On 22 Oct 2023, at 2:30 pm, Adrian Fewster <vk4tux@...> wrote:

?

The thing with LDMOS is to run the voltage a bit lower at higher current. This is way more thermally efficient.

Most of the first 50% rated current draw is wasted on heat, and the rest then adds to RF % as you raise current further?

with lower voltage for same power as higher voltage with less current (hotter).

On a single LDMOS SPE it can be run in low, up to 800w, much cooler than the same in Mid or Max power profile.

Also in Low the LDMOS will survive antenna/coax? failures swr events etc,? much better, than in Mid/Max.

Keep max temperature 50 deg C for a nice long device life. The SPE is an auto antenna switch and also via node-red?

can control the FTDX101MP drive. via node link out/link in ;

function node ;

"

This function node allows a user of this flow to define the drive
power for an exciter based on band and power level (low, middle
and high) much like the way the SPE controls the power level of
a FlexRadio via the CAT port.

The drive levels in the table below are fictional and provided to
test the flow itself. The values must be updated to reflect the
correct drive level for your exciter and amplifier combination.

The "link out" node that follows this node in the flow must be
coupled to a "link in" node in your radio's flow.

*/

var mode = msg.payload.col3
var band = msg.payload.col7;
var pwr_level = msg.payload.col10;
var drive_pwr=0;
var slmh_index;
var slmh_string="SLMH";

/*
The drive power table is unit-agnostic and must be configured for
the units expected by your exciter (e.g., watts, percentage,
fractional value, etc.)

Sample drive power table is configured for:
??? Standby drive power: 100
??? Drive power for???? Low power setting: 1 (all bands)
??? Drive power for? Middle power setting: 2 (all bands)
??? Drive power for Maximum power setting: 3 (all bands)
*/

"
var drive_pwr_table = [

//??? Standby?? Low??? Middle? High
??? [? 5?? ,?? 5? ,?? 12?? ,?? 12],? //160M
??? [? 5?? ,?? 5? ,?? 12?? ,?? 12],? //80M
??? [? 5?? ,?? 5? ,?? 12?? ,?? 12],? //60M (US 5W PEP ERP Max)
??? [? 5?? ,?? 5? ,?? 12?? ,?? 12],? //40M
??? [? 5?? ,?? 5? ,?? 12?? ,?? 12],? //30M (US 200W PEP Max)
??? [? 5?? ,?? 5? ,?? 12?? ,?? 12],? //20M
??? [? 5?? ,?? 5? ,?? 12?? ,?? 12],? //17M
??? [? 5?? ,?? 6? ,?? 12?? ,?? 12],? //15M
??? [? 5?? ,?? 5? ,?? 12?? ,?? 12],? //12M
??? [? 5?? ,?? 5? ,?? 12?? ,?? 12],? //10M
??? [? 5?? ,?? 5? ,?? 14?? ,?? 12],? // 6M
??? [? 5?? ,?? 5? ,?? 12?? ,?? 12],? // 4M
];

/*Note regarding parseInt:
The value to parse. If this argument is not a string, then it is
converted to one using the ToString abstract operation.
*/

band_index = parseInt(band,10);

switch (mode) {
??? case "S":
??????? slmh_index = slmh_string.indexOf("S");
??????? break;
??? case "O":
??????? slmh_index = slmh_string.indexOf(pwr_level);
??????? break;
??? default:
??????? slmh_index = -1;? //infaclid mode returned, flag for zero power
??????? break;
}


if (slmh_index >= 0) {
??? drive_pwr = drive_pwr_table[band_index][slmh_index];
??? }
else {
??? drive_pwr = 0;
??? }

msg.payload = drive_pwr;

return msg;

SPE

<HjQZttX3uTJtL460.png>

FTDX101MP (hamlib flow with rigctld server)

<0BLV09EvuVe03l1z.png>

<jKa0HKh80wIGWwyl.png>

<9mQvCI2bQMe6s24r.png>

73

vk4tux

Run at 1/3 rated power.

On 22/10/23 15:41, John Sparkes via groups.io wrote:

Thanks very much, Adrian !

I have one of those new-fangled SS amps - a 2.5kW PEP out unit from Onder at VK-AMPS. Very nice on CW and SSB, but it doesn’t have the ability to run decent power out on digital modes, so I stick with my DX-2SP for that.

Perhaps I need to by a couple more and combine the output, broadcast style !

Cheers and thanks again,

John VK6JX?

On 21 Oct 2023, at 12:24 pm, Adrian Fewster <vk4tux@...> wrote:

?

Some good material here ;

73

vk4tux

On 21/10/23 14:19, Adrian Fewster via groups.io wrote:

On Thu, Oct 19, 2023 at 08:12 PM, John Sparkes wrote:

Thanks gents - the below was awesome. If you have any other scientific papers/references on tubes, please post the links.

Many thanks.

John VK6JX?

Glad to help with the post John. Tube amps are a dying breed in VK, with solid state taking over, as pricing and devices improve.
It is good to save all the tube amp info one can find.

73

vk4tux

?

On 20 Oct 2023, at 6:45 am, Adrian Fewster <vk4tux@...> wrote:

?On Mon, Oct 16, 2023 at 10:01 AM, Alan - W5ARM wrote:

If anything will kill an 8877 tube, it's LOW filament voltage.? An under-temp/cold cathode will cause striping of the coating off the cathode, dramatically shortening its life

This is not true, 'strip off' of the cathode coating is caused by cathode overdrive. Low 'heater' voltage in the oxide indirectly heated cathode increases cathode poisoning.

also see ;

Oxide Cathode Life: Investigations into the Causes of Loss of Emission

A paper* read recently at the Institution of Electrical Engineers described the results of work by the Electronics Division of the Post Office Research Station (with its associated small valve factory) on the development of long-lived valves. The Post Office is interested in such valves mainly because of the need for them in submarine repeaters and other inaccessible apparatus; but their development is of considerable moment to others as well.

Apart from structural failures, with which the paper was not concerned, the life of a valve depends mainly upon the rate at which the emitting qualities of its cathode deteriorate with use. Loss of emission is the disease; if its causes are completely understood, we are more than half-way on the road towards finding a cure. There are two main accepted causes of oxide cathode deterioration: poisoning by attacks from residual gases, and the development and growth of inter-face resistance; on both of these the paper throws much new light.

Interface resistance was the subject of a recent article in?Wireless World.** The authors of the paper agree with Eaglesfield in accepting Eisenstein’s view that interface resistance is due to the growth of a film between the cathode body and the oxide matrix, and that its production is due to deliberately introduced impurities, chiefly silicon.

They find, though, that the film does not increase in thickness as the valve ages. It appears to build rapidly up to its maximum thickness, after which a steady change in its nature sets in; it is to this change that the increase in resistance is due. They consider that it is caused, in part at any rate, by deactivation of the interface by gas poisoning, much as the matrix itself is deactivated; hence the complete elimination of residual gas would be likely to check the growth of interface resistance, in addition to ensuring longer life for the emitting surface of the cathode.

A method has been developed of making a triode or pentode measure its own residual gas pressure. As electrons flow from cathode to anode some collide with gas molecules. The positive ions, so formed, travel to the negatively biased control-grid and set up reverse grid current ?rg, from which the residual pressure can be derived. It has, however, been found more convenient to use a “vacuum factor”:

?rg?(??A)
k?= ————
?a?(mA)

Investigation of the behaviour of the residual gas under working conditions showed that when?k?was plotted against time there was always a sharp initial rise, followed by a slow, roughly exponential fall until a value?k0?(the “residual vacuum factor”) was reached; the value of?k0?is constant. The area enclosed by the?k=f(t) and?k0?curves is a measure of the residual gas driven into the cathode and has been named the “gas integral.” It was found that valves with a high gas-integral were short-lived and that a low gas integral was an indication that long life might be expected.

Here, then, was one method of forecasting valve life after a test of comparatively brief duration; reliable tests of this kind are clearly needed for dealing with valves whose working lives may range up to 60,000 hours—say seven years of continuous running! Another of great value that has been evolved is the low-temperature total-emission test. Under working conditions emission is limited by the space charge; to measure the total emission there must be no such limiting factor. It is also desirable that the cathode temperature should be low enough for ionic equilibrium to be maintained within it. The method developed is to use the control grid as collector, making its potential +5V and earthing the other electrodes; for 6.3-V valves the heater is at about 2.6V.

In practice, valves are taken from the life-test rack, where they are running under working condition, and put through the total-emission test. The total emission, after a given number of working hours, can thus be plotted as a percentage of its original value.

The authors have no doubt that the amount of barium used for gettering the average valve is amply sufficient to absorb all residual gas if (and that is one of the big problems) physical association of gas and getter can be established. They have given much attention to the preparation of electrodes and supports and to pumping, gettering and ageing valves. It has been found that when residual gas is reduced (by methods suited so far to the laboratory rather than to the mass-production factory) to amounts far smaller than those in commercial valves, no deterioration in the emission occurs after thousands of hours of use. The authors’ estimates are always conservative; they see no reason why valves, with assured lives of 40,000 hours or more, should not be produced.

Poisoning of the cathode by occluded gases released from metal parts produces non-emitting patches on the surface of the cathode, which may be small and evenly distributed, or large and irregular. The authors in their investigations have found a new and unexpected source of cathode-poisoning gas. “A gas derived either directly or indirectly from the heated glass envelope,” they state, “is more destructive in action than any of the normal gas so far examined.” This gas is believed to be water vapour, which has been shown to have dire effects on a cathode at 1,000? K.

A second possibility is that the water vapour reacts with metallic carbides in the valve to produce unsaturated hydrocarbons of the acetylene type, which dissociate to form non-emitting carbon patches on the cathode.

R. W. H.
WIRELESS WORLD FEBRUARY 1952

* “The Life of Oxide Cathodes in Modern Receiving Valves.” G. H. Metson, S. Wagener, M. F. Holmes
and M. R. Child.
** “Valve Cathode Life.” C, C. Eaglesfield.?Wireless World, December, 1951

"? src >?

73

vk4tux

On Thursday, October 19, 2023, 3:02 PM, Adrian Fewster <vk4tux@...> wrote:

On 20/10/23 04:37, Dave w6de wrote:

In this article Richard Measures AG6K (SK) suggested using a smaller wire to feed the 3-500Z tube to knock down the filament voltage.

?.. was one of a few methods, and with measurement being a priority ;

"FILAMENT VOLTAGE
The filament-voltage, measured at the sockets, in my stock TL-922 was approx. 5.31v RMS @120V/240V line input.[2] This voltage exceeds the manufacturer's maximum allowable filament-voltage for the 3-500Z.
The filament-voltage of low-operating-time 3-500Zs can be lowered to approx. 4.8v for much longer tube life with no reduction in RF power output. This approx. 9% decrease may not sound like much, but according to one 3-500Z manufacturer, Eimac?, every 3% decrease in thoriated-tungsten filament-voltage doubles the useful emission life of the cathode, provided that the filament-voltage is kept slightly above the level that causes a decrease in output power. A 9% decrease in filament-voltage can increase the useful emission life by 2-cubed or 8-times. In other words, one pair of tubes will last as long as 8 pairs of tubes.
Reducing filament voltage to achieve maximum power-grid tube life is a considered to be good engineering practice in commercial transmitters.
The filament-voltage can be lowered to the desired level by connecting (2) approx. 16milli-Ohm, 5W resistors in series with the filament-leads on the filament-transformer. An easier way to lower the filament-voltage is to replace the #14 wires from the filament-transformer to the filament- choke with #22 high temperature insulated hook-up wire. Each wire will dissipate about 4W [14.7A rms X .25v] over its approx. 40cm length.[3] This raises the wire temperature only slightly to the touch. The new wires can be loosely attached to the cable harness, but they should not be buried in the cable harness; they need to breathe. Although 200 degree C Teflon? insulation would be nice, 105 degree C vinyl insulation is satisfactory.
Because of regional variation in line-voltage /electric-mains voltage, the actual filament-voltage should be measured, before and after modification, at the sockets, with the amplifier upsidedown and the bottom cover removed.
To perform this measurement, the amplifier is switched on and the standby/operate switch is set to standby.
If a mains-voltage of 108V/216V is used with a TL-922 whose filament-transformer taps are set for 120V/240V, the filament-voltage probably does not need to be lowered.
Caution: Bodily contact with the 120V/240V primary circuits, the +2000V / 3200V, or the +110V power-supplies can be fatal. The built-in "safety interlocks" do NOT protect the operator from all of these dangerous voltages - even if the amplifier is switched off. To be foolproof, the amplifier must be disconnected from the electric-mains. "

73

vk4tux

?

Dear Mike,

?

Some years ago on the Amps @ Cont…Com

forum, mention was made on methods of

limiting thew inrush current to transmitting

tubes and I believe to remember someone

suggesting to run a lighter diameter piece

of wire in the filament circuit to limit the

颈苍谤耻蝉丑….

?

Hal Mandel

W4HBM

?

Dear Mike,

?

Some years ago on the Amps @ Cont…Com

forum, mention was made on methods of

limiting thew inrush current to transmitting

tubes and I believe to remember someone

suggesting to run a lighter diameter piece

of wire in the filament circuit to limit the

颈苍谤耻蝉丑….

?

Hal Mandel

W4HBM

Recently looking at a FL2100B that I wanted to switch over to run on 240 instead of 120. ?Going to the manual tor switching the line voltage you’ll notice that a range of input voltages are offered even 100 and 200 volts as would be needed in Japan. ?For the US the offerings “listed” in the manual/ schematic ?are 110-117-220. ?Being an older vintage amplifier we no longer have 110-117-220 voltages! ?The nominal voltage these days are 120-240 across the country. ?Other only offering even close would be 117 and?220. ?Well the 117 wouldn’t be too bad for the nominal 120v, however, ?220 is way too little to put 240 volts on to. ?We have all probably done it as it appears to be the only offering for the higher voltage. ?UPON CLOSER INSPECTION of the schematic you’ll notice the transformer is a dual primary winding ?off the same taps ?both leading up to 117v each. ?Have a look. ?They do not offer?the selection to strap the primary for dual 117v winds allowing for 234v total. ?That would be way better to put 240 on 234 that on 220. ?So recently I did just that. ?I strapped it for 234v as it?would be. ?The HV is much closer to what it should be and the filament voltage would be better also. ?Does anyone have an idea why they didn’t offer that? ?Only thing I can think of is they were unaware exactly how our voltage was back in the day. ?Ideas from anyone? ?Lou

Sent from the all new AOL app for iOS

On Wednesday, October 18, 2023, 11:02 PM, Jim VE7RF <jim.thom@...> wrote:

I would not recommend? using a BIG? 240 vac variac to run the entire amplifier.? You will end up with poorer V regulation.? ?The peak current on the 240 line, every 8.3 msecs will make you gag.? W8JI measured 60 amps every 8.3 msecs on an AL-1500 running 1.5 kw? CCS? CXR.? ?However, I have seen? BIG variacs used on 1-2 kw output amps.? But they gotta be big, in order to not get sag on peaks.?

?

I have seen? constant V xfmrs? (Sola and other brands)? that were as high as 10-50 kva.? ?To run just the 5V @ 10 amp fil on the 8877, a small, OUTBOARD? 125 va? ?sola could be used.?

?

The alpha 9500? only has taps for 220 vac...and also 240 vac.? ?They say not to use > 250 vac.? Below is from their manual.

"High: >250 V Lifetime of the tubes may be reduced. Ask your utility company if they can reduce your line voltage. If this is not possible, consider placing your own step-down transformer in line between the AC outlet and the amplifier. A transformer with at least 4-kVA rating is required, due to the nature of the current waveform in the primary. Another choice for voltage control, a ferro resonant voltage regulator, is an expensive solution, but is a good way to stabilize primary voltage."

250 vac is probably not going to damage anything.... except for perhaps the higher than normal fil V.? ?Sure, the B+ will be on the high side of normal, but that's really a non issue.?

Myself, I would be inclined to use a 5 vdc outboard supply..... and modify the rear apron, to? feed the external 5 vdc into the amp.? But that's just me.? ? I doubt you will get anywhere with the local power company.....you might, would not hurt to ask.?

?

Another possible option (instead of using an external 4 kva rated 250 to 240 xfmr)..... is to use a buck - boost xfmr.....in buck mode.? ? IE:? 240-250 vac primary, and a 10 vac (@ 50 amp)? secondary.? ?The 10 vac sec is wired in? series with one leg of the incoming 250 vac.? ?Then you end up with 240 vac? going into the amplifier.? This method has been used before with excellent results.? BUT,? you have to know when to use it, and when to remove it from the line.?

IE: keep track of seasonal? ?incoming V changes.?

?

I know several folks? who have 253 vac....and in some cases, even a bit higher..... in summertime.? ? (? AZ, Ga? etc).?

Jim? VE7RF

?

On Tue, Oct 17, 2023 at 05:52 PM, W7WRX wrote:

<This whole thing comes up from time to time. Meanwhile this is a completely useless thing to try in a ham radio setting. This information was Intended for broadcast use where they try to stretch life out of the tube. No ham is ever going to <benefit in any way.

## For directly heated, thoriated tungsten tubes like? expensive 3CX-3000 / 6000 / 10,000? triodes, or 4CX-5000 / 10,000 / 15,000? tetrodes,? ?I'm 90% convinced that the grid to cathode shorts are caused by the high inrush current, when no form of step start is used.? Measure the peak current when T=0. You will gag.? ?The fil xfmrs that Henry Radio used are Z limited, such that the max inrush current is no? more than double the tube's rated current....(which is still too much imo).? ?Everybody else's fil xfmr are capable of a lot more than that.? The problem gets worse when the fil xfmr used has a higher current rating than required.? ?Larry,? W7IUV? used a 5 vac @ 30 amp fil xfmr on a single 4-400? amp.? With no inrush protection, that resulted in numerous grid to cathode shorts.? ?

?

##? Scott,? KB1SEL? modified a 5.0 vdc @ 200 amp? CCS? server supply, so it outputs 6.3 vdc? @ 160 amps.? ?He's been using that on his 4x15 tube for the last 20 years.?

?

##? In the OP's? case, if no room for a 5.0 vdc regulated supply, the? 75 ohm @ 5-10 watt? resistor in one leg of the 240 vac primary will work (or a 0-100 ohm, 25 watt rheostat).? That will not only reduce the fil V on his 8877 to an acceptable level, it will also? provide for step start, and eliminate any inrush. The beauty is.... the resistor stays in the primary at all times.?

?

## Some broadcast PA's have used a rheostat in the fil pri..... instead of a variac.? ?The rheostat, once dialed in correctly, provided for the correct heater / fil voltage...and also provided for step start / current limiting on turn on.?

Broadcasting is different in that the PA is run 24/7/365? and down for periodic maintenance.??

?

##? IF a variac is used on the bigger, directly heated tubes, it still needs the step start circuit / resistor / relay.? Variac is set, then left alone.? Plan B is what I do, and just dial the variac up each night to desired voltage.? Then the fil current rises slowly from zero? to normal current. ( I have fil V panel meters, and also? a set of jacks for the fluke 87..and also a fil current panel meter.? Fil current meters uses an external 75:1? or? 100:1? xfmr.?

?

##? At the cost of these tubes,? I'm not about to be using fil V that's? too high / too low, nor slamming on a ton of inrush current each night.?

?

##? between my incoming? 234? vac sagging 8-9 vac on? TX.....and not knowing what it is from hr to hr, or day to day,? ?I had to go the sola route.? On the small? Drake L4B amps,? it's a non issue.? The drake amps get the entire B+? and fil xfmr step started with a 20 ohm resistor in one leg of the mains....that's it.? Done externally.? And the step start relay is manually activated.?

?

##? I used a pair of DPST-30 amp relays in a 8x8x4 box...on the floor.? 1st relay applies the 240 vac.? ?Pole #1 of the 2nd relay? shunts the 20 ohm resistor.? ?Pole #2 of 2nd relay? is wired to a pair of RCA jacks...with keyline run in /out? of them.?

A small control cable is run from the 8x8x4 electrical box (with loads of knock outs, home depot)....? to a small mini box on the desk.? Mini box has 2 x mini toggle switches. Toggle #1 turns on relay #1.? ?Toggle #2? turns on relay #2.? ?Amp can not be keyed until? relay #2 is activated. Dead simple mech interlock.? Normal deal is to activate toggle? #1..... then a few secs later, activate toggle? #2.? B+ comes up to 90%..and fils of? 3-500Z's come up to 70% of normal brilliance with the 20 ohms inline.

##? When done for the night,? reverse? sequence is used.? With the 20 ohms back inline, prior to shut down, it kills the back emf 100%.? ? Due to the high C filter caps I used,? I also put the resistor back inline, when switching from CW? (1900 vdc)? to? SSB? (2650 vdc).?

I cant afford a tube failure.? ?As is, the On / OFF? switch on one of my drake amps is fried.? Below the rocker is just a cheap 10 amp rated on / off slide switch.

?

Jim? ?VE7RF

?

?

I have an Alpha 9500 and I find it difficult to get 1500 Watts out of the current Thompson 8877--age unknown.
The symptom is: I can easily get 1,000 to 1,100 Watts out of the amplifier but continuing to increase the drive level (to get power above 1.3KW) power output does not continue its somewhat linear increase in power output.?
I reach a level where I am concerned about increasing the drive because I don't see increase in output power.? And the grid current is reaching 90 Milliamps where I stop trying.

There is 3,200 Volts on the Plate and the plate current won't increase above ≈ 0.7 amps without exceeding grid current limits. Running class AB2 a linear is about 60% efficiency I should be getting about 1,344 Watts and I'm seeing 1370 Watts on the built-in power meter which matches my Bird power meter pretty closely.? But When I try to increase the drive, the amplifier will momentarily indicate 1500 watts but immediately drop back to 1300 watts.
All testing into a large surplus 50 Ohm dummy load.

Side Note: the Alpha 9500 has automatic tuning of the plate/output circuit.? I leave it on as I do several band and mode changes during an operating session.? And I and use a Steppir antenna and the Steppir doesn't always go to the same resonant frequency as I change bands and modes within those bands. However, that automatic plate circuit tuning goes nuts when I try to push the power to 1500 Watts.? Automatic tuning doesn't like to go above 1100 to 1200 watts (depends on the band) and stay still.

Any thoughts?? I do have a supposed NOS 8877 in the original Eimac box.? I just want to know if this is what to expect from an aging Thompson 8877 or any aging 8877.

73,
Dave, w6de