of course, but he also has some tilted bottle 6L6GC-STR Tung-Sol reissues on sale at the moment for the bargain price of $35.50 per pair. If Jim thinks they'll handle the ST-70s 410 VDC on the plates, they might be interesting to experiment with.
If he gives you the green light, and you don't care for them in your ST-70, they'd be good back-ups for your Mac.
Yes, my mistake. Substituting a 6L6 type for the EL34 is indeed possible. It's the other scenario that's different and more difficult.
One thing that concerns me about all this is the screen rating of the 6P3S-E. Within the 6L6 family, only the 6L6GC is rated to withstand more than 400V on the screen. Many 6L6 types are rated 300V or less. It's apparent the 6P3S-E isn't the equivalent of the 6L6GC in terms of anode dissipation, and that raises the question of what the maximum screen voltage and dissipation might be. No one really seems to know, and the Russian data sheet, which shows a maximum of 250V on the anode, is no help.
I'm aware that many owners have installed the 6P3S-E in their ST-70, presumably without immediate failure. However, there are reports of the sound changing over a period of 50 or 100 hours, and that's a concern. What's happening in these tubes to cause that? Could it be some aspect of screen or anode integrity? No one seems to have made even the most fundamental electrical measurements, such as output power, so there's really no way to know.
My current project will use the 6P3S-E with more than 400V on the anodes. However, screens will be regulated down to about 300V. I don't know if this is absolutely necessary, but it will at least provide peace of mind and the ability to use most 6L6 types in the future.
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Buy Chinese. Bury freedom.
I posted the Dynaco KT-66 note more for my own clarification rather than to correct you.
I did a search for 6P3S-E and read some of your previous exchanges with Mike Samra regarding that tube. I copied and pasted one of his replies to you below.
"I have made many measurements but mostly in 6L6 and KT66 amps. Most of the disputed argument I presented in past posts was to reiterate the fact that these tubes can handle much more than 350v rating claimed in the Data by the Russian military"
I know I haven't put 50 to 100 hours on those tubes in my ST-70, which puts about 410 V on the plates, so I can't give you any longevity results. Probably more like ten hours, enough to determine that I liked them better than EL-34 based tubes, but not enough to keep the amp in my system any longer than that.
Mike was sometimes casual regarding voltage specs. I remember him once good-naturedly telling me I had no balls, since I expressed concern about running a 200 volt rated Russian Teflon FT-3 cap in excess of that. Mike swore they were good to 600 V (or more), but I admit that I usually try and keep within set guidelines. Losing a $10 (or whatever the 6P3S-Es went for) tube was one thing, but creating a fire and / or shock hazard by running a cap 300% over rated voltage was something I admit I wasn't comfortable with.
If you have the cash then go for the M125 monoblocks. And get the Weber copper cap SS rectifier. This way you are guaranteed plenty of power and still have a choice of some great tubes.
If power is a concern then just skip over the ST120 and go for it.
KT88's have always been a winner. As Jim McShane if he has heard back any preferences on the amp.
IF I go with the yet-unheard KLIPSCH Forte IV speakers, the ST120 would be more than enough power.....I like the idea of a single chassis. A FEW things I'd change....like a replaceable IEC plug with built-in fuse. Move the INPUTS to the back panel, maybe, depending on lead length?
SS recifier means you need to ALSO install the time delay board. And maybe for long-term non-adjustment? Go with the AutoBias board, too......
Yes, the KT88 is a sweet-spot in all of tubedom. Input board choice is Less Obvious, but needs only the 'middle' of 3 replaced.
Too much is never enough
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