rf deck exam

[N3DRB The Derb]

I'm considering using this rf deck after cleanup. looks like it was a single 813 to me. How much power do you guys think the roller inductor is good for? might it withstand a single 4-400 at 2200 volts? cap spacing looks more or less ok.

I'm not crazy how the builder mounted the tube socket elevated with no grounding fingers or clips for the tube base. I'd re do that part.  Also not crazy how he switches fixed micas in/out to load the thing.

[KD6VXI]

I'm considering using this rf deck after cleanup. looks like it was a single 813 to me. How much power do you guys think the roller inductor is good for? might it withstand a single 4-400 at 2200 volts? cap spacing looks more or less ok.

I'm not crazy how the builder mounted the tube socket elevated with no grounding fingers or clips for the tube base. I'd re do that part.  Also not crazy how he switches fixed micas in/out to load the thing.

This is a joke, first and foremost:

"If you ask MFJ, they'd probably tell you it's good for 3kw+++"




--Shane

[WQ9E]

Tim,

It is difficult to judge wire gauge from a photo but the overall roller inductor construction looks OK.  For the lower frequencies you can get away with smaller wire gauge and the biggest question mark is the roller contact (assuming you aren't planning to use this on 20 meters and above).  I don't have my Johnson T-bolt apart but it has what looks like a pretty small roller inductor for a twin 4-400A linear amplifier.  My T-bolt is mounted in position but perhaps someone can snap a photo of the tuning assembly for you for reference.

At this point, I would say build the amp and try it since you already have the roller inductor.  Clean everything up first and then see if the roller inductor gets too hot in testing.  Be careful in choosing your inductance/capacitance ratio with the roller inductor since your choice of "Q" will determine RF current and heating.  Either calculate or use the cheat sheets in the more recent handbooks to determine the proper inductance and capacitance for a given frequency and desired loaded Q.

Since you already have the chassis/parts, try it and if it doesn't work out buy what you need and save this one for a lower power project.  You could always mount a regular tapped coil and use one of the tap switches from Fair if you need to do so.  Try to avoid tuning the roller inductor except at very low power; it should be preset and the final tuning should be done with the capacitor.  Of course you don't have that option with the ganged networks like Johnson used.

Rodger WQ9E

[Jim, W5JO]

Can't be sure but that looks like a roller inductor from an ART 13.   Should handle 200 watts or so provided you clean it well and be sure contact between the wheel and wire is good.

[N3DRB The Derb]

I wasn't thinking about 2 4-400's, just a single. I dont think a pair of those would fit in there. 

option 2 would be a HK 257, 2200 on one of them would get me abt 225 out. my medium powered modulator pictured below would like that ok fine. 572'bs will go in there.

I'm not going to use the dual deck for anything but parts, lot of problems there rust, rust, and more rust.  it does have a bitchen loading cap in it. I cant get the damn thing out because of a rusted
shaft coupler holding the front panel hostage in place.

I'm sure thats a ART 13 roller. I never knew what one of those did not being much of a mil guy.

I'll massage the thing a little and see what I can do. Punch a real tube socket hole in there. Some finger stock to ground the tube base. As the song says, little things mean a lot.

I'm thinking even a single would be a bit too much. I'm going to adopt this over to the HK tubes.

I can build a better deck for 4-400's. 1 of them. I dont need a pair.

[KD6VXI]

I'm not going to use the dual deck for anything but parts, lot of problems there rust, rust, and more rust.  it does have a bitchen loading cap in it. I cant get the damn thing out because of a rusted
shaft coupler holding the front panel hostage in place.

Derb!!!

There is something called PB Catalyst at Autozone / any auto parts store.  It is the BOMB for getting rusted things "fixed".

I used it on a 5th wheel hitch my grandfather BURIED for 10 years.  (not on purpose).  It was COMPLETELY frozen, not even the handheld sludgehammer would free it.

I went in to Autozone in 'Frisco. They gave me a bottle and said BE CAREFUL!!! (it ATE the styrofoam cup it was in).  In 25 minutes, the assembly worked AS FRIGGIN NEW.

This is one of my closely guarded secrets.  It will eat ANYTHING, but gets rid of rust fine business.

Another PB story, I used it on a socket wrench that had been immersed in water for about 2 months, and left to dry.  I couldn't get it free with 12 inch "channel Locks".  PB Catalyst and 10 minutes, my friend had a 'new to him' wrench.

Those couplings are worth gold, give it a shot!



--Shane

[N3DRB The Derb]

ok i will. except these are way gone, I'd never try to use it again. I ot 5 o 6 new ones at the ready. 

Just gotta get rid of the offender. Cutting the panel up is next after the PB. its not a shaft coupler, it a bushing.

the cap is a hammarlund with 440 pf a side, but its spaced like a 2000 volt tuning cap. looks brand new.

It's a TCD something or other. I have a matching tuning cap with 240pf a side. Gonna pair em up.

sorry about spelling let hand no good.

[K1JJ]

Derb,

Judging from the wire diameter and roller wheel of that inductor compared to the door knobs, I think you'll develop "hot spots" and intermittents  - and  smoke that thang rather quickly with a plate modulated 4-400 swinging a big monkey.  I've burned up every one I've tried to use in rigs of that size. (In the plate circuit)


I only use those things for the input grid or cathode tuning of an amplifier. Do yourself a favor and put in a bandswitched coil made out of 1/4" copper tubing or at least 1/8" copper wire.  (Or plug-in coils) 

A much larger roller inductor will work, but they are physically too big for your present layout.
*Maybe an ART-13 inductor is an exception (like its mod transformer) but I doubt it when running a 4-400 plate modulated.

It might be worth a try as-is, but don't be disappointed if it fails.  BTW, I find they usually fail when tuning them under load. Maybe if you always turn it cold and THEN apply RF power it will work out.


T

[N2DTS]

I would scrap it for parts.
Why run something like that?

I would just build a nice RF deck using big caps, no switched in fixed loading caps, and would rather use fixed coils that you replace to switch bands, or one big taped coil.

With roller inductors, unless you gang the plate tuning and loading together, you can have zillions of cap and inductance values with the Q all over the place.
Best to set things up for a fixed Q, makes life so much simpler!

My 2X 813 rig has the roller inductor and vacuum variable ganged together at a fixed Q, and a variable loading cap (very large). That gives a grid band switch and tune cap, and a plate tune (one knob) and load (one knob).
No band switch other than for the grid.

On the other rigs I have built, I found it best to use plug in coils, I put banana jacks on them, make them out of copper tubing or REAL fat copper wire, set the Q with the number of turns, and you dont have any switches to arc or wear out, no extra coil around to cause problems, tune up is easy, dip and load.

Makes construction very simple as well, no huge band switch with its heavy wires all over the front panel area.
Just 2 ceramic posts with the banana sockets, put it anyplace on the chassis...

I know a lot of guys like to fool around with getting various things to work, but I like building something very well, and using it.  Build it well, build it right, build it heavy duty, and use it.

And if you hate changing coils, just build a seperate deck for the bands you use.
In the old ARRL handbooks, there used to be a pair of 813 rig that had seperate amps for each band that used a common power supply.

I would guess most guys do 160, 80 and 40, that is three RF decks, tuned up and ready to go.
All you need is the tubes, sockets, grid tune and output tune stuff.

I did not quite go that way, but park the 3x 4D32 rig on 40 meters (I have coils for 80 also), and the 813 rig is parked on 80 meters mostly. Sometimes for fun, I switch them.

The 813 is a great tube in my book, you can run them at 1000 volts, or over 2000 volts, run one or two, they are cheap, never seem to go bad...a pair can do 700 watts of carrier, 2800 watts pep.

Brett




 

[K1JJ]

[1] I would scrap it for parts.

[2] Best to set things up for a fixed Q, makes life so much simpler!

[3] On the other rigs I have built, I found it best to use plug in coils, I put banana jacks on them, make them out of copper tubing or REAL fat copper wire, set the Q with the number of turns, and you dont have any switches to arc or wear out, no extra coil around to cause problems, tune up is easy, dip and load.

[4] And if you hate changing coils, just build a seperate deck for the bands you use.

[5] The 813 is a great tube in my book, you can run them at 1000 volts, or over 2000 volts, run one or two, they are cheap, never seem to go bad...a pair can do 700 watts of carrier, 2800 watts pep.
Brett

Brett,
Your five statements above show you've been around the block a few times with amplifiers... :-)   I agree with them all.

[1]   Sometimes it's best to strip for parts and start with a new chassis of your own design.

[2]   Yes, optimum Q takes time and effort testing in the real world and a fixed coil is a time saver later on vs: tuning a variable L.  Of course, a turns counter can help to zero in quickly.

[3] An amplifier guru once told me, “If you want a world-class amplifier, then use plug-in coils.”  Three of my amplifiers here use plug-ins.  There’s nothing like the strapping, short and direct path on the higher bands with plug-ins.

4) Separate amp RF decks for each band – I have six amplifiers with common supplies – all tuned to separate bands and ready to use with three toggle switches and a coaxial switch change. It’s a breeze. Otherwise when band changing one amp, I sometimes break stuff when rushing to change bands when I make a big mistake..

5) 813’s – amen. It’s hard to beat that tube. A pair of 813’s in Derb’s rig wud be outstanding.

T

[N2DTS]

Yes, I hear a plug in coil is the way to go when you get up in the higher frequencies.
No wierd stuff going on with long straps, unused coil parts, etc.

I also like to be able to jump bands by just turning switches.
I built a station control box (rack mount) that switches receivers, muting, antenna's, transmitters, just select what you want and go. It also has the mod monitor takeoff, plus the ability to insert something (watt meter or tuner) in the transmitter path, plus the big rubber mounted T/R contactor.

One homebrew rx is parked on 80, the other on 40, I have a resonant 80 meter dipole, and one that does 40 and up (fan). Both receivers are fed through an antenna combiner, so I dont have to select one or the other..

The receiver audio outputs go to the Marantz audio amp, which gives line out and in for recording, and good audio through ONE speaker.

The TX audio chain goes to a bridging power amp to drive 2 modulators at the same time, one for each rig.

That allows me to jump between 80 and 40 meters in about 10 seconds, change antenna's, change the marantz input, change the TX, change the antenna relay input.
If I was smart, I would gang the TX and antenna relay knobs together, reducing it to 3 knobs from 4, but I never bothered to do so.

Nothing to tune, I dont use an antenna tuner, I dont have to get out of the chair.

I just need to build a beer myster into the racks...
Nothing like a cold draft molson golden while operating....

One drawback at the moment is the exciter for the transmitters, I sold the 756 pro 3 for motorcycle money, and have to manualy switch the 32v3 output, and tune the thing.

In fall, I will be looking to get a used pro 3 or maybe an Elecraft K3 with the new bandscope.
I really liked the bandscope and the band stacking registers on the 756.
The receive AM audio on the 756 was poor, and I think the K3 is worse.

Maybe a flex radio as a band scope/3rd receiver/RF exciter?

Brett

[N3DRB The Derb]

I dont really want band switching.  I guess the idea is to save as much metal working as possible, since thats what the most difficult for me to do. but if I have to rework everything, that logic goes away.

now that I have my greenlee's I can start punching out tube holes. I better just bite the big one and pull out those 4 virgin crackle chassis i have and start doing battle. I'm not sure I'd ever be really satisfied with someone else's construction anyway.  I like it LIKE THAT ya know.

[N2DTS]

To make holes in things, I use the chassis punches, hole saws (good ones cut well) the nibble tool, and files.
You can enlarge a hole quickly with a good sharp file.
On my latest projects, I used new alluminum chassis, Hammond makes them I think, they are not real expensive, I lay everything out, then drill, saw, punch....

I then like to paint the top and sides grey, mount the parts, then label it with the P touch.

Bare alluminum looks grungy after a while, black crinkle is old fashoned and hard to label well.
My first projects were black crinkle and they look a bit poor after years of dust.

I do the side chassis supports in hammertone silver, same with the oil filled cap mount straps.

I have a big (sorted) collection of screws with the built in lockwashers, nuts with the same, and even gold colored ones for highlights!

I think that is the real fun part, to have all new shinny matching hardware, nice paint, nice markings, colorful wires. Most people can build something and have it work ok, but its fun to build something that looks nice and neat.

I once got an RF deck at a fest, and there was not one matching screw or nut, holes wherever they wound up, nothing lined up at all, 4 different style and size meters on the front panel, wireing a total mess and all in one color (when it had insulation on it), globs of solder on things, someones pride and joy....

Brett

[Steve - WB3HUZ]

The 813 is a great tube in my book, you can run them at 1000 volts, or over 2000 volts, run one or two, they are cheap, never seem to go bad...a pair can do 700 watts of carrier, 2800 watts pep.

For sure. A 4-lander used to run a pair at a KW input back in the days when that was the legal limt.

I saw a pair put OUT a KW modulated at an amplifier guru's QTH once. Very impressive.

[KD6VXI]

The 813 is a great tube in my book, you can run them at 1000 volts, or over 2000 volts, run one or two, they are cheap, never seem to go bad...a pair can do 700 watts of carrier, 2800 watts pep.

For sure. A 4-lander used to run a pair at a KW input back in the days when that was the legal limt.

I saw a pair put OUT a KW modulated at an amplifier guru's QTH once. Very impressive.

I've seen 10 do > 7 kw.  Didn't have a "Tune" control...  Just a roller and load cap.

--Shane

[K1JJ]

I saw a pair put OUT a KW modulated at an amplifier guru's QTH once. Very impressive.

 

3KV on a pair modulated by a pair, no doubt -  whirlwide.

[N2DTS]

On a side note, anyone know what the 813 was used for?
Why were/are there so many around cheap?

I dont think they were used in most ham amplifiers, transmitters or broadcast service.
The art 13 used one I think, but I cant think of anything else...

I have 10 or 12 spares, but never used them.

Brett

[Steve - WB3HUZ]

RCA made a BC TX that used them. They were used as drivers in other higher powered BC rigs.

On a side note, anyone know what the 813 was used for?
Why were/are there so many around cheap?

I dont think they were used in most ham amplifiers, transmitters or broadcast service.
The art 13 used one I think, but I cant think of anything else...

I have 10 or 12 spares, but never used them.

Brett

[W3SLK]

Brett said:

On a side note, anyone know what the 813 was used for?
Why were/are there so many around cheap?

I would say that there were a ton of Military rigs that utilized the 813. Steve had said about the BC rigs using them but I don't recall any from the early 1940's that used them as opposed to the military rigs. Even my ET-4336 uses them and that was out in 1944.

[W2VW]

Raytheon and maybe RCA used them in pairs as RF drivers for 5/10KW MW TX OM.

[Steve - WB3HUZ]

The Raytheon RA1000 also used a pair for RF drivers.

[N3DRB The Derb]

the 813 was RCA's big splash for 1938 IIRC. It was the expansion of beam power out of the small tube territory.

it's hard to beat a big ass graphite plate with 100 watts dissipation. 813 is a stout MF. It can deliver a lot of rf at smaller plate voltages.

[W3RSW]

Yep, the zenith of RCA's wonder years.

.....and it has pyrex type glass,  can be mounted hor. or vert. , can be and was placed in cramped, tiny airless cages, was abused unmercifully in mil. and amateur service.

With just a little fan, it's a real beast.   Think of the s.s. equivalent in heat sinks , protective circuitry, etc. that it takes to duplicate the 813's POWER! and ruggedness.

"Got '13's?"
Then use 'em.

"Walk me up, walk me down.
Run me up on level ground."

[w1vtp]

<snip>
Maybe a flex radio as a band scope/3rd receiver/RF exciter?

Brett

Brett -- I vote for the Flex!!!  Great receiver -- the Flex 3000 is nice and compact.  Here's a nice article on receivers in general.  Flex gets a nice mention good performance without roofing filters.

http://www.sherweng.com/documents/Barc2008.pdf

Hopefully you have broadband for that connection.