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Here is Part 8. The vac tune cap is installed vertically. The vac load cap is also installed vertically. And both have right angle drives. The massive model 90 bandswitch, made by multi-tech industries is also installed. The bandswitch is huge at 9" tall x 7" across. Contacts rated at 40 amps @ 20 kv. That '40 amp' rating is at 60 hz... and NOT RF freqs. Scott modified the switch by adding another identical set of contacts on the other side of the ceramic wafer, then paralleling the contacts. So it's now a 80 amp switch. It's a progressively shorting switch, so all un-used taps are shunted out. https://www.youtube.com/watch?v=ngYUTerziyY

All, Question for the group. I am working on an Ameritron AL-80 (not A or B). When tuning it up I run out of load. I max the load cap out at zero on all bands. (fully meshed/max capacitance). It behaves the same on a two different dummy loads so I believe it to be an issue with the amp. Before I add another doorknob across the load cap, I figured I would ask the group for other ideas. -- 73 Nick KC0YKO

Here is part 7. The 160-15m manually tuned, tuned input is now complete. And yes, the input swr is dead flat across each band . https://www.youtube.com/watch?v=ev-648v_G0I

Here is part 6, where the manually tuned, tuned input is almost complete. https://www.youtube.com/watch?v=_V8om_cRk-o

Here is part 5, with the manually tuned, tuned input + input RJ1A vac relay, input coax etc. https://www.youtube.com/watch?v=sk-nmCjWa7I

Here is part 4, where the fil choke is installed, rated to handle the 78 amps CCS of fil current....and work down to 160m. https://www.youtube.com/watch?v=UWR39bxa_64

Bill K3HZP, Contact Heyboer, they have all the PWDahl specs and can build a PWDP13170 cheaper than a rewind. They did a Globe King 500A modulation transformer for me and it's great. 73 Bill N4LG At 12:29 PM 12/10/2023, Nick Jones KC0YKO wrote: >Nationwide radio has a good selection of Collins transformers but >it looks like they currently do not have one for the 30L-1. > >Peter Dahl makes a replacement p/n > >PWDP13170 > > > >-- >73 Nick KC0YKO >

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