Home Brew GS-31B HF Linear Amplifier

[W3DRK]

Greetings! This is my first post on this forum and I thought I would share my GS-31B linear and perhaps ask a few questions as well since there seems to be some builders on this forum with quite a bit of experience using the Russian triodes.

This is my first home-brew amplifier...I caught the bug after retrofitting a GI-7B into my GLA-1000 so I wanted to try building one from scratch.

The goal of this amplifier is to have a 10-160 meter amplifier that would safely achieve 1500 watts output on all bands and fit nicely on the desk at my operating position.

The triode is a single GS-31B and the plate transformer is a custom 80lbs 5KVA unit which will eventually be enclosed in a separate cabinet under the desk. Depending on which primary tap I use I can apply anywhere from 3600 to 4300 volts @ 1.5 amps continuous on the plate.

The amp is monitored and protected by a WD7S Triode Control Board and I also used his HV-2 rectifier/filter board as well as his TU-6B tuned input board, all of which I built from PCB blanks I purchased from him.

The amp was completely hand built by me, all 150-something screw holes hand tapped out in the garage. Some of the more complex pieces like the stainless shaft couplings were made at work on a lathe and a milling machine was used to mill the chassis openings for the meters, switches, and the opening on the bottom to access the cathode/tuned input.

I just recently got the thing up and on the air and so far it's been working really well, but I've noticed except for 160 meters the GS-31B seems to struggle to maintain 1500 watts output. I know the official specifications for this tube state a 1000 plate dissipation rating which I am exceeding, but some web sites mention in amateur service 1500 watts pdis should be achievable. I'm currently running about 4000 volts on the plate and grid current rarely climbs above about 220ma.

The problem I'm experiencing is after about 15 seconds of flat-out 1400-1500 watts CW output into a dummy load, the grid current will begin to steadily drop as well as the output. If I un-key and give the tube 10 or 20 seconds to recover it will return to normal Ig until I keep it steadily keyed again. I never leave it keyed long enough to see what eventually happens since I'd like to avoid long-term damage or catastrophic failure of the tube. Is this due to heat buildup in the tube perhaps temporary distorting the grid structure?

I'd also like to note that varying the plate voltage seems to have little effect on output power above 7 MHz...anything from 3600-4300 volts and 1400-1500 watts is about the most I'll get...and it tops out at about 600-700mA Ip. On the other hand, down on 160 meters it'll do >1amp on the plate and peg the watt-meter at 2KW.

I am considering the purchase of a GS-35B to see if it will be better suited for QRO use. Even though laying on the key isn't a practical test of capability, I'd feel more comfortable knowing the tube isn't being run on ragged edge and have plenty of headroom rather than thrash on this poor GS-31B.

Anyway here are a few cell phone pictures of the amp. Ignore the Vp scale on the plate meter...I need to re-scale it. Also, after these pictures were taken I've eliminated the temporary parasitic suppressor since this amp doesn't appear to need one and I've also added gas arc protection devices from B- and cathode to ground as a preventive measure.

Questions and comments are welcome!!

Thanks and 73

[NQ6U]

Way over my head. This looks like a job for...Super Amp Man!

That's Bob, VK3ZL; he builds a new amp whenever he's got nothing else to do and every one of them is a work of art.

[K7SGJ]

Greetings! This is my first post on this forum and I thought I would share my GS-31B linear and perhaps ask a few questions as well since there seems to be some builders on this forum with quite a bit of experience using the Russian triodes.


This is my first home-brew amplifier...I caught the bug after retrofitting a GI-7B into my GLA-1000 and wanted to try building one from scratch.


The goal of this amplifier is to have a 10-160 meter amplifier that would safely achieve 1500 watts output on all bands and fit nicely on the desk at my operating position.


The triode is a single GS-31B and the plate transformer is a custom 80lbs 5KVA unit which will eventually be enclosed in a separate cabinet under the desk. Depending on which primary tap I use I can apply anywhere from 3600 to 4300 volts @ 1.5 amps continuous on the plate.


The amp is monitored and protected by a WD7S Triode Control Board and I also used his HV-2 rectifier/filter board as well as his TU-6B tuned input board, all of which I built from PCB blanks I purchased from him.


The amp was completely hand built by be, all screw holes drilled and hand tapped tapped out in the garage. Some of the more complex pieces like the stainless shaft couplings were made at work on a lathe and a milling machine was used to mill the chassis openings for the meters, switches, and access to the cathode/tuned input.


I just recently got the thing up on the air and so far it's been working really well but I've noticed except for 160 meters the GS-31B seems to struggle to maintain 1500 watts output. I know the official specifications for this tube state a 1000 plate dissipation rating which I am exceeding, but some web sites mention in amateur service 1500 watts pdis should be achievable. Since I run about 4000 volts on the plate grid current rarely climbs above about 220ma.


What happens is after about 15 seconds of flat-out 1400-1500 watts CW output into a dummy load, the grid current will begin to steadily drop as well as the output. If I un-key and give the tube 10 or 20 seconds to recover it will return to normal Ig until I keep it steadily keyed again. I never leave it keyed long enough to see what eventually happens since I'd to avoid long-term damage or catastrophic failure of the tube. Is this due to heat buildup in the tube perhaps temporary distorting the grid structure?


I'd also like to note that varying the plate voltage seems to have little effect on output power above 7 MHz...anything from 3600-4300 volts and 1400-1500 watts is about the most I'll get...and it tops out at about 600-700mA Ip. On the other hand, down on 160 meters it'll do >1amp on the plate and peg the watt-meter at 2KW.


I am considering the purchase of a GS-35B to see if it will be better suited for QRO use. Even tough laying on the key isn't a practical test of capability, I'd feel more comfortable knowing I'm not on the ragged edge and have plenty of headroom rather than thrash on this poor GS-31B.


Anyway here are a few cell phone pictures of the amp. gnore the Vp scale on the plate meter...I need to re-scale it. Also, after these pictures were taken I've eliminated the temporary parasitic suppressor since this amp doesn't appear to need one and I've also added gas arc protection devices from B- and cathode to ground.


Questions and comments are welcome!!

Thanks and 73

1026710265102661026410263

Nice job on the amp. As Carl said, Bob is the man when it comes to homebrew amps. They look nicer than store bought ones, too. I think all is uses are Russian tubes. You guys should be right at home talking amps.

[NQ6U]

Let me state right off that I know very little about this topic. That said, I did a little research and it seems that the GS-31B is very sensitive when it comes to filament voltage. Anything less that the optimal 12.6 volts will result in low output. Have you checked that?

[W3DRK]

Thanks for the complements! And yes, the filament varies between 12.8-13 VAC. Approx 12 ohms in series with the filament transformer primary provides a soft-start for the filament and keeps it right in that range. HV and keying is held-off until after the configured 2-minute warm-up time has passed.

[KG4CGC]

Welcome to the Island!


http://i25.photobucket.com/albums/c79/bebop5/drinks/Copy_of_IMG_01731_zpsd1f9f3ae.jpg

[W3DRK]

Thanks for the welcome!

I just noticed there was a five picture limit and three of my pics didn't post. Here's the transfer relay enclosure which houses the Jennings vacuum relays and RF detectors that are used for the hot-switching prevention. The 2nd picture is the 50 amp SSRs for the plate transformer step-start. Third is of the massive 80lbs 29M6 EI core plate transformer sitting next to a beer can for size reference. The transformer is wound with GP-200 #8 primary and #18 secondary windings with plenty of kapton insulation used throughout...hi-pot tested to over 9kv with no sign of leakage. After hours of QRO rag chewing it barely gets warm to the touch.

[K7SGJ]

Guinness? Beer? BWHAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA Just kidding

[NQ6U]

Guinness? Beer? BWHAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA Just kidding

Guinness is more than mere beer, it's an entire meal.

[W3DRK]

Guinness is more than mere beer, it's an entire meal.

Indeed! I've been living off of it in the evenings after work for the past couple weeks while I tinker with this thing.

[K7SGJ]

Guinness is more than mere beer, it's an entire meal.


So..................that would make a 12 pack......................a....................... ..happy meal?

[kb2vxa]

The more you drink the happier you get.

[NY4Q]

I love Guinness, and GS-31b's.

[W3DRK]

Well, a GS-35B to try is on it's way. I planned for the possibility of using one when I decided how tall to make the amp so it should drop right in and fit under the cover just fine.

[N8YX]

What's the measured Q of the tank circuit per band, and does PO drop on all bands when the amp is run at its maximums...or just on certain bands?

[W3DRK]

Well, I haven't measured for Q but I did design for a Q of 12 on all bands except for 12 and 10 meters where I need a Q of about 15 to maintain a reasonable minimum tune C on those bands. I have tried varying the Q by changing L a full turn or two in either direction without much effect.

Input Q is 2 on all bands.

The problem appears to be more prevalent on the higher bands.

[N8YX]

Take a careful look at the tank circuit...with an IR thermometer if you can get hold of one. I'm leaning towards heating caused by circulating currents, which results in detuning of the circuit.

What are you doing with regards to grounding of the grid - directly to chassis or are they floating a bit above it a la the Heathkit SB-22x series?

Have you looked at the amp's output on a spectrum analyzer when under load and experiencing the power drop-off condition?

[W3DRK]

The grid is directly grounded....the ring of the tube which is bolted right to the the chassis is the grid.

Unless I'm somehow heating 1/4" copper pipe enough to de-tune it, the only other thing in in the tank I can think of that would de-tune from heat would be the blocking caps at the plate choke but those are Soviet K15-5 ceramics which handle quite a bit of RF current...and I used 3 of them in parallel. They also feel cool to the touch as soon as the plate supply bleeds off HV and its safe for me to touch them, but I suppose they could be cooling off by then.

The IR thermometer is a good idea...I'll see if I can get my hands on one because that would eliminate a lot of guessing.

I do find it odd that as the grid current is steadily dropping along with output, the plate current remains steady. If the output tank circuit were drifting out of resonance, shouldn't I see Ip climb?

I wish I had a spectrum analyzer.

[W3DRK]

I just stopped over at the meteorology lab at work....IR thermometer acquired :)

[N8YX]

The grid is directly grounded....the ring of the tube which is bolted right to the the chassis is the grid.
Good. Floating grounds and subsequent heating of the resistive component will cause gain drift, as will heating of cathode resistors. Doesn't look to be the case here but there's the matter of IG vs IP...


Unless I'm somehow heating 1/4" copper pipe enough to de-tune it, the only other thing in in the tank I can think of that would de-tune from heat would be the blocking caps at the plate choke but those are Soviet K15-5 ceramics which handle quite a bit of RF current...and I used 3 of them in parallel. They also feel cool to the touch as soon as the plate supply bleeds off HV and its safe for me to touch them, but I suppose they could be cooling off by then.
Have access to a GDO? Connect a two-turn coil of wire across one of those caps and sweep it through the HF range. See any funny dips which indicate a series resonance condition? If so, is it anywhere near the frequency range where the power drop-off is occurring?


The IR thermometer is a good idea...I'll see if I can get my hands on one because that would eliminate a lot of guessing.
Check the input section of the amp with it too. Which leads me to my next comment:


I do find it odd that as the grid current is steadily dropping along with output, the plate current remains steady. If the output tank circuit were drifting out of resonance, shouldn't I see Ip climb?
You would think so. How does the input SWR look when the power drops?


I wish I had a spectrum analyzer.
If you were nearby I would tote one of mine over. I have this funny feeling about parasitics.

What value in pF are the blocking caps that you're using? Also, with the tank terminated in its characteristic resistance at both ends and the tube removed, what do you see with regards to resonances when you check the plate choke and bypass circuitry with a GDO?

[K7SGJ]

Something I am curious about is what happens if you don't drive it as hard, and lower the output to ~500 watts, is it stable? Then try walking it up and see what happens at the different drive/output levels. You may just have a situation that what is changing is occurring in the tube itself.

[W3DRK]

Have access to a GDO? Connect a two-turn coil of wire across one of those caps and sweep it through the HF range. See any funny dips which indicate a series resonance condition? If so, is it anywhere near the frequency range where the power drop-off is occurring? ... Check the input section of the amp with it too. Which leads me to my next comment:

Yep, will do! I don't see any reason why I can't use my MFJ analyzer for this...


You would think so. How does the input SWR look when the power drops?

That's a very good question! Honestly, I've been so careful not to let the condition continue for more than a few seconds that I have not glanced over at the input SWR while it's occurring. That will be one of my action items for tonight and I will report back with the result.


If you were nearby I would tote one of mine over. I have this funny feeling about parasitics.

Thanks! Being new to amp building I must admit my collection of useful tools is somewhat limited. Besides the tools I use for everyday electronics tinkering and occasional repair for local hams such as a couple of scopes, some Fluke bench-top multimeters, Boonton sig gen, and a portable L/C meter...I don't have very much to work with.


What value in pF are the blocking caps that you're using? Also, with the tank terminated in its characteristic resistance at both ends and the tube removed, what do you see with regards to resonances when you check the plate choke and bypass circuitry with a GDO?

The blocking caps are 3x 1000pf 6.3kv parts. They are Soviet K15-5 components and, according to what I read although the dielectric and thermal coefficient seems to be unknown, the old datasheets claimed high current RF capability. I guess that doesn't rule out the possibility of them drifting all over the place and going way out of tolerance. I do know I once tried using one as a padding cap for 80 meters in a smaller GI-7B amp and it did NOT take kindly to that. Extreme heating and "sweating" of the cap occurred, although it amazingly survived the ordeal without going out of tolerance.

I haven't checked for series resonances in the plate choke/supply circuitry. I (perhaps foolishly) assumed since the choke I used is so popular in home-brew amps without much trouble I wouldn't have to worry about this. I will look into this more thoroughly and consider it an opportunity to learn more about what I'm doing. :)

[N8YX]

Those caps...6.3KV...I wonder if their breakdown voltage is being exceeded on peak excursions? Have any 10KV or greater parts you can sub? Or perhaps a different style of cap? I think I have a few 1000pF/5KV Centralab 850 series floating around here somewhere; maybe those could be subbed?

What happens if you place two of the Russian caps in series and parallel two of those assemblies, giving an effective 12KV breakdown and 2000pF capacitance?

[W3DRK]

Hmm, I may have enough spares to try the series/parallel arrangement you suggest. Otherwise, I do have one or two 1000pf High Energy doorknobs but I don't remember their voltage ratings...maybe 7.5KV or something but I believe they are both different dielectrics.

When the breakdown voltage is exceeded....am I right to assume that will effectively leak DC into the tank circuit?

And sure! If you'd like to offer for me to try some spares you may have just send me a PM and we can work out the details. Anything you can offer that might help shed some light on what's happening would be greatly appreciated.

Otherwise I'll have to do some poking around to see what other kinds of suitable high voltage and high RF current caps are available.

And K7SGC...if I keep the output down to around a 1KW to 1.2KW it seems like I can leave a brick on the key and it just hums along until my dummy load starts spitting transformer oil out of the vent.

[N8YX]

...if I keep the output down to around a 1KW to 1.2KW it seems like I can leave a brick on the key and it just hums along until my dummy load starts spitting transformer oil out of the vent.

This right here says some sort of breakdown threshold is being reached. Plate blocking caps are high on my list of possibilities.

[W3DRK]

This right here says some sort of breakdown threshold is being reached. Plate blocking caps are high on my list of possibilities.

That may also explain why no matter how much I increase my plate voltage the output barely goes up...maybe I'm just leaking DC to ground through my safety choke.

Ok I'll see what I can come up with to improve plate blocking...

[mw0uzo]

Great thread, nice amp too, good work :)

[W3DRK]

Thanks!

Well, I didn't get as much time to tinker last night as I had hoped, but I did do some testing with the IR temp probe. There doesn't appear to be any significant heating of any components in the tank circuit except for the 40-160 meter coil and those bands don't exhibit the dropping grid current/output so I'll chalk that up as normal heating. The blocking capacitors remain at room temperature so if I'm exceeding their breakdown threshold, they're not showing it in the form of heat.

I did notice, however, that my plate current IS dropping with the grid current and output on 20 meters after long key-downs, and I appear to be getting an odor that smells like overheating enameled wire coming from the air being blown up through the tube.

So the problem appears to be component heating in the cathode/input area of the amplifier. The input SWR remains the same so whatever the smell is coming from, it's not having an effect on input matching. The last time I had the cover off the underside of the amp I don't remember noticing any of my tuned input toroids being discolored, but I plan to further investigate tonight.

I also wanted to note that even after VERY long key-downs at about 1400-1500 watts CW on 75 meters...according to the IR probe the anode heatsink hangs right around 180 degrees F. My dummy load eventually gets too hot to touch and I start smelling the transformer oil spitting out of the vent so I have to lift, but it looks like the GS-31B's anode heat-sink is efficient enough to keep up with legal limit HF even during high duty-cycles. I guess if I want to further test endurance I'll need a better dummy load...perhaps a 55 gal drum of oil with the 50 ohm resistor in the middle would be a more suitable load? :)

My GS-35B should be here next week, I look forwarding comparing it's operating characteristics to the GS-31B...some folks say it's the same tube with a different heatsink but the datasheets say otherwise since the filament current and grid dissipation ratings are different. A comparison of the way it behaves compared to my GS-31B should be interesting.

[NQ6U]

This is all very interesting, Dieter. Keep us informed on your progress.

[WX7P]

This is all very interesting, Dieter. Keep us informed on your progress.

And keep your hands off of my Mercury Cougar!:lol:

[NQ6U]

And keep your hands off of my Mercury Cougar!:lol:

Say what?

I'm being serious here (for once)—I'm enjoying this thread. Even learning something.

[WX7P]

Say what?

I'm being serious here (for once)—I'm enjoying this thread. Even learning something.

I thought that reference might be a little too obscure. Back in the 90's, Mercury had a series of ads with Dieter the German car mechanic who always charged way more for repairs than the Mercury mechanic. Some of the ads were pretty funny.

My apolizes for dumping in the thread, it is very informative and extremely WAY over my head!

[N8YX]

Million-dollar questions regarding That Smell and the input circuit layout:

What did you use for a design? PI matching, L match...PI-L, dual PI?

Toroid vs linear-wound coils? If toroids, what mix did you use for these...and is the mix prone to core saturation at the frequency ranges you're having trouble with?

What of the filament choke: Describe its construction, bypassing and orientation to the balance of the circuit. How is the RF drive power being coupled to the cathode once it leaves the input matching network?

Another SWAG here - since the IP is now dropping along with the IG at drive levels that are approaching maximum, I think you're getting into a core-saturation/core-heating situation in the input matching network and related circuitry. How this is laid out and implemented will determine what has to be done to correct the condition. Since VSWR at the transceiver doesn't change during power degradation events, this also tells me the saturation condition is occurring on the tube side of the input matching network. Power is being dissipated in the form of heat in the output portion of this network, and the input side is maintaining its characteristic impedance. Thus, an unchanging SWR at the transmitter.

A posted schematic along with some photos might be helpful.

[W3DRK]

I found the source. It's the BIAS choke! I provide BIAS via a dedicated choke directly to the cathode instead of through one leg of the filament choke. I'm not sure of the cause yet but it's a pre-made 100uh choke with some pretty lightweight wire from RadioShack if I recall. I'm going to rewind with heavier wire for 50uh and try again...

Filament choke is good for 20 amps, my tube has a 3 amp filament so no problem there. Tuned input is PI, this picture should answer most of your questions about it's construction.

[N8YX]

I found the source. It's the BIAS choke! I provide BIAS via a dedicated choke directly to the cathode instead of through one leg of the filament choke. I'm not sure of the cause yet but it's a pre-made 90uh choke with some pretty lightweight wire from RadioShack if I recall. I'm going to rewind with heavier wire for 50uh and try again...
GDO that section of the circuit and see what the impedance does as the frequency goes up.

[W3DRK]

OK I only had about 5 minutes to work with and I didn't get a chance to GDO the BIAS choke section, but I imagine your hunch is there was a series resonance issue going on there which I agree with 100%.

I quickly rewound the choke with #22 enameled wire and ended up with 45uh so I stuck it in and after some quick testing the problem appears to be gone! At least on 20 meters. I also noticed the drive requirement went WAY down....full power out (~1500 watts) with 75 watts of drive now where before I needed the full 100 watts from my TS-570 bench exciter. I can keep the amp keyed at full power on 20 meters and grid current stays rock solid...no more drooping grid current/output, no more hot choke smells...everything looks great!

I will further test on the other bands tonight and report back.

[W3WN]

Very impressive. Thanks for sharing this!

I would love to find a way to turn your posts and pictures into a newsletter article. Even if it's a "work in progress" type -- this is the type of thing that I think people like to read about, but never hear about. What do you think? Interested? (No, no money, merely eternal glory)

[K7SGJ]

Very impressive. Thanks for sharing this!

I would love to find a way to turn your posts and pictures into a newsletter article. Even if it's a "work in progress" type -- this is the type of thing that I think people like to read about, but never hear about. What do you think? Interested? (No, no money, merely eternal glory)

You're going to make them Mormons?

[W3DRK]

Here is the cathode/tuned input with the rewound BIAS choke and gas discharge device in place. Everything is working great so far.

[NQ6U]

Looks good. And it should fit in well here on the Island, where there's no shortage of gas discharge.

[K7SGJ]

Looks good. And it should fit in well here on the Island, where there's no shortage of gas discharge.

That's why everyone was flicking their Bic. I thought they were getting ready for a concert or something.

[W3WN]

You're going to make them Mormons?Nah. That would mean he'd have to have multiple spouses. I wouldn't do that to him.

[WØTKX]

Flicking the Bic is old skool... There's an app for that.

http://www.mybiclighter.com/sites/default/files/mobile.jpg

[K7SGJ]

Flicking the Bic is old skool... There's an app for that.

http://www.mybiclighter.com/sites/default/files/mobile.jpg

Damn, I have to get out of the cave more.

[Bubba]

That looks easy.

[W3DRK]

OK, just a small update. The GS-35B is in place and working great. I ran it on filament only for about 2 hours, then 200ma idle current at 2KV for 2 hours, 300ma for another hour, then 250ma at full plate voltage for a couple minutes to get it good and toasty to make sure its was well gettered. After that I let it rip at full 3800-4000 volts under load with no signs of flashing over.

Long story short, 2KW is easy on any band with 100 watts of drive and 75 watts puts me right at 1500 watts out. Perfect!

All I can say is 2KW is hard on equipment...my watt meter gets hot, my RG8X coax was getting warm, and after a few minutes of testing various bands my oil filled dummy load let out a horrendous smell and now the SWR is too high. Oops.

I noticed the GS-35B glows quite a bit brighter than my GS-31B.

10431

[K7SGJ]

Glad you got it all figured out and up and running. It also makes a nice night lite.

[N8YX]

Nice job with the amp, and I'm glad you got it sorted!

[mw0uzo]

Does the tube produce X rays when run at such high power? Might be interesting to put a geiger counter on the top of the amp.

[kb2vxa]

No X-rays until you get up around 16KV and the tube would go south at half that. I would however like to know what's producing that eerie glow.

[W3DRK]

I think the running theory is electron bombardment reacting with the ceramic and causing a fluorescence effect of some kind.

[W3DRK]

Sorry, duplicate post.

[kb2vxa]

The thought had crossed my mind BUT knowing a bit about electron tube theory I was leaning toward ionic bombardment from the anode. Remember early CRTs with cocked electron guns and ion trap magnets? Yeah, something like that but it must be awfully intense on the inside for the glow to shine through OR the ceramic is more translucent that it ordinarily appears. Considering the color there's another possibility, the tube is gassy and the ion cloud inside is glowing like an 866. Do tubes with an "external" copper anode even HAVE getters?

[W3DRK]

Yep, the getter is an oxide coating on the indirectly heated cathode. Simply heating the cathode will getter the tube...no plate dissipation necessary. This is why everyone who uses these old external anode Russian triodes recommends running on filament only for a while before applying plate voltage to make sure any residual gasses are gettered.

As far as I know all GS-35Bs glow and apparently it's little brother the GS-31B glows too since mine does. It seems every one of these tube has a unique color glow-blue, green, purple, white...it depends on the tube. My GS-35B glows light blue to almost white, and my GS-31B glows more of a dark blue.

I doubt it's gassy, the tube in the picture highpots to 9kv before it starts leaking. :)

[WØTKX]

Looks like the grin from the Chesire Cat to me...

Good job sorting it out. :clap:

[K7SGJ]

Looks like the grin from the Chesire Cat to me...

Good job sorting it out. :clap:

It looked more like an Oreo double stuff cookie in low lighting.

[kb2vxa]

OK, toss out gas. Now it comes down to the ceramic fluorescing and a really poor quality control during its manufacture since metallic salts content varies widely. Oh, how 'bout the Cheshire Cat with a double stuff Oreo in it's mouth?

[W3DRK]

Hey, $160 shipped for a triode that will handle 1500 watts plate dissipation in it's sleep and glows neat colors when you put them to work...sign me up. :)

I don't have a SA on hand but when looking at my transmitted signal on a SDR's waterfall this amp's transmitted signal looks clean as a whistle so far.

[W3WN]

I would not run 1500 W or more through RG8X. Off the top of my head, I don't believe it's rated for more than 800 W - 1 kW, and that under ideal conditions.

I've never run more than about 600 W through it, and it got a little warm then. I could just imagine what running almost triple that power level could do.

Other than that... great news on the amp. Have fun with it.

[W3DRK]

HAH! Actually, for the most part my entire shack is wired with LMR-400 all the way out to the antenna but in this case I grabbed some RG8X patch cables to quickly hook up the watt meter. LMR-400 is so rigid that it takes a little patience to bend and twist short patches and make them stay where you want without pulling lightweight meters and switches off the bench.

But yeah, the 8X was getting REALLY warm even feeding the perfect match a dummy load provides.

[kb2vxa]

Oh dear, you reminded me of the time I destroyed an RG-58 jumper, it blistered so badly it looked like it had a disease. Odd one that, the only time I ran more than 100W it was the antenna that went south, a couple of 4CX250s actually scared it to death. Better replace those 8X jumpers with 8U before the amp finds itself looking into an open or shorted stub and SWR through the roof. ГЛУПЫЙ АМЕРИКАНКА!

"LMR-400 is so rigid that it takes a little patience to bend and twist short patches and make them stay where you want without pulling lightweight meters and switches off the bench."
That tells me you're trying to bend it shorter than the minimum bending radius. Unless you want the center conductor to migrate and cause a lumped impedance or worse, a short, I suggest finding a solution before you find another problem.

[W3DRK]

Nope, LMR-400 has a 4" bend radius which I am careful comply with. The stuff just has a mind of it's own and it likes to "spring" back to whatever it's previous form was. Eventually it gives in...but it takes patience when you have it connected to gizmos that don't have much heft to them or aren't screwed down like a watt meter.

Like I said, I just grabbed some 8X for some quick measurements with my watt meter. Now that the amp is off the the workbench and in it's operating position everything has been nicely connected with LMR-400 patch cables.

Anyway it's just coax...This "stupid american" can handle it. ;)

[kb2vxa]

Cursed on line translator! (;->) Well, you DID find a solution before finding a problem. <whew>