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starting work on the amp




 
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KD6VXI
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« Reply #225 on: February 05, 2017, 10:24:22 AM »

Pat,

Do you have the schematics for the control circuitry?  You may need to build op amp meter drivers,  depending on your meter sensitivity. 

I've found the diodes in the bridge for the fil circuit metering to be...   Barely adequate?   Which was because the chokes feeding them,  as well,  where barely enough in Uh to keep rf out of the bridge. 

Here's a pic of the one here.   Have engraved placards on order,  but the 'Dymo'  tape helps to remember what's what.   It has a grounded grid and a variable bias position,  bias voltage up into the 50s, so I can cut plate current off.

Also has a ptt in out,  and a FTT or Flip To Talk.

--Shane
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« Reply #226 on: February 05, 2017, 10:27:54 AM »

FAIR sold those Sola regulators.

I don't remember them being cheap or lightweight.

What about a power conditioner,  Pat?   That might be an easier find from an IT shop.

Basically,  a SOLA box.

--Shane
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« Reply #227 on: February 06, 2017, 06:33:56 AM »

Pat,

Do you have the schematics for the control circuitry?  You may need to build op amp meter drivers,  depending on your meter sensitivity. 

I've found the diodes in the bridge for the fil circuit metering to be...   Barely adequate?   Which was because the chokes feeding them,  as well,  where barely enough in Uh to keep rf out of the bridge. 

Here's a pic of the one here.   Have engraved placards on order,  but the 'Dymo'  tape helps to remember what's what.   It has a grounded grid and a variable bias position,  bias voltage up into the 50s, so I can cut plate current off.

Also has a ptt in out,  and a FTT or Flip To Talk.

--Shane
KD6VXI




I have the few manuals that are online. The controls on this one seem to be just relays, etc. There is a remote control section on one variant manuals (Randex) but this unit apparently did not include it.

The metering on this looking at its schematics used no op-amps but yes indeed my 'nice' meters are according to Murphy's Law not going to be the correct mA readings. Usually I've attacked this kind of problem by changing the shunt values within reason. Any reason that could cause troubles?

I didn't think about adjustable bias yet. With the grid grounded and the cathode being a high current path, what did you do to make that work in a variable manner?
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« Reply #228 on: February 06, 2017, 06:39:04 AM »

FAIR sold those Sola regulators.

I don't remember them being cheap or lightweight.

What about a power conditioner,  Pat?   That might be an easier find from an IT shop.

Basically,  a SOLA box.

--Shane
KD6VXI

That's the trouble, they are not cheap. I'm open to either the transformer-like package or the cased units sold as conditioners. The 230V units are less common. I'll check Fair. There are some on ebay, not sure if I'll get 'stuck' with a bad one -no one wants to guarantee any of it. Still $100 average price and the way some of them overcharge for shipping is pushing the budget.
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« Reply #229 on: February 06, 2017, 11:24:22 AM »

Shipping isn't charged in the fees.   Hence them having a low sales price and an extreme shipping.

Sounds like you have the same as my 2000D.  That one has a door for the front panel and was designed for a remote controlled sputtering head......   Whatever that is.  I also have one that has the rf deck and fil xformer changed.   That one has full metering,  etc.  And a 4-250 driver stage.  With an 8877 final.....!   Needless to say,  stoked about the power supply for that one!

The first bias circuit I used was a string of 15 diodes.   As others found,  it's not really necessary.   But,  looks cool,  and provides for the ability to change things.   I like that.

I'm using a variant of the W4ZT bias circuit with a modification to use 3 pass transistors instead of one.   This will work for tubes up to a single 10 triode,  according to GM3SEK.   This rf deck may have a 3x6 installed if the 3 ever goes soft according to the end user.   He says a single Darlington would be sufficient for a single 3000.  For a YC156 (5k) or larger,  more pass xisters.

--Shane
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« Reply #230 on: February 26, 2017, 08:04:18 PM »

The tube is the limiting factor on this project. I don't think I'll ever have to replace it from wearing it out.

Today I guess the RF deck could be said to have been started. Been so busy the last couple months. The front to back partition on the Henry was removed since there will be no output signals under the chassis. The coaxial filament choke from a GPT-10 was mounted. A 4" tall chassis will be inverted to serve as a bottom cover on the RF deck. This leaves enough room for the large filament choke and probably a tuned circuit. The 13.56MHz Henry had its own filament choke but it was lower inductance than wanted.

A 2" ID piece of PVC pipe holds the filament choke and the ends of the choke were adjusted to reach the filament input terminals and also the socket. This cost me less than a turn.

The pipe is mounted by some rack brackets and #10 thread stock. The threads go through the PVC pipe and the pipe is clamped to them by some washers modified to fit the inner and outer curve of the pipe to reduce stress from any jiggling of the unit. This arrangement uses cut-washers so the nuts will stay in place well.  The two large holes in the PVC pipe allow a nut driver to be inserted to work with the fasteners of the pipe.

The filament voltage monitoring board has to be relocated and a power resistor put back in place then the Henry amp's original 'monitoring' wiring can be re-used.

The filament choke is at least 1.5" from any metal. It's the best that could be done there.


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« Reply #231 on: February 26, 2017, 08:05:02 PM »

more pictures.
My assistant remarked that this part of the job, the amplifier chassis, seems to already be a lot harder than the power supply. I could only say, we have not seen nothin' yet, this is the simple part.


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« Reply #232 on: February 27, 2017, 04:39:48 AM »

I have a question - what type ferrite rod material should be used to cover 2-30Mhz?

The reactance of the filament choke will be low at 160M so the material should be active there.

If it drops off in adding inductance as the frequency increases, that may be ok, right? The coil as it is measured about 4uH.

next, will 2" ferrite 'donut' cores slip into a 2" PVC pipe? can those be used for this same purpose?
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« Reply #233 on: February 27, 2017, 06:54:55 AM »

Patrick,

   Off the top of my head, I'd say type 43 material for 160m, and 31 for the higher bands.

One option that may or may not be relevant would be to isolate the filament transformer from ground, and put a common mode RF choke on the filament transformer primary wires. This might work for 160, 80m, and then above that the existing air wound filament choke takes over.

You would still need a single wire choke for the filament centertap to ground or zener wire, but that would only need to pass an amp or two.

Question: Could this AMP be a driver for a larger amplifier project yet to be built?  Grin

Jim
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« Reply #234 on: February 27, 2017, 08:36:25 AM »

Here are some "before and after" numbers my choke.
I stuffed it with type 43 ferrite rods to get more inductance.


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« Reply #235 on: February 27, 2017, 10:38:54 AM »

That filament choke looks like it came from a GPT 10K .....it is coaxial......for a 4X5...TMC mounted it on a fibre glas rod...
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« Reply #236 on: February 27, 2017, 11:36:27 AM »

Jim/ WD5JKO:

Your avatar picture above of a car radio with "All Transistor" reminded me of something from 1962. Back in those days kids walked around with the new 2 transistor radios listening to local AM rock and roll stations.   The first question was always, "How many transistors does yours' have?" As time went on, it would increase from two transistors to four, then six, then ten as radios became better.  

Then one day I met a girl who answered, " Mine is ALL transistor!"  It said so on the radio. We didn't know what to think except that she had trumped us all no matter how many we had.  Little did we realize that even the older 2 transistor radios were "ALL Transistor."    :-)

T
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« Reply #237 on: February 27, 2017, 07:39:39 PM »

Jim/ WD5JKO:
Then one day I met a girl who answered, " Mine is ALL transistor!"  It said so on the radio. We didn't know what to think except that she had trumped us all no matter how many we had.  Little did we realize that even the older 2 transistor radios were "ALL Transistor."    :-)
T

About 55 years later she got "trumped", but this time it was for saying, "what difference does it make"!  Tongue

I do like that Avatar. I sent that radio carcass to an AMFONE member who was wanting to experiment with permeability tuned circuitry. I bought that radio to get the audio output transformer which was a tapped inductor for the single ended class A PNP germanium transistor (2N176?). It seemed to act as a good modulation transformer for my Retro75.

Jim
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« Reply #238 on: March 02, 2017, 01:22:55 AM »

I swear it's not a driver for a larger stage. I have only 100A service to the lab so with the Texas heat and HVAC requirements that leaves me about 50A for playtoys.

The choke is indeed from a GPT-10. It seemed appropriate to use a higher rated choke. The Henry's driver was rated 100W. The operating conditions in the tube datasheet call for up to 400W of drive. The GPT-10's driver is rated 1KW.

To figure out how many ferrite rods will fit in the 2" section of PVC, there is a formula somewhere but this web site has a calculator on it. 
http://www.engineeringtoolbox.com/smaller-circles-in-larger-circle-d_1849.html

Material 43 or 31 Ferrite rods seem costly. Am I missing something?

Lastly I don't know that much about ferrite material. Will type 43 material be overly lossy or dissipative at 28 or 50 Mhz? Or will it just have a reduced effect?
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« Reply #239 on: March 02, 2017, 10:33:18 AM »

The original Henry choke will handle an 8877 for drive.

Ferrite load it for 160 to 10.  As is good for 20 and up, maybe 40.

You can use different mixes in your various stuffed rods to equalize the bandwidth.

--Shane
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« Reply #240 on: March 16, 2017, 11:06:30 PM »

The original Henry choke will handle an 8877 for drive.

Ferrite load it for 160 to 10.  As is good for 20 and up, maybe 40.

You can use different mixes in your various stuffed rods to equalize the bandwidth.

--Shane
KD6VXI

I thought about a mix of ferrites and also about filling 1/2 or 2/3 of the length of the filament choke with the ferrites and leaving the rest free to help in case the material was messing it up for the highest frequencies. -There will be an attempt to have 6 meters as well as HF.

These ferrite rods were found and bought so it's just the waiting now. I have no idea what they are and there seems to be no data available from the salvage resale company except that they are Russian, which at least means the quality will be good.

The offer seems fortuitous because exactly 8 of them will fill in the 2" ID of the PVC pipe supporting the choke.
http://www.engineeringtoolbox.com/smaller-circles-in-larger-circle-d_1849.html



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« Reply #241 on: March 22, 2017, 12:46:57 PM »

Wow, can you believe it's been almost a year already? So much time devoted to this, it's shaping up nicely at least for you.

I finally got an account on here; this is your apprentice by the way.

To any and all who may be wondering about the side project mentioned in this thread (audio modulated vacuum tube tesla coil) I've had to largely depart from my design and much of what I had constructed because the 75khz grid driver remained plagued with parasitic oscillations.

During the attempts at constructing this, I began thinking about the possibility of combining a plate modulator and a plate power supply; basically a much larger version of the grid modulator I had been constructing with a ferrite transformer from an inverter-microwave oven power supply.

This solid-state supply would drive a ferrite transformer at the resonant frequency of the tesla coil secondary, the tube would be operating at half-wave, and the audio modulation would be applied at the grid.

I'll make a thread about my current thoughts on this project and come back to post a link to it.
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« Reply #242 on: March 24, 2017, 09:52:37 PM »

Ahh yess my not-so-evil apprentice. It's best to use a separate topic. The Tesla coil and driver thereto are indeed radio frequency gear for practical purposes and the amplitude modulation does make it an AM transmitter. That is why the work right now is being done in a metal building. No guarantees how faraday-cage-ish but give it the big W for now.

The ferrite rods showed up for the filament choke. Anyway, some experiment will be done with a VFO to see what the reactance of the choke is with the rods in and try to find out if they are causing a loss at high frequencies due to this unknown material, etc. It will be kind of an elaborate setup I think. I do not have a lot of experience with ferrites.

A piano hinge was found to permit the chassis bottom to be opened and closed for testing and later after the input circuit is done and tested the shielding of the filament area/wind chest can be fixed up.
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« Reply #243 on: March 26, 2017, 01:48:17 AM »

Measurements with a Boonton LC meter at 1MHz show 21uH when 6 or 7 rods are put in the PVC pipe supporting the filament choke. As many rods as in the KJ4OLL was not possible due to the support for the choke. The 7th rod didn't make much difference at all.

7 rods fit snugly once the SCH40 2" pipe was slit lengthwise to allow it to be expanded a hair, otherwise it was very tight and I did not like that because ferrite can crack. Each rod was partly sleeved with heatshrink tubing to avoid abrasion and 7 were slipped in the tube tightly. Heat shrink tubing was put over the 2" PVC pipe and recovered. The rods were held in the cylindrical shape by some heat shrink tubing on the pack of them. This was 4" tubing.

Once the rod assembly was done, the lengthwise slit on the pipe was opened with screwdrivers and the rod pack was slipped into the PVC pipe and the screwdriver/spacers removed. Then the heat shrink tubing was used to cover the PVC tube. Looks nice.

Because the rods were 10" long, a new 11.5" long piece of PVC pipe was required. It all mounts the same. 

So here are some figures on the inductance with 0 to 6 rods, and based on that, what I calculated for reactance over the frequency ranges to be tried, 160-10, plus 6M.  It would be possible to resonate the filament choke but with 7 ferrite rods inside, stray capacitance takes over above 8MHz.

It should have added to this some low Q LC circuits for the bands. Not sure where to find design examples for sanity checks.

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« Reply #244 on: March 26, 2017, 09:56:15 PM »

I should apologize to interested parties for the lack of progress and pictures. I have not given up on it or become disinterested. My parents' estate of which I am co-exec., and the additional process of re-homing Mom's Cats leaves me only the occasional weekend.
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« Reply #245 on: April 02, 2017, 02:43:20 AM »

pictures of the choke etc.

The 'socket' end of the choke was a brain teaser. What I did is very ugly but the resistance from the end of the choke to the socket is 2.5 Milliohms and it's mechanically solid and very strong. A clamp-on-and-solder type of copper strap arrangement could have been used but this worked as well and was simple to put lugs on the tube socket end.


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« Reply #246 on: April 02, 2017, 02:49:12 AM »

The 'transformer' end of the choke has very thick copper strap with holes. To get it to connect to the existing filament power feed-through capacitors' terminals in the chassis, one was bolted directly to one capacitor and the other connected with a #6 jumper.

The original filament voltage monitoring board was slightly relocated. It is close to the outer conductor of the filament choke but this is the 'cold' end just inches from the feedthrough caps. It should not bother things but we will see.

A test was done with the MFJ259B. A 50 Ohm NI resistor was attached to the tube socket and RF put in to the cathode connection. The SWR and the R and X  are plotted in the chart. It seems satisfactory.

haha yeah 11m was included in the chart for my little joke, but only fussbudgets would care as it's a 1.75-30MHz and hopefully 6M amplifier. The band switch and plate coil don't match ham bands but are from a general coverage unit so it does not matter what tests were done as long as coverage of the ham bands is included. There was only one 'bad' area where the SWR rose to 2, and it was at 46Mhz. No operation there (or on 11M for those who may scowl).

There are rusty fasteners in some pictures. These will at least be cleaned up at some future time so the connections are good and there are no unwanted diodes..

to be continued..


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« Reply #247 on: April 02, 2017, 03:16:31 AM »

here is the way it was tested. Comments or suggestions are welcome. 50 Ohms is conveniently the datasheet Z for the tube driving.


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« Reply #248 on: April 04, 2017, 11:23:48 PM »

Jameco sent me a catalog and inside are Dialight brand products. I am amazed at how inexpensive most classical style jewell type lamp holders are.

http://www.jameco.com/Jameco/catalogs/c171/P25.pdf
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« Reply #249 on: April 05, 2017, 07:42:21 AM »

here is the way it was tested. Comments or suggestions are welcome. 50 Ohms is conveniently the datasheet Z for the tube driving.

Pat,

I just love this thread, and the incremental updates as you move along.

You touch on many issues with your RF input circuit. Every designer has to go through the process of selecting the options of tuned versus untuned input while weighing the pros/cons of each method. The tube makers often publish a grounded grid input impedance for a set of operating conditions. In this case that value is conveniently 50 ohms. The part that is often ignored is that the tube loading is every half cycle when the tube is running class B.
This uneven loading is why a broadband solid state driver might have trouble driving a big amplifier like this when the big amplifier RF input is untuned. Of course, a driver like a 100 watt tuned amplifier such as a DX-100 would have no trouble driving this amplifier.

Over the years I have seen circuits from the 1960's, and more recently discussed on some of the amplifier reflector boards where they take a stab at the 1/2 cycle loading when using an untuned input. Some have proposed using a power supply high vacuum diode to load the other 1/2 cycle. Others have proposed using a high speed silicon diode. I suppose the diode could be terminated into a resistor that matches the tube RF input impedance.

I am not saying you should or should not make any changes, but for purposes of discussion, I thought to bring up the topic.

Keep up the great progress.

Jim
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