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Author Topic: Do USED vacuum tubes continue to deteriorate while in storage?  (Read 3647 times)
KE2KB
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Posts: 633




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« on: September 23, 2017, 06:36:11 PM »

Hi;
I have an HW-101 that is around 40 years old. I just finished re-capping it and the power supply.
The radio was used regularly for about 10 years, then put in storage in the attic (where temps can reach 110F and low as 40F) for about 30 years before I decided to attempt to revive it.

After re-capping, there aren't any fireworks, etc, and the rig is working, more or less, but there are some issues.
I have performed some of the alignment - adjusting the het oscillators, driver and plate slugs. But I left the other alignment alone, thinking it isn't likely for it to change. For example, I didn't touch the VFO since it appears to be properly calibrated. I also did not touch the neutralizing capacitor or the carrier null cap.

Some of the problems:

1) The 7Mhz band is intermittent. Sometimes it works, sometimes I hear nothing and there is no power output in transmit.
If I move the band switch back and forth it may come back on, but other times it does not.

2) All bands except 3.5Mhz have low transmit output. On 7Mhz, I get a max of 50W (while on 3.5Mhz I get the 100W specified). On higher bands, the power diminishes to about 20W at 29Mhz.

All power measurements are being made on a bran-new Diamond SX200 wattmeter with a 50 ohm dummy load connteted directly to the wattmeter's Ant connector.
I have checked the SWR of my test gear (about 3ft of RG58 cable connecting the radio to the wattmeter, the wattmeter itself, and the dummy load) with a RigExpert AA170 analyzer and found it to be good for all bands.
While measuring power on the Diamond meter, I am able to confirm the relative power output on the rig's own meter.

There are a couple of things I am thinking could be the problem:

1) Bad switch contacts. I have applied some DeOxit to the band switch contacts (as best I could), but that didn't really seem to do anything.
2) Bad relay contacts. I did try applying DeOxit to the contacts of the relay that is outside the coil cage. That didn't do anything either.
3) Bad vacuum tubes. Most of the tubes are the originals, so are 40 years old. The finals have been replaced more recently, but not within the last 30 years.
If the finals are going bad, would I get full output on 3.5Mhz but not on any band above that?

What are your thoughts?

Thanks
Frank - KE2KB
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NO2A
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Posts: 1198




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« Reply #1 on: September 24, 2017, 10:48:49 PM »

The normal output on 80m with much less on the higher bands would typically indicate the finals,but I would replace the 6CL6 driver first. If that doesn't help then I'd replace the 6146's. The mechanical bandswitch is often the weak link in older transceivers. I would let it run every so often and transmit with it,to keep the tubes from getting gassy,just like an amplifier that's not used much.
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G3RZP
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Posts: 8123




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« Reply #2 on: September 25, 2017, 08:29:33 AM »

The other possibility when only one band goes out and cleaning the band switch doesn't work is that the crystal for that band is low activity. The crystals are solder sealed HC-6/U, and it's pretty well known that such crystals age a lot and reduce activity because of flux fumes building up on the crystals. Getting a new crystal is likely to be expensive IF you can get one. I have had success in desoldering both HC-6/U and HC49/U cans and very carefully washing the crystal in acetone or denatured alcohol, letting it evaporate dry (faster with acetone) and reassembling into the can and resoldering. It's not a job for someone whose hasn't got steady hands.....

Otherwise, on power output, NO2A's suggestion of changing the 6CL6 first and then the 6146s sounds good to me. My FT102 uses a 12BY7A driver. Never, since I inherited it in 1984  from my father, when it was 6 months old, could I get full output on 12m. Then I changed  the 12BY7A and Bingo! Full output on 12m!
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KD0REQ
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Posts: 2018




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« Reply #3 on: September 25, 2017, 11:08:14 AM »

receiving tubes generally don't have a large enough Kovar seal to gas up, barring bad handling or rust at the seals (pins.)  big-arse transmitting tubes can.

tubes that have been run hard and put away wet for a long time can outgas the crud that gettered out. cooking it a while in a tube tester might bring them back. or, there are enough NOS tubes out there to just get a couple more, on the theory that if you buy one and a spare, you'll never need the spare. unless it's an Audiophool favorite, most common tubes are pretty much at or below the last list price sheet published.
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AC7CW
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« Reply #4 on: September 25, 2017, 02:31:35 PM »

Among newer equipment in industry 95% of failures have been found to be electromechanical in nature. That's a starting point for repairing anything at all: cables, cable connections, tube sockets, tube pins, switches, pots, variable caps and their related mechanical connections, loose parts, bad solder joints, etc..
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Novice 1958, 20WPM Extra now... (and get off my lawn)
KE2KB
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Posts: 633




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« Reply #5 on: September 27, 2017, 10:02:48 AM »

Thanks for your suggestions/advice;
I re-aligned the rig, and now getting 100W out on 3.5Mhz, and on 14Mhz. Still only 50W on 7Mhz, with somewhere between 50 and about 75W on higher bands.
My gut feeling is that it is the 7Mhz xtal. I would think that if the problem was the driver or final tubes, the output on 14Mhz would be low as well as on 7Mhz.
That said, I may do some searching on Ebay for NOS, and eventually try to open the xtal can. If I had an oscilloscope, I would assume that I would be able to determine whether the xtal is bad. But spending even $300 on a used O-scope would be counter-intuitive. I can buy bran-new HF mobile rig for about $500, and would rather spend my money there, rather than on test equipment or expensive parts to fix the 101.
I have spent about $100 in parts thus far to replace all of the electrolytic caps in the rig and the psu. That and many hours, often resulting in frustration.

I wish that I still had the patience I had when I was 21 years old building this rig. And I thought getting older would make me more "mellow". Hi Hi.

For now, I am going to hook up a mic to the rig, and see if I can make some contacts. Perhaps after some use, the culprit of this problem will show itself.
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W2WDX
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Posts: 215




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« Reply #6 on: October 06, 2017, 11:19:57 AM »

I would say driver tube or crystal are a possibility. However, given the description of the storage situation tubes and crystals are not degraded from such a situation. Even lack of use. However, metals do corrode much faster in hot environments. So I suspect the problem lies in the band-switching.

De-oxit is not a cleaner; this is a common misinterpretation of what it actually is chemically. It enhances conductivity at a molecular level but does nothing to remove oxidation, especially silver-oxide. It is a conduction enhancer and oxidation inhibitor only; this is assuming there is no oxidation already present. This is why I go nutz when I hear people hosing down an old radio with it. It's pointless, (and messy) unless you remove all the oxidation from the contacts first.

Yes ... this could involve taking the switches apart in an ideal world. Short of that headache, getting in there with some tiny cleaning tools and polishing the blades and points till they shine will be the fix. Then SPARINGLY apply De-oxit. I use the 100% formula with the little needle applicator. I had my last the tiny bottle for years, and I do a lot of restorations. You only need a minuscule amount; but you have to clean first. For cleaning the contacts, any liquid silver cleaning solution is fine, and not the ones with any pumice-like materials. "Silver-Dips" work fine. Silver is silver after all.

And as a sidenote; never use De-oxit on carbon composition pots. (They make a different product for those). De-Oxit will eventually break down the carbon surface. That's why spraying De-oxit willy-nilly with a spray bottle is bad bad bad. People don't read or read manuals. Same goes for labels on De-oxit bottles and literature.
« Last Edit: October 06, 2017, 11:28:42 AM by W2WDX » Logged

KE2KB
Member

Posts: 633




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« Reply #7 on: October 14, 2017, 06:17:07 PM »

I've got a question about the crystals.
If the 7Mhz xtal is bad, then wouldn't the receive function be affected as well? The rig is fine on receive. Same sensitivity as my SDRPlay.
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KE2KB
Member

Posts: 633




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« Reply #8 on: October 15, 2017, 04:41:07 PM »

Did some testing today, and it appears that not only is the xmit power on 40m lower than on any other band, but the receive sensitivity is lower as well.
Injecting a a signal into the antenna jack on the HW-101, I found that the same signal level that will produce S9 on all other bands only produces about an S6 on the 40m band. In order to get S9 on 40m, I had to increase signal input (by reducing the attenuation on a Kay 439A switch attenuator) by 5dB.
I used a RigExpert AA170 as my signal generator as per its instruction manual, and confirmed that the AA170 was indeed putting out the same signal level at all frequencies. I used an SDRPlay with SDRUno to verify the signal I was sending to the HW-101.

So, from what has already been said in this thread, I am thinking that the problem is the 7Mhz crystal. I believe that I have already checked everything else that could cause only one band to have this problem.
Would it actually be possible to repair a crystal? I'm afraid that by applying the heat I would need to the crystal housing, I will destroy the crystal itself, leaving me with nothing on 40m. So perhaps I'm better off leaving it alone.

One other thought: Is there a way I could replace the het oscillator for 40m (and maybe all bands) with a PLL circuit?
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AA4HA
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Posts: 2381




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« Reply #9 on: October 17, 2017, 01:36:47 PM »

One other thought: Is there a way I could replace the het oscillator for 40m (and maybe all bands) with a PLL circuit?

I was able to find an HC-6/U, 7 MHz crystal in about two minutes by searching on Google. Even at the one (rather overpriced) seller it would cost $16 for a crystal. You would spend way more than that in fabbing up a PLL circuit that would also ruin any legacy appeal of an older radio.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Free space loss (dB) = 32.4 + 20 × log10d + 20 × log10 f
KE2KB
Member

Posts: 633




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« Reply #10 on: October 17, 2017, 06:08:52 PM »

One other thought: Is there a way I could replace the het oscillator for 40m (and maybe all bands) with a PLL circuit?

I was able to find an HC-6/U, 7 MHz crystal in about two minutes by searching on Google. Even at the one (rather overpriced) seller it would cost $16 for a crystal. You would spend way more than that in fabbing up a PLL circuit that would also ruin any legacy appeal of an older radio.
So, for 7Mhz band, the crystal frequency is 15.895Mhz. Can I buy any HC-6/U crystal at that frequency, or does it need to be specific for the HW-101?
It's been a while since I did any RF work (or any electronics for that matter...), but I recall having to know whether a crystal was series or parallel when purchasing.
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WA2ISE
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Posts: 1051




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« Reply #11 on: October 20, 2017, 04:03:38 PM »

Maybe you could use, as a test, your signal generator at 15.895Mhz in place of the crystal.  And see if varying the generator level makes a difference in receive or transmit strength. 
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KM1H
Member

Posts: 2486




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« Reply #12 on: October 25, 2017, 07:35:29 AM »

Quote
De-oxit is not a cleaner; this is a common misinterpretation of what it actually is chemically. It enhances conductivity at a molecular level but does nothing to remove oxidation, especially silver-oxide. It is a conduction enhancer and oxidation inhibitor only; this is assuming there is no oxidation already present. This is why I go nutz when I hear people hosing down an old radio with it. It's pointless, (and messy) unless you remove all the oxidation from the contacts first.

Yes ... this could involve taking the switches apart in an ideal world. Short of that headache, getting in there with some tiny cleaning tools and polishing the blades and points till they shine will be the fix. Then SPARINGLY apply De-oxit. I use the 100% formula with the little needle applicator. I had my last the tiny bottle for years, and I do a lot of restorations. You only need a minuscule amount; but you have to clean first. For cleaning the contacts, any liquid silver cleaning solution is fine, and not the ones with any pumice-like materials. "Silver-Dips" work fine. Silver is silver after all.

Finally someone else who understands the reality of what I often call DeWrex It.

Whenever possible I use Tarn-X with a Q Tip or needle dispenser to remove the silver sulphate which is not a good conductor. Then flush with a non chlorinated disc brake cleaner which can destroy some plastics. In that case I use distilled water and air from a small air brush size compressor.

De Oxit in the D-100 needle dispenser is sometimes used as a first step in some situations to get the cleaning process started. It is somewhat conductive and can ruin phenolic wafers when allowed to penetrate. My feeling is that it does remove oxidation to some degree. The D-5 spray is even worse since it is usually used as an insect spray covering a wide area....

With over 60 years experience with vintage electronics of maintaining, using and restoring for myself and others, Ive pretty much decided what really works and is repeatable. Ive also seen a lot of snake oil products trap the unwary.

Carl
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