Check Out My Solid State Semi-Big Mawl Linear for AM

[Glenn NY4NC]

Question..... what do you do when you're paying two mortgages, eating Mac and cheese for dinner every night and can't afford to put gas in your car?....... you buy another linear amplifier of course!!

Just scored this baby. The link shows another buyer but I was offered another unit the seller had as a second chance offer being the next highest bidder.

I'll pick it up when I get down to NC at the end of the month. Now I have to look for a power supply.
Either a single 50v @ 60 amps, or two 50v @ 30amps, or four 50v @ 15amp supplies. There are quite a few HP models on E-bay that will fit the bill.

Should do 300-400w carrier on AM with sufficient headroom assuming decent supplies. 

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=48700&item=5814923086

[KE1GF]

YEAH BABY... YEAH

[KE1GF]

YEAH BABY... YEAH

Looks like a nice piece of gear glenn, good find dood.

[Glenn NY4NC]

Thanks Bill...

Not Mosfet but still cool!!!!.... Now I have to hunt the surplus places for power supplies..

I plan on setting it up in the room adjacent to my ham shack so I don't have to hear the blower noise.
I have a feeling those fans will make quite a racket!

[K1JJ]

Good find, Glenn!

I've always had an interest in solid state linears for IPA service. But the problem has been poor 3rd order IMD for most of the ones I've checked out. They are usually about -25db at best... compared to tube linears that can be as high as -40db for 3-500Z's, etc.

Anyway, it's a good point that they are using 50V, since this improves things greatly. 

If you come across the actual factory written specs for IMD, please let me know, as if they are -32db or better, I may be interested in finding one of those too.

[BTW, there was a time in 1974 when I lived on peanut butter and jelly sandwiches. The money went for ham stuff and dog food... ]

73,
T

[Glenn NY4NC]

Hi Tom;

-36db IMD worst case, as stated in the technical manual. (which I'm getting with the amp) That's pretty decent.

I was originally looking at the Icom and Yaesu amps but the $4k and $5k prices pretty much put an end to that.  This was a great deal for the price, commercial quality build, etc...
 

Good find, Glenn!

I've always had an interest in solid state linears for IPA service. But the problem has been poor 3rd order IMD for most of the ones I've checked out. They are usually about -25db at best... compared to tube linears that can be as high as -40db for 3-500Z's, etc.

Anyway, it's a good point that they are using 50V, since this improves things greatly. 

If you come across the actual factory written specs for IMD, please let me know, as if they are -32db or better, I may be interested in finding one of those too.

[BTW, there was a time in 1974 when I lived on peanut butter and jelly sandwiches. The money went for ham stuff and dog food... ]

73,
T

[K1JJ]

Wow, -36db 3rd is fantastic for a solid state amp. 

I wonder if they are using some form of RF feedback to get that figure or maybe the 50V helps do it. Do look at the manual/schematic when you get it and post later.

Most of the ham amps show about -25db in their manuals.

I looked at the eBay listing pics and it appears you will need to either interface to that complex 40 pin? system or just rip out the stuff and manually control it.

Either way, let us know how you finally configure it and how it works out on the air, OM.

T

[WA1GFZ]

Grear Deal Glen,
Looks Harris. I have the board from the 400 watt amplifier and Harris uses a cool RF feedback method through transformer coupling. You will lose IMD if you try to run above 1 KW out. Those look like MRF150s in 300 watt modules derated to 250 for long life. Now you need a RF590 and matching exciter to feed it and you will be set for life. Jap crap does not compare to this top of the line mil stuff.
I think the RF590A RX is the best analog RX designs I have ever seen but have been told the Racal RA6830 is comparable.

[WA1GFZ]

BTW Glen.....I may have the power supply modules for the day when I find one.
They are about a foot cube off line switchers 48 V 36A each.

[W2VW]

Nice deal. They must be doing something pretty funky with inverse feedback. Look at the power output figures verses frequency. Fooling Harris stuff to work with plain old ham gear is usually not a big deal.

[KE1GF]

Thanks Bill...

Not Mosfet but still cool!!!!.... Now I have to hunt the surplus places for power supplies..

I plan on setting it up in the room adjacent to my ham shack so I don't have to hear the blower noise.
I have a feeling those fans will make quite a racket!

Glenn that's pretty much the reality for solid-state PA's with uniform drive levels for the input. MOSFET's gates as you know in the linear region are purely capacitive... For switchmode into miller plateu is a different story. So getting a uniform drive level across the entire HF spectrum requires a lot of fancy footwork with swamping and switching ratios etc... Bipolars are still the best for multi-banded linears as far as broadband input across 30Mhz.

My mobile amp uses bipolars, broadband input/output and they're very rugged. I've got 1kW of collector dissapation good for about 600W PEP. The screwdriver is the output filter. I disabled the input power/output SWR overload in the amp, it's just for goof-balls that will dump 100W into the amp for extended periods. It sill has the thermal shutdown... The heatsink really isn't big enough for AM so I put lots of air through it with no problems yet.

[Glenn NY4NC]

I would imagine they are using feedback. The amp uses MRF448 transistors, a pair in each of the four amp modules. I found a spec sheet for the transistor online and it claims -30db IMD (max) so I guess feedback may improve that to the -36db stated in the amp's tech manual?

The 40 pin connector (that goes to the radio) was intended for connecting to the matching Mackay HF transceiver. You'll notice in the listing the seller states he obtained the output test data using a Kenwood ham transceiver. He states "The only control lines were TX from the Kenwood (no ALC). " He's not clear how band switching was done.

I am assuming band switching can be accomplished by one of three ways... the amp sensing the frequency of the RF from the exciter and auto band switching, applying the correct logic signals to the pins on that connector to change bands, or by manual button pushing on the front panel.

I won't have my hands on it until the first week in November so I'll know more after that.

Wow, -36db 3rd is fantastic for a solid state amp. 

I wonder if they are using some form of RF feedback to get that figure or maybe the 50V helps do it. Do look at the manual/schematic when you get it and post later.

Most of the ham amps show about -25db in their manuals.

I looked at the eBay listing pics and it appears you will need to either interface to that complex 40 pin? system or just rip out the stuff and manually control it.

Either way, let us know how you finally configure it and how it works out on the air, OM.

T

[Glenn NY4NC]

The amp is made by Mackay Marine out of Raieigh, NC. Similar to Harris I guess... The power output vs freq figures he listed may also be related to the cutoff freq's of the various bandpass filters that are switched in and out depending on freq of operation.

Nice deal. They must be doing something pretty funky with inverse feedback. Look at the power output figures verses frequency. Fooling Harris stuff to work with plain old ham gear is usually not a big deal.

[WA1GFZ]

Gee I think 448s are rated for more power. They are very rare. Start looking for spares today. MRF429s similar but less power. When I have nothing to do I have collected the parts to build 9- 300 watt modules into a combiner and 1:3 output transformer. MRF150s or MRF 429s There is an old Mot app note of 8 modules
but 9 is a good multiple for the output transformer.
Still your rig is very nice. I would like to see the transformer design and the bias point. Bigger devices may have more bias to make them cleaner at 1 KW.

[w3jn]

My TransWorld 1500W (PEP) sand state is rated at -35 dB to -40 dB 3rd order, depending on power input/output.  I don't know what it uses for sandsistors but IIRC the internal PS is 28V.

73 John

[Glenn NY4NC]

Hi Frank,

Yes, 448's are rated for more power, I guess Mackay design runs them light to make them last. I found replacements online but they're not cheap... about $140 for a matched pair... yes, I will stock up when the money is flowing again 

I'm getting the full technical manual.... I'm anxious to start reading!!.....

Gee I think 448s are rated for more power. They are very rare. Start looking for spares today. MRF429s similar but less power. When I have nothing to do I have collected the parts to build 9- 300 watt modules into a combiner and 1:3 output transformer. MRF150s or MRF 429s There is an old Mot app note of 8 modules
but 9 is a good multiple for the output transformer.
Still your rig is very nice. I would like to see the transformer design and the bias point. Bigger devices may have more bias to make them cleaner at 1 KW.

[Glenn NY4NC]

I'd rather use linear supplies to keep the hash level down   ..... Those HP supplies I've been looking at are very nice... The Mackay amp allows you to use individual supplies for each module which is pretty cool.

Here's one I'm watching.... Four of these would do the trick

http://cgi.ebay.com/HP-6274B-0-60-VDC-0-15-AMP_W0QQitemZ7552126544QQcategoryZ58288QQrdZ1QQcmdZViewItem

Or two of these... (but not at this price)

http://cgi.ebay.com/HP-6012A-DC-Power-Supply-0-60V-0-50A_W0QQitemZ7552526525QQcategoryZ58288QQrdZ1QQcmdZViewItem

BTW Glen.....I may have the power supply modules for the day when I find one.
They are about a foot cube off line switchers 48 V 36A each.

[Glenn NY4NC]

Yep, it will be cool to use my Racal 6790 and a good exciter with this baby... I love the semi modern mil stuff! The problem with most of these mil exciters like the harris is that they only run 100mw output... ya need a pre-driver caw mawn!  I used to own a Harris 1310 exciter but like a dummy I sold it about 7 years ago,,, I realized that I could use one of the HP synthesized signal generators in it's place for an AM exciter and it wouldn't cost as much.  (right Dave?)

Grear Deal Glen,
Looks Harris. I have the board from the 400 watt amplifier and Harris uses a cool RF feedback method through transformer coupling. You will lose IMD if you try to run above 1 KW out. Those look like MRF150s in 300 watt modules derated to 250 for long life. Now you need a RF590 and matching exciter to feed it and you will be set for life. Jap crap does not compare to this top of the line mil stuff.
I think the RF590A RX is the best analog RX designs I have ever seen but have been told the Racal RA6830 is comparable.

[Glenn NY4NC]

Speaking of exciters, here's a nice one for not too much $$ The Harris RF-131

[WA1GFZ]

you sold a 1310, you poor thing I don't know what is inside the one in the picture.

Bipolars have a longer life than FETs so if you treat them right they should out last you. Get some spares though...you never know. Yes a linear power supply is the way to go for clean. HP does make some old rack mount stuff that has some BAs but I think you will need two.

[WA1GFZ]

Glen the RA6830 has 2 synthesizer outputs. I have played with the idea of building an exciter to track the RX. Racal just put a splitter at the output of the synthesizer. It would be easy to modify the 6790 to do the same thing.
The BFO has a spare output also so just need to grab some 40 MHz from the second mixer. the three outputs and some balanced mixers and mmic amps and your in business. OH yea an op amp or two for audio chain.

[Steve - WB3HUZ]

Nice find Glenn! The photo of of the amp boards looks very much like one John-JN and I were saw at the Gaithersburg fest. I think that one was a Harris. Do you recall JN. I do remember is was very strappping!

[Vortex Joe - N3IBX]

Glenn - Not "hollow state" but definitely FBOM just the same. High power STRAPS be it coming from toob or solid state. It looks like it's very well cornstructed.

The best of luck with it and hope to hear you on the band(s).
                                                                                  Regards,
                                                                                            Joe Cro N3IBX

[Glenn NY4NC]

Hi Steve;

I guess a there are a few companies using this same design scheme, several amp boards into a combiner.
Sunair was the other company I was trying to think of that makes mil grade comm gear similar to Mackay, Harris and as John mentioned, Transworld. Cubic is another one, and of course Watkins Johnson although I don't think they make exciters and amps. Great stuff! It's great to see the prices on some of this gear coming down to "earthly" levels.... I think it will be a blast to get an all mil/commercial gear station on the air. Very manley, very strapping indeed! 

Hey Frank, check out this awesome mint re-built RF590 on E-bay...

http://cgi.ebay.com/Harris-RF-590A-R-2368-HF-Receiver-AS-NEW_W0QQitemZ5818448873QQcategoryZ4673QQrdZ1QQcmdZViewItem

Nice find Glenn! The photo of of the amp boards looks very much like one John-JN and I were saw at the Gaithersburg fest. I think that one was a Harris. Do you recall JN. I do remember is was very strappping!

[Steve - WB3HUZ]

Yep. The one we were looking at the fest was built like the proverbial brick crap house! Hope to hear that thing on the air soon. I need some other big AM signals down here in the mid-South land to keep away the slopbuckets!