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Author Topic: Neutralising  (Read 13032 times)
W1QJ
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« Reply #30 on: August 07, 2015, 03:27:13 PM »

A perfect example of what Tom is saying is well documented by simply looking at the Swan Mark II amplifiers.  Originally Swan grounded the grids on edition A of the Mark II.  I assume this was before the pressure from Orr to float grids on the caps.  When the B version of the Mark II came out you can see where Swan took the bait and floated the grids.  Around the same time the SB-220 and the Drake L4B came out, and they had already been coaxed to float the grids.  Then Kenwood with the TL-922 followed with floating and then Viewstar.  The only amplifier that did not fall for it was Dentron and later Amp Supply who all grounded the grids on all their models.  I assume since Tom knew Denny they discussed this issue and Denny sided with Tom. 
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G3RZP
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« Reply #31 on: August 08, 2015, 12:08:34 AM »

As far as I can make out, 572B's (I can find no mention anywhere of a '572' or a '572A') appeared in the early 1950s as a Class B modulator tube for transmitters in the 1kW DC input range. As such, long grid leads, high Cpk and so on didn't matter.......

When used in gg linear service, the better designs did neutralise them.....
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SM0AOM
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« Reply #32 on: August 08, 2015, 01:50:27 AM »

There were a number of 30L1 used by airlines at Heathrow at one time. They weren't very reliable, which asn't their fault - the people using them would change frequency and 'forget' to tune up the amplifier. Too technical for them......

Quite interesting.
Since I earn part of my living on airline HF communications, it would be nice to hear some more about this if possible.
In what time period and which airlines?

In a way it parallels the use of Drake TR-44B's and L-4B's at the Swedish embassies from the 60's into the 80's.
There the equipment was operated by office clerks.

Reportedly, the casualty rates among the L-4B's and the B&W T2FD antennas were quite high.
In the long run however, it provided a lot of 'bang for buck'.

The concept was coined by an old colleague from Swedish Telecom Radio, Olle Ekblom SM5KV, who sadly passed away this summer after a long fight with Parkinson's Disease.

73/
Karl-Arne
SM0AOM
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G3RZP
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« Reply #33 on: August 08, 2015, 05:33:40 AM »

Can't remember which airlines, although BOAC (Better On A Camel) would have been one, and it would have been early to mid 1960s. The 30L1 was around before the KW1000C, but the KW1000C was cheaper, which was another advantage. One 'Speedbird' frequency was 21885.
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SM0AOM
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« Reply #34 on: August 08, 2015, 06:47:56 AM »

Can't remember which airlines, although BOAC (Better On A Camel) would have been one, and it would have been early to mid 1960s. The 30L1 was around before the KW1000C, but the KW1000C was cheaper, which was another advantage. One 'Speedbird' frequency was 21885.

This must have been in the AM days,  as SSB took until about 1967 before it started to become common in airline communications.
Collins had the 618T since 1959, but it was quite expensive so airlines used their 18S,618S and similar equipment quite for some time...

73/
Karl-Arne
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« Last Edit: August 08, 2015, 10:53:57 PM by SM0AOM » Logged
G3RZP
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« Reply #35 on: August 08, 2015, 09:25:25 AM »

KW were selling their KW2000CA transceiver and KW1000C amplifier from about '64 or '65 to airlines and even some embassies. I believe at that time, the airlines were using them for base to base communications, rather than base to aircraft.
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SM0AOM
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« Reply #36 on: August 08, 2015, 11:30:13 AM »

KW were selling their KW2000CA transceiver and KW1000C amplifier from about '64 or '65 to airlines and even some embassies. I believe at that time, the airlines were using them for base to base communications, rather than base to aircraft.

Well its seems reasonable that airlines used HF for liaison between bases in the era of expensive landlines and slow TTY circuits.
It reminds me to bring his up with Transairs retired communications manager at a suitable occasion.

73/
Karl-Arne
SM0AOM
 
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KM1H
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« Reply #37 on: August 09, 2015, 10:30:19 AM »

Quote
As far as I can make out, 572B's (I can find no mention anywhere of a '572' or a '572A') appeared in the early 1950s as a Class B modulator tube for transmitters in the 1kW DC input range. As such, long grid leads, high Cpk and so on didn't matter.......

The predecessor of the 572 was the Taylor T-160 which was built for modulator service for which there was no market when introduced in the later 50's and they went looking for a buyer. United Electronics and Cetron obtained the tube thru a rather convoluted path and the initial 572 designator was dropped for the 572A for United and 572B for Cetron. For several years the T-160 was also on the label. Since the A and B was confusing and UE wasnt interested in pushing the tube the B became the label used by both.  I know of a few low volume production 572's in collections and I own a pair of UE 572A's along with all the various other tube manufacturer and private labels used on 572B's Ive been able to find. All round top tubes were built by UE and the shoulder type by Cetron. You will find many round top Cetrons which were built by UE to keep up with Heathkit, Dentron, and other orders as needed.
Svetlana produced a physically smaller version with the 572B label but the dissipation was only 125W, the same as Shuguang in China.

The 811A, which shared the grid structure and long leads of the 572, was rated to 54 mHz by RCA and the 572A/B work just as well at 6M with a little attention to detail. Ive converted several hundred SB-200/201's and other two tube amps to 6M since the mid 1960's.

As far as blaming Orr for all the problems, and since he isnt around to defend himself nor have I seen anything in writing by him or others but one, I'll keep an open mind on what really went on.

I do remember that many published GG amp articles used a .01 cap as a grid bypass for RF and then off to the grid current meter and/or bias. The few I built that way back then worked quite well (very stable on HF and 6M) but were mostly 4-250A/400A's and no 811/572 varieties.

Carl
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K9AXN
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« Reply #38 on: August 11, 2015, 12:51:47 PM »

What is the purpose of 5pf cap connected between anode and control grid in the 30S1?

For the Collins guys.  What are the values of the components in Z101?
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W1BR
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« Reply #39 on: August 11, 2015, 02:32:28 PM »

Negative feedback. Read the manual.

http://www.radiomanual.info/schemi/ACC_PA/Collins_30S-1_user_GAF-FAPI.pdf

Pete
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K9AXN
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« Reply #40 on: August 11, 2015, 03:06:15 PM »

Pete,

You must be the Collins guy I was looking for.  What the manual states and you concur, that the capacitor provides negative feed back to the control grid.  Is it fair to reason that it is a component of the super cathode drive configuration and not intended to influence neutralization as the feed back has the same phase relationship as the cathode to grid feed back leg?  Is the 5pf cap necessary because the screen was grounded minimizing effective interelectrode capacity? 

One last question.  What are the values of the components that represent Z101?  I have to assume it is a parasitic suppressor.

Thanks again for your time.

Regards Jim   
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W8JI
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« Reply #41 on: August 15, 2015, 05:23:29 AM »

The manual "claims" the capacitance division adds negative feedback, and it can reduce grid-cathode voltage.

However..... if the tube draws grid current, if significant resistances or inductive reactances are involved, or if the tube is physically large or leads are long enough to act like delay lines or introduce phase shift, that notion or claim all goes out the window.

We can pretend like it is negative feedback, but unless specific conditions exist which exclude any amount of grid current or other things that shift phase, it will NOT be linear feedback over the RF cycle. That idea went bad when applied to things with grid current.
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K9AXN
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« Reply #42 on: August 15, 2015, 08:32:32 AM »

The manual "claims" the capacitance division adds negative feedback, and it can reduce grid-cathode voltage.

However..... if the tube draws grid current, if significant resistances or inductive reactances are involved, or if the tube is physically large or leads are long enough to act like delay lines or introduce phase shift, that notion or claim all goes out the window.

We can pretend like it is negative feedback, but unless specific conditions exist which exclude any amount of grid current or other things that shift phase, it will NOT be linear feedback over the RF cycle. That idea went bad when applied to things with grid current.

Tom,

Remember, the 30S1 does not draw grid current --- you must be confused.

BTW, the Z101 inductor/resistor is a parasitic suppressor in series with the 5pf cap.    

You didn't answer the question asked and you might want to rethink your opinion regarding the design of the 30S1.

A super day to you Kindest regards Jim

« Last Edit: May 21, 2016, 08:53:01 AM by K9AXN » Logged
W8JI
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« Reply #43 on: August 16, 2015, 02:11:03 PM »

It works the way it works, no matter what someone claims.

It really isn't that complicated. It is a pretty simple system. It is a simple capacitive divider with a vacuum tube diode across it.

How complicated can that be to understand?
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