LPB Pictures & Info

Which model are you referring to?

I can tell you that there are a few things to change out for a particular part of the MW band. Most of these changes takes place in the low pass filter on the power amplifier board, as well as a minor bias adjustment.

Here is a link to an LPB AM-30 units manual in PDF format. It includes schematics, parts list and the proper parts to the low pass filter for each of the 3 segments of the MW band.

http://krocksradioone.com/files/lpbam30manual.pdf

RFB

Thanks RF, I don't know what happened to the rest of my post, but I was asking about the am-25/am-30. I think they are exactly the same, at least as far as I have been able to tell? I have an am-25 here that has been butchered a bit by the previous owner, and I need a picture to see what is changed and/or missing. Just listened to your interview on kdxradio, & thought it was really good. Might need to fly you back to Texas to get mine running right!

Tommy J.
"The Cat-AM"
Cat Spring, Texas

holy crap look who resurfaces after many years!!!! i approved you for my facebook tommy.

tommy what ever happened with your E-H antenna experiments?

Hey Robert, glad to be back! After my wife passed in '05, I boxed everything up and even sold my company. Never got to finish the EH experiment, unfortunately. I took a 10ft section of 10" PVC, wrapped it with 5ft of copper sheet, and had 3 feet worth of copper windings below that. It was a bear to handle, but someone stole it out of my yard one night, I assume for the copper... I did have a revelation while stacking that monster on top of a metal-roofed mobile home (which makes a nice ground radial), and that is the P15 rules specify a 3m limit on antenna length, but nothing on WIDTH. I'll have to do some calculations on that one. My plan is still to run a synced multi-site, carrier current station. So far I have dug out two CP-15's, a TCU-30, and an AM-25 with a PLL board from Jack Gittings. I still have not found my two TR-20's, but I'm back in the game! Good to hear from you!!

Tommy J.
"The Cat-AM"
Cat Spring, Texas

funny you mention gittings pll i have one of his p15am tx's and was thinking of sticking that pll in my cunningham transmitter i also have an ax10 cquam to run with the cunningham which is pll

I'm still waiting for the guy that makes those CQUAM exciters to answer my email, would love to get one and do what RFB did. Gonna see if I can my TR-20's today, and start getting things coordinated. The power supply board on my am-25 is butchered, need to see someone else's and get this thing back to factory.

Tommy J.
"The Cat-AM"
Cat Spring, Texas

The LPB AM-25 and AM-30 are pretty much identical in every aspect. The only difference between them are the finals bias setting and their B+ fuse, and the metering resistor divider network. The manual I posted will give you all the proper components and placements for the AM-25 and the power supply board.

I will snap a picture of my AM-25's power supply board and post the link to it.

I am not sure if Chris Cuff is still making those C-QUAM units any longer. The last time I communicated with him via email, he was in the process of selling the remaining units he had as kits on ebay. This was about 6 months ago. I purchased 2 complete units and 2 in kit form during that ebay listing and bought 1 complete unit from him back in late 2009, which I removed the pc board from the supplied cabinet and integrated it into my LPB AM 2-20 unit.

I will have a link to the picture in my next post. 🙂

RFB

Thanks RFB! Been looking around online, and really like those Aspisys units from Greece. I know that many licensed stations I have worked on, have engineering mods that do not invalidate their type acceptance, but I'm wondering if the field agent that shows up to check my CC station will say that I have "modified" my type-accepted P15 transmitters by changing the exciter? Another cloudy area I think, because they have done it to other P15 stations that modded their transmitters... Neither the Cuff or the Aspisys is type accepted, might give them a reason to take my gear.

Tommy J.
"The Cat-AM"
Cat Spring, Texas

Well for one, the LPB exciter, though a very good one, has two inherent problems. The first is the power swings wildly when making adjustments due to the stand-up power control pot. Replacing it with a flush mount pot solves that problem. The second problem is the exciter's output transistor tends to develop poor connections around the emitter resistor and on the transistors leads themselves.

But the main issue I bring up is the fact that LPB is practically non-existent. Replacing a bad exciter is a shot in the dark at best. Installing a newer type with better performance plus one from a manufacturer still in existence is also a plus. AND...this is the 21st century....the components manufactured today are far better than those even in the original LPB exciters. And of course..going C-QUAM stereo is another move into the 21st century, though the FCC does not care if your in stereo or not. What they care about is preventing interference and that your station is operating within those specifications called for in Part 15, which both the Chris Cuff and the ASMAX units exceed quite well respectively.

Parts for the power supply board and final amplifier are still commonly available. If the finals blow and you need to have the unit fixed, and have the know how to do that, then why should you be forced to submit your amp module to a company that does not even exist anymore when you can simply replace the transistors?!!

Im sure those licensed radio station engineers can swap out a power module or replace final elements in a 1970's Harris MW-1 without having to resort to sending in modules to get back on the air quickly.

And when they do fix stuff..what do they do next? Well they proceed to check their work, hook up an analyzer and measure the performance. Standard practice that ANY engineer should be doing anyway...be it for a Part 15 or Part 73.

Those infamous 3 words.."Good Engineering Practices".

Pic for the power supply board forthcoming.

RFB

as long as you can prove your operating within the emission limits you dont need type acceptance under part 15 which for carrier current is harmonics out of band and fundamental emission field strengths. modding a lpb to use a apsisys or ccuff for an exciter is legal as long as the emission specs for part 15 are met. in your case (carrier current), a scope, spec analyzer, and FIM

i mentioned the ccuff i have in response to your mentioning waiting to hear back from the guy selling stereo transmitters

Here is the pic of the power supply board in the LPB AM-25 unit. I apologize for the fuzziness, not a whole lot of room in there to navigate a camera for a clear shot, but you can see the components location and what should be there for a stock unmodified ps board.

Hope that helps.

Another big consideration in regards to meeting the specs for spurious emission limits are the in-band harmonics. Those MUST be at least 20db down from the fundamental.

With an ASMAX or C-CUFF exciter, that in-band harmonic is 45db down with the ASMAX and 30db down with the C-CUFF.

I use an HP 8590A analyzer and a Motorola RD2012 analyzer to check things...which I was informed are more than adequate to make proper measurements.

RFB

what do you have to trade??? I have a CCuff/Alfredot Transmitter with extra crystals or i will sell you get Tx, PSU, and crystals

i can email pic's

also have a ramsey FM25a, THII amd STC-1

for grabs.

looking to clear out some space and put $$$ in my pocket.

kc8gpd hotmail com

Thanks guys! Do you know what the exciter section puts out on the LPB's? I'm guessing it would only take about 25mw to drive the amplifier to its potential.

Tommy J.
"The Cat-AM"
Cat Spring, Texas

The LPB 2-20, AM25 and AM 30 exciters put out about a half watt drive. But the final amp module can take as little as 25mW to drive it, along with a bias adjustment.

RFB