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Most 8877 tubes that I test draw 11 amps of filament current at 5 volts. I have tested three recently that draw 15 amps of filament current. All of these tubes are used and have little “dings”. Is 15 amps an indication of a problem tube? Or should I apply HV to the plate and see what happens? 73 Tim K3LR

These tubes have been sold. I am sorry I could not provide them to all who asked, but the first respondent got all three. Thanks & 73 – Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 848-245-9115

Mine used to turn freely throughout its range, but now, it’s gotten kind of stuff. Annoying. Maybe a shot of penetrating oil on the “bearings,” or what? Richard WB5NEN

I designed this amp (back in 2007) for a buddy, who is now SK. Current owner is in MT. It uses a custom 253 lb Dahl plate xfmr and 24 x 3900uf lytics. Vac relays used for the input + cut off bias. Paralleled Jennings RJ2B's used for the output. We tested the manually tuned, tuned input with a 800 watt CCS cxr for 10 mins, on each band. Input swr is dead flat across all bands. Triple wafer model 85 switch used for the 12 kw PI net. Multronics MI-14 1/2" tubing coil used for 160-80-60-40-30m. HB 1/2 tubing coil used for 20-17-15-12m. This is a 9 band amp. 1000 pf @ 15 kv jennings tune cap. 3000 pf @ 5 kv jennings load cap. Bias is adjustable, on the fly with a 20 position rotary switch. Dual line section bird, with 25 kw forward slug and 1 kw reverse slug. Pep board also installed. Kicks offline if reflected power too high. 10 kw out with 500w of drive. 12 kw with 600 watts of drive. 7-16 DIN output connector. I also have a spare, nib blower, on my shelf. 253 lb dal xfmr has pri taps at 198-208-218 vac....and also 230-240-250 vac. Sec taps at 2300, 2900, 3900, 4600, 5000, 5400 vac. ( single phase 60 hz). 3 x 300 amp contactors used on the 240 vac input. One per each leg..and the 3rd one used for the step start. Separate step start and variac used for the fil xfmr. There is only 5600 hrs on the hour meter. You need 200 amp service...and also a 100 amp breaker installed in the main 200 amp panel...and a min of 3 ga copper wire from main panel to amp. If interested, contact the seller below. A SUPERBLY HAND BUILT 3CX-6000A7 HF AMPLIFIER IN A 6 FT RACK ON WHEELS. DESIGNED BY A PROFESSIONAL ENGINEER. PETER DAHL HV SUPPLY WITH TAPS DELIVERS UP TO 8000 VDC AT 3 AMPS. ANY TRANSCEIVER WITH A 500 WATT INTERMEDIATE AMP CAN PRODUCE OVER 10KW OUTPUT. INPUT AND OUTPUT BAND SWITCHES WITH TUNED PI NETWORKS FOR ALL HAM BANDS 160-12 METERS AND TUNABLE TO OTHER HF FREQUENCIES 3.5-24 MHZ. HUGE ADJUSTABLE OUTPUT VACUUM CAPS AND VACUUM RELAYS. ADJUSTABLE BIAS FOR BOTH LINEAR AND CLASS C. EXTENSIVE METERING, PROTECTION CIRCUITS AND FUSING THROUGHOUT. OVER $10,000 IN PARTS AT 2010 PRICES AND UNTOLD HOURS WERE SPENT BUILDING AND PERFECTING THIS INCREDIBLE MACHINE. WE CALL IT THE MONSTER AMP. ASKING $10,000 OR BEST OFFER. WE HAVE DETAILED PHOTOS. ONSITE DEMONSTRATION OF THIS AMP’S OPERATION AND CAPABILITES IS AVAILABLE IN MONTANA. TOO HEAVY TO SHIP. SERIOUS BUYERS CALL 406-240-5428 OR 406-830-6360 FOR MORE INFORMATION. NOTE: OPERATION HIGHER THAN 1500 WATTS IN US HAM BANDS VIOLATES FCC RULES.

A friend's GONSET 201mk3 power tranny is bad. Where is a good rebuilder or similar sized transformer for replacement ? Mucho Thanks !! Don W4DNR

Gents, Looking at resistive DL’s for QRO is an interesting pursuit, and the recommendation about employing a VNA makes it a good return on investment when selecting the “bits.” One of my DL’s is a Palstar 5K. It’s not brand new and it’s seen some excitation, and has smoked, even, with whatever Murphy dumped when I wasn’t looking. Now here’s the rub: The DL returns a 60.1 Ohm DC resistance. To my understanding a 60 Ohm (R) is not 50 Ohms, (Zero) j. So I telephones the factory and ask about buying some in-spec tubulars for my Load, and I was told that “Fifty ohms or sixty ohms doesn’t matter. A null anywhere near the resonant frequency of your tank circuit is good enough.” “And besides, they don’t make resistors in that wattage at fifty, only sixty.” I have a DL in the shed that’s fifty at J zero, but it’s liquid cooled and I can’t shlep it from building to building anymore. And I don’t think a 245 foot chunka RG8 will pass the Wiltron test for Non-Baloney. Comment? Suggestions? TNX Hal Mandel W4HBM

I'm wondering if a Planar resistor can be used for an RF dummy load. I have a couple 1KW 100 ohm Planar resistors and an 18# heat sink, I can't find my answer anywhere. Any information will be greatly appreciated.

Scott, KB1SEL (amprepairguy.com) has a recently rebuilt (by Econco) Svetlana 3CX-10,000A7 for sale. ZERO hours on the rebuilt tube....and also a full warranty. Contact Scott Mitchell at KB1SEL@... or phone him at (203) 892-4119

Hi, New to RTTY. Looking to see what I need to know regarding the use of the Alpha 86 and FSK on RTTY at recommended power settings if any. 73 Ron KK7GO

Hi all, I'll condense this, you'lll get the idea. A friend has an 811H with 3 year old 572B's. One shorted and causes the fuse to blow immediately. Tube replaced and all is well. Measuring with a DVOM shows no shorts at all. I do know some tubes will short after they get warm/hot but this one blows the fuse immediately (no time to get hot) but does not measure any short circuit. I've now talked to two other hams on the air that say the exact same thing happened to them. What causes this? 73, Bob W4JFA

Ceramic Vac tune and load caps mounted vertically, both with right angle drives below chassis. Between the front panel and sub front panel, they will both feed a sprocket assy, so the actual turns counters will be above the chassis. Multi-tech industries Model 90 bandswitch has been modified, such that there is now 40 amp contacts on both sides of the single wafer. Contacts on both sides to be strapped in parallel. There is a pair of multiple pole rotor assy's, (aka progressively shorting type bandswitch). Neither vac cap has to be padded on 160M. https://www.youtube.com/watch?v=1q-XC2rAM5A

A recent event of unknown cause or origin has totaled the existing plate current meter. I have replaced R5, R6, and R7 (R6 was toast). Diodes D2 and D7 are on there way and will be replaced upon arrival, although I have not tested the existing ones to determine if they are faulty. Does anyone have a Ip meter available? Jim McPhee Placitas, NM W5ABA

Here the manually tuned, tuned input is installed. Typ a pair of 4 section broadcast caps are used for this application...and has been used several times in the past. (17-540 pf per section, and all 4 x sections strapped in parallel.....= 68- 2160 pf ). With a pair of 4 x section caps used, they only have to be padded on 160M. In this case, the 4 section broadcast caps are too long. Plan B. A pair of 2 x section broadcast caps are used (load cap used on a SB-220).....and padded on 160M and 80M). Each section of the 2 section caps are 15-450 pf...and again, both sections are strapped in parallel. The progressively shorting bandswitch is from the kw tank circuit of a TL-922 amp. The bandswitch is used to change taps on the (aprx) 3.5 to 4 uh coil seen in the video, and also add padding to each 2 x section cap on 80m, and 160m. Each air variable gets it's own 6:1 vernier reduction drive assy. A small 2" diameter turns counter drives each 6:1 vernier. Each cap only rotates 180 degs to get from min to max (1/2 rev). With a 6:1 vernier installed, it then requires 3 full revolutions to get from min to max C. With the mini turns counter installed, (0-99 increments per rev) it's then 0-300 tiny increments to get from min to max C. This will provide for the ultimate repeatable.... 'dial it up by the numbers'. A simple cheat cheat is then made up for several parts of each band. In normal operation, it's just change the bandswitch to the correct band, and dial up both caps to their respective pre-sets...done. Then the input SWR is always 1:1 across each band. In the past, when using the same manually tuned, tuned inputs, we also have to factor in the tube's stray C (grid to cathode) as the tube C is directly in parallel with the C2 cap of the tuned input. We also have to factor in the stray C from each fil lug to chassis, as there is more stray C at the hot end of the fil choke. We also have to factor in the length of coax from IPA (intermediate power amp) to input of the tuned input. We also have to factor in the bias used (fully adjustable), drive level, (also adjustable).. and also B+ used...(can be altered by varying the taps). We also have to factor in the length of coax from tuned input to the cathode. Ideally, you want the C2 cap as close to the cathode as possible, esp on upper HF, but that is not always possible. Typ eff will suffer on 10 + 6m, with 50 ohm coax lengths > 1' on 10m, and even less on 6M. Typ 'fixes' include using paralleled 50 ohm coaxes ( which effectively adds C to the cathode), or adding C to the cathode (cathode to chassis) In the past, we tested the manually tuned, tuned input by applying a 800 watt cxr for 10 mins on each band. Done with wattmeter's on both sides of the tuned input....then into a 50 ohm DL. The 3CX-6000A7 (and also the smaller 3CX-3000A7) have a 50 ohm input Z. With input swr tweaked for 1:1 we get max drive applied to the cathode...and also max grid current. Trying to design and fabricate 5-9 separate, bandswitched / relay switched PI tuned inputs....that will each handle 800 watts CCS cxr, is an exercise in futility. Arco compression trimmers are only good for 200 w pep...and also have to be padded on 80 +160m. Correct sized toroid's and magnet wire are a non issue. Been there, done that. If fixed caps are used, they have to handle the current, and you need a box of em to arrive at the final tweak...pita. Then either a 2 x wafer bandswitch is used, or a small single wafer bandswitch is used to activate a mess of relays. You end up with a convoluted, complicated mess on your hands....and even more complicated if the tuned input bandswitch is mechanically ganged to the 10 kw output bandswitch. The dead simple, manually tuned, tuned input is far simpler, and bullet proof...and fast to design and install. With 800 watts into 50 ohms, it's only 4 amps into 50 ohms, and only 200 V rms (283 V peak). Those broadcast style caps typ have .032" spacing, and rated for 1.1 kv. With older, dirty ones, toss em into the dishwasher....(with plates un-meshed), and they come out squeaky clean.....and hi

Ok, new project started. 160-15M amp using the 3CX-6000A7. I re-designed the 160m coil, made from 1/4" tubing, so it's shorter, but bigger diameter, so it will fit. 80-40m coil already made...from 3/8" tubing. 20-15m coil made from 1/2" tubing. The whole thing is a tight fit. https://www.youtube.com/watch?v=XWytaQwcWZ0

17 x pix of the 10 kw 6M amp...using the new Pentalab 3CX-6000A7 tube. If you want to see pix of both top + bottom of the RF deck, + pix of the HV supply, here is the link. https://amprepairguy.com/10kw-6-meter-custom-pa-3cx6000a7... The next amp is the 80-15m bandswitched unit, using the same 3CX-6000A7 tube. I have finalized the design for the RF deck. Components of course are a lot bigger. 1/2" silver plated tubing used for the 20-17-15m coil (and also the L coil before the main PI-net). The 80-40-30 coil will be hand wound, using 3/8" tubing. 500 pf ceramic vacuum tune cap, and a 3000 pf vacuum load cap. Same setup for the TR relays. RJ1A for the cutoff bias, and a 2nd RJ1A for the input. 2 x paralleled RJ2B's for the output. 7-16 DIN connector for the output. 4 x 200pf HT-57 plate blockers used. I have also finalized the design for the 160-80-40-20-17-15m version. It uses a 4000 pf vac load cap, and one extra coil.... for 160m (silver plated 1/4" tubing used). 8-9 x 200pf HT-57 plate blockers used. The HV supply will use a lot more B+ (7500 vdc)...and will use 2 x identical plate xfmrs in parallel. Both designs employ a bandswitched PI tuned input. (C1 + C2 are padded on 160m) Stay tuned. Jim VE7RF