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Author Topic: Roller Inductor ?  (Read 3841 times)
NT0A
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Posts: 97




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« on: May 12, 2013, 12:22:23 PM »

Has anyone every heard of a modifying the Kenwood TL-922A by putting a roller inductor in place of the tapped tank coil? The amp is a real rugged beast of an HF amplifier, but I cannot use it on MARS frequencies where 100 watts just will not do the job.

73s de Bob NT0A
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N6AJR
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Posts: 9908




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« Reply #1 on: May 12, 2013, 12:53:50 PM »

How about adding an external tuner to the amp.  I actually prefer a switched inductor on any type of tuner as the roller ones take too long to use, and don't function much better in my view, But a tuner will probably be better, or even think about a tuneable antenna like a steppir vertical.
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K6AER
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Posts: 3515




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« Reply #2 on: May 12, 2013, 01:30:00 PM »

There is no room inside the TL-922 for a roller inductor. In addition the input tuning would also be off. Most MARS frequencies are very close to the ham bands. What is the frequency you are trying to use.

If you are very far from the ham bans the resonance of the HV choke can also be a problem.

The band switch is very fragile in the TL-922 along with the padder caps. I would go with a amplifier with more current reserve like a Drake, Alpha ORO or a new amplifier.
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NT0A
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Posts: 97




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« Reply #3 on: May 13, 2013, 09:45:03 AM »

There is no room inside the TL-922 for a roller inductor. In addition the input tuning would also be off. If you are very far from the ham bans the resonance of the HV choke can also be a problem. The band switch is very fragile in the TL-922 along with the padder caps.

Well, mechanically it doesn't sound as if it is possible. I've looked at the schematics, but I haven't popped the hood and dropped the oil pan to go exploring.

Quote
Most MARS frequencies are very close to the ham bands. What is the frequency you are trying to use.

Some MARS frequencies are close to the legacy ham bands, but many are not. The TL-922A design allows the amp to tune roughly 500 kHz above and below each of the legacy ham bands, but many of the MARS frequencies are much further away than that from the band edges. Here are some approximate examples:

2.6 MHz
5.8 MHz
9.3 MHz
12.1 MHz
16.2 MHz
Etc.

Quote
I would go with a amplifier with more current reserve like a Drake, Alpha ORO or a new amplifier.

I will probably build one from scratch using the Communications Concepts AR347 assembly. That will cover the entire range from 2 MHz to 50 MHz.
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NT0A
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Posts: 97




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« Reply #4 on: May 13, 2013, 09:57:13 AM »

How about adding an external tuner to the amp.

More than 30 years ago, I built the W1ICP (Lewis McCoy) designed Ultimate Transmatch that was featured in the July 1970 QST magazine. It's a rugged unit with 5 kV variable capacitors and a roller inductor that will damn near match anything from a coat hanger to a mile long random wire from 80m through the 10m band.

That still does not solve the problems inherent with a tank circuit in the amp that cannot be tuned to resonance.

73s de Bob NT0A

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K5RT
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Posts: 144




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« Reply #5 on: May 13, 2013, 04:27:21 PM »

Bob, it's not just the plate circuit that you have to be concerned about. The TL-922 has tuned input circuits that you have to deal with. You could bypass them and the SWR that your transceiver sees wouldn't be too bad. I've never heard of anyone doing the mod you suggest.

The TL-922 is not the easiest amp to work on. They still command a decent price too.
You might want to pick up an SB-220 if you want to experiment. Don't forget to check the plate choke resonant points too.

vy 73 Paul
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NT0A
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Posts: 97




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« Reply #6 on: May 13, 2013, 05:12:59 PM »

Bob, it's not just the plate circuit that you have to be concerned about. The TL-922 has tuned input circuits that you have to deal with. You could bypass them and the SWR that your transceiver sees wouldn't be too bad.

That is true, and it is why once I have tuned the transmatch to the frequency using the basic radio, I tune the amplifier and then tune the rig to the amplifier input. The TL-922A input circuits are not the problem. Once everything is tuned, the rig will put 70 to 100 watts to the amp, and the amp will deliver 1 kW to the feed line.

Quote
I've never heard of anyone doing the mod you suggest.

From the other posts here, that's probably because there is not enough room in the case.

Quote
The TL-922 is not the easiest amp to work on. They still command a decent price too.

Very true. I think I put out 1 1/4 k$ for mine.

Quote
You might want to pick up an SB-220 if you want to experiment. Don't forget to check the plate choke resonant points too.

That's not a bad idea, but I'll probably invest the $$ in the parts for a home-brew, solid-state amp built around the CCI 347 board.

vy 73 Paul
[/quote]
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KU7I
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Posts: 122




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« Reply #7 on: May 16, 2013, 11:02:03 PM »

I would check for plate choke resonance points close to your operating ranges you are interested in. I very much enjoy using the TL-922 and agree it is not the easiest amp to service. I also like the idea of picking up a cheap and very easy to service SB-200 or SB-220. The old Hunber Bandits are pretty easy to service also.
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KC4MOP
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Posts: 734




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« Reply #8 on: May 17, 2013, 04:30:56 PM »

I am not understanding why a transmatch is mentioned.
The Amplifier has to be brought to resonance for the non-ham frequencies the OP wants to use for MARS. Apparently the 922 is strictly Ham bands only. The transmatch  does its magic after the amplifier is tuned to the operating freq and you want that amplifier to see a 50 ohm load at the output. The transmatch will create something the amplifier wants to see and transfer as much power as possible to the antenna.
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NT0A
Member

Posts: 97




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« Reply #9 on: May 24, 2013, 08:42:33 PM »

I am not understanding why a transmatch is mentioned . . .

It is immaterial whether you tune the transmatch to present a 50Ω load to the basic transceiver and then tune the amplifier into the transmatch or tune the amplifier into a 50Ω dummy load  and then use the transmatch mate the antenna to the to the amplifier, the end result is all the same.
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KC4MOP
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Posts: 734




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« Reply #10 on: May 25, 2013, 04:31:50 AM »

I am not understanding why a transmatch is mentioned . . .

It is immaterial whether you tune the transmatch to present a 50Ω load to the basic transceiver and then tune the amplifier into the transmatch or tune the amplifier into a 50Ω dummy load  and then use the transmatch mate the antenna to the to the amplifier, the end result is all the same.

I read the N6AJR's response and should have clarified what I was trying to say. The amplifier needs to tune to resonance first....then we move on to the antenna tuner.
The TL-922A seems to be Ham Bands only. It is unusual that it would not tune a little beyond the Ham bands. I had the Heathkit version of the AL 80 and it tuned to the MARS freqs. with no problem.
Fred
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NT0A
Member

Posts: 97




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« Reply #11 on: May 25, 2013, 05:33:08 AM »

The TL-922A seems to be Ham Bands only. It is unusual that it would not tune a little beyond the Ham bands. I had the Heathkit version of the AL 80 and it tuned to the MARS freqs. with no problem.

As I mentioned early in this thread, some MARS frequencies are close to the legacy ham bands, but many are not. The TL-922A design allows the amp to tune roughly 500 kHz above and below each of the legacy ham bands with ease, but many of the MARS frequencies are much further away than that from the band edges. Here are some approximate examples:

2.6 MHz
5.8 MHz
9.3 MHz
12.1 MHz
16.2 MHz
Etc.

On those frequencies, it is impossible to tune the amplifier's tank circuit to resonance not to mention the impact of the amplifier's input circuits.

73s de Bob NT0A
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KC4MOP
Member

Posts: 734




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« Reply #12 on: May 26, 2013, 05:04:22 AM »

The TL-922A seems to be Ham Bands only. It is unusual that it would not tune a little beyond the Ham bands. I had the Heathkit version of the AL 80 and it tuned to the MARS freqs. with no problem.

As I mentioned early in this thread, some MARS frequencies are close to the legacy ham bands, but many are not. The TL-922A design allows the amp to tune roughly 500 kHz above and below each of the legacy ham bands with ease, but many of the MARS frequencies are much further away than that from the band edges. Here are some approximate examples:

2.6 MHz
5.8 MHz
9.3 MHz
12.1 MHz
16.2 MHz
Etc.

On those frequencies, it is impossible to tune the amplifier's tank circuit to resonance not to mention the impact of the amplifier's input circuits.

73s de Bob NT0A

We seem to be going in a technical circle with the amplifier. The amp would need major re-work / design / re-engineering, to be able to get to the MARS freqs. You might be able to buy a used amp known to tune to the MARS freq. without all of the modification to the TL-922A. That is a very nice power house amp that has a long track record of reliability. Maybe a 600 W no-tune Solid State amp would be way to work around your situation.
Fred
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W9GB
Member

Posts: 2623




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« Reply #13 on: May 26, 2013, 09:46:57 AM »

Bob -

Your ideal answer appeared on eBay last week, auction # 300902281737

Datron/Transworld TW1000B 1kW ex-military / US State department HF linear amplifier,
INCLUDING the 28 VDC, 70 Amp power supply!

Item was posted by rs-surplus in Baldwin Park, CA.  Sold for $1,303.00
Compare that price to ANY solid-state Ameritron/MFJ, Tokyo HyPower, Yaesu Quadra, Icom PW-1
and you see what a $$ bargain this was.


The transistors used are MRF-422, sometimes private labeled or TRW PT-series equivalents.

Handles about everything (SSB, FSK, etc.) from 2 to 30 MHz.
MARS, no problem -- it was designed for government/military communications.

« Last Edit: May 26, 2013, 09:54:19 AM by W9GB » Logged
NT0A
Member

Posts: 97




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« Reply #14 on: May 26, 2013, 11:07:26 AM »

Your ideal answer appeared on eBay last week, auction # 300902281737

Yep! That would have done it very nicely, especially with the 14-day return period. I've been bitten on eBay with ham equipment before, so I've stopped looking there. Guess I should start watching again.

73s de Bob NT0A
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