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All, I have an old homebrew RF deck that the T/R rely is a Potter & Brumfield LM11-2500. I can't find what the coil voltage is. In the 1954 P&B catalog the LM series is titled Sensitive Plate Circuit Relays and only list coil resistance and pull MA ratings. What was the typical application for a Sensitive Plate Circuit Relay, and what voltage energized the coil? Not sure why I am struggling to understand this but do not recognize the Sensitive Plate Circuit Relay application. Thanks Nick

Old news to some, perhaps... I think he died some time ago; but W4ZT's amplifier web sites, mostly showing big Russian tubes such as the GS-35B but also with links to many European Russian tube sites, seem to have been dropped by the ISP in the last month or so. He also advertised sockets from K4POZ, who also died a decade or more ago, who used to build professional-looking sockets for such as the GI-7B. I cannot remember who I got them from, but I was able to buy new sockets as recently as several years ago from someone that I found on the W4ZT site. 73, Steve K0XP

Hi, I've been trying to gather parts for a 3CX1200D7 build. I had trouble locating a sufficient filament transformer. Tube requires 6.3V @ 25A. Ended up finding one for 6.3V @ 28A - Would like to have more overhead but thought it would be the best I'd find, and only $50 brand new! Perfect! BUT In my haste to complete an order of needed parts, I wasn't paying close enough attention. It turns out that it doesn't have a CT. (it's dual secondary - parallel is 6.3V@28A and series is 12.6V@14A) - D'oh! Now what... when I used to play with guitar/audio amps, a semi-common thing to do would be to take a pair of low value resistors, put one end of each to each end of the filament winding, and ground the joint in the middle for a fake CT. Unsure how this will affect a cathode bias. I've also heard of using the secondary winding of a totally separate transformer that does have a CT, and using it in parallel across my filament winding, then using that transformers centre tap. Further, I've heard of using a pair of diodes, each anode to each end of my filament winding and tie the cathodes together in the middle... or maybe that was t'other way around... either way I dunno about this either. Anyways, obviously the best way forward would be to actually use a proper transformer, but since I can't find one and I already made this oopsie... I'm wondering what the next-best-way forward is? :) Thanks :)

Got an 80B here and I am having meter issues. The swr and power meter were not working properly and I put in a new op amp on the meter board and I also changed out the 2 2n3904's going to the op amp. Now the meters are at full scale. At this point its over my head. Was wondering if anyone had any ideas. The grid and plate meter is fine and the amp puts out bear a KW. I am just using me external meter for the time being. Tia Dave N8DC

Looking for a good working transformer. Any one of the three. Send email direct to me , gudguyham@.... Thank you. Sent from the all new AOL app for iOS

Gentlemen, If you can spare the time, calibrate your nanoVNA boxes and run some profiles on various coax jumpers. Setting up the IRIG-B network at work required any number of coax jumpers between various panelboard instruments because everybody in the band hadda be on the same beat. So one day it all had to be proof-tested by a third party, just like most of the other control widgets, and this guy showed up with a R&S VNA with a bag full of factory jumpers, and the tech ran a Calibrate between all tests, and we could plainly see that $50 jumpers were nowhere near one another on the curve screen. So yes, using a longer chunka coax does make a difference, especially if it’s premium flavor. Hal Mandel W4HBM

Hi all, I thought this would be the best group to get an opinion from. I have an old tube tester in it's wooden cabinet. I would like to store it in the garage/shed. What do you all think about winter temperatures that can get to the middle 20 degrees fahrenheit in the winter, and 95 degrees fahrenheit in the summer? It will be wrapped in plastic or in a plastic bag and then inside a cabinet drawer. Thanks guys. Bob W4JFA

I am aware of this voltage dissipation relationship, but Onder said the software is written for the 50-odd volts the amp uses. Perhaps he needs to develop his software so you can vary the drain volts to suit the power output level. You’re right - it is veeery inefficient at low output levels !

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

Gents, One of the bug-a-boos about QRO tubism is the regulation and acceptability of filament voltages. Okay, tube manufacturers tell us “10%,” and we have to live with whatever Con Edison or Kentucky Power ends up at our QTH to ply our signals out and about. I know, I know Continental and all them have Buck’n’boosters, automated variacs on 3-phase mains: Just everything money can buy. So here’s Dave saying his filament voltage droops a bit, and I’m sure there are others out there, running 8877’s or CPX’s and other thoriated devices, and what can we as technicians offer them? Would it not be fabulous for QST to publish in its last edition this December, a sure-fire and affordable means to conquer filament squirrels? Let’s say Joe Ham has a wonderful $6K to $10K linear running tubes that are in need of regulation. Would it not be remiss to afford 10% more for a regulation gizmo? I know how much a good set of finals cost, and frankly, I don’t know if I can ante up for a new set if I pop the ones I got right now. So like owning a car that’s beginning to use a bit more oil, I keep the drive down a bit on my inputs, and just hope the beast can gently grow old like the old man. Hal W4HBM

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