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

Albany County Fasteners:



K9ER

Lowes have them for delivery!! Home Depot seems to be down here in UK this morning

Im sure some specialists would have them cheaper for mail order

When I am in the US on business I try and visit Home Dept and/or Lowes and have been surprised in recent visits about the availability of Metric parts and tools to the extent of buying some small sized long reach Metric sockets at a very good price, as well as small US screws for Drake kit and the like

73 Fred

I have recently acquired a Ten-Tec Centurion model 422 that is in very nice condition, but has a blown up bandswitch and the plate tuning capacitor was arced.? I might be able to salvage the capacitor, but the bandswich will need to be rebuilt or replaced.? If anyone has a switch/parts and/or a capacitor please contact me off list to let me know what you have.

Lowes have them for delivery!! Home Depot seems to be down here in UK this morning

Im sure some specialists would have them cheaper for mail order

When I am in the US on business I try and visit Home Dept and/or Lowes and have been surprised in recent visits about the availability of Metric parts and tools to the extent of buying some small sized long reach Metric sockets at a very good price, as well as small US screws for Drake kit and the like

73 Fred

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Did the caps short and put high voltage on the antenna causing the amp meter to peg? Is there a rf choke at the output connector?

As in any quality-designed-and-built power amplifier, yes, there is a good-sized, large inductor from the output of the pi-network to ground to guard against exactly this kind of failure mode.

What seems particularly impressive, in this case, is the fact that when those caps arced over, they did not cause a BIG BANG, as most of us might have expected. I never heard anything (but then again, I don't hear much other than CW, anyway). Instead, the HV simply rapidly drained off and the amplifier shut down (except for the afore-mentioned logic power supply, which apparently kept the front panel LEDs lit up although they never indicated what was going on, let alone that a fault had just occurred).

This experience makes me hopeful that when the day comes that one of the 4CX1000s flashes over (if ever), the amp will shut down gracefully just like that instead of announcing the failure by emulating a shotgun going off in my ear? 8-D? I've had my share of those but no, that's not why I'm so deaf.

73,

Steve K0XP

On 12/8/2023 9:09 AM, Jim VE7RF wrote:

Those oem 220M? caps are each 2200 pf.? ( 6600 pf in total for all 3 of em in parallel).

Actually, they read "222M"; so it was clear they were 2200 pF.

The actual correct component for plate blocking is a? 5 / 7.5 kv rated HT-50/58 sized doorknob.....and 2 are used in parallel...and work good on 160-10m.? ?These days, you can only get the HT-50/58 doorknob caps in 7.5 kv.? They will handle one helluva lot of current on upper HF....per the detailed specs in the HEC catalog.

A 5 kV-rated cap is not likely to withstand 3 kV plate voltage under highly-mismatched circumstances at the legal power limit (such as your antler tuner arcing over during a wind storm). 7.5 kV is not much better, but better than 6 kV, obviously. The higher, the better. Here, with nearly 3 kV plate voltage, I wouldn't have designed in anything less than 10 kV; yet, Alpha put in those 6 kV-rated capacitors. I have been told that my failures are not the only ones that have been experienced in Alpha 8410s. The AL-1500 has a pair of HT-50 doorknobs but they're only 500 pF; 1000 pF is a capacitive reactance of only 88.4 ohms at 1.8 MHz, somewhat marginal IMHO at the legal limit. But W8-no-name apparently originally specified/dictated their use, unless he specified something larger, and then MFJ, in their ever-cheapening-mindset, reduced the original values to something more-affordable; so there they are.

?I have never seen a plate blocker blow up from high swr / no ant, open ant, shorted ant etc..at least not when using HT-50/58 sized caps.

I've "snapped" a 7.5 kV, 1000 pF doorknob years ago on an early 4-1000 amplifier at Ep=4500 volts; the body audibly cracked then arced internally during tuneup of the roller inductor.

These days, I use my dwindling stash of the previously-widely-and-cheaply-available Russian monster-sized doorknobs VERY SPARINGLY, as who knows when, or whether, those will ever become available again? I had a handful of the 1000 pF/10 kV discs and decided this was as good a place as any to try them out as plate blocking caps. I wish I could rember where I bought them; but I know it was within the past several years.

73,

Steve K0XP

Those oem 220M? caps are each 2200 pf.? ( 6600 pf in total for all 3 of em in parallel).??

?

The problem with discs is..... current handling capability.? ?Upper HF will result in the highest RF current through a block cap.? And high duty cycle modes like? 10M FM,? ?data, rtty, FT-8? will stress em.

?

I bought some Ceramite brand 4700 pf @ 10 kv disc caps from Henry radio.? Then bought some Ceramite? 4700 pf disc caps, but this time in 15 kv, also from Henry radio.? ?Typ the higher voltage rated? disc caps also handle more current.

A few months back, I bought 3 x dozen? chinese? .01 uf (10,000 pf? or 103M)? rated at 30 kv....bought off their ebay site.? ?They came in 10-20-30 kv.? These 30 kv versions are monsters.... at 1.3" diam x 7/16" thick.? ?My hi-pot tester only goes as high as 15 kv.... and they draw 0 leakage current, even after 10 mins.... good enough.? ?They are cheap..and the shipping is dirt cheap.? ?The 11m ops use just one of the .01uf @ 20 kv versions for a coupling cap into the cathode of a GG high mu triode amp.

?

So far, so good....with my limiting experimenting.? These chinese discs handle a stupid amount of current.?

?

The pair of discs in the Drake? L7 ( also used for plate blocking)? ?are failure prone.

?

The actual correct component for plate blocking is a? 5 / 7.5 kv rated HT-50/58 sized doorknob.....and 2 are used in parallel...and work good on 160-10m.? ?These days, you can only get the HT-50/58 doorknob caps in 7.5 kv.? They will handle one helluva lot of current on upper HF....per the detailed specs in the HEC catalog.?

?

I have never seen a plate blocker blow up from high swr / no ant, open ant, shorted ant etc..at least not when using HT-50/58 sized caps.??

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Actually, Adrian, I'm glad I didn't buy one of those, because finding short M5 metric screws here in the back-country of the USA would have been a real challenge? 8-D

73,

Steve K0XP

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I asked to join the 9500 group a week or two ago, but never heard back. I did search the 87A group's archives and have seen Glenn post there. But I've never seen any discussion of any other amp other than the 87A on that group, so I'm very reluctant to join it, break protocol and bring up my 8410.

Besides, I doubt Glenn would be of much help as regards the AE9K 8410 monitor program.

And besides all that, I did resolve the problem I'd been having with my 8410. From time to time, it would seem to fault; the HV would drop to zero after a few seconds, and if you were watching when it happened, you'd notice the plate current LEDS suddenly lite all the way to 1.5A before dropping to zero. The curious thing to me was the LEDs would remain lit up; yet, there was never a Fault LED. The blower would shut off completely. This happened before I connected the amplifier to my computer, so the amplifier was NOT getting power for the LEDs from my USB line.

After awhile, I got around to examining things carefully, and finally found this:

?

I wound up replacing those with six paralleled 1000 pF/10 kV discs, spread out so they wouldn't arc to one another, and the amplifier has been working fine since. I suspect the caps were blown due to high-SWR events, one at a time. I was very surprised to find only six kilovolt discs being used where the plate voltage was already half the voltage rating of the cap leaving little margin for "mistakes".

TNX,

Steve K0XP

On Wed, Nov 29, 2023 at 06:34 PM, Steve wrote:

Anybody know whether there is an active Alpha amplifier group anywhere?
I have a cupla questions about the AE9K monitor program for Alpha amps.
TNX,
Steve K0XP

There is an Alpha 9500 group HERE: /g/Alpha9500

Glenn, AE0Q posts/replies there often.


73,
Alan
W5ARM

On Wed, Nov 29, 2023 at 06:34 PM, Steve wrote:

Anybody know whether there is an active Alpha amplifier group anywhere?
I have a cupla questions about the AE9K monitor program for Alpha amps.
TNX,
Steve K0XP

There is an Alpha 9500 group HERE: /g/Alpha9500

Glenn, AE0Q posts/replies there often.


73,
Alan
W5ARM

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True, for that one cover page; however, the links don't go through the Wayback machine, so they don't come up with pages. One has to copy the indicated url for a link into wayback machine in order to get to a desired page.

73,

Steve K0XP

?IS GOOD.

73,

Mike Mysliwiec

KF8OD

On Dec 6, 2023, at 9:25 AM, va3dxv <va3dxv@...> wrote:

Try with

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?IS GOOD.

On 12/6/2023 6:26 AM, Mike Sawyer via groups.io wrote:

Try the Internet Wayback Machine. There's a good chance you will find it there.

Yes, indeed; but my point is that all of this fantastic old amplifier reference material is now on it's way gone... so anybody wishing to personally archive any of it had better get busy saving archived pages.

My own original web site disappeared over a dozen years ago, some ten years or so after my old, original ISP died. I can only access my old material on things such as Oldsmobile engines, and my AM-6154/6155 modifications, via the Wayback site.

73,

Steve K0XP

Try the Internet Wayback Machine. There's a good chance you will find it there.

Mod-U-Lator,
Mike(y)/W3SLK

Try with http://www.archive.org

https://web.archive.org/web/20230830230406/https://w4zt.com/

On 12/6/2023 6:00 AM, Louis Parascondola via groups.io wrote:

W4EMF was another fellow who did numerous tube transplants on many different Dentron amps. ?He put GI7b tubes in just about everything. ?W4EMF has numerous photos on the net on his many conversions he’s done. ?It’s worth a Google search on W4EMF to see the many things he did! ?Just thought I’d share with you.

Unfortunately, it seems that any reference to the original W4EMT's material is gone, too? 8-(

73,

Steve K0XP

FYI….I met Tony King many years ago for the first time at the Shelby, NC. Hamfest. ?Toby was with a group of guys including Ron K4POZ. ?They were best of friends and worked together on converting different smaller US amps to Russian tubes. ?They made bias boards and homemade tube sockets. ?Tony and I headed it off great. ?You see Tony had a heart transplant a few years prior to me meeting him. ?His heart came from a 40!year old woman. ?He kidded that if ?he?was bitchy sometimes it was due to his female heart. ?I was scheduled for my kidney transplant when I met Tony and he told me he would come and wait for me to wake up from my anesthesia and be at my side. ?Unfortunately Tony passed away from melanoma cancer afterwards and wasn’t able to visit me. ?After Tony passed away Ron K4POZ kept selling tube sockets and bias boards that Tony designed. ?W4EMF was another fellow who did numerous tube transplants on many different Dentron amps. ?He put GI7b tubes in just about everything. ?W4EMF has numerous photos on the net on his many conversions he’s done. ?It’s worth a Google search on W4EMF to see the many things he did! ?Just thought I’d share with you.

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

On Sun, Dec 3, 2023 at 01:58 AM, Dave w6de wrote:

Ceramic Disk Capacitors are used as RF bypass capacitors in RF circuitry--that is to short RF to ground.? And Capacitors can be also used to block DC and low frequency current form passing through them. How to use the in your situation is described below.

?

Use a set of High Voltage Ceramic disk capacitors, wired from each of the two filament leads to ground—this will allow the high frequency RF to pass through and block the low frequency AC filament voltage..?

-Disk ceramic Capacitors are also used in High Power Tube Amplifiers as a DC blocking capacitor to Pass through only the RF from the plate to the PA plate circuit and then the antennas system.?

-Since this works in the plate circuit and it will work in the ground/common circuit too.?

-I am not certain about the voltage requirement for this filament grounding circuit. ?Look at the Filament transformer’s insulation value.? You aren’t going to need much higher voltage for the capacitors than that.

?

Turns out, high voltage disk capacitors are becoming hard to find:? I found this at RF Parts:

? 0.01 micro farad @ 2KV

-Assuming you will use a 0.05 microfarad capacitance value you will need 10 of these to make your filament grounding system.? Double than quantity if you need a high voltage of 4KV.

-Alternate choice but more expensive are doorknob capacitors.? While these might be awkward to mount a capacitance above 2000pf may work for you, these will certainly work and look impressive.? You are going to need one of these door-knob capacitors for your amplifier plate circuit too.---just buy 3 and you’ll be set :>).

?

A capacitance of? 0.05 microfarad will present only 3.8 Ohms (2 x 1.8) resistance to the RF signal at 1.8 MHz even lower resistance as the frequency goes up.? But will present 106K Ohms (2 x 53K) ohms to the 6.3 volts 60 Hz AC voltage.? Use this calculator to determine alternate capacitance values if you desire:

?

73,

Dave, w6de

I bought? .01uf @ 1.4 kv disc caps from RF parts.? Huge things at 1" diam x 3/16" thick.? ?
Also bought a bunch of Ceramite brand? disc ceramic 4700pf caps (.0047uf) @ 15 kv? from Henry radio.? They too will handle a lot of current....and are big things.

Then bought dozens of the chinese .01uf @ 30 kv disc caps off their? ebay store.? Massive things? at 1 3/8"? diam x 7/16" thick.? These hi pot tests to? 15 kv? ( limit of my hi-pot). Max current of all of em.? ?11m ops use em for coupling caps into the cathodes of GG amps...and stuff several kw through em. The chinese disc caps also come in 10 kv..and also 20 kv.? ?They are so cheap, and shipping is dirt cheap,? I decided to just stock pile 3 x doz of the 30 kv types.? ?I hi-pot tested all of em....and also the C... which was typ 9200-9600 pf.?

?

I put 2 of em in series.... and wire that mess across the cathode of the 3x3, 3x6, YC-243, and bigger tubes.? Drive applied to the junction of the caps.? Done that way, the drive current splits in half...and makes for better use of caps.? ?Z at 60 hz is sky high.? Z at 1.8 mhz is low.?

?

For the OP's situation, a small fil xfmr with the CT on the sec? will easily work.? Then the? CT becomes your fake CT....that can be used for the cathode return current.? ? Sec of small xfmr wire in parallel with his existing fil xfmr( that has no CT).

And like Reid sez.... the 120 vac primary of the? small fil xfmr has it's 120 vac primary leads taped off...... not used.?

?

Jim? VE7RF