3-500Z tube amplifier help & questions

[Foxhunter]

Hi all, was hoping to catch the attention of any of you guys familiar with Amateur tube transmitters and amplfiers, using the vintage "big tubes". Hoping some would be kind enough to help me out and give some advice.


My questions are about the 3-500Z tubes and their use. Although I haven't used it yet, I have a HF Ham amplifier with a pair of Eimac 3-500Z tubes. I spent alot of time and money (that I didn't have) on reconditioning this thing and still have a little while yet before it gets put into actual use. Been trying to do my homework and familiarize myself on this type before hooking it all up. I am very proud of it and will be keeping it 'til my dying day I think. I could've spent the time & money on a big pill maulbox with more output, but instead I wanted to have a unit of vintage radio history and am trying to broaden my horizons a little.


I've read some really conflicting information about the 3-500's and their use. Some of it certainly seems to back both what I've read online and what the amplifier restorer said to me and warned me about. He told me that by using the amplifier in the AM mode it will quickly shorten the life of the ($ expensive $) real Eimac 3-500Z tubes. Like most Amateur gear, much of it is designed for the SSB mode of transmitting, both radios and amplifiers.


I understand very well the principles behind how that all works with SSB----the power-consuming one sideband and central carrier are surpressed. So on AM it seems to make sense all what I read as well as his warnings. The 3-500Z will only hit max's on voice peaks and will not be under the load of more continuous duty as is with the double-sidebanded and central carrier AM operation. The AM mode puts maximum demand on the tubes & amplifier or radios and their components. The SSB is the ultimate in power conservation, efficiency and increasing transmit distance.


But how is it, that by the same token I've read in countless places where guys are using the 3-500Z's (safely?) on AM transmit ?? The majority are 11M guys using them here in this slice of the band. Others are licensed Amateurs that are aficionado's of the older once-more-popular AM mode. There are still whole "vintage gear" nets in place that meet regularly for the sole purpose of talking AM on old equipment----and I like the idea of that. Even with 11M, although I do "stop in" and chat with the SSB guys on 16 or 38 sometimes---I really like the challenges of AM.


In the future, when the tubes show their age more, I will upgrade them to the Graphite versions of the 3-500ZG which are supposed to be a bit better. I care about all my equipment like they are my babies and want to operate them properly, with care and longevity in mind. These guys are expensive and I don't treat them as disposeable, I am a working-class guy and don't have vast resources. Even if I did, out of principle, I still wouldn't abuse any my things. Especially growing up poor, you learn to take care of what you have.


So, what are anyone's thoughts on this AM vs SSB methods of operation with these type tubes? Reading just about anywhere online leaves confusion and mixed messages. The arguments against AM mode 3-500Z operations appear to be pretty sound and convincing. How are the 11M guys doing it, or the vintage AM Amateurs doing it?


I'd really appreciate the input and value any information or advice. Please explain what you are saying. Thanks----Mr. Foxhunter

['Doc]

Very basically, that '500' is the plate dissipation that the tube is capable of, 500 watts -> total. That means you can't 'push' them at all by doing 500 +1 watt total output. Main reason is that AM is a 100% duty cycle type mode. I also wouldn't go by the typical watt meter most people have. That thing has a plate current meter and plate voltage meter, so use them. Most amplifier manuals have some hints about what you should expect as the max plat/grid currents. They are serious about those numbers. Pushing just a little bit will probably work, but it's reducing the life span of the tube/amplifier. If you see that grid current approaching max, reduce the drive. It's your wallet, treat it accordingly.
- 'Doc

[lonesome 500]

what box?

ab or c?

voltage?

plate...cathode ...grid?

lots of variables

[Rich]

The main thing is duty cycle. On am it is 100%, so you need to run on the low tap, if equipped. Most of the better amps have a CW/RTTY postion, that drops the plate voltage. I have a friend that has a L4B, he runs on the low tap, 1000watts and it sounds great and clean. Most CB'ers run all knobs to the right. That will wear the tubes out in a hurry. Also exceed the IMD rating on the tubes.
Rich

[drdx]

I've in the past ran a pair in grounded grid on am and did fine. I think the posters above nail it, in that you dont' want to push them. I too wonder, as I hear crazy output stories for these tubes, how some do it and get away with it, as they aren't cheap. I plan to go tube, steel tube that is, mobile, as time goes on and I'm eager to learn the ins and outs.

-drdx

[Foxhunter]

I mean to get back to this thread and what I was trying to find out is important. Thanks for the replies so far, they're very much appreciated.


Yes that AM continuous duty and peak demand is of course what concerns me. And like I'd said, I've read online quite a bit of conflicting information about the use of these 3-500Z tubes on AM.


Like usual I've read where guys claim they have "continuous keydown" all night long without "any trouble". Others warn that these will smoke before long, with even simple average AM operation over time, basically saying SSB only. And yes I know that there will always be guys that dial all knobs to the right (lol?) for maximum smoke.


I've got the original operating manual in front of me. I still don't know what Class of amplifier this is---it's not mentioned and I can't tell I'm afraid to say---and I am "assuming" AB biasing (?). It's a HF amplifier from Henry Radio Electronics of Los Angeles California.


It is a relatively rare "Henry Radio 3K Linear Amplifier". A few months back I spoke twice to 'ol Ted Henry himself via telephone inquiring about the amplifier and availability of parts & service for it. A nice older knowledgeable gentleman I can say. Also had several e-mail discussions with Dan Magro aka "Radio Dan" about it. Although not their "absolute biggest amplifier", it's an unusual model Henry and they didn't make many of them, was told several times it's quite rare and the most heavy-duty of all the paired 3-500Z types. Was also told that, unlike many amplifiers that have somewhat "stretched" high output claims, the Henry Radio units were intentionally factory underrated.


Like I said I don't know how it's biased for absolute sure, and do hate to assume. It does say "The 3K linear amplifier is a one-stage grounded grid amplifier designed for CW, FSK and AM operation from 3.5 to 29.7 MHz". It is 220VAC fed.


It does have the selector switch for both CW (I take that as AM also) and SSB. It is certainly capable up to 4000VDC plate voltage but that of course is at the utmost upper end.


There is all sorts of data in the manual for different modes and scenarios.


It does say for CW:
"a multimeter reading beetween 250ma and 280 should be obtained, indicating a plate voltage of 2500 to 2800 volts. Then set the switch to SSB. The multimeter should indicate from 3300 to 3600 volts".

It does say for AM linear operation:
"set the power switch to the TUNE-CW position, tune and load the amplifier. For actual operation, the drive should be reduced to 100ma, where the 3K will operate at one kilowatt input and about 350 watts carrier output."

The Multimeter panel meter reads from 0-400 DC
The Amperes panel meter reads from 0-1.0 DC

I know when it comes time to actually put this thing in-line I'm going to need some help & advice when the time comes. Although there are some very basic similarities, it's more involved than my Elkin, Palomar or Kris tube amplifiers.


I been debating to put one of the Kenwoods either the TS940SAT or TS820S in front of it, or maybe the Yaesu FT101ZD. (?)


The biggest concerns I also had is how well the Eimac 3-500Z tubes can take AM transmitting. So the HF amplifier itself may be designed for and capable of AM---but I wondered if there is merit to the guys who say the tubes themselves don't like AM mode useage. Tried to give a little more information here for the questions asked about variables.

Eimac 3-500Z Data Sheet Page (very nicely laid out)
[Please login or register to view this link]

[North Texas Mudduck]

i have a modified heathkit sb220
it has 5 tubes
3-500zg
it was built back in in 2005
it has gone from base to mobile from mobile to base and it has never given me any problems
why because the man who built it knows how to build them

last year a 4tuber came back in to be fixed couldnt imagine what would have went wrong
it was the relay burnt out
tubes still working fine
it was built back in 1975
talks on the Superbowl on Am
i bet your 500z restorer guy would flip out if he seen this


my 5tuber requires 500 bird watt deadkey and modulate to 1000 will drive it all day long
i drive it at 250 watts deadkey and modulate to 1000 thats just driver
it will talk all day long and strong

[Foxhunter]

NorthTexasMudduck thanks for replying and I've seen you mention that modified SB-220 a number of times in the past. I've seen how you described it and can you show us some pictures of it? I've been curious about it since last year when I first saw it mentioned. Is it a 2-piece deal? I'd imagine it has to be. Post some pic's if you don't mind it would be cool to see.

I've seen the Heathkit SB-220 before in-person and almost bought one. My Heathkit SB-200 isn't much smaller cabinet-wise. Considering how big the 3-500Z's are, the chimney's and the ceramic bases for them are big also---the (5x) 3-500Z I'd imagine would be a 2-box setup with the SB-220 as a driver for a 2nd box with the (3x) other 3-500Z's?

Not sure how that works but it sounds of course interesting. I just can't picture fitting all 5x 3-500Z's in the SB-220 cabinet by it's size. And the other reason for cooling. Cooling is inadequate with the two tubes alone! Most will install the glass chimneys and/or do one of the Harbach fan mods on the SB-220 or 221 to generate more cooling to save the tubes.

For cooling mine has the industrial Dayton blower. I saw on another site where someone had a 12 TUBE 3-500Z AMP ! Boy, talk about a shack heater! You'd be roasting next to that thing. It was built some time ago and the way things are now the steel or ceramic tubes are the way to go. One of them could rival several 3-500's. The Eimac steel tube is definitely in my future at some point for monoband operating.

But still again, many like yourself say they have had such good luck with running them on AM. And yet so many others say to let them coast or loaf and it preferrable to use them for SSB if possible. I'm not sure it's so much a matter of the amp builder or manufacturer, as it it the nature of the tubes. Or thinking about it, perhaps it's both?

[North Texas Mudduck]

we have a 4tuber running right now in lubbock texas its a smaller box
it takes a 2 tube 3-500z to drive it
but the 2 tuber can drive the 5 tuber alot better
as far as cooling oh yes it has to have a blower
another guy actually has a blower on one side and i puller on the other side and its hooked to a dryer vent hose going to a dryer vent he installed in his shack
so hot air goes outside

the 4tuber that just went online was on sunday
he bought it from a superbowler and its been running with him for 14 years same tubes

you been looking around and i cant find where i seen it
its a Aluminuim case or cabinet that will hold 3 - 500z

im fixing to part with my 5tuber and get either a 6 or 8 tuber and use the 3 tuber as a driver
and have like a tuber or maybe a varmit 600 or 1000 as driver on supermod hi
or maybe just another 1 tuber

opps did i typoe that outloud
dang
well anyway
im looking for the 3 tube cabinet

[North Texas Mudduck]

oh and just for grins ans shens
the 4 tuber and the 5tuber will lay the needle in the 45 degree angle on a pdc 6000 on a deadkey
now if you say audio it will leave the needle in the corner and its over with for that meter
done been there
and yes that is in the 5000 watt scale

[216]

The chinese versions from Rf Parts are awesome.Ive been using a pair of these for around 15 years in a homebrew i built and they havent lost a watt.My am deadkey is 900 watts swinging to 1650 pep.Make sure the tube pins get plenty of airflow.I also built mine grounded grid.

[Red Warrior]

I almost bought a Heathkit SB220 last week. Two of my Elmers cornered me at a local hamburger hut and bent my ear for over an hour. They told me the SB220 is a fine design for SSB but was not designed for continuous duty on AM. Seems the Heathkit company was looking for a way to reduce footprint and weight in the amplifier and designed the power supply for SSB operation. Airflow was also a creative design feature. Continuous duty on AM will eventually damage the 3-500Z tubes but before that happens the power supply will fail. Beefing up the power supply is a possibility but if one is going to all that trouble you may as well get an amplifier with steel tubes that will handle the continuous duty of AM.

[Foxhunter]

I just replied, but it was kicked-back-----as I see Red Warrior also had also recently replied. Now see---what he said that is exactly what I was saying that I was told about AM & 3-500Z's---"they don't mix", or atleast not for long. That seems entirely plausible despite assurances from what I've read elsewhere where others claimed to the contrary. I don't know for sure. Some actual manufacturer recommendations, specifications for duty or instructions, clarifying this issue specifically would be really be in order.

As far as the power supply, for mine particularly, it is a monster and will never fall-short, nothing like the SB220 or similar other 3-500Z amps. So in that one aspect, I have nothing to worry about whatsoever. Definitely not all 3-500Z amplifiers are created equally. Mine particularly has an actual industrial Dayton blower, made for heavy-machinery/industrial useage, so the cooling is pretty much covered. Still, as for the actual properties of the tubes themselves......?

216----Here is a small 3-500Z Eimac (Original) vs RF Parts (China made) tube & chimney comparison PDF I read a couple months back. It's a PDF link so a PDF file download-prompt will follow the link.
[Please login or register to view this link]


When I change tubes at some point, I will go for the 3-500ZG using the graphite models, as they have been reported to perform better. Although, I really like using Factory-OEM equipment with everything I own when possible. High-quality aftermarket parts can be decent, if the manufacturing standards are kept high. I've read mixed reviews with the RF Parts "Taylor" made-in-china tubes etc. Not sure.


I've seen some original, unopened "still brand new in-the-box" Eimac 3-500Z's----go for really high-dollar amounts on Ebay recently. As I said I love OEM parts, but with 3-500's, they degrade without use. Although almost anything can vary, most agree that the 3-500's have a limited shelf-life. Someone somewhere will beg to differ, but that's generally reported as a given with these particular tubes unfortunately. So although unopened and still new in the box, those high-dollar unused Eimacs might not be viable! They would make collector pieces just for the sake of owning original unopened tubes I guess, I can see that if you have the money for collecting things of that nature.


And like I originally said in the thread topic, there are many warnings posted online (and given to me in-person by an expert) telling us that AM use is horrible on these tubes and severely shorten tube life. Then you read others who say they've done it for years. I just worry that people that use 3-500Z on long AM key-downs are the same that volt a Toshiba to 24VDC and hammer their boxes too hard overdriving. It's tricky to read around online and sift through it all, I wish I could read some real data on AM useage vs SSB on the 3-500's.


Northtexasmudduck----I thought you were going to post some pics of that 5-tube 3-500Z amplifier, what happened? It sounds cool and would like to see it, probably many others reading this thread would too. Post some pics!

[Mr510inFl]

Foxhunter my good friend has used his L4B for 8 yrs now on AM with the same tubes. I think he has the Taylor made 3-500z tube's. Like others have stated he doesnt get on there and have long conversations nor does he run wide open. I think he his driving it with a 300 watt Thunderbolt tuber.

[North Texas Mudduck]

[Please login or register to view this link]

heres even better than a 5 tuber

its seems in our changeover we lost our picture section
where did our pictures go

['Doc]

What's the maximum plate dissipation for a 3-500 tube? Since AM is a 100% duty cycle, don't exceed that max plate dissipation for output. Simple. Two tubes? Slightly less than twice the plate dissipation. Nine tubes? Besides being a very idiotic idea, slightly less than nine times the max plate dissipation. None of which accounts for the power needed for the heat dissipation. I'll bet the power company just loves them 16 tuber guys!
- 'Doc

If my opinion hurts your feelings I'm sorry. It's still a very stupid way of doing things.

[North Texas Mudduck]

and then you can turn to the superbowl and listen to all them stupid folks that have money locking down the channel
using them 3 4 5 and 8 and 9 12 tuber 3-500zg

it dont hurt my feelings
if we got money to pay then we got money to play

these tubes are very easy to come buy and alot cheaper than the bigger tubes
but anyway
different strokes for different folks

[engineslick]

the first thing you should have done with new tubes is to cook them in for a min. of 48 hours that is put them in box turn on and dont key for 48 hours. if you want more power drive it with a modulator some came with one built in like jb2000 has a built in jb150 which uses an 8417 tube drive that you adjust on back. use the lowest deadkey as possible without over-modulating. you can get a lot out of 2 of these tubes on pep and will last as long as you swing in the drive not high driving tubes make it like side band low deadkey and a lot of swing. any where from 50-200 watts out deadkey and sould swing 1200-2000watts depending on meter and radio and driver used.

[Slowdraw]

A few things can affect the longevity of 500z's besides totally abusing them.....

Airflow. Heathkit amps barely get by in this department. Most Henry amps have overkill. I've seen Heathkit amps run so hot they melt the base pins off the tubes. Not a pretty sight.

Tuning & Loading. Tune the amps for a little bit lower peak power than they can actually achieve. Don't be greedy. If you need more power, buy a bigger amp.

Parasitic oscillations. Some amps have poorly designed parasitic suppressors. These are those little resistor/coil things that connect to the tops of the tubes. Stock Heathkit suppressors are notoriously poor. Some work o.k., but change the tubes and problems can crop up. Here is a good website I found with SB220 mod parts: [Please login or register to view this link]

The transformer is the weakest link in a SB-220. I've replaced a few over the years with Peter Dahl hypersil transformers. They are a tight fit, but a much, much better transformer.

Slowdraw

['Doc]

Just some odds and ends.

I like 3-500 tubes. Got several years of experience with them, probably made every mistake using them that can be made (at least once). If I had all of the dead or flattened ones I've ever made back, I could decorate a pretty good sized Christmas tree with them.
The biggest regret I have is that Eimac hasn't made a 3-500 tube in over 10 years, and they DO have a limited shelf-life.
Best advice is to don't think of them as miracle workers, that '500' on the end tells you just how much they are rated for, and depending on the particular mode they are used with, that '500' does not stretch much. Most will accept something between 65 and 100 watts drive. A bit more/less isn't going to make a huge difference. Dropping the filament voltage to what it's supposed to be is the best modification you can possibly do as far as life expectancy goes. A 1/10th of a volt makes a HUGE difference. Maybe the absolute best advice about modifications is from Richard Measures (sp), especially with SB-220's. The three things about an SB-220 you really need to pay attention to is that when they were designed/sold, they talked about input power, not output power levels. They have difficulty with the power supplies, they were never adequate. And they sort of got close with cooling, and it was never adequate. Those three things are true for any amplifier, not just the SB-220's. Even more so for the 'metal' tubes.
Metal tubes. The most forgiving that I've seen so far has been the 3CX1200's. I like that thing too. It is sort of forgiving with stuff (which is a biggy for me!). They have limits just like everything else, but don't tend to bite quite as fast as some others (3CX1500's for instance).
Oh well, 'nuff of that stuff.
- 'Doc