I just read through the entire manual.??

On data modes, like FT-8, that amplifier HAS to be operated in the LOWER 1400 vdc? B+ position. And no? more than 1 kw dc input (aprx 500-650 watts PO).?

IE:? 1400 vdc @ .710 amps? (= 1 kw DC? INPUT).? ?I would suggest no more than 600-700 ma on FT-8.?

DO NOT run it in the SSB / 2100 vdc position.? ?You will just overheat the L5 toroid again.? ?L5 is used on 160-80-40m.?

I would use the manual tune (instead of the broadband tune).?

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Well, that's no surprise.

Don't run any more than 30% of maximum power in FT8 mode. That goes for radios and amplifiers.

Stick to that and you'll never have a problem.

73, Alek VK6APK.

That Alpha? 78 is interesting.? It appears to be an updated version of the older Alpha 374A.? ? Both had the option of either...'manual tune' ..... or? 'bandpass? mode'.? The...'bandpass mode' only works on the? Alpha? 78 on 80-40-20-15m. On 160m, and also 10m, it's manual tune only.? ?They used a 10 position bandswitch, which is NOT a progressive shorting type.?

Looking at the schematic, in 'bandpass mode', they used small variable TUNE? caps for 15-20-40-80m (padded on 80+40m)? that were pre-set for the middle of each band....(and internally adjustable).? ?Ditto with the LOAD cap setup.? On the load setup, there is relays in there to switch in (grnd the cold end) of small caps to add more load C? for lower end of each band.??

?

Here's the interesting part.? In 'bandpass mode', they use MORE inductance on the main tubing coil (L4)....and also the? toroid coil (L5).? ?It's a PI-L network....and on the L coil, they use the same coil taps,? regardless of manual tune or 'bandpass mode'.?

I always suspected this scheme, but never saw the schematic.? KM1H told me they used a series of L networks to broadband it....they don't.? It's just a mess of pre-tuned PI-L networks, one for 80-40-20-15m.?

The way they broadband it is.... by using MORE coil ( between the tune and load caps), they have lowered the tank Q by a huge amount.? That alone will broadband it by a huge amount, albeit, the harmonic suppression will suffer.? ?BUT being a PI-L to begin with, no big deal, since the typ PI-L already has way more harmonic suppression? ?vs a plane PI network.? ?End result is it's broad banded, and still has reasonable harmonic suppression.? The scheme was later? dumped by Alpha, since it did not meet the newer FCC 2nd + higher harmonic specs.? (which are now -44 dbc for 1.5 kw PO)...even though the Alpha 78 manual sez it has 50 db of harmonic suppression...go figure.?

The alpha 374A is similar, albeit it has no 160M.?

?

On these hb amps,? I use a plane jane PI net.....but with a lot lower loaded Q than normal.? More broad banded, more eff, less current in the tank coils and bandswitch...and harmonic suppression is not high on my list anyway, since the mono band ants are not resonant on their harmonics.? The 40m yagi, due to it's coil loading scheme, does not resonate on 21 mhz... ( it resonates on 24 mhz) .?

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Clark, u are correct. The 374A has 160m...the 374 does not have 160m.? And on all of em, 160+10m is strictly manual tune.?

Glen, AE0Q ( who used to work for alpha....(and still answers their tech email) tells me the... 'bandpass tuning' was dumped since it did not meet the new FCC? -44 db harmonic specs. ( even though the 87A / 374 et all manuals all say they have-50 db down for harmonics).? They also don't use a progressively shorting bandswitch either.? They all used a 10 position, single pole? switch, with positions 1 + 10 used for 160+10m.? ? Positions 2-9 ( remaining 8 x positions) are used for 'manual / bandpass? for 80-40-20-15m.? ( 2 positions per band, manual + bandpass).? ? ?That's when the 87A? etc, came out, with their motorized bandswitch, and motorized tune + load caps...and microprocessor.? Later..'alpha max' software was installed on the 87A...., which fine tweaked the caps for optimized output .? IE: say ur on 3502 khz....and ur swr is 2:1.? ??

?

All those pre-sets on the 87A / 9500 are into a DL.... not an ant, that may or may not look like 50 ohms and no reactance.?

?

For the OP,? USE the low B+ setting...(1400 vdc).... AND also use the 'bandpass' tuning option.? And no more than 500-600 watts out on FT-8 / data modes.? ?By using the 'bandpass'? setting (80-15m), the tank Q is WAY down, which will result in way LESS RF? current through the coils, toroid's and bandswitch...and both? C1 + C2 caps + loading padder caps.? To really optimize it on bandpass mode, he may well have to get in there, and tweak the C1+C2 caps for the FT-8 freqs on 80-40-20-15m .?

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On a side note, on these hb amps,? I design the PI net in software...but I also use a LOT lower loaded Q.? (I gave up on the PI-L...major pita.? The PI-L config uses a LOT more L1 coil between the caps...and a LOT smaller C1 + C2 caps.? That results in L1 coil values that are absurdly too big on lower bands.? It also results in impractical extremely low values of C1 on upper HF.? ?It also means the extra L2 coil, plus tapping the L2 coil...pita.? ?It also means much higher voltage across the C2 load cap, since it's then at a 200-400 ohm point.? It also means when using a lower loaded tank Q, the C1 + C2 values decrease even more...and the L1 coil increases even more).??

I have done a lot of experimenting over the years....(PI net) esp on hb amps that used a roller coil.? Like trying both the calculated L1 value for a 'normal' tank Q of 12.? (input Q of 10..and an output Q of 2)..... then progressively using MORE L1...( and progressively using LESS? C1 + C2) and the results always astound me.? With the lower Q? (amp re-tuned each time for max PO), the PO kept increasing.? Anode diss kept decreasing.? The amp is far more broad banded ( doesn't require constant re-tuning, esp on the lower bands), and way less heat in the tank coil.....and? way less current though both caps...and the tank coil (roller or bandswitched)..and roller contacts ( weak point in any roller)...and less current in bandswitch contacts.?

The tradeoff being... slightly less harmonic reduction.? IMO, that's a good trade off.? As noted before, monoband ants are not resonant on their even harmonics..... and even with a? lower tank? Q, harmonic suppression is still, greater? on the 3rd-4th-5th harmonics...vs 2nd harmonic.? And on loaded 40m yagis, mine does not resonate on 21 mhz ( it resonates on 24 mhz...and will screw up a nearby 12m ant).??

?

I recently experimented with the adjustable hb manually tuned input, and VARYING the tuned input Q.? ? ? Without any tuned input (or the un-un gong show they used in the henry 3/8 k ultra) harmonic? suppression is degraded.? ?Eff is reduced, and IMD increases a bunch...(and that's with a tube that already has a 50 ohm input Z).? ? ? With the PI? tuned input (and the typ low Q), amplifier harmonic suppression increases a bunch ( as Clark noted when he installed the new relay switched PI tuned inputs on his 8K).? ?Typ a low Q is used, so the tuned input is tweaked for the middle of each band...then left alone.?

With the new 0 - 4.4 uh roller coil (8 ga solid wire) and the pair of broadcast caps, I can vary the tuned input Q between extremes...on any band.? What I found was, it's a trade off.? With a? slightly higher tuned input Q, (more C1+C2..and less L)? everything improves, BUT on the lower bands, it's not broad enough to cover the entire band.... but almost.? ?Being manually tuned, it's a non issue.? ?IE: run into the shop to tweak the vac? tune+ load caps? from 3900 khz...down to 3504 khz ( using the handy dandy cheat sheets), it only takes a few more seconds to tweak the C1 + C2 broadcast caps on the manually tuned, tuned input. ( same cheat sheet. Cheat sheet divided up for each band, with 2 x columns... Vac C1+C2 caps...and tuned input? broadcast C1 +C2 caps.? ?Then everything done at 3 x freqs per band.? Bottom-middle-top.?

?

On the bandswitched, manually tuned, tuned inputs... they are configured for a slightly? higher tuned input Q.? Same deal, just tweak the C1/C2 broadcast caps? via cheat sheet.? ? Get the tuned input Q too high, and the resulting? current through the tapped? coil? /? roller contacts? /? bandswitch contacts becomes too great.....esp on upper HF....and esp when? more drive is used...like 500-700 watts on the bigger tubes.?

?

On these 50 ohm input 3CX-3000A7's....and also the 3CX-6000A7's,? I designed the tuned inputs with an overall network Q of ...'4'.? ?( input Q =2.? Output Q = 2).? This results in the best compromise.? ?The C1 + C2 values are tabulated below.?

160m -? 3600 pf
80m - 1800 pf
40m - 900 pf
20m - 450 pf
15m - 300 pf
10m - 225 pf.?

?

As you can see from above, the C1 + C2 values are a lot higher vs what you normally find in typ amplifiers.....with their fixed fixed values, tweaked for the middle of each band.?

?

I also put watt meters on both sides of the manually tuned, tuned inputs, and measured PI vs PO. (that came from John, K5PRO).? ?On my 3x3 amp, with it's manually tuned, tuned input, complete with bandswitched? 4 uh coil ( made from 17 turns of? 6 ga solid cu, with a 1.5" ID).? ?Pin = PO.... except on 15m.? On 15m, the Pin was 200 watts, but the PO was only 160 watts !? ?I had the Q too high on 15m..... and that 40 watts lost was dumped into the remaining 2 turns used on the 4 uh coil.? I could easily feel the heat on those last 2 x turns.? ?40 watts is a lotta watts for 2 turns of 6 ga wire.? ?My fix was to increase the inductance on 15m by re-tapping the coil? by just 1/4 turn. ..which then required slightly less C1 + C2.? ?PO increased to 195 watts on 21.225 mhz..... good enough.? ? It's not always easy to do exact coil taps.? IE: the? 1/4" wide interconnecting copper strap may have to go over the top of the coil (or beneath it) to get to the opposite side....( 9 o'clock)? ?A longer strap also has more XL...and also has to be factored into the equation, along with the total path through the bandswitch used. IE: from C1 to coil, then through the various taps, back to the bandswitch, then to C2 cap.? ? IE: bandswitch contacts face the coil at the .....3 o'clock? position. On upper HF, each turn is a lot of XL, so fractional turns are used, like top of coil...and bottom of coil? ?(12 o'clock and 6 o'clock).

So I use a lower Q on the multi? KW? output PI network, but a? slightly high Q on the tuned input.? Then u get ur cake ...and eat it too.? Good imd, flat input swr across each band, excellent harmonic reduction,? easily handles up to 1 kw CCS CXR of drive.?

I wasn't about to attempt to construct 6-9 fixed? fixed tuned inputs, and either bandswitched or relay switched, that would handle 500-800 watts? CCS of drive.? ?Ok, that's my sob story for this week.?

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Pi-L is great.

Not only the capacitors become smaller in size also the coils and band switch can be made much smaller with that far lower current through them.

?

73

Peter

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-----Original-Nachricht-----

Betreff: Re: [ham-amplifiers] High Temperature in Toroid of the PI-L network (Alpha 78)

Datum: 2024-03-07T20:03:28+0100

Von: "W7WRX" <clark@...>

An: "[email protected]" <[email protected]>

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<Pi-L is great.

<Not only the capacitors become smaller in size also the coils and band switch can be made much smaller with that far lower current through them.

?

<73

<Peter

## Not quite.? In software, or in Orr's books, on any PI-L,? BOTH the C1 and C2 caps are a lot lower value, BUT the main Coil ('L1')? is one helluva lot bigger in value. Coil has to be a lot bigger in value, since the C1 tune cap is a LOT smaller in value.? ? ?In the GM3SEK? PI / PI-L software, he uses a specific common? formulae to?arrive at the ...'image Z'.... that the PI-L initially transforms the plate load Z? down to....and is typ in the 200-400 ohm range.? Then the 200-400 ohms is transformed down to 50 ohms.? On the software? spreadsheet, the actual image Z can be manually changed to anything you want... like 100-1000 ohms.?

?

###? In both the ORR book? and GM3SEK software, the Q remains the same for both the PI and also PI-L.? Done that way, the harmonic suppression is substantially increased by using the PI-L config.? BUT the C1 + C2 values are much reduced? vs the PI ( using the same loaded tank Q)..and the main Coil (L1) is increased substantially.?

## here's the rub.? Use the PI-L config, then reduce the Q by a bunch, the C1 + C2 values? become even smaller still, BUT the main coil..L1, become even bigger in value...too big.? So you end up with a huge main coil value, but less current through it, and degraded harmonic suppression ( but still adequate), and you still have the 2nd coil (L2) to install, and tap the 2nd coil...pita.?

?

##? after running all of this several times through software, and actually testing it on the bench, I came to the conclusion, the PI-L was a wasted effort.? It's easy to test on the bench. PI or PI-L built on a spare sheet of aluminum, with a resistor on input side ( to simulate the tube's plate load Z)...and an analyzer plugged into output side.? Both caps are individually mapped out beforehand? for fractional turns on turns counter vs pf.? Calculated coil values are done via lcr meter, and taps done in the correct spots.? ?If a roller used, the fractional turns are 1st mapped out? vs turns counter.?

?

##? with tune + load caps tweaked for 1:1 swr, then compared to the mapping cheat sheet...they always come out dead on, or within? a few pf.?

?

Below is what the software spits out for PI, and also a PI-L? using 2 x different loaded Q values.??

?

##? ?3x6 tube. 7 kv loaded @ 2.5 amps.? 1.8 mhz.? ?68% eff.? PO = 11.9 kw? ?Plate load Z = 1556 ohms.? ?400 uh plate choke used.

For the PI network only, the overall network Q = 12? ?( Input Q= 10.4 )? ( output Q = 1.6)? Note Overall network Q =? input Q + output Q.? In the older arrl books, and also EIMAC, they only used the INPUT Q...and a value of 10 was common.? These days, they use total network Q...and use a value of? 12.? ?In software, only the overall network Q can be changed (but the input + output Q values are also spat out lower down in the results.?

##? FOR the PI-L config only, the overall Input Q is?also 12. (? PI network portion input Q = 9.9).? Input Q1 = 7.0? Output Q2 = 2.8? L network QL = 2.1?

.............................................................................................................................................................................................................................................................................................................................................................................................

PI config.? Overall network Q of 12? 1.8 mhz.?
C1 = 563.4? pf
L1 = 15.1 uh?
C2 = 2815.7 pf?

?

PI-L config? Same overall network Q of 12? 1.8 mhz.?

C1 =? 370 pf
L1 = 26.78 uh
C2 = 1581.8 pf
L2 =? 9.44 uh?

.................................................................................................................................................................................................................................................................................................................................................................................................

OK, now let's reduce the overall network Q down to 9.?

PI config. Overall network Q of 9.

C1= 423.4 pf
L1 =? 19.12 uh
C2 = 1839.0 pf

?

PI-L config. Overall? network Q of 9

C1 =? 252.0? pf
L1 =? 36.6 uh?
C2 =? 1283.5 uh
L2 =? 9.44 uh?

?

Ok, notice a few things here.
On the PI-L config, the L2 value remains the SAME, at 9.44 uh, whether the higher OR lower overall network Q is used.?
On the PI-L config, with the higher Q, the L1 coil value is insanely high. (26.78 uh)
On the PI-L config, with the LOWER Q, the L1 coil is now into the stratosphere. (36.6 uh).
OK, now you know why (failure prone) TORRIDS are typ used on the main coil? ( and also on the L2 coil on an alpha 77)

You folks have any idea how big the 1/4" tubing coil for the 160m portion of the tank circuit has to be? when? sky high values of L1 are used ???? ?Hint, it's just not happening.?

?

On Scotts latest 160-15m amp, I used a simple PI, and used an overall network Q of just 9.....on all bands.? ( see the PI config with the lower Q).
PI config. Overall network Q of 9.

C1= 423.4 pf
L1 =? 19.12 uh
C2 = 1839.0 pf

Done that way, his ceramic? 12-500 pf (@ 15 kv rated) vac tune cap will easily suffice for the C1 tune cap. Actual vac cap measures 12-540 pf...and they are small things.? Calculated value required at 1.8 mhz = 423.4 pf. ( vs 563.4 pf if the higher Q is used).

L1 coil only has to be increased a bit.? ( from 15.1 uh to 19.2 uh)
His ceramic 50-3000 pf @ 5 kv vac load cap is ample? for the C2 cap with the lower Q config.? ( but marginal with the higher Q config....2815.7 pf required).?
Ok, then it's dead simple, and NO padders used for either the tune or load caps..... or? having to use even? bigger tune + load caps, like a 12- 750 pf tune...and a 50-4000 pf load.? ( note I have several 50-4000 pf vac caps, and they are small things.? But my 10-1000 pf @ 15 kv motorized vac caps are big....and ditto with my plane jane 17-1000 pf @ 15 kv Jennings ceramic vac cap).?

?

His tank circuit? consists of a total of 3 x tubing coils used.?
1/2" tubing used for the 20+15M coil (and also the small value uh used between the plate block cap assy and the C1 tune cap)
3/8" tubing used for the 80+40M coil.?
1/4"? tubing used for the 160M? coil.?

Of course, in normal operation the? required 19.12 uh for 160m consist of the total of all 3 x coils in series being used.? So the actual 1/4" tubing coil for 160m is a lot lower value than 19.12 uh? ( it's 10 uh)?
On 75m, the required 9.02 uh consist of the 1/2" tubing coil? plus the? 3/8" tubing coil in series.? ?Actual 3/8" tubing coil is just? 7.3 uh
On 20m, the required? coil is just 1.72 uh .? Since we incorporated the 'pre-coil' (.6 uh between block cap and C1 tune cap)? the actual value of the 1/2" tubing coil is now 1.72 + .6 = 2.32 uh. ( Scott just happened to have a mess of 2.32 uh 1/2" silver plated tubing coils in the junk box, used in henry RF generators, so we lucked out.? Only 2 x copper tubing coils had to be fabricated...( 10 uh, made from 1/4" tubing...and 7.3 uh, made from 3/8" tubing).??

?

NOTE, when a PI-L used, on the upper bands, like 20m-10m, you can't use the lower Q value,? even with the .6 uh pre-coil installed.? The C1 values end up negative pf.? The only fix is to increase the loaded Q a lot higher than 12.? This is the problem when using large metal tubes on upper HF..( with the 24.5 pf anode to grid C on a 3x6...which rises to 42 pf, when tube plugged into the grid ring. The extra 18 pf? comes from the proximity of the lower anode fins, to the chassis below em.? ? The PI-L values? ?don't work on upper HF...unless the Q is increased by a bunch.?

?

On the simple PI network? I designed in software, a loaded Q of 9 can be used...... including 15m. It's a 160-80-40-20-15m amp.? ?The .6uh pre-coil is used so the lower Q can be used on 15m.? ?The tube's 42 pf of anode to grid C plus the .6 uh coil, form a step down L network.? That steps down the 1556 ohms plate load Z....down to just 487 ohms on 21.225 mhz.? Ok, now a practical? PI network can be used, with reasonable values.?

Harmonic suppression is ample. On upper HF, with the extra pre-coil installed it's sometimes called a L-PI? (or a L-PI-L, if a PI-L used) .? Harmonic suppression on the lower bands is more than ample.
Per the VK expert, (Owen Duffy)? any tube already has 7 db of 2nd harmonic suppression in class A.... and close to that in class AB or B. (6db).? ?Then toss in the harmonic suppression of the PI network.? Then toss in the additional suppression from the PI tuned input circuit...and it's more than ample.??

W8JI sez he measured? 50 db of? 2nd harmonic suppression on an AL-1200? on 40m...(and even more on 3rd and 4th harmonics).? ?That amp uses a simple PI network on 40-10m.? JI sez the only reason they used a PI-L on 160+80m on that amp is so smaller tune and load caps could be used.? Trade off is, he still had to pad both the tune + load caps, and use a toroid on low bands.? Exact same, identical network used on the AL-1500 + AL-1200.?

A 26.78 uh / 36.6 uh total uh for 160m if either a higher Q / lower Q,? ?PI-L network on 160m, gimme a break, not happening.? Just look at how big that 10.0 uh (1/4")? tubing coil is in the u tube video (plus the other 2 x coils).? The RF deck would have to be double the size to even fit? the oversized coils in.?

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As already mentioned, the physical size of L and C is meant with smaller of course.

And a Q of 5-6 with Pi-L is sufficient where 9 with a simple Pi might not be sufficient for harmonic supression.

?

With Pi-L you don?t need 1/2" coil tubing and multiple band switch sections in parallel with a 3CX6K

?

73

Peter

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?

?

-----Original-Nachricht-----

Betreff: Re: [ham-amplifiers] High Temperature in Toroid of the PI-L network (Alpha 78)

Datum: 2024-03-08T18:56:21+0100

Von: "Jim VE7RF" <jim.thom@...>

An: "[email protected]" <[email protected]>

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And a Q of 5-6 with Pi-L is sufficient where 9 with a simple Pi might not be sufficient for harmonic suppression.

With Pi-L you don?t need 1/2" coil tubing and multiple band switch sections in parallel with a 3CX6K

?

73

Peter

##? Nice try....still does not work on 40-10m.?

On 40m, min overall network Q that can be used with a PI-L? is? 8? ? (This is all based on having the MIN C1 being at least 14 pf).?
On 30m, min Q is? 10
On 20m, min Q is? 12
On 17m, min Q is? 12
On 15m, min Q is? 12
On 12m, min Q is? 9
On 10m, min Q is? 16

?

Your concept will work on 160m, with the lowest Q being? 5.... albeit? 56.65 uh required....which is looney tunes.? That would require a? huge chunk of? 8/10 ga? airdux.?

Your concept will work on 80m, with the lowest Q being? 5....albeit? 27.35 uh required.?

Then u still have that stupid L coil that has to be bandswitched...which requires one extra wafer....and it needs to be 1/4"? tubing.?

The bigger tubing would still be required on 40 -10m.?

?

I can understand the concept, and tested it on the bench.? But the bench tests jive 100% with the software.? ?The problem is, the 3x6 tube has? 42 pf? (between anode to grid)...and the above calcs are also? using the extra .6 uh pre-coil installed too.? With that removed, it all gets much worse.?

I checked my old notes.... and years ago thought.....'why not use a PI-L, but with a lot lower Q'.? Nice try on my part, but it does not work with the 3x3 /10/15/20.? ?All those tubes have too much anode to grid C when installed in the socket.?

It works on the alpha table top amps.... (on 80-15m only) with the small tubes they used, which have very low anode to grid C.?

And that pre-coil trick only works? on tubes that do NOT require a parasitic suppressor.?

?

The best I can come up with? is the simple PI network, with the Q of 9 on all bands.? ?The tube already has 6 db of 2nd harmonic attenuation ..then toss in the? slightly higher tuned input Q, and? the output tank Q of 9,? trust me, harmonic suppression is more than adequate.? ?Then toss in the ants provide an additional 9-13 db of harmonic attenuation.?

On? SSB, the 2nd harmonic will be double the BW. ( 6 khz).? ?3rd is? 9 khz .? 4th is 12 khz.? ?Nobody can copy harmonics of ssb signals.? On 40m ssb, all the harmonics are not only? stretched, they are also on the wrong sideband.? If on any freq > 7175 khz, the 2nd harmonic is above 20m band.?

?Side note, copper tubing in? 1/4" - 3/8" - 1/2"? is cheap? in the plumbing section of Home depot? ( aisle 16).? Cheap to silver plate too...with the cool-amp goop.?

End of rant.?

?

Jim? VE7RF

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Sorry Jim,

?

I can?t follow your calculations and for what reason a Q of <8 should not be possible on 40m.

?

Lets assume a YC179 with 6kV on the anode and 2.75A anode current.

Tube output impedance will be 1.1kOhm at 10kW.

Pi-L intermediate impedance 200 ohms.

Coil currents will be about 15A.

?

Example for 160 and 40m at a Q of 6.

?

160m:

?

Ca 350pf, La 29?H, Cb 1500pf, Lb 7.65?H

?

40m:

?

Ca 90pf, La 7.5?H, Cb 380pf, Lb 1.97?H

?

3CX6000A7 has 12pf less output capacitance, at 6kV output impedance will be lower then 1.1kOhm as current will be higher and therefore La smaller , I guess a Q of 6 will be possible even on 20m with a Pi-L.

?

The whole tube family does not need a harmonic supressor.

?

Harmonics of SSB signals can be copied. Once I did the CQ 160m contest and were phoned by a ham 120km away, he found my signal in the 80m dx window.

?

Copper / copper tubing is very expensive nowadays here and silver plating does nothing on HF.

I get more then 7 Euros for 1kg scrap copper like LDF cable leftovers.?

?

73

Peter

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?

-----Original-Nachricht-----

Betreff: Re: [ham-amplifiers] High Temperature in Toroid of the PI-L network (Alpha 78)

Datum: 2024-03-09T21:33:32+0100

Von: "Jim VE7RF" <jim.thom@...>

An: "[email protected]" <[email protected]>

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?

?

Sorry Jim,

?

I can?t follow your calculations and for what reason a Q of <8 should not be possible on 40m.

?

Lets assume a YC179 with 6kV on the anode and 2.75A anode current.

Tube output impedance will be 1.1kOhm at 10kW.

Pi-L intermediate impedance 200 ohms.

Coil currents will be about 15A.

?

Example for 160 and 40m at a Q of 6.

?

160m:

?

Ca 350pf, La 29?H, Cb 1500pf, Lb 7.65?H

?

40m:

?

Ca 90pf, La 7.5?H, Cb 380pf, Lb 1.97?H

?

3CX6000A7 has 12pf less output capacitance, at 6kV output impedance will be lower then 1.1kOhm as current will be higher and therefore La smaller , I guess a Q of 6 will be possible even on 20m with a Pi-L.

?

The whole tube family does not need a harmonic suppressor.

?

Harmonics of SSB signals can be copied. Once I did the CQ 160m contest and were phoned by a ham 120km away, he found my signal in the 80m dx window.

?

Copper / copper tubing is very expensive nowadays here and silver plating does nothing on HF.

I get more then 7 Euros for 1kg scrap copper like LDF cable leftovers.?

?

73

Peter

##? I just? plugged ur? YC-179 numbers into the GM3SEK PI-L software.? ?The YC-179 has 35 pf anode to grid C... which rises to 52 pf with grid flange bolted to chassis. I also allowed for an extra 5 pf of stray C on top of the 52 pf..( so a total of 57 pf used).? ? ?I also used ur 6 kv loaded @ 2.75 amps...and also used? your? 200 ohm image Z....and also ur? 61% eff, and used 1840 khz for the design freq.? ?And also used a 400 uh plate choke.? And also used ur 1100 ohm plate load Z....and also ur 10 kw output.??

##? This is what it spits out...for a total network Q of 6.? ( Input Q = 3.2? Output? Q = 1.0? ?L network Q =? 1.7 )? ?Coil current in L1? should be input Q X plate current or 3.2 x 2.75 =? 8.8 amps.?
C1- 215.7 pf
L1 - 35.53 uh
C2 - 1198.2 pf
L2-? 7.49 uh?

?

The above is not even close to ur calcs.? (?Ca 350pf, La 29?H, Cb 1500pf, Lb 7.65?H )? ?What are u using for software ????

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Ok, let's try 40m (7150 khz)? and again using your numbers.?
C1-? 9.6 pf
L1 -? 9.14 uh
C2 -? 308.3 pf
L2 -? 1.93 uh?

Again, not even close to your numbers.? ? ?(?Ca 90pf, La 7.5?H, Cb 380pf, Lb 1.97?H? )? What are u using for making ur calcs ???????

A 1/4 wave shorted stub will kill all the even harmonics.... by 15-23 db.? Try listening to urself on a 2nd RX on the 2nd, 3rd, 4th harmonics..... while Tx'ing on SSB.? Say TX on LSB / USB on 7100, then listen on 14.200 and 21.300 and 28.400 mhz.?

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Flexible Copper tubing has risen a bit in price, but is still relatively cheap.? Typ comes in 10'- 15' - 25'- 50' rolls.? And in 1/8"? to? 1.125" OD sizes....and every size in between.??

I hate the look of bare copper,? which really looks bad after several years.? ?The silver plating is cheap, and is strictly an aesthetic? thing.?

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Hi Jim,

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I use the formulas by Eimac and also the PIEL software depending on what computer I use.

My values for the anode capacitors are the total values.

Any strays and tube capacitance etc. as well as inductor lead length are not taken into account.

I guess you deducted capacitances like that of the tube from your figures.

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The current through the coil of the pi part is indeed Q*Ia where you used 3.2 and not 6.

With a Q of 6 the current is 6*.2.75A= 16.5A.

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You also used different frequencies, I used 1.8 and 7MHz but that will not change much.

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I am operator at the M/M contest station DR1A so familiar with fighting harmonics.

But how many stubs will you connect to a multiband amplifier?

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A single stub will kill some harmonics but not sufficient enough, we use cacaded stubs made from LDF cable behind the mono band amplifiers.

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I measured a YC-179 bolted to the chassis.

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73

Peter

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?And this is copper after >40 years:

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-----Original-Nachricht-----

Betreff: Re: [ham-amplifiers] High Temperature in Toroid of the PI-L network (Alpha 78)

Datum: 2024-03-10T16:29:32+0100

Von: "Jim VE7RF" <jim.thom@...>

An: "[email protected]" <[email protected]>

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