Started my first homebrew amp project!

[KJ4OLL]

Hi,
I have started my first homebrew amp project!
The goal is to have an amp that will let me participate in more AM nets, and also possibly get on 160m too.

The two amps I have now don't do 160m and have not been recommended for AM use. (Collins 30L-1, 30S-1)
Will be using a Collins 32V-2, 32S-3 or a Harris RF-1310 exciter to drive the amp.

I read many things on the forum before picking a design.
Did not go w/ 813's driven by 813's.
The costs and complexity for 4 tubes, and the fact that I could only find chinese sockets & caps killed that option.

Went with a simple one tube design.

This is all way over my technical level anyway, but that is how I hope to learn, with help from as many elmers as I can get.

So here is the pile'o parts I have collected so far.

- EIMAC 3CX3000F7, w/ chimney, homebrew filament transformer.
- Big ROTRON blower from a Gates something or other
- Dahl plate transformer: 240 in, 2600, 4000, 4500 out.
- Components to build the rectifier
- A bunch of torroids to make the filament choke
- A selection of big tank coils and big band switches
- A selection of Mica and ceramic caps
- Two - 6 Mfd 6000v oil filled caps
- A 10H choke from an old Gates
- Six 100k ohm 225 watt Ohmite bleeder resistors
- A big aluminum cabinet on wheels to put it all in.

I have not bought the two tuning and loading vacuum variable capacitors yet, am still learning how to do all the calculations for each band using the "match.exe" program provided with the ARRL Handbook.

Plus I know there are 9 million little parts and pieces to collect for all the safety and control circuits.

But at least I have started!
My goal is to have it working before I retire in 2017 @ age 67.

73
Frank
KJ4OLL

[K1JJ]

Looks like a nice project, Frank.

You might shoot for about 40 uf for filtering in the HV supply.  

Test the blower. If it is loud, consider locating the amp far away or running a Variac to slow it down or get a quieter blower.  Little or NO background noise is important on AM.  On SSB we can use a noise gate effectively, but on AM a gate is unnerving.  Loud blower noise on AM is distracting and will intermod with your audio.

The 3CX-3000A7 is a FB tube making -40 to -45dB 3rd order IMD figures. Very clean.  You will need a very clean driver that is at least -45  3rd order to do it justice.  This is a big challenge since most rice boxes or old AM rigs will be hard pressed to do better than -35 or so.

What are the figures on your Harris RF-1310 exciter?  I think the 32S3 has RF NFB, so you may be in good shape once modified for AM use.


Good luck with it and keep posting as it progresses.

Tom, K1JJ

[wb3eii]

Frank, look here for some ideas.

http://w2dtc.com/w2dtc-plasma-amp-page.htm

and here

http://w2dtc.com/index-amplifiers.htm

here also
http://w2dtc.com/w2dtc-class-a-rf-amp-page.htm

I have a Henry 2000d plasma generator amp that runs the 3cx3000a7, am in the process of multi-banding it, have gone through a few design permutations so far, think I have settled on  Vac cap for C1, roller for my inductor and bread slicer for c2, you may want to investigate using the same, as the c2 position in a pi-l net hasn't as much voltage as the c1. Keep us posted. 73 Ed AB3HT

[kb3ouk]

There's only one problem with using the Harris RF-1310, it only does 100mw of power, so assuming you are going with grounded grid, that's not anywhere near enough drive. That exciter was meant to be used with the RF-110A amplifier, which used a pair of 4CX1500Bs driven by a 4CX250B. Also, I'm not sure about the 32S-3, but the 32V-2 is a 100 watt rig, so you're going to definitely want to cut back on the power output somehow.

[KJ4OLL]

Thanks for the tips & comments!
I'll add more filtering for the HV supply, would like to understand more about how the capacitance value is arrived at/calculated.

The blower is going inside the cabinet, and the intake/exhaust can be run through a muffler, if needed.
But the blower is pretty quiet in testing (w/o any back-pressure, however).

Forgot about the Harris RF-1310 100mw max drive, I won't be using it to drive this amp.
(But I am always looking for a Harris RF-100A and the single-phase power supply for sale within driving distance of my QTH...hint hint)

Interestingly, I might try to use the RF-1310 for QRP - I recently restored an HP 230B RF amp, it should be a hoot to drive the ancient Hewlett Packard amp w/ the Harris exciter!
http://www.youtube.com/watch?v=X_bTy0RIo2Q

The w2dtc web site was my inspiration for using the 3CX3000F7, GREAT!

I have a BIRD 30db in-line attenuator to use between the exciter and the amp input.
However, the amp that w2dtc built did 100 watts in---1500 watts out, so possibly I won't need the attenuator.

Open to suggestions for other options to drive the amp with so as to obtain the low IMD - what would you use?

73
Frank
KJ4OLL

[KM1H]

You might shoot for about 40 uf for filtering in the HV supply.

If the choke will be used then 12uF is more than adequate for both filtering and regulation. OTOH around 25-30uF will get the job done by itself. At 4-5KV more is not better and just costs more.

Carl

[flintstone mop]

I still lust after that Harris Amp RF110A. That is POWER..
Good luck with your project. Does the 3CX3000 have handles??? That's where it's happening these days.

[KM1H]

I have the Boonton 230 which was renamed after HP bought them. A good 10-500mc coverage at up to about 5W out.
It and a HP-608C was used for antenna tuning out in the back yard back when that was the "easiest" things to move outside. They havent been used for almost 20 years.

Wasnt there a Harris amp that took a 100mw input and wound up with an 8122 to drive the final stage?

Carl

[K1JJ]

You might shoot for about 40 uf for filtering in the HV supply.

-----------------------

If the choke will be used then 12uF is more than adequate for both filtering and regulation. OTOH around 25-30uF will get the job done by itself. At 4-5KV more is not better and just costs more.

Much will depend on how much current the transfomer can supply under full load and how hard he pushes the 3CX-3000.   My power transformer is fair and I ocassionally push things hard, so have about 110 uf in my supply.  Still, it sags a little and detracts from IMD figures.   I feel we can never have enuff filter capacitance if it is available, especially to smooth out dynamic, syllabic fluctuations as generated by ssb.

I prefer capacitor-only filtering for my own use here.  I have a big fixed choke that gets switched in, but never use it except when testing a new rig.  Maybe a swinging choke would suit me better.


T

[KM1H]

Big cap + little transformer = smoke

[KJ4OLL]

Hi,

I have been reading about HV power supply chokes, WOW, that gets into some esoteric territory!
So far I seem to understand that if I use the choke, I need to know if it is a "swinging" type or non-swinging.

It also seems that there can be quite a challenge to match the choke and capacitors so as to obtain the correct resonance, apparently somewhere at or slightly over 120Hz.

Can you tell anything from the photos as to which design GATES choke is?

The capacitors might go w/ the choke, it looked like Fair Radio parted out a GATES,
and I bought the choke and caps from them at the same time (appeared on their site simultaneously)







73
Frank
KJ4OLL

[KM1H]

That is a straight smoothing choke, no resonating cap needed. The resonated choke was in the ham and lower commercial tiers such as Henry as a way to save money and weight.

Carl

[W7TFO]

You may want a swinging choke if you power both the mod & RF sections from the same supply.  It is gapped little or none at all, such that the inductance varies inversely proportional to the current drawn, such as in the case of a class 'B' modulator.

With it in line it gives more smoothing when you need it for quiet passages, less for when things are closer to the edge in terms of modulation percentage.  This also lessens the voltage 'droop' caused by increasing heavy mod demand.

The lineup traditionally is raw B+ to a swinging choke, first cap, (this is where the mod section typically gets it's B+), to the smoothing choke, then another cap.  The RF amp demand hooks here.

Smoothing chokes have a more pronounced gap, so they exhibit little change in inductance when current varies within design limits.

The above is seldom used today, as bigger caps are available to keep things in line when modulation is heavy, but the old way was best for fidelity and low distortion requirements of BC rigs.

73DG

[kb3ouk]

Sounds like he's building a linear, so there won't be any modulator, but a plate modulated 3CX3000A7 would definitely be cool. Create your own band openings with that much power. 

[W2VW]

Looking at the calender it appears to say 2013. Where is anyone going to find a swinging choke suitable for single phase choke input for a decent price?

That Dahl xfmr is going to be low resistance secondary and should work without a choke. Swinging choke supplies are popular with AM folks because of literature which says they are better for regulation and necessary for class B modulators. They also make things easier on the power transformer. Older high resistance transformers can benefit. That's not what is being used here.

Since this amplifier is to be used on AM it should be just fine without parts that are very difficult to obtain. Capacitor input supplies have been the norm for amateur power amplifiers for a lifetime.

A step start should be used.

A 30L-1 will work in AM service if you ditch the 811s and install 572Bs. I'd stay away from rocket science suggestions like only putting (3) 572Bs in. Those tubes already have a relatively poor filament emission/plate dissipation ratio. 4 work fine. Even the Asian tubes will work. I had one in service on AM for a year before selling it to a friend. 125 watts carrier and no more.
Some late Asian tubes have a bayonet locator tang which is in the way when plugging into a 30L-1. One tube socket screw must be removed in order to temporarily re-clock the socket about a dozen degrees. It can be put back after plugging the tube in.

The 30S-1 makes a FB am linear amplifier especially with a few tweeks. The screen power supply modification which uses a 125 volt isolation transformer in series with the original screen winding really wakes the amplifier up. The 4CX1500B fits right in for more plate dissipation but the factory blower will not deliver enough air for AM. The easy way out is to get a commercial transmitter cabinet exhaust fan and mock up an air handler box. Fit the box over the existing hot air exhaust so the air is sucked out. This will keep the tube nice and cool. If you keep the amp near your mike people will think you already have the 3CX3000 : ) The above is tried and true. Your amp should not wilt at legal limit AM. Remember to keep the air inlets and tube clean. The air inlets are located in the cabinet recesses in the pedestal. 

If you like to waste power run your +20 dBm exciter into the 30L-1 and then the 30S-1. Output will land up with 5 or 10 watts from the pipe. I did this on the AM QRP net once.   

[KJ4OLL]

Interesting you should mention the 30L-1, mine has 4 Svetlana 572B's and the Young Kim power supply upgrade,
plus I did all the mods that Dennis Brothers said to do.

But I have not used it for AM as the 32V-2 I normally use has almost 100 watts of carrier.

Does the additional 25 watts provided by the 30L-1 result in significantly better signal reports? 

[K1JJ]

But I have not used it for AM as the 32V-2 I normally use has almost 100 watts of carrier.

Does the additional 25 watts provided by the 30L-1 result in significantly better signal reports?  

No, 100 watts to 125 watts will not even be discernible.  We generally need at least X4 power, which equals about 6 dB, to make it worthwhile in the real world.  This is about like comparing a Yagi to a dipole at the same height. (5 dB)

X2 = 3 dB
X4= 6 dB
X10 = 10 dB


The only difference may be that the low level exciter and 30L-1 may be able to generate a cleaner signal than the 32V-2.   Run some IMD and THD tests to see.


The difference between 100 watts and what the 3CX-3000 can put out is quite meaningful and worth the effort.

T

[ka4koe]

Are you using any software to analyze your network? If so, let us know what you are using.

Tnx.

Philip
KA4KOE

[KJ4OLL]

Software used so far:

I downloaded this amplifier design software:
http://www.duncanamps.com/psud2/index.html

Took a while to find a system to run it on @ my QTH, (all my computers are LINUX),
but I installed VirtualBox to run windoze7 under LINUX.

Now I have to figure out how to option the psud2 program configuration to describe the variables in my amp setup, which are very different from the psud2 program defaults.

I also used "match.exe" from the ARRL handbook CD to calculate the capacitance and inductance values for the tank circuits.
Am about 30% done on those calculations.
Need son: "Mr. math wizard" to come home from engineering college (UF) to check my work.

This is about as far as I have delved into the HAM software arena.

I don't have any software to analyze the antennas, I just use an MFJ 259B to get the tuning close for each band.
Then I use an AGILENT spectrum analyzer w/ tracking generator and a return loss bridge to get the tuning exactly where I want it.

[W2VW]

Interesting you should mention the 30L-1, mine has 4 Svetlana 572B's and the Young Kim power supply upgrade,
plus I did all the mods that Dennis Brothers said to do.

But I have not used it for AM as the 32V-2 I normally use has almost 100 watts of carrier.

Does the additional 25 watts provided by the 30L-1 result in significantly better signal reports? 

Generally the extra 25 watts carrier will not change on the air results. The 32V-2 most likely already has a good percentage of relatively clean modulation.

There are other circumstances where the use of an amplifier such as the 30L-1 will make a difference. One would be use with a Johnson Ranger.

Yes the Ranger will make almost half what the 30L-1 will do but it isn't all that simple. The Ranger's modulator is out of suds when used at full power. It is running into gain compression.

When configured with the low power mod which leaves the modulator on high B+ but only asks it to make about 1/4 of it's design power, gain compression is no longer an issue.

Take this and pipe it into the 30L-1 and look at peak power verses the originally configured Ranger. The increase will be a little under 6 dB which now makes it a worthwhile increase.

The same could be said for a few other transmitters whose modulators remind me of an early Chrysler Hemi with a tiny carburetor.

Those old calculations in ARRL publications which show AM is useless are skewed to promote that other phone mode. You won't find that junk in the Orr handbooks.

[ka4koe]

MMANA GAL is a great free antenna modeling program. You just have to input the proper gozeintas to get correct gozeouttas.

Philip

[KM1H]

All you ever need to know for amp design in one place.

http://www.ifwtech.co.uk/g3sek/

[KJ4OLL]

Thanks for the link!
It looks like I will have to become a member of the Radio Society of Great Britain
to gain access to some of the content I need on the site.

[KM1H]

Send an email to Ian, he may help.

Carl

[KJ4OLL]

Hi,
Made some progress this weekend - rectifier is coming together!

(It might be a rectifier, or possibly some type of incendiary device....time will tell)

I copied a DELCON T210 design.

- Used drafting tools to lay out the pins on a sheet of fiberglass.
- Made a simple fixture for directing the swaging forces on to the pin shoulder to avoid bending them.
- Installed components, almost ready to apply some voltage!




73
Frank