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Author Topic: SB220 with Harbaugh mods  (Read 2997 times)
K1ZJH
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« Reply #15 on: November 04, 2017, 01:38:44 PM »

It is far safer to get the plates red for a period of time, at the lowest possible plate voltage.  A tube may be fine a 2000 volts, and immediately flash when the voltage goes up a few hundred more. Increasing the plate voltage and praying for no fireworks is a bit risky.

Pete
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KM1H
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« Reply #16 on: November 05, 2017, 07:24:37 AM »

Quote
This is not my amplifier, so I'm not going to do any other mods beyond what the owner has already done. This is essentially a brand new SB-220!

A very smart choice considering the several thousands of those amps that are still in service without Hammy Hambone fixes.

Quote
Question though.... I don't have a 220 Vac variac, but I do have a 5A 0-150 Vac one.  Can I just bring the amp (still wired with for 220) up on the 150 Vac variac to full voltage? The HV should go up to about half (1500 Vdc or so on SSB, about 1200 Vdc on CW/TUNE) when the variac is on full. (Of course I'll have to short out the soft start resistors first.)

That will also destroy the tube with half its needed filament voltage.

Another option and one Ive used many times is to add a low value and wattage resistor in series with the HV (anywhere before the plate choke) to act as a fast blow fuse. A 1 Ohm 1/2W carbon film resistor works well. In the CW position turn the amp on without keying it. If the resistor survives then key it with no drive. Check to see if there is any inert gas glow inside the tube which is a normal result with long stored tubes. If the glass seals have let in outside air you will see a bright flash and deposits inside and that tube was junk long before you got the amp.

If it survives that step then jumper the zener diode and creating a zero bias condition which is well withing the tube specs.
Then with NO DRIVE the tubes will draw sufficient idle current to show color and start the gettering process. Let that run 20 minutes or so as long as the fan is running at full speed....already checked without tubes and lubed if needed.

Now comes the real test. Switch to SSB without keying and if no fireworks then key it again with the zener jumper and NO DRIVE. The tubes will get a bright red/dull orange which is the ideal color for gettering. Let that run another 20 minutes if the resistor fuse doesnt blow. Get back to me at any point in the process and also check your PM's.

Carl
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W7VO
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« Reply #17 on: November 05, 2017, 02:12:07 PM »

Thanks, Carl. I forgot about the damn filaments, that is a great point.

That is exactly the answer I was looking for, the best one I've seen so far. I'll do exactly what you suggest!

73;
Mike
W7VO
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K1ZJH
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« Reply #18 on: November 05, 2017, 07:31:29 PM »

Depending on your ambition and how far you want to go... you can run the filament transformer on 110 and the high voltage transformer on a heavy duty variac. 
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KM1H
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« Reply #19 on: November 06, 2017, 05:25:12 PM »

Quote
Depending on your ambition and how far you want to go... you can run the filament transformer on 110 and the high voltage transformer on a heavy duty variac.

As Ive stated several times on various forums over a few decades. I use a seriously CB hacked SB-220 as a tube test and regettering platform that can handle several different tubes.

Carl
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W7VO
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« Reply #20 on: November 08, 2017, 05:13:44 PM »

Thanks to the detailed procedure provided by Carl, KM1H, I have successfully gettered the 40 year old NOS 3-500Z tubes in this NOS amp, and all is well! On SSB/TUNE mode the HV was about 2200V under load, and Ig was about 200 mA with the Harbaugh "simulated zener string" shorted out. The plates were a red color, pushing orange during this process. On SSB the HV went to about 2750V under load, and Ig was about 300 mA. The plates went pretty orange. There was no evidence of any blue glow, or other internal surprises within the tubes, so at least they appear to be good-to-go! I got about 20 minutes of gettering on the low power position, and about 25 minutes on high (SSB) power.

There are still a couple of issues with the amp build (the relative power meter instantly pegs when the meter switch is put into that position as one), but at least the HV supply and tubes appear to be A-OK. The metering problem is probably a mis-wire, but that is a problem for another day..... ;-)

Thanks again, Carl!

73;
Mike
W7VO
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W1QJ
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« Reply #21 on: November 09, 2017, 05:47:52 AM »


 I have successfully gettered the 40 year old NOS 3-500Z tubes in this NOS amp,



73;
Mike
W7VO

Although going through the process didn't hurt any, it is pretty obvious that the tubes were probably good from the get go.  if you did not see any gas evidence at the CW 2450 plate voltage, chances are the tubes were good and not gassy.  So you wouldn't have had to de-gas them.  But it didn't hurt to do it.  Did you put a 1 ohm 1.2watt resistor in line and turn the amp on in CW and then switch to SSB to check for any sign of gas before going through the de-gas process?
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KM1H
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« Reply #22 on: November 09, 2017, 06:48:59 AM »

Quote
Although going through the process didn't hurt any, it is pretty obvious that the tubes were probably good from the get go.  if you did not see any gas evidence at the CW 2450 plate voltage, chances are the tubes were good and not gassy.

I strongly disagree. Just because there was no glow at a mild DC load doesnt mean they wouldnt flash under RF and Mikes time was certainly not wasted. The odds on a perfect set of 40 year old Eimacs or Amperex is slim to none during my extensive experience.

In some extreme cases I had to go to my other jig which runs at only 900 VDC and apply positive bias in order to get enough anode color and at a voltage that does not sustain an arc.

Carl
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W1QJ
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« Reply #23 on: November 09, 2017, 11:28:56 AM »

Interesting topic.  Begs some questions for thought.  In this case a routine de- gas procedure was performed without qualifying its necessity.  The OP never qualified for sure if it was needed.  An all out test obviously was never performed.  I ONLY claimed it was a waste of time if it wasn’t necessary.  It didn’t hurt to do it however, if I had to pass a set of tubes on to a customer I would probably want to know from the get go if I was dealing with a potentially leaky tube.   Unfortunately many people have lovely ornaments with tubes I’ve rejected due to them being gassy.  I simply do not pass on any tube that I know to have been gassy at any time in its life.  This is why I would like to know for sure and give the tubes a full testing right from the beginning.  The OP said he successfully gettered  meaning de-gassed the tubes.  But we don’t know if they were gassy.  I would have been more interested in knowing the situation with the tubes before he did it only because of my curiosity if nothing else. 
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KM1H
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« Reply #24 on: November 09, 2017, 01:29:46 PM »

Good side stepping Lou but consider this.

Do you blindly accept any indirect heated ceramic tube as OK or do you take the time to run them filaments only for up to a day? Some of those tubes have a reputation for outgassing just as do some glass tubes.

Ive saved scores of 8072, 8122, various 4CX-250 family including the 8930 and DX-393.

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W7VO
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« Reply #25 on: November 09, 2017, 11:02:22 PM »

I don't feel that it was a waste of time, especially given the reputation of 3-500Zs that have been laying around a while (let alone 40 years!). I've had one fail in my LK-500ZC in a hail of internal fireworks and blown fuses, and a friend of mine that bought an older Henry 2KD had a pair of very gassy tubes (from sitting), that made for good mood lighting!  Better to be safe than sorry with somebody else's "new" 40 year old amp!

Yes, I used a pair of 2.2 ohm 1/4 W resistors in parallel connected in series with the small choke located right before the main plate choke. Easiest place to put them. Then tested one tube alone in the CW/TUNE position unkeyed, then keyed with normal bias, then both tubes with normal bias, then in SSB, normal bias,  then the gettering process with the Harbaugh zener string shorted in the CW/TUNE position for 20 minutes, and then in SSB, per Carl's suggestion. 

Yes, it took a while to do all this, but I  like to think that I have given the tubes a good "burn-in" under load, if nothing else, along with the rest of the 40 year old HV components.

73;
Mike
W7VO
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KM1H
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« Reply #26 on: November 10, 2017, 08:01:17 AM »

That sounds great Mike; my dad and grandfather stressed to me at a very young age that if you are going to do something then do it right and dont be a dummkopf  Grin Roll Eyes

My one owner 1986 LK-500ZC with the optional external PAK-5 plus QSK board with vacuum and DIP relay still has the original Eimacs and got well gettered in contests and DX pileups; it still runs 1200W with 70-80W drive.

For the past 10 years or so it also gets regular use as an AM linear with a TS-950SD as the driver. Another 2X 3-500 amp here is a Hunter Bandit 2000C that is driven by a number of low power vintage AM rigs. A Dentron DTR-2000L also gets in the act at times to keep it happy.

There are several other amps available for whatever mode I want.

Carl

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W7VO
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« Reply #27 on: November 10, 2017, 11:50:52 AM »

Thanks, Carl. I am also the original owner of my LK-500ZC, (bought in 1987, right before they folded), and unfortunately, it's on its second set of tubes. (Still the original HV caps though). In my 700 mile move from CA to OR in 2007 something happened to one of the original tubes that was catastrophic. The second original tube is now in a friend's LK550 amp in Hawaii (bought at the same time I bought mine), and still running strong!

The LK500 amp is now used in my "second op" position, my main amp is an AL-1500 (that has had it's share of problems over the years), and I also have a SB-200 I rebuilt that is matched to a pair of old Drake C twins. I actually enjoy using the LK500-ZC more, it's a LOT less tweaky and broadbanded than the AL-1500. The big difference between a 3-500 based amp and one using the 8877.

Now I have to get back to troubleshooting the owner's assembly of this NOS SB-220. For some reason the REL PWR meter setting is absolutely pegging the meter with no drive. Not good....  ;-)

73;
Mike
W7VO
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KM1H
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« Reply #28 on: November 10, 2017, 06:00:54 PM »

It appears that we have a lot in common there Mike.

The LK-500ZC was a good seller but very few show up for sale which speaks well for its reliability and excellent choice of components, especially in the RF section.

I did replace my filter caps with new ones from Ameritron that are 270 uF. The fan was replaced with a more efficient, all metal, and quieter EBM Papst 4600X.  The PAK-5 was the same as standard for the LK-550 and it loafs and barely budges the HV here.

I used a pair of Drake C lines with two NCL-2000's until they were no longer contest competitive and went to a pair of TS-930's, then 940's and now the 950SD and one 940. Im in no real mood to upgrade as Im long done with serious contesting and DXCC has become a laugh. I could be tempted with a new generation of SDR's that cover 2200 to 6M, use adaptive distortion for fantastic IMD and work excellent on all modes without having to reset every time going from AM, SSB, CW, FT-8, WSPR, JT-65, and whatever other data mode comes along. Im about ready for PnP and use the VHF and above bands to keep my fingers in the hardware along with no software Roll Eyes
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KM4AH
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« Reply #29 on: November 10, 2017, 07:18:41 PM »

It's the same plate transformer he used on the LK800TNY although the 3CX800A7 was only rated by Eimac for 2400 volts DC  I'm thinking.  And, the first LK800A's with the outboard pack were 2400 volts. I have had the LK500 ZC, LK800 A with the 2400 volt outboard transformer,  the LK550 with the 3100 volt outboard pack, and the LK800 TNY with 3100 volt pack .

I've seen a TNY do 5000 watts PEP on a Bird 43 with the PEP kit.

So yeah, plenty of power supply.
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