Palomar Elite 900HD technical info requested

[VA3ES]

I have a Palomar Elite 900HD which I purchased from ePowerAmps.Com. It runs four 2SC2879 Finals. Does anyone have any info on this amp, specifically what type of bias (class C or AB1)? Any experience with this amp?

I'm getting ready to use it on 10M and need to know whether I need to upgrade the bias on this amp.

 

[Robalo]

Palomar Elite 900 HD Linear Amplifier

for higher powered radios

• Recommended for radios with less than 15 watt dead key and 75 watts of swing​
• 25 db Preamp​
• 4 - 2879 Transistors; requires radio with 40 watts plus to drive ampl​
• Power: Approx. 400-500 watts; Max peek envelope power input approx 900 watts
• Approx 80 AMPS OF 12 VDC POWER TO RUN THIS AMP AT FULL POWER​
• LED INDICATORS FOR Power ON/OFF - Pre-Amp On/Off - Power Output​
• hi-med-low switch​
• Size 11" x 6 5/8' x 3'​
• SSB Delay triggered by ​

 

[VA3ES]

Thank you, Robalo.

Yes, I am quite aware of the amp's specifications. There is no "hi-med-lo" switch; this amp is direct drive, and power is controlled by the exciter.

What I'm specifically looking for is details about the bias circuit, and any user reports and experiences. How has the amp performed for the typical user? How has the reliability been?

 

[Toll_Free]

I really don't mean to be a dick here, but a licensed ham for 42 years, and you can't look inside the covers and see if their is a diode clamp bias in it?

If you HONESTLY want to put it on '10 meters', then first you need to destroy whatever CB bias circuit is in it, put in a real thermal tracking bias, and then put in low pass filtering.

A pi network on the input side with a very low Q would also be helpful on your distortion generator. Will help to keep your "4 watt' ham radio loaded correctly, just like on a grounded grid amplifier.

Hope that helps. NO CB amplifier has a real bias circuit in it, sans a VERY small handful, and even those where generally junk.
--Toll_Free

 

[VA3ES]

I really don't mean to be a dick here, but a licensed ham for 42 years, and you can't look inside the covers and see if their is a diode clamp bias in it?

If you HONESTLY want to put it on '10 meters', then first you need to destroy whatever CB bias circuit is in it, put in a real thermal tracking bias, and then put in low pass filtering.

A pi network on the input side with a very low Q would also be helpful on your distortion generator. Will help to keep your "4 watt' ham radio loaded correctly, just like on a grounded grid amplifier.

Hope that helps. NO CB amplifier has a real bias circuit in it, sans a VERY small handful, and even those where generally junk.
--Toll_Free

Thank you. Now we're getting somewhere!. I haven't opened up the amp yet.

If you HONESTLY want to put it on '10 meters', then first you need to destroy whatever CB bias circuit is in it, put in a real thermal tracking bias, and then put in low pass filtering.

That's precisely what I intend to do.

I have the manual for the Ameritron ALS500 and was going to copy their bias system. I'm not thoroughly experienced with solid state amps, having dealt with tube amps all my life.

I bought it because it was cheap, and I figured I could modify it to suit my needs. Rather than rag on me for not peering inside (I do have a life, ya know!) you might suggest a suitable biasing circuit I could use.

BTW - I'm going to drive it with (variably) either an HR2600, or possibly a Magnum 257HP, or my Yaesu FT857D. I'm also going to use Ameritron's ARF100 bandpass filter box. As I also intend to use it on other bands, a fixed pi-network on the input wouldn't be practical.

Any other advice?

 

[VA3ES]

A note to mackmobile43: It has no driver stage. it runs 4 X 2SC2879's.

 

[Toll_Free]

1. Odd order harmonics are going to be through the roof. I really hope you don't have any 75 mhz to 90 mhz stuff in your area actively being used.

2. Ameritron and other mfgs, as well as Messenger (A CB linear company) either have, or are coming out with, bandpass filters that are switchable.

3. Not sure that I'd call something Ameritron really good, but it HAS to be better than what you see in the CB linears..


According to Toshiba, your amp will saturate with about 4 watts of carrier per device, and about 10-12 watts (15 max) on SSB. That's with a properly configured input circuit, so watch the output on a scope and adjust it accordingly. If you incorporate a variable bias network then you can adjust the bias for the cleanest output waveform, and not worry about resting current... This is what I normally do, as I prefer to actually have modulated RF coming out of my amplifiers, and not just idle them as shack heaters

If you're hell bent on not running switch output filters on it, please email me and let me know what freq's you'll be on when running it on HF, so I can ensure I don't run on the 3rd harmonics.... And PLEASE don't use wideband dipoles or other antennas... At least a HiQ tuned antenna would tend to block some of the garbage going in and out.

Also, the ferrite in that amplifier I'd be willing to bet is a type 60 something mix... Most CB amps nowadays are, as it gives a much better power transfer at 27-35 mhz than does the 'older' 40 series ferrites. My Texas Star Sweet Sixteen (8 x 2879s) and Messenger M2000 (16 x 2879s) all fall apart below 40 meters, and 40 will start getting the output xformers warmer than normal. The splitters and combiners are all fine to MF, it's the transformers that give you problems. And realize, as the transformers heat up, it's just like the bias problem.... You'll have loads more garbage on the output. One way to mitigate this is to 'shunt feed' the transistors, using a seperate choke on each 'pill' to feed DC, and pull the DC OUT of the transformers... Pass RF to them via a .1 uf chip or unelco.

Welcome to CBTricks should have a schematic of your amp... They are usually the first place I check when working on CB stuff.

Also, remember on your 857 (I have one, too), it's the same chassis as the 897, meaning it has the '20 watt mode'. I can't recall if it's +12v or ground to the brown wire hanging off the power harness, but that puts the radio into 20 watt PEP mode on HF.... Pretty much perfect for driving the '4 pill' you have now.

I use a 2510 to drive 4 2879s in a highly modified Texas Star 500, a sweet sixteen, and the 500 reduced a LOT to drive the 16 transistor amp. 2.4kw output of the mobile is nice, but finding an antenna that will handle it


--Toll_Free

 

[VA3ES]

1. Odd order harmonics are going to be through the roof. I really hope you don't have any 75 mhz to 90 mhz stuff in your area actively being used.

I intend to use a remote tuner (such as an SGC or equivalent). They use small pi-network BP filters in the output which should suppress any 3rd order trash.

2. Ameritron and other mfgs, as well as Messenger (A CB linear company) either have, or are coming out with, bandpass filters that are switchable.

Ameritron uses their ARF1000 switchable BP filter built-in to the ALS500.

3. Not sure that I'd call something Ameritron really good, but it HAS to be better than what you see in the CB linears..

According to Toshiba, your amp will saturate with about 4 watts of carrier per device, and about 10-12 watts (15 max) on SSB. That's with a properly configured input circuit, so watch the output on a scope and adjust it accordingly. If you incorporate a variable bias network then you can adjust the bias for the cleanest output waveform, and not worry about resting current... This is what I normally do, as I prefer to actually have modulated RF coming out of my amplifiers, and not just idle them as shack heaters

If you're hell bent on not running switch output filters on it, please email me and let me know what freq's you'll be on when running it on HF, so I can ensure I don't run on the 3rd harmonics.... And PLEASE don't use wideband dipoles or other antennas... At least a HiQ tuned antenna would tend to block some of the garbage going in and out.

As I mentioned, I intend on using the Ameritron ALF1000 switchable filter on the output.

Also, the ferrite in that amplifier I'd be willing to bet is a type 60 something mix... Most CB amps nowadays are, as it gives a much better power transfer at 27-35 mhz than does the 'older' 40 series ferrites. My Texas Star Sweet Sixteen (8 x 2879s) and Messenger M2000 (16 x 2879s) all fall apart below 40 meters, and 40 will start getting the output xformers warmer than normal. The splitters and combiners are all fine to MF, it's the transformers that give you problems. And realize, as the transformers heat up, it's just like the bias problem.... You'll have loads more garbage on the output. One way to mitigate this is to 'shunt feed' the transistors, using a seperate choke on each 'pill' to feed DC, and pull the DC OUT of the transformers... Pass RF to them via a .1 uf chip or unelco.

Welcome to CBTricks should have a schematic of your amp... They are usually the first place I check when working on CB stuff.

Also, remember on your 857 (I have one, too), it's the same chassis as the 897, meaning it has the '20 watt mode'. I can't recall if it's +12v or ground to the brown wire hanging off the power harness, but that puts the radio into 20 watt PEP mode on HF.... Pretty much perfect for driving the '4 pill' you have now.

I use a 2510 to drive 4 2879s in a highly modified Texas Star 500, a sweet sixteen, and the 500 reduced a LOT to drive the 16 transistor amp. 2.4kw output of the mobile is nice, but finding an antenna that will handle it

--Toll_Free

Thank you! An excellent dissertation! This have given me much food for thought. There is more work involved here than I thought. Hmmmm.... I wonder if I'm not better off getting an Ameritron ALS550 (runs the same 4 X 2879's) and selling the Palomar? At very least, the Ameritron is designed for amateur service!

 

[Toll_Free]

If you want 60, 78/80 and 160, then you need to get a new amp.

OTHERWISE, what you have will work FB, with a bit of work.

--Toll_Free

 

[bob85]

i have a 900v with a useless class C drive stage,
it has a bias circuit for the 2879 finals supplied from a 3 terminal regulator but its poorly implemented,
theres nothing wrong with the bias circuit design but plenty wrong with how that circuit has been installed in the amp, ie no thermal tracking due to misplacement of two diodes seen just above the bias adjustment pot, the regulator and pass transistor are bolted to the board and not heatsinked,
the circuit is not too difficult to modify to make it work correctly if you have some experience with biasing but there are other issues with the amp.

 

[mackmobile43]

A note to mackmobile43: It has no driver stage. it runs 4 X 2SC2879's.

That's why I deleted my prior post after re-reading the title after assuming it was the normal 900 which was biased on the final stage only.

Not to be a dick.

 

[VA3ES]

Unless one is running strictly FM, don't understand the use of class C biasing? All class C does is cause distortion on any amplitude modulated signals, whether AM or SSB.

 

[mackmobile43]

Unless one is running strictly FM, don't understand the use of class C biasing? All class C does is cause distortion on any amplitude modulated signals, whether AM or SSB.

I've not tested that theory as of yet on AM but have done extensive testing on SSB and will do so as time permits.

 

[Toll_Free]

Unless one is running strictly FM, don't understand the use of class C biasing? All class C does is cause distortion on any amplitude modulated signals, whether AM or SSB.

It's cheaper, easier to implement, eases thermal issues and above all else, allows a greater amount of Pout (saturated) than a biased amplifier.

It also allows higher levels of Vce, allowing higher again amounts of power output, etc.

--Toll_Free

 

[mackmobile43]

It's cheaper, easier to implement, eases thermal issues and above all else, allows a greater amount of Pout (saturated) than a biased amplifier.

It also allows higher levels of Vce, allowing higher again amounts of power output, etc.

--Toll_Free

so this means my rig is gettin out with my davemade 2x4, right?