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Test # 2 Removing grid shorts
Doug Renwick
开云体育I have a GU-78B that has developed a grid short. I have determined the grid short initiates about 2 minutes after power on and ends after about 5 minutes. I have tried unsuccessfully to 'burn' the short by hooking up a 560?f capacitor fed with 300vdc. What other methods that can be tried to 'burn' this short? Doug ? |
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Removing grid shorts
Doug Renwick
开云体育OK the reflector is working now. Before, my message disappeared. ? I have a GU-78B that has developed a grid short. I have determined the grid short initiates about 2 minutes after power on and ends after about 5 minutes. I have tried unsuccessfully to 'burn' the short by hooking up a 560?f capacitor fed with 300vdc. What other methods that can be tried to 'burn' this short? Doug ? |
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Re: C-L-C update
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Did you try tuning the choke about 30 Hz
higher?
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Carl
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Re: C-L-C update
I? made a serious? error? when plugging numbers into the PSUD-2? ?power supply software.? Like an idiot,? I used the? wrong? plate xfmr? ?DC? primary? resistance.? I was plugging in? ".1 ohm"..... when it shoulda
been? ",01 ohm" .? ? ?Well that? makes a helluva? difference? to the calculated? ?source? Z? of the? plate? xfmr.?? I did have the? secondary? ?DC? resistance correct though? ( 4.5 ohms? across the 3900? tap....and? 6 ohms across the? 5200? tap).? On the 3900 tap, source? Z? is actually? just 7.411? ohms.....? and? NOT? ?33.61? ohms.? ?? On the? 5200? tap,? source Z? ?is actually just 11.61? ohms.... and NOT? ? 57.6? ohms.? B+? ?V drops? under a steady...or? varying load are of course? much improved.? ?Hardly any drop at all.? The resonant choke? setup is still? a dud? though.? ?It's? a glorified? 120 hz? notch? filter...and let's all the? harmonics? pass on through.? ?? Too? easy to make? errors.? Jim? VERF? |
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C-L-C update
Ok, here is why a....? C1 -? resonant choke -? C2? cap is? 1 step forward and? ?6 steps backwards.?? Ditto? with a? classic? ( henry radio style)? ?.. resonant choke -? Cap? config.? When you resonate the choke, at 120 hz,? ?you now have a glorified? 120 hz? notch filter.? ? You no longer have a? good? LP filter, with a low freq? cut off.? ? Reason is.... the small cap that's in parallel with the choke (used to resonate the choke)? will? simply pass all the? harmonics, like? 240/360/480/ 600? hz? ?etc, etc.?? Typ value parallel? resonating caps have low? XC? at? >240 hz.? ?The ONLY thing that is killing the harmonics is the cap on either side of the choke ( in the case of a C-? resonant choke - C filter).......? or the output cap ( in the case of a? ...Resonant choke -? C filter.? ?Ok, now you know why? FM broadcast? TX..that use the? classic? ?resonant choke +? cap setup.... also follow it up with a? 2nd choke? +? 2nd cap.? ?The? 2nd choke (NOT resonated)? ?+? 2nd cap is? there strictly to kill the harmonics.? ?Now in essence? they end up with a resonant choke notch filter..... followed by a? ?C-LC? filter.?? With a simple? ?C- choke - C? ?filter.... it forms a bonafide? real deal? LP? filter..with a real low freq? cut off.? ?In my case, the? cut off freq is real low, like 3.7 hz.? ? ?Attenuation at 120 hz? is? -131 db ... and lower still on the? harmonics? at? 240/360/480/600/ etc.? ? ? Max? gross overkill,? I like it.? ? So do the glass tube? audio geeks. I can see why the FM broadcast folks? want? loads of? 120..and also? 240/360/480? etc? ?harmonic redux? (this is on single phase? B+? supplies).? ? FM is about the only mode I can think of, that sucks max plate current.... with no modulation / audio / program? material /? music? applied to the TX.? ?IE:? 100 kw? ERP? and during pauses? etc, if there is any 120/240/360? etc products, they? will be heard on the RX end.? ?Esp if the? 100 kw erp station is fairly local,? full quieting, and? S meter? pegged.? A few folks? tried? 75M? ?FM late one night..that was an eye opener.? ?Locally,? FM is used on 11 M band !? later.... Jim? ?VE7RF |
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Re: 6 Meters Parasitic for 3-500Z
Hi Jim,?
Sorry about the late answer. I ending? 1300W with 70W amp and grid current on the limit.? I will keep it like this for now. Several coil have been tested and the last one was the best compromise, btw i not and tested the L to cancel the C of tube.. i have put so much time in this box.. i want it to go :)? ?This is for a friend,. The YC-156 is not a 6M amp, it is a HF low band.? I have a 4400 V 2A CCS Xformer, rectifier diode from a FM transmitter and 26 uF 7500V oil cap for HV. Pi Net will be like many, roller inductor + variable Vac Capacitor for both..nothing fancy but i can't wait to see? and what will be the output and IMD ( with and without Puresignal).? This amp will be used with a ANAN 8000 exciter the 200W out will help for sure. Guillaume |
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Re: RG-213 Hi pot ?
Excellent!? That is exactly what I have used for decades when trying to move extremely angry electrical pixies from one place to another.? Sometimes, I have run the 440 through Teflon? tubing before inserting the whole assembly into the braid.
Packard 440 is, by itself, usually sufficient; but, when routed through another layer of insulation, especially when protected by grounded braid from coaxial cable, it is safe for toddlers to play with while doing its job (Not a recommendation!).
Ed. KI6DCB
Although the author has received many significant electrical shocks and burns, among which were several from potentials greater than 30 kV and a few others from RF sources [much] greater than 1 kW PEP, some of which required medical attention, these events have not impaired his ability to have opinions about many things, especially the care and feeding of high-voltage/high-current electrical power sources.? Furthermore, no toddlers were injured in gaining the knowledge and experience required to have this opinion, although many smaller things -- most notably, various insects, bugs, small rodents, several screwdrivers, three or four voltmeters, and one oscilloscope -- have made the ultimate sacrifice in the furtherance of the author's knowledge and experience.? It must be noted that everyone's constellation of experiences is different from that of every other person, and that the author's experiences may not be applicable in any or every other situation.? Your experiences may be substantially different from those of the author of this post. -----Original Message-----
From: donroden@... [ham_amplifiers] To: jim.thom@... [ham_amplifiers] Sent: Fri, May 10, 2019 10:14 am Subject: Re: [ham_amplifiers] RG-213 Hi pot ?
?
I'm using neon sign HV wire on a 10,000 volt 30KW FM transmitter
( Inside a run of metallic conduit ) Packard 440 ignition cable is tinned / stranded from Auto Parts stores... you could run it inside a braid stripped from RG8 or RG 58. Don W4DNR Quoting "jim.thom@... [ham_amplifiers]" : > Does anybody know how much max V is on RG-213 ? Like what are the > results if a hi-pot tester used..and say cranked up to the point > where just a few microamps occurs . I have an application where > I need a HV cable, less than 10 ft, that will easily handle 5700 / > 7700 vdc. It will be hardwired at both ends, no HV connectors. > And with braid peeled way back from the center conductor, like 2-4 inches . > The plan was to also wrap some red electrical tape every few > inches along its entire length, to readily identify it as a HV > cable. > > > I have loads of RG-393, but don't want to waste it for this application. > > Tnx.... JIm VE7RF |
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Re: 6 Meters Parasitic for 3-500Z
If? you use? GM3SEK's? ?pi? spreadsheet,? ?you will have some wiggle room.? The trick is to insert a tiny bit
of uh... between plate block cap and C1 main tune cap.? ?The combined tube C? from both tubes? ( anode? to chassis).....? +? that extra? tiny? uh? between? plate block caps..and? C1? tune cap..... will then form a step down? L network.? ? IE:? it will step down the plate load Z..way down.... to a lower value.? ?Then? the PI net will? easily match the lower value.... down to? 50 ohms.? ?Then you won't end up with a sky high loaded? Q.? To pull this off,? you need to measure the pf? ?between either anode..and chassis..... with both tubes plugged into sockets..... and also with all 6 x grid pins? bonded to chassis.? ?Knowing that info..it's then? plugged into the spreadsheet? ?as? ? "stray pf? between anode and chassis".? ? Enter calculated plate load Z... and let it spit out results.? ?You may? well have to increase the loaded Q? on the spreadsheet? to get a C1? value? that your tune cap can handle.? ? ?Then start inserting a tiny bit of? uh,? like? .1 uh....? in the stray uh column for the spreadsheet.? ? It will then spit out the lowered plate load Z the PI net is now trying to match.? ?At that point,? you should also be able to also lower the Q? in the spreadsheet.? Then? try a tiny bit more? uh before the C1 cap.... like say .15 uh..or? even? .17 uh.? ? You want to insert just enough? uh? ?to do the job, and no more.? ?That extra uh? should be made of? strap material...and ditto with the main? 6m? coil? ( between? tune and load cap).?? Same trick is used on the YC-156? to get it to work on 6M....? dues to the c 50 pf? ?between? anode and chassis.? ?YC-156? is? 35 pf as is.... on a wooden bench..... but rises to 50 pf...when bolted to chassis.? The extra 15 pf comes from the proximity of the lower anode fins to the chassis below the fins.? later.... Jim? ?VE7RF? |
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Re: RG-213 Hi pot ?
I'm using neon sign HV wire on a 10,000 volt 30KW FM transmitter
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( Inside a run of metallic conduit ) Packard 440 ignition cable is tinned / stranded from Auto Parts stores... you could run it inside a braid stripped from RG8 or RG 58. Don W4DNR Quoting "jim.thom@... [ham_amplifiers]" <ham_amplifiers@...>: Does anybody know how much max V is on RG-213 ? Like what are the results if a hi-pot tester used..and say cranked up to the point where just a few microamps occurs . I have an application where I need a HV cable, less than 10 ft, that will easily handle 5700 / 7700 vdc. It will be hardwired at both ends, no HV connectors. |
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RG-213 Hi pot ?
Does anybody know how much max V is on? RG-213 ??? Like what are the
results if a hi-pot tester used..and say cranked up to the point where? just a few microamps occurs .???? I have an
application where I need a? HV?cable, less than 10 ft, that will? easily handle 5700 /? 7700? vdc.?? It
will be hardwired at both ends, no HV connectors.
And with braid peeled way back from the center conductor, like? 2-4 inches
.?
The plan was to also wrap some red electrical tape? every few inches? along
its? entire? length, to readily identify it as a HV cable. I have loads of? RG-393, but don't? want to waste it for this application.? ?
?
Tnx....? JIm?? VE7RF |
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Re: 6 Meters Parasitic for 3-500Z
Hello Jim,
Thank for your feedback. Yep resting current is on higher side Eimac recommand 58 mA per tube so your dead on. I finally finding a good combinaison of resistor-L.? The commercial unit was having a big parasitic using 60W non inductive 50 Ohms resistor on each tube..so i reuse it but put a nice wide strap to replace the coil form and it is working 100% now. I ending showing up 1kw with 58 W of drive.? Yes i know it can be more efficient? I play with 2 different L in the pi-network to lower Q but each time i hit the limit of the low value of my 3-30 Pf...stray C was the limit.? So i addend inductance in the Pi-network still it is manageable with the TUNE cap.? The Q was probably in the 20 value but complete redesign of the component placement was the solution i think for better efficiency. HV was 3kv full load. Jim nice to read you as usual and will talk to you soon about the YC156 sitting here and waiting for the 6 meters amp to get out the shop :) 73 Guillaume |
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Re: 6 Meters Parasitic for 3-500Z
##? with? 150ma +? 3500 vdc, idle power =? 525 watts.??
##? I would reduce the idle? current down to? 100 ma.? ............................................................................................................................................................................ ##? The trick is...to? reduce the size of your loop just a TINY bit.? ?IF you reduce it too much, it will go into osc.? ?IF it's too big, then you couple too much power into the pair of resistors.?? ##? Ideally you want...JUST enough loop to suppress the osc, and no more.? It's a delicate balancing act..esp on 6m.? ##? ?5 x 250 ohm, 3 watt MOF's? would result in the same 50 ohms, albeit a lot more power handling capability. MOF's? are not? pure resistive either, they have some built in stray XL to them.? ?I believe KM1H's? fix for that was to? cancel out the XL? with a series? cap.....one cap per resistor.? ?Or 4 x 200 ohm MOF's? with caps. ##? Ideal resistor? would be a? 10-15-20 watt? /? ?50 ohm globar.? ?Carbon comp resistors would also work, then no compensating caps? required.? ? ?Like 4 x 200 ohm CC, or? 5 x 250 ohm CC.? I assume you have the? 3 x grid pins bonded to chassis with strap...per tube ?? Jim? ?VE7RF ?? ? ---In ham_amplifiers@..., <va2na@...> wrote : Hi amp builder, I just finishing a 6 meters amp using a pair of 3-500Z on old Marconi BH-30 case. Everything is working as it should but i can't find the right parasitic supressor setup. I am using large copper loop with 2 X 100 ohms 2W Metal oxide resistor for the last design and at 500W resistor get pretty hot quickly. I try much smaller loop but ending having the amp goes in oscillation as soon as i apply bias hihihi. Amp is running 3500V on the plate and having 150 mA of resting current. Right now? with 17-20W in getting 500W out so it feel very healthy.. i only need to address this parasitic and I will be ready, Need your input here...? if you mention W8ji site and other reference i already take a bunch of reading... Best 73 Guillaume |
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6 Meters Parasitic for 3-500Z
Hi amp builder, I just finishing a 6 meters amp using a pair of 3-500Z on old Marconi BH-30 case. Everything is working as it should but i can't find the right parasitic supressor setup. I am using large copper loop with 2 X 100 ohms 2W Metal oxide resistor for the last design and at 500W resistor get pretty hot quickly. I try much smaller loop but ending having the amp goes in oscillation as soon as i apply bias hihihi. Amp is running 3500V on the plate and having 150 mA of resting current. Right now? with 17-20W in getting 500W out so it feel very healthy.. i only need to adress this parasitic and i will be ready, Need your input here...? if you mention W8ji site and other reference i already take a bunch of reading... Best 73 Guillaume |
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Re: Henry 2k4A problem
开云体育RF parts replaced the tube. The owner had the optional warranty.? Its back up and running great. C On 4/25/2019 5:26 AM, Alek Petkovic
vk6apk@... [ham_amplifiers] wrote:
? -- Please let me quote you for your parts needs! I offer a discount on Protunes with parts order! Clark Turner 480-695-2898 |
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Re: Henry 2k4A problem
Compare it with a known good tube, idle current and PO should be within 20% or so.
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Otherwise use it in a single tube amp until it dies of old age. Carl ----- Original Message -----
From: Alek Petkovic vk6apk@... [ham_amplifiers] To: ham_amplifiers@... Sent: Thursday, April 25, 2019 8:26 AM Subject: Re: [ham_amplifiers] Henry 2k4A problem On 25/04/2019 8:03 PM, jim.thom@... [ham_amplifiers] wrote: <Yeah, I have done that with a 3-500Z which showed a short. I stuck the <shorted element pins across the 12V battery in my car. <It certainly cleared the short and I have kept the tube but I'm too <chicken to plug it in to the amp. :-) <I guess that's a bit silly, as there is surely not a great deal that can <go wrong but it would be nice to hear of other people's success or <failure, before hitting the on switch, in the home brew amp. <73, Alek ## Applying 12 vdc between grid and cathode will usually do one of 2 things. 1) weld it shut. 2) blow it wide open A 12 vdc car battery has enough current capability to do either of the above. Jim VE7RF Yep. It blew it wide open, which I verified with the Ohmmeter and 1000V Megger. The thing I do not know, is how much, if any, of the grid is left intact, inside the valve. Hence the reluctance, to date, to try it in an amplifier. :-) Cheers, Alek. VK6APK -- From sunny Binningup Family Businesses: SP Electrical. www.spelectrical.net.au The Velvet Fox. Smart Design Electrical. Perth Interiors. --- This email has been checked for viruses by AVG. |
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Re: Henry 2k4A problem
开云体育On 25/04/2019 8:03 PM, jim.thom@... [ham_amplifiers] wrote:
Yep. It blew it wide open, which I verified with the Ohmmeter and 1000V Megger. The thing I do not know, is how much, if any, of the grid is left intact, inside the valve. Hence the reluctance, to date, to try it in an amplifier. :-) Cheers, Alek. VK6APK -- From sunny Binningup Family Businesses: SP Electrical. The Velvet Fox. Smart Design Electrical. Perth Interiors. |
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Re: Henry 2k4A problem
<Yeah, I have done that with a 3-500Z which showed a short. I stuck the?
<shorted element pins across the 12V battery in my car. <It certainly cleared the short and I have kept the tube but I'm too? <chicken to plug it in to the amp. :-) <I guess that's a bit silly, as there is surely not a great deal that can? <go wrong but it would be nice to hear of other people's success or? <failure, before hitting the on switch, in the home brew amp. <73, Alek ##? Applying 12? vdc? between? grid and cathode? will? usually do one of 2 things. 1)? weld it shut. 2) blow it wide open A? 12 vdc? car battery has enough current capability to do either? of the above.? Jim? ?VE7RF? |
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Re: Henry 2k4A problem
Yeah, I have done that with a 3-500Z which showed a short. I stuck the shorted element pins across the 12V battery in my car.
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It certainly cleared the short and I have kept the tube but I'm too chicken to plug it in to the amp. :-) I guess that's a bit silly, as there is surely not a great deal that can go wrong but it would be nice to hear of other people's success or failure, before hitting the on switch, in the home brew amp. 73, Alek On 17/04/2019 11:08 PM, 'Carl' km1h@... [ham_amplifiers] wrote:
You might be able to blow the short out with a bit of voltage. --
From sunny Binningup Family Businesses: SP Electrical. www.spelectrical.net.au The Velvet Fox. Smart Design Electrical. Perth Interiors. |
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Re: Henry 2k4A problem
You might be able to blow the short out with a bit of voltage.
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Show quoted text
Using a variac or a seperate supply, AC or DC, instantaneously apply the voltage; I do it with the tube on the bench, a pair of clip leads and just brush one against a pin and see a momentary spark or meter jump. Start at some low voltage like 10V and increase as needed. No guarantee but Ive been about 50% successful over the decades with Eimac and import tubes. Carl ----- Original Message -----
From: Clark Turner clark@... [ham_amplifiers] To: ham_amplifiers@... Sent: Tuesday, April 16, 2019 3:03 PM Subject: Re: [ham_amplifiers] Henry 2k4A problem Swapped the right tube out and the condition is gone. Looks like a problem in cold start with grid short. C On 4/16/2019 9:04 AM, Clark Turner clark@... [ham_amplifiers] wrote: That is not possible on this brand of amplifier. The filament are in series. C On 4/15/2019 6:28 PM, Alek Petkovic vk6apk@... [ham_amplifiers] wrote: Pull the tubes and turn on from cold. If all ok, insert one tube at a time and retest. If it is a temporary short, as you suggest, then it will surely show itself and you can determine which tube is dodgy. Cheers, Alek. VK6APK PS: Murphy says that the action of pulling the tube and reinserting it, will be sufficient to remove the cold short and you'll never find which tube it was in. Ha ha. On 16/04/2019 6:33 AM, Clark Turner clark@... [ham_amplifiers] wrote: A friend has a 2k4A amp with two 3-500Z tubes(RF parts). It has an odd-- From sunny Binningup Family Businesses: SP Electrical. www.spelectrical.net.au The Velvet Fox. Smart Design Electrical. Perth Interiors. -- Please let me quote you for your parts needs! I offer a discount on Protunes with parts order! Clark Turner 480-695-2898 -- Please let me quote you for your parts needs! I offer a discount on Protunes with parts order! Clark Turner 480-695-2898 --- This email has been checked for viruses by AVG. |
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