New Tung Sol- KT's

[pbman1953]

Has anyone used or looked into the newer Tung Sol Kt 120 or 150?

I was wondering if they would be ok to use in my Sunn 2000s or Sunn (Fender) 300t

Thanks

[ernie_jr]

I have already check with TRIODE electonics, the P/T's in the sunn 200s and 2000s will support KT 120's. Also, if you go with a solid state rectifier, that will ease the overall load on the P/T.
I have a pair of KT 120's on order for my 200s.
Ernie

[pbman1953]

Thanks for then info,

I was written that the bias resistor on the 2000s may have to be changed. This amp already has resistors installed to make it  SS. This forum helped me with that :), thanks !

Sounded like very good advise-

"I would suspect that the extra heater current of the KT120 may cause the power transformer to run too hot. With four KT120s it is a draw of 1.2 amps higher than it would usually see. The bias circuit could be modified by increasing the value of the 18K resistor next to the bias control if there is not enough bias range. The only way to find out if the amplifier can use KT120 tubes is to try the tubes in the amplifier and see if the power transformer runs too hot. This is something a good amp tech should be able to determine"

[pbman1953]

Thanks  for the help

[ernie_jr]

although the 120's and 150's are capable of producing more power, this only happens in an amp built for them. when used in a Sunn, there will be very little increase in power. they will last alot longer. so, if you take a sunn 2000s and put in 2 kt 120 instead of 4 kt 88's you will only make about 1/2 the power, plus you will have a mismatch on the O/P impedance since the O/P was designed for 4 tubes (ie around 2000 ohm) where 2 tubes prefer around 4300 ohm that sunn used on there 200s.
ernie

[pbman1953]

The 200s is a 60 watt amp, what do you think the out come would be with 120's or 150's?

[Ed_Chambley]

The Sunn 200s with KT88-KT120, will produce the same output is you make no other changes.  If you take load from the transformer via SS rectification you will get s slight increase in wattage.  I am getting 80mwatts from a pair if KT88's which is fairly normal if they are pushed.  The guy that makes Redplate amps uses KT88 in one of his models.  I had the opportunity to see the inside and get voltages.  He uses the same PT as on the attached schematic

With the KT120 with fixed bias, you will need a minimum of -80vdc, -90vdc is even better at the tube.  These tubes really are not the same as KT88's.  Since there is really not much info on the tube most have been treating it like KT88 and they work well this way and simply last a long time.  I have had the bias as high a 60ma per tube with no red plating and still fairly quiet.  You many bat a little more from them this way, but at the expense of the tube.  I am running them at around -42ma.

I did try an experiment with 2 tubes and a old Thordarson PT, 490-0-490, 300ma, 5vac 4A, 6.3vac 5A.  This thing is a beast.  I ended up with 655 on the plates, but I had to change the bias circuit to get lower as they red plated immediately.  Since there is really no audible difference in 70 or 82 watts, I was looking to see if I could get a little more for the 5 string bass.  Not enough difference to be replacing tubes all them time.

PRR posted that I should consider simply adding 2 more tube or even total of 6 saying if one died during a gig, you would hardly notice.

I believe the KT120 was designed to replace all the KT88's that simply will not hold up.  Not sure about the KT150, but I am betting it is simply a gimmick since there is really not an amp designed to use the tube in the way they say it can be used.  There are no standard filter caps, so you will need to series at the very lease the first 2 nodes in their C-L-C.  I put them all in series to double voltages, but that is because Sluckey mentioned he would as well, so I consider is a good safety measure.

You will already have 2 holes for 2 extra tubes when you do SS recification and series axial caps inside the chassis.  Stick 2 parallel octals and get an OT with the proper reflected impedance or simply use a multitap and use the proper secondary leads to get the proper impedance on the output.

Since plate dissipation is not output wattage, we really do not know what these tubes are capable of.  There is no track record except for the people trying them.

I ordered some KT150's for 2 reasons.  First is they look cool and I have some HI-FI they would look cool in.  The other reason is I want to see if the are more like old KT88.

[SoundmasterG]

Here is a link to people talking about them on another forum. you might get some info from that.

Greg

http://www.diytube.com/phpBB2/viewtopic.php?f=4&t=6074

[HotBluePlates]

although the 120's and 150's are capable of producing more power, this only happens in an amp built for them. when used in a Sunn, there will be very little increase in power. ...

The Sunn 200s with KT88-KT120, will produce the same output is you make no other changes. ...

Ernie & Ed are exactly right; tubes are only 1/3 of what determines output power in an amp. Here's the math behind what they are telling you:

The 200s and 2000s both have a B+ at/near 500v. You can find from the KT88 plate curves on a data sheet that in UL mode, they can only pull the plate down to around 30-40v. Let's assume the higher number, 40v. This leaves a peak voltage swing on one-half the primary of 500v - 40v = 460v, and that's 460v * 0.7071 = ~325v RMS.

The 200s is a 60 watt amp...

... 4300 ohm that sunn used on there 200s.

We figured the 500v B+ allows a maximum plate voltage swing on 1/2 the primary of 325v RMS. What is it really in the 200s?

The voltage on the 8Ω tap for 60w output is √(60w * 8Ω) = 21.91v RMS. The voltage on the primary is higher by the turns ratio of the transformer, which is the square-root of the impedance ratio: √(4300Ω/8Ω) = 23.184:1. So the voltage across the total primary is 21.91v RMS * 23.184 = ~508v RMS. That means there is 254v RMS across each half-primary, well within the capability of the KT88's with 500v B+ (meaning less than the 325v RMS we calculated earlier).

A double-check would be to see what plate current is implied by the pimay impedance and voltage swing for 60w: 508v RMS / 4300Ω = ~118mA RMS for the whole output stage. 118mA / 2 = 59mA RMS -> 59mA * 1.414 = 83mA and change peak. The tubes and PT can easily accommodate this, so the amp makes 60w with ease (I bet it will really measure well in excess of 60w by the onset of obvious distortion).

[HotBluePlates]

Now all of the above just looks like the formula for power and Ohm's Law, which is exactly what it is. This process assumes the tube is perfectly linear, so actual clean output power will be somewhat less than what the above process predicts. Alternatively, for a known amp with known parameters and output power, the actual plate voltage and current swings will need to be bigger to yield the stated output power.

If you designed from scratch without reference to a known-good amp plan, you'd have to make more reference to tube data sheets to verify the tube can do what you want.

So how does Sunn double output power when going from the 200s to the 2000s? B+ stays basically the same, so you know maximum possible plate voltage swing is unchanged. That means we have to double current swing.

You can't change current directly in any electrical circuit; you can only increase voltage or decrease resistance to cause a current increase. Sunn kept voltage the same (B+ is basically-same), so we know they must have reduced resistance. In fact, what they did was halve the OT primary impedance to allow double-current with the same plate voltage swing.

That double-current is probably more than the original output tube pair can handle, because it would have been uneconomical to run them at half-capacity in the 200s. So tubes were doubled to pass the double-current needed.

The PT needs to be able to supply double-current as well, so the high voltage winding in the 2000s would be up-rated to accommodate this as well.

Therefore, we see that without a major topology (or operating class) change, getting more output power with similar B+ voltage requires:
1. Half primary impedance to allow double-current with the given plate voltage swing.
2. Doubling of the same-tube type, or upgrading to a doubly-capable tube type.
3. Doubling of PT high voltage current capacity.

In other amps, there might be a slightly different path for increasing output power, but it will always come down to possible voltage swing due to B+, possible current swing due to OT primary impedance, possible current swing of output tubes, available current output of the PT.

If you made it this far, here's a visual to help remember:
You're a farmer and want to pump more water to irrigate your fields. Your system consists of a water reservoir (PT), pipes (OT primary impedance and tubes) and a pump (B+; plate voltage swing).

To get more water to the fields, you decide to install bigger pipes (either bigger tubes, more tubes, or lower OT primary impedance). But you don't get any more water to the field. Why?

You have bigger pipes to carry more gallons-per-minute, but your pump pushes the same gallons-per-minute it always did. So you get a bigger pump (more B+ voltage). More water, right?

Nope... Now you drain your reservoir faster, and simply don't have enough available water to pump at the higher rate.

So you need all the pieces to pump more water to the field, and more watts to the speaker.

[sluckey]

I wish you had used a better analogy, than pumping water, because the tubes are closer in application to pumps, than pipes, where as the wires are closer in function to pipes, (unfortunately, resistance to flow, in pipes, is a function of resistance squared), and not linear as suggested by Ohm's law.  

That seems to be a snide attempt to antagonize HBP. Please don't do that.

[HotBluePlates]

Items to consider
...

... what are the consequences of ...

If anyone else also has these questions, you'll need to ask them independently for a response.

[sluckey]

I did not mean to antagonize HPB.  I just stated a wish,

That snide remark was aimed directly at HBP. You know he wants nothing to do with you. LET IT BE.

[Willabe]

I think it was an excellent analogy.


           Brad     

[PRR]

> tubes are closer in application to pumps

Tubes are valves. Ask the english.

And while I know you have experience in pumps, I observe that most people have only a foggy notion of hydraulics. We need specific examples. I've learned more about fluid dynamics in a few years here in the woods (with a bog, ditch, culverts, ledges; also a well and pump and indoor plumbing; also a strangled hot-air furnace) than I did in decades of not really "needing" to think about these things.

> I think it was....

Anyway.... to extend HBP's thoughts to a "tubes are valves" thought....

Takes a long time to fill my bathtub. It has a 2-inch valve in the pump-pipe. I go to the industrial plumbing supply and get a 6-inch valve. Bathtub is still slow to fill.

From HBP's thoughts, I should look to the "power supply" (my well-pump) and my indoor plumbing. The inside plumbing (load resistance) is as direct as I can make it, but mostly 1/2". I know from city-water that this will flow with city water pressure, but when the tub is filling I don't get a lot of pressure from my pump (power supply). A half-horse pump 90 feet down can only flow so much at good pressure, then it sags.

You *can* have a system where the valve is the bottleneck. When I moved in I had a 3/4" valve off the tank which was 9/10 full of small stones. Working the stones out helped a lot. Going to a 1" valve helped very little. Mostly we can economically pick our valves to pass nearly the maximum flow of power supply and load resistance. Up-sizing to a KT-2000 valve won't make much difference. Except in the wallet.

One difference. Valves waste energy. Air and water valves are air or water cooled. They "never" get hot (ultra-high pressure liquid valves can). Electric valves don't have a way to dump heat back into the "fluid" they control. In that case an over-size valve "may" give better life. However with these KT jobs, the 2X rating comes with a 3X price so it is unlikely to save money.

[ernie_jr]

Getting back to PBMAN's original question. Yes you can use KT 120's in your SUNN 2000s. The P/T used has plenty of reserve. If you go with a  SS rectifier, it will give even more reserve. As for the output, it will be about the same, (slight increase if you use SS rectifier), but your tubes should last longer.
Ernie

[Ritchie200]

Once bitten, twice shy...

A lot of the new age manufacturers of KT88's will reference the old MO Valve spec sheets.  These old charts and graphs may be good references for general use and design.  However, VERY FEW will perform reliably north of about 550v on the plate - VERY FEW.  800vmax   If you could get into your TARDIS and go back to the 70's you might be able to find some.

Jim