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Author Topic: Which comes first? Chicken or egg.  (Read 6840 times)
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W4TWA
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« on: June 29, 2014, 12:31:19 AM »

AM'ers,
I have been batting around the idea of a high powered kilowatt plate modulated rig for some time now. My plans are never even begun due to my confusion over the choices that would fill reams of information, and even more reams of opinions. I am hoping you can steer a fellow in a direction that would make it less confusing to even begin to quantify what I want to try. My post title stemmed from an am guy I was hoping to tap for info. I asked what mod iron should I be looking for? a: what tube do you wanna use. My answer back was a blank stare.
Fortunatlely I have a bud that will give me any number of n.o.s tubes capable of the task, he just wants to know which ones to give. Then once the valve is selected, what are my chances of finding appropriate iron for it. Those wonderful catalogs full of all those mod transformers an chokes are no more with us. I see from time to time a plethora of big mod iron on screw-bay, but really don't know if they are appropriate for the cause.
So which, when building your rigs, do you try and procure first? The iron or the bottles? I.e, the chicken or the egg?
Is my fate to creep through hamfests for the next 20 years in hopes of finding all the doo-dadds?
All of this before I even think of other things like insulators, hi voltage caps, chassis fabrication(dear god in heaven)....the list goes on.
On a positive note, I have a functioning soldering iron, haha
Any thoughts?
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W4TWA
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« Reply #1 on: June 29, 2014, 12:43:28 AM »

Allow me to clarify what I think might be some possibilities of what I would like. I have a 32v3, that according to the west coast handbook would make an excellent exciter service for a big amp. On the other hand, I think it would be rewarding to build the thing from ground up for the satisfaction of building the entire system.
When you big guns start a project, do you pick a sub system like power supply, then move to the next sub system, or jus do it all at the same time? If you use sub system technique, is there and order as to which sequence you use?mim assuming one starts with the power supply.
Thanks for letting me ramble. My xyl is absolutely not giving me any useful feedback,haha
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Patrick J. / KD5OEI
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« Reply #2 on: June 29, 2014, 05:39:49 AM »

The modulation iron is the hardest thing to get and is probably the one thing that will define the transmitter the most. My suggestion is to start by obtaining a modulation transformer and choose the rest to fit.

Some people prefer to use two fairly equal size plate transformers, one for the RF stage and one for the modulator. That improves regulation of the RF by avoiding reduction in potential output when the modulator loads down a common power supply. If a common transformer is used and is oversized well, it may not matter as much.

An additional advantage to using two plate transformers is that the HV can be adjusted differently for the modulator and the RF stage. Using a higher voltage on the modulator than on the RF stage has an effect of increasing the turns ration and modulation, compensating for a less than good turns ratio in the modulation transformer.
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« Reply #3 on: June 29, 2014, 11:32:43 AM »

A good source of parts for a high-level plate modulated rig is to buy an old AM broadcast transmitter like a Gates BC-1G or H.

If you don't have room for it as-is (converted and used for 160, 75, and 40), break it down and you have everything needed for 833A's.

The same can be said for an old Sparta, Bauer, or CCA rig using 4-400's.

Not a whole lot of $$, and you get a matching set of proven & tough parts.

73DG
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K1JJ
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« Reply #4 on: June 29, 2014, 03:23:12 PM »

Put a bunch of "wanted" ads on the various Ham trader sites. Look for 1 KW  to 2.5 KW broadcash iron.  If the ratio is anywhere between 1:1 and  2:1 step down, you will be fine with most tube line ups.

1.5 : 1   step down is a good central number.

These popular BC mod xfmrs will handle 3-500Zs, 4-400As, 833As, 4X1s, 813s, 810s - most anything you want to run.

There are probably some older hams who have big iron stored and now realize they will never build the big plate modulated rig.  They have settled on Flexes or ricebox / linear combos for AM.

Axe for a matching Heising reactor - they usually come as a pair.


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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W4TWA
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« Reply #5 on: June 29, 2014, 06:05:22 PM »

Thanks for the replies. Here is a mod x-former on e-bay. It says it's a 500w mod transformer by rca it's the rca 901769-501.
Anyone have info on this one?


* image.jpg (107.24 KB, 1024x768 - viewed 376 times.)
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WQ9E
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« Reply #6 on: June 29, 2014, 06:24:47 PM »

I am not familiar with the RCA iron, hopefully someone else is.  However one general thing to keep in mind is many of the broadcast modulation transformers were designed for use with a modulation reactor (choke) to keep DC off the secondary of the modulation transformer.   Reactors are very difficult to find these days so make sure if you buy a mod transformer from an old broadcast transmitter to also get the reactor with it if one was required.
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Rodger WQ9E
w1vtp
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« Reply #7 on: June 29, 2014, 06:41:06 PM »

Thanks for the replies. Here is a mod x-former on e-bay. It says it's a 500w mod transformer by rca it's the rca 901769-501.
Anyone have info on this one?

That looks a lot like mine.  We need a pic of the laminations to see if there is a gapped spacing or if it is alternated.  One will work by itself the other will require a modulation reactor.[1]

The other question is if you are looking for just communications grade audio or if you want to have an extended range frequency response.  Yet another factor would be to remember that with the typical male voice, you should figure for 125% modulation on the positive peaks (actually more but that's a good starting point).

This is the right bunch of guys to consult with. Good luck

Al



[1]  I see someone else has addressed this point.

PS:  I see the listing says that it weighs 50 lbs.  Mine weighs 80.  Just be mindful should the shipping cost escalate
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w1vtp
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« Reply #8 on: June 29, 2014, 07:08:37 PM »

Here are some high res pics of some of my stuff.  The side view shows the gap I was talking about. I still got the mod reactor.  Key for this stuff is to seize the moment and BUY when the opportunity affords itself

GL, Al


* RCA MOD IRON SIDE SIDE VIEW SHOWING GAP(COMP).jpg (420.14 KB, 2720x2630 - viewed 348 times.)

* RCA MOD IRON TOP VIEW(COMP).jpg (777.84 KB, 4928x3264 - viewed 467 times.)

* MODULATION REACTOR(COMP).jpg (488.18 KB, 2242x2694 - viewed 360 times.)
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WBear2GCR
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« Reply #9 on: June 29, 2014, 08:43:23 PM »

as mentioned, it's not a bad idea to try to build around the major components that you have or can get.

but you might want to take a good look at the K1JJ design here, it may be found in the "technical info" button that is in the upper left of this and most pages here on AMfone. A number of ops have built this rig and gotten very good results. The design is surprisingly flexible in that you can run the 2 x 813 finals with a fairly wide range of B+, with a reasonably amount of current behind them and modulating is not too difficult, and can be done by a variety of methods, using a variety of medium power iron or larger... it gets you into the 300+ watt carrier class nicely.

                       _-_-
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_-_- bear WB2GCR                   http://www.bearlabs.com
WBear2GCR
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« Reply #10 on: June 29, 2014, 08:44:22 PM »



forgot to mention there are a number of threads on that design and various builds that can be searched out here.
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_-_- bear WB2GCR                   http://www.bearlabs.com
K1JJ
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« Reply #11 on: June 29, 2014, 09:12:14 PM »

" I see the listing says that it weighs 50 lbs.  "

Interesting this mod xfmr is listed at 500 watts. It matches the TimTron rule which states that a mod xfmr is good for 10 watts per pound.      10 watts X 50 pounds = 500 w.


Here's a link to the 813s X 813s rig that Bear mentioned:

http://www.amwindow.org/tech/htm/813/813.htm

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.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
WD5JKO
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WD5JKO


« Reply #12 on: June 29, 2014, 09:22:47 PM »


If I were wanting to build a big plate modulated rig today, I would look hard at skipping the mod transformer concept unless I happened to stub my toe on a nice mod transformer and reactor. Since this thread is about wrapping tubes around a mod transformer, or wrapping a mod transformer around tubes, then skip the pricey used stuff, and get a new one:

http://pwdahl.com/PWD_HamCatalog.html

At the above link there are 6 mod transformers for sale. Here are a few:

COLLINS KW-1 MODULATION XFMR
PP 810 MODULATORS TO PARALLEL 4-250A'S
CORE) EI-175  EE-STACK       STYLE #) 80  E-I LAMINATED CORE
PR) 1800/2400 VCT, 18000/11600 OHMS PP
S1) 1768 VAC @ 283 MA CCS (6250 OHMS RFPA)
DM) HT =  6.400 WT =  7.000 DT =  7.000 MD =  6.812 MW =  4.750
PRICE)    CALL or e-mail Plus S&H FOB Buffalo, NY    WEIGHT)   35  LBS


COLLINS 30K MODULATION XFMR
P/N 677-0316-00, 200W,+/- 2DB 100-5000HZ
CORE) EI-150 X 2.5" 29GM6X   STYLE #) 07  E-I LAMINATED CORE
PR) 2450 VCT @ 175 MA (32K OHMS)
S1) 1770 VAC @ .150ADC & .113AAC(16.7K OHM)
S2) 248 VAC @ .050ADC
DM) HT =  6.062 WT =  3.750 DT =  4.390 MD =  3.500 MW =  3.000
PRICE)    $595.00 Plus S&H FOB Buffalo, NY    WEIGHT)   12  LBS


JOHNSON VIKING 500 MOD
VIKING 500 MODULATION TRANSFORMER
CORE) EI-212 X 3             STYLE #) 04  E-I LAMINATED CORE
PR) 23000 OHMS P-P 2400 VCT (200-3500 HZ)
S1) 8000 OHMS (2000VDC @ 250MA)1414VAC 250W
DM) HT =  6.375 WT =  5.313 DT =  5.678 MD =  4.250 MW =  4.250
PRICE)    $390.00 Plus S&H FOB Buffalo, NY    WEIGHT)   29  LBS


THORDARSON P/N T-11M77
125-300 WATT MULTI-MATCH MODULATION XFMR
CORE) EI LAMS POTTED CASE    STYLE #) 07  E-I LAMINATED CORE
PR) PP 811A'S @ 1000 VDC
S1) SINGLE 813 @ 2000 VDC @ 225 MA DC
DM) HT =  7.500 WT =  6.000 DT =  7.250 MD =  5.875 MW =  5.375
PRICE)    CALL or e-mail Plus S&H FOB Buffalo, NY    WEIGHT)   26  LBS

Jim
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VE3AJM
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« Reply #13 on: June 30, 2014, 03:53:20 AM »

Thanks for the replies. Here is a mod x-former on e-bay. It says it's a 500w mod transformer by rca it's the rca 901769-501.
Anyone have info on this one?

Heres the info FOB on the AM Window..

Al VE3AJM

http://www.amwindow.org/tech/htm/modtran/rca.htm

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