ZETAGI B300P ANY GOOD

[WARLOCK]

ZETAGI B300P AMP ,your thoughts ? are they any good ? what sort of power supply will be needed to run them .

[StoatTB]

Poor quality, prone to splattering and not much use on SSB. Probably a minimum of a 20amp supply.

[Coppernob]

Amperes = Power divided by Volts..
So at the nominal 13.8v supply..
The amp delivers 300watts
Voltage. 13.8 volts
=21.7391304 Amps.
Thats just the Amp requirements add on top the radios requirements and any other add ons illuminated meters etc..
Minimum 30amp supply 40-50amp supply would be better plenty in reserve.These calculations are based on running the amp at full bore.
Regards Coppernob Roger.

[StoatTB]

These calculations are based on running the amp at full bore.

It doesn't, none of the Zetagi/RM/whatever run at the rating they claim to. The usual hype from the Italian makers...

http://www.youtube.com/watch?v=2Wf8KbWvSSw

[bigpimp347]

i have yet to see a B300P deliver more than 120w on AM/FM

biggest over hyped piece of crap about..
sold a 300w yet you have more chance getting aids from a toilet seat than 200w from a B300p..

the older early square 300p and 300PS do slightly more power but not a lot..
and i've had a few 300P i rarely get over 110w, even having the crap driven out of them they stop around 120w..!!

avoid, get a RM/KL if you must or try and get a decent linear from the US..

[26TM944]

...or spend the money on an antenna & feeder upgrade and do much better without the mess these not-so-linear amps produce.

I had a B300P and a B550P years ago and they were OK for FM stuff when playing about but I never really gained much from them on SSB. Sold them both when my interest went in another direction.

In fact I can remember turning down the power in my 2830 to drive the 550P without it complaining too much!

73

Steve

[simon26OD004]

Amperes = Power divided by Volts..
So at the nominal 13.8v supply..
The amp delivers 300watts
Voltage. 13.8 volts
=21.7391304 Amps.

That's assuming 100% efficiency, which is impossible.

I used to run one on a 45 amp PSU, it was many years ago, but from memory I think it used to pull about 30 amp.

As already said, you'll never see anywhere close to 300W out of one. If you have a look around the web, I think they are actually spec'd at 400W SSB out, lol.

[radio pete]

I have an old 300p works well draws over 35 amps @ 14v on full chat some splatter but no complaints as yet seen 190w+ on 10M FM & works well on SSB with all good audio reports (no bull) not bad for a uint with 2X 60w outputs oh & keeps the shack warm.

[Coppernob]

Amperes = Power divided by Volts..
So at the nominal 13.8v supply..
The amp delivers 300watts
Voltage. 13.8 volts
=21.7391304 Amps.

That's assuming 100% efficiency, which is impossible.

I used to run one on a 45 amp PSU, it was many years ago, but from memory I think it used to pull about 30 amp.

As already said, you'll never see anywhere close to 300W out of one. If you have a look around the web, I think they are actually spec'd at 400W SSB out, lol.

Of course,having not had the chance to evaluate one of these I quoted the figures to the manafacturers spec...Are they really that bad then?
Regards Coppernob Roger.

[RD250]

These calculations are based on running the amp at full bore.

It doesn't, none of the Zetagi/RM/whatever run at the rating they claim to. The usual hype from the Italian makers...

http://www.youtube.com/watch?v=2Wf8KbWvSSw

Looking at the PCB in that video the PA is a push pull design presumably powered from 13.8V.

The big output transformer has probably got 3 or 4 turns of white wire through it. I would expect there to be 4 turns making it a wideband 16:1 transformer.

This will transform 50 ohm to about 3 ohm meaning each PA transistor will see 1.5 Ohms each.

If the transistor is powered from 13.8V then the collector can swing maybe 13.5V peak or 9.5V rms.

This means ((9.5 * 9.5) /1.5) Watts per side = 60W

So a ballpark estimate for the power from this amp will be 120W.

However, to get decent SSB performance (low distortion) I'd expect this would be derated to more like 100W PEP assuming the amp is biased adequately.

I'd assume the PA will be just over 40% efficient so it probably takes about 300W DC input power to deliver 120W of RF and that 300W figure is presumably where the amp gets its name from.

[simon26OD004]

Amperes = Power divided by Volts..
So at the nominal 13.8v supply..
The amp delivers 300watts
Voltage. 13.8 volts
=21.7391304 Amps.

That's assuming 100% efficiency, which is impossible.

I used to run one on a 45 amp PSU, it was many years ago, but from memory I think it used to pull about 30 amp.

As already said, you'll never see anywhere close to 300W out of one. If you have a look around the web, I think they are actually spec'd at 400W SSB out, lol.

Of course,having not had the chance to evaluate one of these I quoted the figures to the manafacturers spec...Are they really that bad then?
Regards Coppernob Roger.

They are not bad for what they are, but what they are is a cheap mobile CB amp, fine for using from the car, but they are quite notorious for causing TVI probs when run from home. Thing with CB amp spec's is they are exaggerated to say the least, best way to work out what they are capable of is by getting the datasheet for the RF transistors it uses and looking at that.

*Edit* Or ask RD250 who seems to have summed it up quite nicely while I was typing

[RD250]

Yes, looking at the MRF455 datasheet the output impedance of the transistor is about 1.7 Ohm resistive at 30MHz at 60W.

So that stacks up with the output transformer being a 16:1 with 4 turns as this transforms a 50 Ohm load down to 3 ohms which is evenly split in the transformer as 1.5 Ohms for each 60W transistor on each side.

Although the MRF455 datasheet says 55% efficiency for this transistor this will be for a tuned design.
The Zetagi is a broadband PA with wideband transformers so the efficiency will not be much better than 40%.

I'd imagine you could use the Zetagi across several HF ham bands (maybe 40m through 10m) because the transformers are wideband although there might be something else in the circuit that limits it to just CB. However, the odd order harmonics would be VERY high if you used it on the lower bands. eg 3rd harmonic or 5th harmonic.

BTW the guy in the youtube video was using a cheapo (i.e. rubbish) PEP wattmeter and was running the amp into an antenna instead of a proper dummy load so I'd ignore the indicated power readings he got for this amplifier. Also, if he wants to experiment with any high power drop in transistors then he'd have to add a turn to the output transformer to get it to 5 turns to transform 50 ohm down to match the lower impedance of the higher power transistors.
But I can't see the point as the heatsinking on the amp is already woefully inadequate for the MRF455 power levels.

[George EI7KO]

I have an old 300p works well draws over 35 amps @ 14v on full chat some splatter but no complaints as yet seen 190w+ on 10M FM & works well on SSB with all good audio reports (no bull) not bad for a uint with 2X 60w outputs oh & keeps the shack warm.

They do get bloody hot all right Pete. Fried egg anyone. Not the best of an amp but not the worst either. They are made to a budget. Whip the lid off one and compare to the guts of a hf linear. No contest. Simple case of you get what you pay for innit??

[bigpimp347]

I'd assume the PA will be just over 40% efficient so it probably takes about 300W DC input power to deliver 120W of RF and that 300W figure is presumably where the amp gets its name from.

Ahh, input and output...!!

Yaesu FT-401/501 500w Input..!! every CBers eyes lit up when they saw the 500w, yet were glazed over when they saw the input bit..

a lot get confused with input and output..
Heathkit SB220 2kw input..about 600w output...big difference.. but show the input over the output means more sales..!!

[RD250]

It's certainly not going to do 300W RF output. However, if you ran it from 13.8V DC with good quality leads from a rock solid PSU and then brutally overdrove it into saturation the PA would try to produce a square wave at the transistor collectors. This would mean mega high third harmonic and high 5th harmonics but you might see >150W on a CW signal even though the devices are only rated at 60W each.

If you ran it from 15V DC it could go even higher but I doubt that it would be very good for reliability

For SSB use I doubt it would produce very high PEP and I'd expect it would produce a dirty signal if you drove it much past 120W PEP when powered from a 13.8V PSU and this assumes the circuit has a decent bias circuit for SSB operation.