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Author Topic: Started my first homebrew amp project!  (Read 56913 times)
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KA2DZT
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« Reply #25 on: April 30, 2013, 10:56:10 PM »

The wires at the bottom of the picture seem to be a bit thin.  You might want to use wire with heavier insulation as there is high voltages at those points, except for the ground point.

Fred
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ke7trp
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« Reply #26 on: May 01, 2013, 12:37:27 AM »

Thats a neat rectumfire board you made there.  Can I ask where you got the pins? 


C
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KJ4OLL
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« Reply #27 on: May 01, 2013, 08:25:56 AM »

I looked up the specs on the white wire - insulation is rated at 5KV, but it is only AWG-15, so I'll see if I can find
something better today @ Skycraft - that is where I found the pins too.
The red wire is AWG-13 / 20KV.

http://www.skycraftsurplus.com/

Frank
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KM1H
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« Reply #28 on: May 01, 2013, 08:57:13 PM »

Even #20 wire is fine for short runs considering that the average 3-4 KW plate choke has several feet of #24-26 wire.  If I want more insulation capability I slip a Teflon sleeve over it which is dirt cheap at the local electronics surplus shop

All the thick wire gets you is that its often harder to dress neatly.

Carl
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ke7trp
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« Reply #29 on: May 01, 2013, 09:00:04 PM »

Just dont use it for your antenna  Shocked


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KJ4OLL
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« Reply #30 on: May 03, 2013, 09:03:36 PM »

Hi,
More progress, as it is raining so much here that I am unable to do yard work,
and thus am forced to putter about in the workshop.

Using a piece of 1/4" steel plate to bolt the main PS components to.

The idea is to produce a modular unit that can be inserted into the cabinet w/ a small crane.

Laying out the components on the plate so I can drill and tap the plate for the fastners:



Facing the 1" Teflon rods to square them up for bolting to the plate and the rectifier:



Drilling for 3/8x16 tap:



Cutting internal threads in the teflon:



Mounting plate drilled, tapped and painted:



All components bolted in place:



Still need to add the 100K 225W bleeder resistors, I think they will fit nicely on the rectifier standoff legs.

Frank
(Hand still sore from all the tapping - the plate is crappy, high-carbon steel,
many hard spots tried to break my taps....)
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« Reply #31 on: May 03, 2013, 09:16:17 PM »

You can move to the head of the class now Wink.

73DG
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KJ4OLL
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« Reply #32 on: May 25, 2013, 08:38:24 PM »

Hi,
A little more progress on the homebrew!

Trying to make a filament choke for 160M.

Need 180uH for this choke.

I read that it might be possible by using toriods, thus obtained some type 43 material and did a test.

23.6uH for the first test with about 16" of toroids.


TYPE 43 TOROID TEST




This choke would have to be too long to fit in the cabinet using this method to obtain 180uH, so on to plan "B".


Obtained some type 43 material 5/8" x 7" rods, put 7 of them in some heat shrink tubing, wound 30' of #12 varnish
coated wire on the lathe.

TYPE 43 CORES TEST
BIFILAR WINDING


TEST CHOKE


SEVEN CORES


NOW WE ARE GETTING SOMEWHERE


Based on these results, I am going to make a 14 (seven in each bundle) core choke and use a longer piece of #12

73
Frank
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KA2DZT
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« Reply #33 on: May 25, 2013, 08:57:35 PM »

I think toroids usually refer to donuts, you're using rods.  I think you may get more inductance using a toroid core but it may be tough to wind #12 on it.

But, keep trying you're making progress. You're up to 98uh, another 80uh and you're there.

Fred
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KM1H
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« Reply #34 on: May 26, 2013, 03:26:25 PM »

You really dont need that much L in the choke. With a much lower amount just reduce the input cap to compensate and part of the choke will be part of the circuit.
I use a 33 mix rod, 1/2" diameter and 7.5" long filled with bifilar #12 for the typical pair of 3-500's which has been in all the HB's for decades. For the 3X3 you need 50A wire capability so use 2 seperate rods with 2 #12 in parallel on each.

Using the plate choke as part of the network is also common in the output pi net and is how many commercial amps got by with 90-110uH on 160 or 50uH on amps that stopped at 80M. It also reduces the maximum C needed in the Tune cap which equals smaller size and less money.

Carl
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KJ4OLL
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« Reply #35 on: May 26, 2013, 09:48:11 PM »

Thanks very much for the tips and ideas Carl!
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KJ4OLL
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« Reply #36 on: June 23, 2013, 07:09:45 PM »

Hi,
Made a little more progress on the amp components!

POWER SUPPLY
I have never worked with plate transformers before, is it typical for one to make this much racket?

http://www.youtube.com/watch?v=GmAQbfU8U1E

FILAMENT TRANSFORMER
Getting very close to the output voltage needed from the new secondary winding that I made for the filament transformer.
Need about .3 to .5 of a volt additional, so will be rewinding the core again, when I obtain more enameled magnet wire.

http://www.youtube.com/watch?v=zxV4qEl4Cwo

73
Frank
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WD5JKO
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« Reply #37 on: June 23, 2013, 09:23:36 PM »


Frank,

   This rig of yours looks serious!

The video of that power transformer being ramped up might be a concern. That 60 hz buzz might just be some loose lamination(s) that vibrate as the core flux density rises, or it could be indicative of core saturation. If it is core saturation, the primary excitation current will rise very quickly after a point. It would be normal to have the current rise pretty much linearly with the applied voltage. If it is linear up to say 200 volts, and then goes up very quickly from there as you hear the buzz, then you have core saturation. This would be bad, and has to be avoided.

The filament transformer looks like it took a bunch of work. Adding more secondary turns at this point could mean almost starting over as you might have to remove the entire secondary winding.  Cry
One thought about the transformer. If the primary had less turns, then the secondary voltage will rise. One way to remove turns from the primary would be to add more primary turns over the secondary, and phase the new turns to 'buck' the original primary turns. Then you have to worry about core saturation.  Huh

Jim
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K1JJ
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« Reply #38 on: June 23, 2013, 10:41:02 PM »

How about using a Variac that can be configured for overstep to make up the last filament voltage fraction?

You need about 5% step up which is not too bad....

Also, with ther Variac you can ramp up the fil on start up.


Another possibility - if the fil xfmr is 120V primary, then a 6.3 fil transformer as an added boost in series with the primary might do the trick.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

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« Reply #39 on: June 24, 2013, 06:32:00 AM »

Hi,
If I put an amp meter on the input and look for non-linear current draw, sounds like I should see if the core is saturating - I'll try that.

I was thinking the same thing about the variac - the ancient Gen Rad only goes up to 135, but I have a Powerstat that goes to 140, I'll test it and see what effect it has on the secondary.

I have rewound the filament transformer secondary many times to get this far, it is not a big deal to do it again, except not much room remaining for many more turns.

The filament transformer secondary is wound with four bonded strands of #12 to get the current capacity, but possible less conductors would work.

I found a chart w/ Google that provides information about capacities:
- four strands of #12 gives about 245A for "chassis wiring" and 150A for "power transmission".

Possibly rewind it with one strand of #8 instead?
The current rating for a short run of #8 is 73A for "chassis wiring" , and 24 for "power transmission"
(51A needed for the EIMAC filament).

Thanks for the comments and ideas!
73
Frank
KJ4OLL


 
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WD5JKO
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WD5JKO


« Reply #40 on: June 24, 2013, 07:45:38 AM »



Frank,

  I suggest you refer to some of the information from Patrick Turner:

http://www.turneraudio.com.au/powertranschokes.htm

 It appears that you intended a turns ratio of 120/7.5 or 16, but due to sag you are getting closer to 19 (135/7). This must be due to a combination of copper loss, and transformer leakage inductance. If you rewind, perhaps split up the primary such that half of it is under the secondary, and the other half is over the secondary. This should increase the coupling since the leakage inductance will be reduced.

How many turns per volt? If it is over 2 Turns/Volt, perhaps you are short on core area?

So as a guess maybe you have 80 primary turns, and 5 secondary turns (1.5 T/V). If you were able to snake in 8 more primary turns (10% more) into your existing transformer without taking it all apart, and then phase it to 'buck' the original primary turns, then you in effect will have 72 primary turns. If so, then the turns ratio will 72/5 or 14.4. Take 120/14.4 and the secondary voltage would be 8.33V (unloaded). This approach would  increase the turns per volt up to 1.67..might be closer to saturation.

Jim
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KJ4OLL
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« Reply #41 on: June 24, 2013, 07:52:24 PM »

Hi,
I put an amp meter on the primary of the plate transformer, can't seen to see any excessive current spike as I turn up the variac.
So hope it is not saturating, just plate vibration.

At maximum 240VAC in to the plate transformer is sinking 1.1A.

I was expecting more DC voltage output from the rectifier.
But possibly having a 10H choke and the 100k bleeders has some significant effect on the rectifier output voltage, loading it down.

I have read that 1.414 x the AC voltage in should yield the DC out of a full wave rectifier. Probably unloaded?

But the readings I get are only about 1.14 times the AC input.


POWER SUPPLY TEST
240vac in to 240 primary tap
secondary 2600 volt tap measures 2760VAC to the rectifier, 3100 VDC out of rectifier

240vac in to  220 primary tap (The transformer does not seem to like this, very noisy, just did it for a test)
secondary 2600 volt tap measures 3000vac to the rectifier, 3400 VDC out of rectifier

240vac in to 240 primary  tap
secondary 4000 volt tap measures 4400vac to the rectifier, 4900 VDC out of rectifier

73
Frank
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Patrick J. / KD5OEI
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« Reply #42 on: June 24, 2013, 10:04:20 PM »

If the audio recording was accurate, it sure sounded like a mechanical buzzing rather than a growing hum. Mine hums, but does not sharply buzz, if the input volts (115 rating) gets above 130 or so via the 'variac'.

That transformer is a candidate for a dual variac of that size. It is the 6.5KVA size, no?
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KJ4OLL
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« Reply #43 on: June 25, 2013, 08:39:04 AM »

The variac I am using for the power supply is a 7.8kva, 1 phase,
240-280 28 amp.
The plate transformer makes noise at full voltage, but in the video, the noise is amplified by the big metal cabinet, so it sounds louder than it would be in open air.
I found that the balancing resistors on the rectifier get hot, so I'm going to install a cooling fan, then let the PS run for a while, see if the plate transformer gets hot.
If the plate transformer does not heat up much, I hope that means the core is not saturated, and the noise is just plates vibrating.


The variac used for the filament transformer is a 1.3kva, 1 phase
135v, 10 amp. No noise here, but at 135v on the primary, the core might saturate.

Will try to rewind the secondary so that a lower primary voltage yields the required secondary 7.5 vac @ 51A.

I looked over the information from the Patrick Turner web pages, WOW, that guy covers every single detail!

73
Frank
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W3RSW
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Rick & "Roosevelt"


« Reply #44 on: June 25, 2013, 11:16:29 AM »

Quote
I was expecting more DC voltage output from the rectifier.
But possibly having a 10H choke and the 100k bleeders has some significant effect on the rectifier output voltage, loading it down.

I have read that 1.414 x the AC voltage in should yield the DC out of a full wave rectifier. Probably unloaded?

But the readings I get are only about 1.14 times the AC input.

That's what you get with a choke input filter with a load sufficient to activate the choke properly.  Just about any ARRL handbook or similar reference will give you the "DC out vs. AC RMS in" formula for a choke input filter:

The handbooks will also give you a chart showing the effect of increasing capacitance in a capacitor input filter (no choke), the output approaching 1.35 DC out/AC RMS in, at very light loading resistance and very large filter capacitance and dropping to 0.75 with very heavy load and little capacitance.

Also there are neat charts showing approximate wattage vs. core cross sectional area from a typical E/I laminated transformer.   A 500 watt transformer needs about four square inches, i.e., 2 x 2 in. 

..and tons of other neat stuff.  Oh, even though you have only 100k bleeder, the class A current of driver amplifiers plus the full carrier current of the class C final in an AM transmitter will sufficiently load the choke such that you get only about 1.1 DC/AC rms output.  CW operation, however, is another story.
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KJ4OLL
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« Reply #45 on: June 25, 2013, 12:26:53 PM »

Thanks for the explanations Rick!
I have a new ARRL handbook, but it is intimidating, vast amounts of information, and I am new to homebrew!!!!
73
Frank
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« Reply #46 on: June 25, 2013, 11:01:10 PM »

How about trying some rubber donuts to set the trans. on? Sort of like a compressor in the condensing unit out back. The piece maybe sits on 1" thick rubber donuts, and on top of its flanges are half -compressed conical springs, held in place by the bolt heads. Just a thought because that hum might still be annoying after you deal with its reduction, if the cabinet amplifies it so much. I like the blower there, saw only part of it.
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KJ4OLL
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« Reply #47 on: July 21, 2013, 02:19:52 PM »

Hi,
I found some dense rubber at the local surplus place (Skycraft) and made shims to go between the
plate transformer and the chassis, that helped the vibration noise, thanks for the idea!

Last weekend my son (KJ4WLW) and I worked on the plenum box for the blower/filament transformer/choke/PA mount.





It was fun to be able to mock-up where the plenum will eventually fit in the amp, and imagine it
operating someday!



Worked on the PA mount assembly this weekend:





Next is finishing the plenum and mounting the blower.

73
Frank
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KJ4OLL
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« Reply #48 on: November 10, 2013, 04:32:31 PM »

Hi,
It has been a while since I updated the AM amplifier project.

Was "out of commission" for a couple months w/ medical stuff, all back to abby-normal now!

Was able to finish all the TIG welding on the plenum, ugly but at least I did not destroy it (I hate welding Aluminum)

Mounted the PA assy:



And started working on mounting the tank circuit:



Hope to get the filament transformer and choke mounted in the plenum next, too hot today, I am beat!

73
Frank


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KJ4OLL
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« Reply #49 on: January 03, 2014, 07:47:56 PM »

Hi,
More progress, will soon be able to power up for the first time and grab fire extinguisher.......





I have no idea what to drive this thing with!!

Was going to use the 32V-2 as exciter.
But many said that would be a waste, suggested a Flex.

After reading:
http://amfone.net/Amforum/index.php?topic=35503.0

Decided Flex might not be the best for the clean  3CX3000A7.

Can't I just build something as a simple exciter w/ good numbers, or is that impossible for homebrew?
 
All the 3CX3000 needs is about 25-30 watts in to make a nice big carrier.
Thanks,
Frank
KJ4OLL
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