Ameritron AL-80B

[TonyV225]

A buddy of mine bought one of these from AES and it may momentarily hit 700 or so but then drops and idles at 500 watts allday long?? This is a single 500Z tube and I thought this amp was capable of 100 watts atleast am I wrong???

Hes driving it with a Icom 746 at 80 watts is 500 watts all hes to see out of this amplifier?? I mean hell my Yaesu 2100B with 2x 572B does that at 60 watts drive mfrom my Yaesu FT-990Im supposed to go look at that tomorrow but what should I look for as far as a cause?? He told me that amp has a built it Tuner??? I dont know until I see this thing but all in all it should be doing more wattage out correct??

What should a single 3-500Z do for output? Thanks for any help

 

[Robb]

3-500Z data sheet

 

[W5LZ]

Sounds like either a 'soft' tube, or it's not being tuned correctly.
A built in tuner? It does have a tuned input. And the output is controlled by the 'Plate' and 'Load' controls. But there's no 'antenna tuner', as such. Guess it just depends on what he means by 'tuner'?
- 'Doc

 

[Shockwave]

This time I agree with the "Crotchety Old Bastard" If it can't be tuned to sustain peaks of 1KW you probably have a soft tube. Was the amp suppose to be new? The drop in power you describe is a classic sign that the tubes cathode cannot support the full flow of current due to the depletion of thorium. Other things to check are make sure the plate voltage is not dropping over time. If the tube is weak the plate voltage will probably go up as the current goes down. If the plate current is over 450 ma or the grid current is over 200 ma, he's probably running the amp out of tune or over driving it.

 

[TonyV225]

well thats what I was saying "a built in tuner"???
I told this guy that no matter what he should have an external tuner on the backside of that amplifier between the am and antenna I mean sheesh when running that kind of power ya need a damn tuner capbable of handling more than the amp puts out to be safe more power often equals Standing Wave Racial increase.

 

[Shockwave]

There is no built in antenna tuner in this amp. It has a tuned input circuit as W5LZ mentioned. This insures the radio sees a good VSWR as it drives the amplifier. The output PI-L network can typically match an output impedance ranging from 30 to 70 ohms. That's certainly not the same capabilities of a antenna tuner. Wow, my 500th post.

 

[TonyV225]

I have 2 Ameritrons and a Yaesu FL-2100B I pretty much use my HF amplifiers on 75-80 meters and I know that the power output PEP fluctuates from band to band but a built it tuner!!?? I thought noway does it have a built in tuner Ive personally never heard of or seen such a thing in (ANY) amplifier but I wasnt gonna argue because I never owned nor have I messed with an AL-80B knowing that it most likely has no internal tuner I had no room to argue due to the fact that I never had one of these particular models which brought me here with my questions.

All I know is if hes getting 500 watts from that 500Z tube with 80 watts drive its funny considering my 2 x 572B 2100B gives me about that on 80 meters with 60 watts drive. :w00t:

 

[hookedon6]

jus a question,.......... is it wired for 110 or 220?

 

[TonyV225]

Ive thought of the 120 220 thing aswell I believe he may be on 110V so 6that may be another issue but 110 should delivw=er enough foe 100 watts.

 

[BJ radionut]

AL80B/output

Tony: The AL80B with fresh tube and good B+ (Plate Voltage) of 3100-3200dc should produce 700 to 1000w's with 50 to 100 watts drive.
When you check it out:
1/ swr between amp and rig...should be less than 1.5/1

2/output setting of the 746...is it cutting back on output?

3/ Watch the B+ voltage drop if using 120v...if more than 3 or 400v...ie:
3200(no load) dropping to 2800(under load)...

Then I would say time to upgrade source wire size (possibly #14 AWG house wire) I use #10 AWG on one amp circuit for 20amp and #8 AWG for 30amp...yes oversize by code but I get very little voltage sag...

4/ If all else looks good/ I agree, the tube is soft...
Good Luck
All the Best
BJ

 

[TonyV225]

He said he called Ameritron or somebody maybe AES and they also explained that 500Watts on 10 meters is about right so Hes ok with it but I still say he needs a tuner inbetween the amplifier and antenna.

 

[Captain Kilowatt]

He said he called Ameritron or somebody maybe AES and they also explained that 500Watts on 10 meters is about right so Hes ok with it but I still say he needs a tuner inbetween the amplifier and antenna.

That tube amp should be able to load into anything with an SWR of less than about 5 or 6 to 1 without any loss of power. One BIG issue reported with some of the Ameritron amps is indeed the tuned input. If it is off tune then power output will suffer as it not only restricts the drive level going into the amp it also generally causes the exciter to roll back power further limiting the available drive to the amp.

 

[packrat]

Most any tube amp I have ever used had lower output on ten than they do on the lower bands. 10 is also much harder on the tubes for some reason. I also agree with CK, no tuner needed if your antenna is even close to right.

 

[Shockwave]

The adjustability of the PI or PI-L output circuit of a tube amp is more about matching tube impedance to the output impedance then it is dealing with extreme VSWR. I know it's common to think of impedance and VSWR as the same thing but they are not. VSWR deals with the ratio between forward and reflected power while impedance deals with the load or current the antenna draws on the source at a given RF voltage. The output of a tube amp can compensate for some degree of impedance variation but it will not compensate for extreme reflected power or the losses associated with it.

I do think there is a strong possibility Captain Kilowatt is absolutely correct that the tuned input circuit may be the problem based on the symptoms. Without being able to check the amp on different bands or knowing what the input VSWR is on the operating frequency, it's not as easy to tell a bad tube from a bad input match. Check the input VSWR and if your on 11 meters, the 10 meter input coil will need adjustment. Power could be easily folding back into protection mode on an amateur transceiver if the input match to the amp is poor.

With respect to many HF tube amps making less power on 10 meters, that just depends on the type of tube used in the amp. It became popular with the use of sweep tubes in the output of everything from transceivers to amps. Even some RF tubes with high inductance leads and inter element capacitance like the 811A have a drop in mu or gain at 10 meters. This usually meant no more then 20% less power on 10. The 3-500Z is rated into VHF spectrum and in any decent RF deck should not drop 50% of it's output on 10.

 

[JustinDePolis]

500 watts on 10 (eh hem 11) is about right... especially if it's on 120 volts. By the way, while the amplifier can do 1kw, that is smacking the sh*t out of the tube. Run it at 500-700 watts, it will last. Do not exceed grid current and it will be happy for years.