Waking the Sleeping Giant - Henry 2K-4

[DMOD]

I just brought home a Henry 2K-4 that has been dormant for at least 5 years.

It came from a non-smoking envirionment and after pulling off a number of covers for inspection, it looks pretty good.

Other than Deoxing the relay conacts, general cleaning, and bring up the voltage slowly, is there any thing else one should do or look for?

Thanks

Phil - AC0OB

[Steve - WB3HUZ]

An antenna to connect it to. Maybe check out the blower. If the bearings are sealed, then just see how loud it is when you fired it up.

I just brought home a Henry 2K-4 that has been dormant for at least 5 years.

It came from a non-smoking envirionment and after pulling off a number of covers for inspection, it looks pretty good.

Other than Deoxing the relay conacts, general cleaning, and bring up the voltage slowly, is there any thing else one should do or look for?

Thanks

Phil - AC0OB

[DMOD]

Well, after powering up and letting the toobs cook for about three hours, I am glad to report that the Henry has 3,200 Volts on standy and only drops to 3,000 volts on transmit. 3-500Z tube age unknown; estimate at least 15 years.

Power gain is anywhere from 9.8 (80m) to 11.5 dB (40m) into a dummy load. There was a slight dip (about 9.2 dB) at 20m but I have yet to tweak the input modules.

I did find what appeared to be a protection mod to the cathode using a TO-3 10V zener for cathode bias. 

Phil - AC0OB

 

[WA1GFZ]

Gain sounds a bit low. How is the resting current. 10 Volts of zener bias sounds a bit high which would reduce resting current and maybe gain.

[DMOD]

How is the resting current.

There is very little resting current, barely noticeable on the meter. I suspect this mod is keeping it very low.

The zener mod goes to L10 which is now a 40 uH 3A choke, as per a note scribbled on the mod sheet; old value was 50 uH, 2 Amps.

The orignal tuning procedure in the manual says the plate resting current should be between 150 and 200 mA (without any mods, of course).


BTW, the blower runs smooth and airflow seems good.

Phl - AC0OB

[WA1GFZ]

Running closer to class b will require more drive and have a higher IMD on voice. A good CW modification though.

[KD6VXI]

Running closer to class b will require more drive and have a higher IMD on voice. A good CW modification though.

Agree on both.

If it where me, I'd pull the zener, run a stack of 6A10 diodes in series...  About 10-12, and then be able to tap the bias to best work with the equipment I have.

All my amps use that method.  The 6A10 is bulletproof, as well.  Take heap gob of current.

About 5-6 volts is factory.  A lot of CBers run up to 20 6A10's, 12 volts of bias.  The plate current meter won't move, like your's, and they run 150-200 PEP into them.  Make heap gobs more Pout on the Dosy.

You can also install a switch with the "stack of diodes" bias method, one for CW, as Frank pointed out, works great, and another for SSB mode.  Then you can run HV (SSB) tap or CW, and the efficiency is about the same, or better, than stock.

One of the ways to make a SB220 live on AM, as well.


--Shane

[DMOD]

Thanks for the suggestions.

After some wiring tracing, examining the schematic more closely, and making some measurements, I find the mod sheet isn't really a mod at all.

It was a replacement for D1, a ten volt zener@1 Amp. There is a voltage divider that keeps the cathode (filament potential) voltage at about 25 volts in receive, but in transmit, a relay shorts out the voltage divider and uses the zener voltage.

Now the sheet with the inserted schematic shows a 1N2808B, which is a 10Volt zener:

http://pdf1.alldatasheet.com/datasheet-pdf/view/76035/MICROSEMI/1N2808B.html

But what is in there is a 1N2810B, a 12 volt zener.

I do think I'll try a lower voltage zener. If that doesn't work, I'll try a string of 6A10 diodes and a switch to tap off the string as Shane suggested, since there seems to be enough room in the Junction Box to do so.

Phil - AC0OB

[WA1GFZ]

Check out RF parts and buy a couple stud mounted Zeners. Diodes change junction voltage with operating temperature and go the wrong way.  A 10 watter heat sunk to the chassis should out live you. 5.6, 6.2 or 6.8 volts would be a possible range.

[KD6VXI]

Check out RF parts and buy a couple stud mounted Zeners. Diodes change junction voltage with operating temperature and go the wrong way.  A 10 watter heat sunk to the chassis should out live you. 5.6, 6.2 or 6.8 volts would be a possible range.

Again, agreed.

When I do a "string of diodes" conversion, I mount them on RS Perfboard, a right angle "clip", and put it DIRECTLY in the airflow of the fan.  Bypass both leads with .01, and you should be good to go.

RF Parts is all our friends

--Shane

[DMOD]

I put in a string of 9 6A100's (got a good deal from a local ham who owns an electronics store here) temporarily which now gives me a bias of 6.6 Volts on transmit with a plate resting current of 120mA.

I ordered, among other things from RF Parts, a TO-3 package 50 W 6.8volt zener for permanent installation, since the old zener is a TO-3 as well, so no new holes to drill or enlarge.

Power gain is now about 12.5dB on the average across the bands.

I will be looking for a good pair of 3-500Z's since the age of these tubes is estimated at 20+ years.

A test to some K4/9ers on SSB to KY and Indiana indicated better than 10/9 from my homebrew 80m vertical, with a PEP of 500W.

AM looks good as well on the scope at 300 Watts carrier with 90% modulation.

Now back to the ClassE rig construction.

Phil - AC0OB