Started my first homebrew amp project!

[W2VW]

The 32V looks great in the photos and already expects to be the exciter. Using anything else would upset it.

That TX can be setup to run at lower power out. There are plenty of connections available for this without hacking the rig.

The best method would be something that allows the modulator to run at full plate voltage while reducing the final B+ to about half. That gives 1/4 output power in a class C final. Leaving the modulator at full B+ and reducing mic gain should provide more modulator dynamic headroom and make for less audio distortion. Some of that distortion lands up as unwanted RF bandwidth. Every effort should be made for a clean signal when high power is involved. Simply padding the RF of the Collins is a bad idea. This is known as the Timtron Low Power Mod. I learned it at The Timtron Instutute of Technology.

Provision should be made for switching to normal power level out of the 32V for final touch up of the linear amplifier. It will need steady carrier tweeking at peak power which will be at least 4 times the carrier power out the pipe.

[N2DTS]

There are lots of ways to go.
The 32v is one of the best sounding stock radios.

I always disliked running a tube rig into an amp though, the solid state stuff makes it easy to tune up, just adjust the power level out, switch modes, no drift, digital readouts, but I have no idea which ones are clean and good sounding.

The flex 5000 can have very good audio out, but has the hash.
A ranger can sound very good and do lower power out, or you can make any tube rig work well with an outboard modulator,  or you could home brew a 6146 rf deck and a hifi modulator for it.

RF wise, the 32v is going to be clean, no digital hash or mixer signals getting out, and for real hifi, driving the grids with an audio amp into the reverse transformer will be very clean if the modulator is run at full voltage and the rf is run lower.
At 30 watts out, the 807's would likely be in AB1 at the power levels needed to get plenty of modulation.

I have an outboard variac on mine, as I use it as an RF exciter for my 813 rig.
Easy to do, and the 32v has most stuff on the rear terminal strips.

All you have to do is make a variac supply for the RF section and feed it into the rear terminal strip.

FT102's used to be all the rage, and they have mods to make them very hifi, all mode, but you need to dip and load...

 

[flintstone mop]

Frank
Looking thru your posts and the great pictures. Congrats! I hope it flies and makes nice powerful RF. Some people on this board just have the gift of building and make neat stuff.
The output P.E.P. and CW carrier capabilities will be interesting.
I do not remember seeing what your expectations are for this amp.
Fred

[KJ4OLL]

Hi Fred,
None of the old store-bought amps I have do 160, and also are not designed for AM.
So I am hoping to use the homebrew for AM on 160 and 80, possibly 40.
And SSB on 160.
And to heat up the shack;)
Power out will conform to rules & regs.

73
Frank

[KJ4OLL]

Hi,
Almost finished with the control board!

There are three steps to power the creature up:

1- Power on the blower, which activates the vane switch.
   If the vane switch "makes", the next stage is available for power up.

2- Power up the Filament stage.
   If the filament powers up OK, voltage is available for the step start phase.

3- Power up the step-start phase, bringing the plate transformer & HV on line.

I finished "Phase-2" today, CLACK is working for the filament.

So This part of the project will be done pretty soon.

The next project will be the PTT circuit and the "dead man" interlock.

I have a question - what technology/design should I be looking for in the parts bins @ the Orlando Hamfest next week in terms of a PTT antenna relay?

Thanks, & 73
Frank
KJ4OLL

[N2DTS]

Very nice metal work!

[KJ4OLL]

N2DTS,
Thanks, been doing various metal bashing hobbies for 50+ years - now trying to learn more about amateur radio electronics - really fun technologies to experiment with!
73
KJ4OLL

[N2DTS]

Well, just be careful with the high voltage.

[KJ4OLL]

Hi,

Made some more progress on the amp!

Finally am at a point where something can be powered up, even if it is only the blower circuit...took a while just
to get to this point........but momentum is necessary, even if it is in very small increments.

www.youtube.com/watch?v=jcsdbGfauLw


Going to try some .004 thick Titanium foil to increase the "sail area" of the vane switch.
But have to keep it far enough away to avoid arcing.
(Not sure how far that should be @ 5000v on the plate???)

73
Frank
KJ4OLL

[Opcom]

This is a really great project! I hope you will take more pictures and publish all the schematics so I can learn from them. The tank circuit -those are some serious looking parts.
I have been collecting stuff too for a 3CX3000A amp. Have most of it. My transformer's only rated 1.6A but it ought be OK.

"The 3CX-3000A7 is a FB tube making -40 to -45dB 3rd order IMD figures. "
Is that figure for GG service or grid driven? It's not clear in the datasheet I have. The reason for asking is that grid driven service is nice because only 150W is required for max QRO, so that a quite small exciter of 35W PEP will do for ham limits, while 400W is required for QRO GG service and only a 100W PEP exciter is needed or ham limits. Or is it a silly question?

"Does the 3CX3000 have handles??? That's where it's happening these days."
No handles but, well anything more than a hand-full is hard to manage! 3CX3000 is just the right size, even if it has to be wiggled a bit to loosen it up

"..a plate modulated 3CX3000A7 would definitely be cool. Create your own band openings with that much power."
Create your own ionosphere opening too!

8-) enjoying this topic!

[wb3eii]

Yes, pictures please. Schematics  too!
  I have a 3cx3000a7 project that has stalled,   this may be   the what  I  need  to get back to building-thanks.
73,  Ed

[KJ4OLL]

Hi,
Thanks for the encouragement!
I have posted many photos on QRZ , look under KJ4OLL.
(Not sure if I should post many photos here, costs the site storage $$$)

I'm no engineer, so this project would not be possible without help from many.

Ken, W2DTC posted most of the core technical information.
I am copying most of that Ken did.
http://w2dtc.com/3cx3000f7.htm

Don, K4KYV gave me a super T/R relay sequencing design.

A retired broadcast engineer I work with, Joe Lang, designed the control circuits, power supply, tuner.
As I see Joe every day at work, it is easy to review new ideas and plans.

For instance, when Joe viewed the recent video of the blower test, and saw that the vane switch did not work
as I planned, he gently informed me:
"IDIOT - put the vane switch directly in front of the blower outlet inside the plenum"

Mark, N2ZAB, gave me more ideas and tips.
And of course, this forum has provided much more guidance and advice!

The amp is a Class AB2, Cathode Driven, as shown in the specs here:
http://www.cpii.com/docs/datasheets/78/3CX3000A7.pdf

Joe's control circuit design is really superb, I will post the schematics someday.

However, as the control circuit schematics were drawn up freehand, then the inevitable corrections were added,
and now it looks like....

Well, imagine you had a live chicken.
You put ink on the bottom of the animal's feet.
Simultaneously administer a large dose of LSD, and also energize electrical terminals installed in the brain.

The resulting marks on the paper would be the current schematic appearance......

73
Frank
KJ4OLL

[KJ4OLL]

Hi,
Too many other things keeping me away from this project!
(Trying to bring a 30S-1 back to life has been a challenge)

Found time to get the vane switch moved into the plenum box, so now it receives airflow
direct from the blower outlet, vane switch now "makes" the circuit properly.

https://www.youtube.com/watch?v=wdkBEc9HHeM

Also installed the Manometer!

https://www.youtube.com/watch?v=MNo1uH9-q38

73
Frank
KJ4OLL

[KJ4OLL]

Hi,
I'm stuck with a weird airflow problem that I'm sure Kelly Johnson (aeronautical engineer) would have known the answer to.
(His fellow engineers said that Kelly could see air, as he was so adept at pointing out flow problems and solutions)

The vane switch is the first safety switch in the control circuit of this amp.

The vane switch is positioned in front of the blower outlet, inside the plenum that contains the filament transformer, choke,
PA base, etc.

The amplifier is started in steps.

Operating the first switch (step-1) turns on the blower, and via the vane switch, makes +24VDC available for the second stage to start.

If the blower fails for any reason, air flow to the vane switch decreases, the vane switch opens the circuit, dropping all the relays and contactors.

Operating switch two (step-2) pulls in the filament contactor and starts heating the filament w/ about 53 amps of 7.5 VAC.
This step also makes +24VDC available for the plate circuit.

Operating switch three (step-3) pulls in the first step-start contactor, beginning flow of AC to the HV power supply, charging the capacitors.
A timer expires and the final contactor activates, providing direct 240VAC line to the plate transformer primary, plate is
now at 4900 VDC.

You can hear each "clunk" behind the blower noise in the video, and see the stupid vane oscillating:

https://www.youtube.com/watch?v=87HIDXmHSvE

I have been experimenting with this all day.
I can get the vane into a position and angle so as to stop oscillating with the plenum open.

Found a vast number of methods that are completely ineffective in stopping the vane oscillation with the plenum sealed up.

There is a vane position and angle that stopped the oscillations, but when I put the plenum cover back on, the pressure and flow inside the plenum changes, and the vane starts oscillating again.
All the relays and contactors drop out.

When I put the plenum cover on, something happens to the airflow inside, and the vane starts oscillating (even though the vane was stable w/ the plenum cover off), causing the vane switch contacts
to open and drop the Filament circuit. (And everything else)



So there must be some kind of standing wave or pulsing that starts when it is all sealed up.

Should I try a baffle to block or redirect airflow near the vane?

Or a little duct inside the plenum that focuses pressure directly on the vane?

Or some better method of performing the "blower on/off" logic for the subsequent stages?

Or just buy an ALPHA and call it a day?

73
Frank
KJ4OLL

[KD6VXI]

Where the blower mounts,  it would appear the plenum is not airtight.

If that's the case,  there is your problem.   The vane needs to be in the only exhaust,  otherwise you can see all kinds of problems.
--Shane
KD6VXI

[KJ4OLL]

Hi,
The blower and plenum are sealed up pretty tight, Manometer reads .7 WC.

Recent info from a guy in the commercial HVAC biz indicates that vane switches are generally a pain to get working and to keep working,
so I am changing the design.

Deleting the vane switch, replacing the function with a "DWYER PRESSURE SWITCH, DIFFERENTIAL"

This is a pressure diaphram that acts on an included electrical switch.

Not dependent on direct airflow, operates like the manometer, just responds to pressure in the plenum.

73
Frank
KJ4OLL

[W4EWH]

The two amps I have now don't do 160m and have not been recommended for AM use. (Collins 30L-1, 30S-1)

Frank,

I agree that the 30L-1 isn't a good choice for AM: it uses 811's.

IIRC, the 30S-1 uses a 4CX-1000A, which runs Class AB₁, so I don't understand why it wouldn't be appropriate for AM. Is there an issue with the power supply?

73,

Bill, W1AC

[KJ4OLL]

Hi Bill,
You are correct, the 30S-1 works fine on AM, so long as I do my part to keep within it's capabilities.
I had read the 30S-1 plate transformer was marginal, and mine was the original from 1959-60 (amp S/N 194).

But after the recent:
- filament transformer arcing (replaced w/ new).
- brittle and corroded HV leads falling off the plate transformer (replaced w/ new)
- Screen Supply rectifier leaking AC upstream (replaced all the "tophat" diodes)

Now the 30S-1 is back to abby-normal, and when driven with the Flex 3000 in AM mode, seems to be happy at 150-200 watts.

73
Frank
KJ4OLL

[KJ4OLL]

Hi,

Finally got all the control circuit pushbutton switches installed and connected.
(spared no expanse on the labels.....)



The blower & filament circuit is working! (filament = 58 amps of 7.5 volts)

(replaced the goofy vane switch with a Dwyer 1910-1 Differential Pressure Switch - problem solved)

(thanks to Mike WA8HNS for the idea!!!!)

https://www.youtube.com/watch?v=mW4yR21eYvg

Plate & HV next.

I have been told that because the EIMAC 3CX3000A7 has been sitting for so many years, the tube
must be run through this cycle before applying full B+:

1- turn on blower & filament
2- bring up about 800 volts of B+
3- run it for about a day to let the getter work.

After this, the plate should accept full B+ w/o arcing.

One lesson learned so far is that this thing puts out lots of noise & heat.
Probably going to have to roll it outside of the shack when operating!

73
Frank
KJ4OLL

[Opcom]

Looking back at that project, the intake duct on the blower is possibly presenting a higher than necessary impedance for the amount and velocity of the flow.

An air horn on the blower open to the interior of the cabinet would probably help. Or just nothing. I'd ditch the duct on the intake, and put one on the tube if necessary, or divide the cabinet.

[KJ4OLL]

Hi,
Did not see any difference in Manometer pressure w/ or w/o the duct in place.
The amp gets really hot inside the cabinet, and the duct brings cool air in to the plenum from under the cabinet.

Made a baffle to fit inside the plenum so as to direct air on to the filament choke, it was operating at 160-170 degrees,
due to the voltage drop across it.

Amp is starting to look like it might actually work someday soon!
https://www.youtube.com/watch?v=hdcv2YPhMhI

Next is to build the Cathode drive circuit, then the PTT/timing circuit.
Finally, a tuner will be built into the amp cabinet, using these components:
(Except the water bottle...)



73
Frank
KJ4OLL

[Opcom]

I wondered what the extra space might be used for. A matcher is perfect. I like the use of a VFD for the blower. No doubt the falling price of used VFDs will be increasing the price of 3 phase blowers including 400Hz ones.

I'm working with a lot of ABB VFDs lately.

http://www.youtube.com/watch?v=boq8JMIRNqc#t=20

Will the matcher be a pi network type circuit? Hopefully a low pass design. hehe next video, show that HV cranking up to 4800!! 

Good job on this progress. I like the amplifier's tank circuit component size. It looks like an assembly, but I can not tell. Can you provide more info on that very interesting area?

[KD6VXI]

How about a Pi-L,  and use the roller for the L.   That would give good harmonic suppression as well as allow a large range of impedances to be matched.

Saves the cost of a cap,  too.

--Shane
KD6VXI

[KJ4OLL]

WOW, pretty wild use of VFD's!!!

Exactly correct on the 3 phase - an old, beat up single Phase Rotron for $300 or a NIB 3 phase Rotron for $100, plus $50 for the VFD.
Seemed like a simple decision.


The tuner can be configured either "Pi" or "L", depending on jumpers. (Kind of like the old Collins 180S-1)




The tank circuit is a Collins 185J-1.



When I bought the thing, Google did not know anything about it.

I took a chance, as it was cheap.

Planned to strip it for parts for the amp project.

When my elmer looked at it, he said ""do not canibalize it - this is a complete tank circuit, ready to plug & play in your amp"

Collins forum folks were also baffled, but there was one 1940's similar design that was auto-tune that they did locate.

Looks much the same, but with three servo motors on the front.

I suspect this one was originally auto-tune, a previous owner fabricated the front panel and added manual-tune knobs.
 
http://s180.photobucket.com/user/fish1_07/library/collins_mystery_tuner?sort=3&page=1

The really interesting thing is that it operates at B+ - thus the PA direct connection.
Here is the tank at 4019 VDC, using a current-limited HP 4kv power supply.




I'm running the plate transformer secondary on the first jumper position 2.6kv.
If that does not produce adequate power from the exciter drive, the next jumper is 4kv.
If that does not do it, the final option is 4.8kv.
I fear it.

73
Frank
KJ4OLL

[Opcom]

No worries! the plate-direct-to-coil thing is or was common on some units. What voltage did the 185J-1 run at?

I agree going to 4KV and higher is scary but it may be needed to try different voltages to get the best performance or lowest distortion.
A wise man advised me to use a 3" tall loop of #30 wire as a fast acting fuse in the HV line. If there is an arc or flashover, only the wire is vaporized.

Those shafts are going to be hot hot hot.. Will you use a long insulated section and a grounded knob-shaft at the front or some other scheme? Things like that worry me when the voltage is so much. I mean, that it could some how get across the insulated shaft section.