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Calculating Grid dissipation revisted
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pentalab
Lemme get this straight
To calculate Grid diss..... we take RMS cathode V x DC grid current ??? If that's the case..... that equates to 1.2 KW of drive to a 3CX-6000A7..... to just max out the grid [rated at 225 W CCS]. On ssb..... I don't think it's a problem anyway. We tried it last night..... 1200 w of drive = 15 kw output... no sweat.... no fuss ..no muss.... and clean too. Amazing.. how the gain keeps going down,as drive increases. With 100 w of drive = 3 kw out. 200 w of drive = 5 kw out. 800 w of drive = 11.5 kw out. You just gotta love all these surplus vac caps, cheap copper tubing from home depot, surplus 7-16 Din's, surplus vac relay's etc. Those 253 lb Dahl's are a bargain..... they just keep pumping it out for hours on end.... they will put taps galore on em for you... freebie. The Dahl primary's are unique too.... they all come tapped now for 198-208-218 - 230-240-250v . The primary has to be built like a tank to run on 198 V [IF u had 198 line V]..... they are.... the primary taps coming out are all 1" wide buss bar !! With the 6 x secondary voltage taps.... and the 230-240-250 primary taps.... you can get 18 x different combo's right there with just a C input filter.... and another 18 x more with a choke input filter. They pump the plate xfmr full of silicone varnish glop, under high pressure.... then suck out the air bubbles in a vac chamber... then back to pressure.. then back to the vac...... then they get a baked in the oven for hours on end. The 253 lb hypersil is aprx 16" h x 16" w x 10.75" deep. For you QRO types... the next core up is 440 lbs.... 19" x 19" x 13" deep. You can buy 5 x of em for the price of just one new alpha. So get crackin........... later Jim VE7RF |
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craxd
--- In ham_amplifiers@..., "pentalab" <jim.thomson@...>
wrote: For the price they charge for the suckers, they out to gold plate them too! The Dahl primary's are unique too.... they all come tapped nowDon't be blinded by all the Dahl-Hipersil hoopla, there's a few other very good companies who make some gem dandy transformers, and for a way better price. I'll dig up a couple of address for you later today. One in Canada who makes the ones for Ten-Tec. There's one in Kentucky, that does a really good job, but I can't remember the name without looking it up. Another is Galaxy Transformer who makes some big ones for a builder down in Florida. If you get a chance, ask Hal Mandel about a dealing he has with Dahl on a custom transformer. It made me wonder who they had there designing them. If things work out, I'll be doing a few C-cores up to 3 kVA output (1. 5 kVA input) for a few friends. I just got an e-mail back from the core supplier today. The 253 lb hypersil is aprx 16" h x 16" w x 10.75" Best, Will |
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On Sep 26, 2006, at 11:25 AM, pentalab wrote:
Lemme get this straightRMS cathode-grid potential multiplied by - meter indicated - DC grid current is an okay approximation. The actual dissipation calculation involves integral calculus. Drive And degree of loading determine grid dissipation. Not so amazing for those who realize that Mu goes down as anode-I increases. With 100 w of drive = 3 kw out. 200 w of drive = 5 kw out.A Dahl 253-pounder is a serious waste of greenbacks for 15k out on SSB because one of his 68-pounders will do 15k out. As I see it, a 253-pounder is more than enough for a 8910/4cx15,000J. ... R L MEASURES, AG6K. 805-386-3734 r@... |
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pentalab
--- In ham_amplifiers@..., R L Measures <r@...> wrote:
I increases.Not so amazing for those who realize that Mu goes down as anode- ### agreed. ### Those 253 lb Dahl's are a bargain..... on SSB because one of his 68-pounders will do 15k out. As I see it, a 253-pounder is more than enough for a8910/4cx15,000J. ### I find that hard to believe !... but I may well be wrong. With 6800 Vdc @ 3A = 20.4 Kw dc input. Primary KVA = 20.4 x 1.22 = 24.88 Kva. ### A Dahl 253 lb'er has a 5200/5400 sec.... rated at just 3 A CCS. [ Sec = 16 KVA CCS.... primary = 17.6kva ] ### So we are running it on SSB at aprx 24.88 /17.6 = 1.41 or 41 % over it's rating.... on ssb. So far so good. ### Average plate current on SSB is about 1/2 that of the dead cxr condition. Average power output [not pep] is only aprx 1/5 th the pep output of the amp. ### Next step is... we will try and meausre the heat on the outer core with a Fluke 62 mini IR thermometer. Of course... the heat deep inside the core will always be way more. I have loads of air blown across it anyway.... and reg is not too bad. ### I'm convinced 2 ga wire from main panel to HV supply [and internal wiring] is not big enough ! Either 3 x 000 CU or just locating the HV supply next to the main 200 A panel would be the ticket... then longer runs of DC HV to the RF deck. ### What's a fairly precise way to measure peak AC current [under load] from the 200 A main panel ???? ### spending $7.5 K to $10 k on a new Alpha /Acom is an even greater waste of greenbacks imo. I put several L4B's nose to tail... on different bands! [the L4b's will handle 2kw on bypass.. with flat bypss swr]. Heck I could afford to blow 1/2 of em up... and still have a few left over. A pair of sb-220's would also work... just tune em up on diff bands...... plus u got a back up amp... if one blows up.... or u got one of em offline.. in the shop.. being modified. Jim VE7RF
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On Sep 26, 2006, at 1:49 PM, pentalab wrote:
--- In ham_amplifiers@..., R L Measures <r@...> wrote:SSB has a duty cycle of less than 20%, so it's quite different than RTTY.I increases.Not so amazing for those who realize that Mu goes down as anode- ... closer to 1/3 Average power output [not pep] is onlyResin potting helps dissipate heat from deep in the core. I have loads of air blown across it anyway.... andThe Plywood Box amplifier was 100' from the breaker box. It did 14k out pep and the wire was #4 Cu. Either 3 x 000 CU or just A 1-milliohm resistor in series with a calibrated oscilloscope to measure the V-drop across it. The Plywood Box drew so much peak current that the 240v wires could be heard vibrating in the attic when I used a 30pps pulser to tune the sucker up. Also, at night, the neighbor's porch-light blinked. Agreed, Jim, and the educational fun value is zero. I put several L4B's nose toR L MEASURES, AG6K. 805-386-3734 r@... |
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pentalab
--- In ham_amplifiers@..., R L Measures <r@...> wrote:
different than RTTY. ### Dream On.... unless you chopped all the audio off below 350 hz..... or the plate current meter ballistics are out to lunch. ### see above.### Average plate current on SSB is about 1/2 that of the... closer to 1/3 [and internal wiring] is not big enough !Average power output [not pep] is onlyResin potting helps dissipate heat from deep in the core. box. It did 14k out pep and the wire was #4 Cu. ### #4 is too puny...esp 100' away. Heck that amounts to a 200' loop !! 4 ga CU won't handle 400+ A on peaks... without a big v drop.... esp with 200' of loop resistance.... never mind ur small ga aluminium drop wires coming into the house.. on top of that. #### The next question is/was gonna be.... how was ur HV regulation... with a dead cxr ???? [static] and also on ssb [dynamic] ??? You can't even run a dead cxr.... with just your 40 A breaker. You need a bare minimum of a 100 A breaker. the neighbor's porch-light blinked.A 1-milliohm resistor in series with a calibrated oscilloscope to #### A 1 milliohm resistor... inserted in one leg of the 240 v line that will handle 400 + A is gonna be a trick. Since we know the exact length of the cable.... and it's exact dc resistance... perhaps measuring the V drop end to end will work?? .... or perhaps measuring the peak v across the 240v line.... using the peak max/min function on a fluke 87 [1 msec snap shots] .... or my scope might work... and trigger off the 'lows' in the acv ?? ### A fwb gives better reg than a doubler... for the same size caps. That 50 ohm glitch R we have in the B+ doesn't help matter's any.... I lose 150 vdc right there. Later..... Jim VE7RF |
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On Sep 26, 2006, at 5:02 PM, pentalab wrote:
--- In ham_amplifiers@..., R L Measures <r@...> wrote:During an ahhhhhhhh, I see about 1/3 of A0 anode current. If one transmits half the time, that's a duty-cycle of 1/6.different than RTTY. It's just a matter of execution.### see above.### Average plate current on SSB is about 1/2 that of the... closer to 1/3 Since weThat would work. With a C-filter, for every ampere indicated, expect 10 amperes peak. or perhaps measuring the peak v across the 240vSure, but with the required size caps for a FWD, the % regulation is pretty much the same. That 50 ohm glitch R we have in the B+ doesn't help... which is not noticeable at the Rx end. Originally, the Plywood Box amplifier stupidly had a 25w glitch resistor -- most definitely a blunderous mistake. Later..... Jim VE7RFR L MEASURES, AG6K. 805-386-3734 r@... |
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FRANCIS CARCIA
The best way to measure a transformer gut temp is measure the winding resistance cold then hot and determine the real temperature rise by the copper constant. I think it is about .4%/degreeC. wa1gfz
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R L Measures wrote:
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Bill Turner
ORIGINAL MESSAGE:
On Wed, 27 Sep 2006 00:02:51 -0000, "pentalab" <jim.thomson@...> wrote: ------------ REPLY FOLLOWS ------------RICH SEZ.. SSB has a duty cycle of less than 20%, so it's quitedifferent than RTTY. It really depends on one's manner of speaking and one's individual voice. Some people put relatively large pauses between words and othersrunthingsalltogetherwithnopausesatall. Bill, W6WRT a pauser |
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pentalab
--- In ham_amplifiers@..., R L Measures <r@...> wrote:
wrote: During an ahhhhhhhh, I see about 1/3 of A0 anode current. If onedifferent than RTTY. #### I'd call that 1/3.... NOT 1/6th. What if I give a 5 min disertation? or some contester calss 'cq' for 3 mins straight? ### The big kicker is gonna be CW. Dashes are gonna be at least 3 x as long as dots. I set my dashes so they are 3.6 x longer than dots.... send cw at 10-16 wpm.... and u are in for a big surprise....... duty cycle is WAY UP. RICH SEZ Resin potting helps dissipate heat from deep in the core. ### agreed. RICH SEZ ....That would work. With a C-filter, for every ampere indicated, expect 10 amperes peak. ### SAY WHAT ?? I used Duncan's pwr supply modeller.... and even though the dc resistance of the primary is only .08 ohm..... Z on primary... using their software is more like 68-70 ohms.... and peak current on the 240 v side is aprx 3.75 X steady state readings. ### ANYTHING between 3-10 X just means EVERYTHING from contactor's to wire, buss bar, breakers, etc... between main 200 A panel.... and up to and including the connections to the Dahl plate xfmr primary has to be way over sized.... to minimize V drops !! ### We took those surplus 135 A rated 3 x pole contactor's.. and simply paralled em with 1" x1" aluminum angle stock.... to make em into one big 400 A SPST-DM contactor assy. Then stick one such assy in each leg of the 240 line..... and the 3rd one does the step start. ....works good too. So does slopping on 'cool amp' silver plating compound on tall the contacts... dc resistance drops to zero every time. ### A fwb gives better reg than a doubler... for the same size is pretty much the same.caps.Sure, but with the required size caps for a FWD, the % regulation ### You would have to at least double the size of the caps in a doubler. A doubler's caps only gets charged 60 x per second....... a FWB's caps get charged 120 x per second. Plywood Box amplifier stupidly had a 25w glitch resistor -- mostThat 50 ohm glitch R we have in the B+ doesn't help... which is not noticeable at the Rx end. Originally, the definitely a blunderous mistake. ### agreed... BUT 150 v is a 150v... which sucks. You don't want any less than 50 ohms either........ but any more than 50 ohms means more v drop... and more heat. ### We used 2 x paralled 100 ohm-225 watt wire wounds in the latest project...... works good. Even with some initial HV faults during testing [which took out one or both BUSS 3 A sandfilled HV fuses]... the resistors didn't flinch. I was expecting the huge instantaneous magnetic field from the resulting 160 A to be strong enough.. to destroy em. ### 4 x 200 ohm 275 watt globars in parallel [older 60's CX type] also work superb in glitch service. Later.........Jim VE7RF |
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Tony King - W4ZT
pentalab wrote:
<snip> ### You would have to at least double the size of the caps in a doubler. A doubler's caps only gets charged 60 x per second....... a FWB's caps get charged 120 x per second.<snip> true, but in the FWD, each half of the stack is charged on opposite half cycles so half the stack is always being charged. 73, Tony W4ZT |
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pentalab
--- In ham_amplifiers@..., Tony King - W4ZT <w4zt-
060920@...> wrote: in a doubler. A doubler's caps only gets charged 60 x per opposite half cycles so half the stack is always being charged.second....... a FWB's caps get charged 120 x per second.<snip> ### A FWDoubler is nothing more than two 1/2 wave rectifiers... in series ! ### True.. BUT.... the load is across both series stacks of caps ! The theory is... since each stack only gets charged up 60 x per second..... [instead of 120 x per second ..like a FWB]... the caps in a doubler have to hold their charge TWICE as long.... hence they gotta be TWICE as big to start with ! ### There is no free lunch. The advantage of a doubler is you only need 1/2 the voltage on the xfmr sec..... and that's where it ends. You should be able to make the wire bigger on a xfmr with only 1/2 the V.... which should be capable of pumping out way more current.......which it will have to........ in order to charge up caps that have a capacitance value that is double that of the FWB.... the saving grace is... u only have to charge one stack ..at a time. ### If Rich wanted a 9900 V HV supply....... he shoulda used a 7200 V pole pig..[come in 10-15-25 kva... with or without the oil]... in a FWB. ### The doublers in my 3 x L4B's work not too bad... reg is pretty good..... ripple is 3%.... u can see the ripple on any RF scope.. with max dead cxr. [25 uf total]. Back then... u couldn't get bigger lytics...... now u can. 73... Jim VE7RF
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