# Completed ProjectIs it normal for the OC2 vacuum tubes to glow bright orange & OA2 to flicker while running?

#### Rahulk70

Joined Dec 16, 2016
521
I just got this vintage Heathkit IO-10 oscilloscope from ebay. Just tried powering it up and it seems to be working fine. But I noticed that the OC2 tube seems to glow very bright orange and the OA2 glows purple and works fine. Occasionally there is flickering in the OA2 tube as shown in the video. Is this normal for both the tubes?

I've added a video to help understand better.

Also I've a question regarding replacing the two can electrolytic capacitors. Can the first cap 150V-100MFD(3 caps in one)be replaced with a 250V- 100MFD and the second one (400V-350V-250V-150V - 40-40-30-40MFD(4caps in one) with 450v-68MFD?

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#### LesJones

Joined Jan 8, 2017
3,490
I seem to remember fom may decades ago that they were filled with different gas. Orange neon, purple argon. I think that is how they regulated at different voltages.

Les.

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Joined Jul 18, 2013
23,612
Yeah, they are not Vacuum tubes but gas filled.
Max.

#### Rahulk70

Joined Dec 16, 2016
521
I seem to remember fom may decades ago that they were filled with different gas. Orange neon, purpol argon. I think that is how they regulated at different voltages.

Les.
So, it’s safe to say the OC2 tube is working as it should be. Right? What about the OA2 tube? It is also a voltage regulator. It does glow in purple color and works fine. But the bright flickering at 0:19 is kinda worrying. What might be causing it?

#### Rahulk70

Joined Dec 16, 2016
521
Yeah, they are not Vacuum tubes but gas filled.
Max.
Hi Max,
Yeah you are right I should have just mentioned tube.
Could you help me with the capacitor replacement question? I tested the oscilloscope with a mica cap and it showed a sine wave so it works fine. But I’m pretty sure that the 1960s electrolytic cap definitely needs a replacement

Joined Jul 18, 2013
23,612
It is usually normal for gas filled valves and lamps to flicker.
Going higher voltage on the Caps is fine.
If different values you would have to check if they are in parallel or different circuits.
Max.

#### BR-549

Joined Sep 22, 2013
4,938
I am not familiar with that scope. But I don't think that is right. That was arcing. Find a manual and check voltages.

Check for quality of construction. Check the wiring insulation.

Joined Jan 15, 2015
6,058
They were pretty cool voltage regulators. If you look at your manual and the power supply you will see the 0A2 is a 150 volt cold cathode regulator and the 0C2 is a 72 volt cold cathode regulator. When a voltage about 15% to 20% greater than the breakdown voltage the gas ionizes so unlike a zener breakdown you get a 150 volt short or a 72 volt short. The glow will be around the cathode much like when we ionize the gas in a neon bulb. The color being a result of the gas used. Again, if you look at the manual and at the power supply you will see how they work in the scheme of regulating voltage. Pretty cool stuff and they worked well before being replaced.

Ron

Joined Jul 18, 2013
23,612
When I started out in my career, most electronics contained tubes of some kind and we used all the forerunners of SCR's and Triacs etc, there was the Nixie, Decatron, Ignitron, Thyratron, to name but a few.
All gas filled.
Max.

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#### Rahulk70

Joined Dec 16, 2016
521
First thanks to all you guys for the valuable informations.
So, today I changed the two can electrolytic with the capacitors I had asked in the original question. So after the recap fired up the oscilloscope, except for the OA2 all of them worked which made me worried that I blew the tube. So put back my old caps to see if that was the issue and again only a dot on the screen no waveforms. Rechecked all connections throughly and found a connection from the cap not making good contact. So soldiers that and it worked fine. So put back the new caps and now everything seems to okay. Unfortunately I’m having a hard time finding film capacitors above 250V to replace the wax caps in this. I’ll have to do some thorough shopping to find the 600&1200V replacements.
meanwhile I’ve also ordered all the spare tubes just in case.

#### Rahulk70

Joined Dec 16, 2016
521
Okay, guys wanted to give an update. So, ordered a new Pinnacle OA2 tube from the UK. Replace the old RCA OA2 tube and now the flickering seems to have gone and also calibrated the oscilloscope. Seems like it was a bad tube. I definitely need to get a tube tester.

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#### MisterBill2

Joined Jan 23, 2018
9,258
Probably you will not find a tester for the cold-cathode regulator tubes. The purple-blue glow is OK, the orange glow I don't believe is OK. My guess is way too much current. Check the voltage across the tubes, a schematic should tell you which pin is positive and which is negative. Given that it is a kit there is no assurance that all is OK. And the capacitor substitution you mention is fine, just don't go less than the original voltage specification.
And good luck! I wish you success.

#### takao21203

Joined Apr 28, 2012
3,702
First thanks to all you guys for the valuable informations.
So, today I changed the two can electrolytic with the capacitors I had asked in the original question. So after the recap fired up the oscilloscope, except for the OA2 all of them worked which made me worried that I blew the tube. So put back my old caps to see if that was the issue and again only a dot on the screen no waveforms. Rechecked all connections throughly and found a connection from the cap not making good contact. So soldiers that and it worked fine. So put back the new caps and now everything seems to okay. Unfortunately I’m having a hard time finding film capacitors above 250V to replace the wax caps in this. I’ll have to do some thorough shopping to find the 600&1200V replacements.
meanwhile I’ve also ordered all the spare tubes just in case.
I have many high voltage capacitors 400V 630 1000 1500 some 2000

#### DickCappels

Joined Aug 21, 2008
7,702
Orange is normal for some regulatir tubes. The color is a function of the gas used.

#### ebp

Joined Feb 8, 2018
2,332
It shouldn't be hard to find film capacitors with high voltage rating from vendors like DigiKey or Mouser. Depending on the value, it may be next to impossible to find tubular axial lead types like the old ones. Box style radials rule these days for moderate values. Also, caps from days gone by were often in values that are no longer made, but you should be able to find something close. Unless the scope was stored at high humidity, chances are the original paper caps will still be OK. Paper caps are still made and used primarily for RFI suppression.

#### Rahulk70

Joined Dec 16, 2016
521
It shouldn't be hard to find film capacitors with high voltage rating from vendors like DigiKey or Mouser. Depending on the value, it may be next to impossible to find tubular axial lead types like the old ones. Box style radials rule these days for moderate values. Also, caps from days gone by were often in values that are no longer made, but you should be able to find something close. Unless the scope was stored at high humidity, chances are the original paper caps will still be OK. Paper caps are still made and used primarily for RFI suppression.
In the beginning I replaced only the two electrolytic capacitors. I left the General Instrument paper capacitors and powered it up but it was fine. But later on replaced them with newer ones (those blue colored ones in the above video). Also I guess like you mentioned Mouser is the best place to order these high voltage caps.

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#### Rahulk70

Joined Dec 16, 2016
521
I have many high voltage capacitors 400V 630 1000 1500 some 2000
For me the hard part is getting the 0.1MFD and 0.2MFD of the 250V, 630 & 1500V ones. Most retail shops have only upto the 630V 0.47MFD etc. So, have to resort to ebay or Amazon. I have a few Cornell ones but they are too pricey to buy in large quantities. The worst part is even if I get a bunch of caps for like $5-$8, the shipping charge exceeds \$8 or if its free the shipping is terrible and sometimes gets lost or takes 30-60 days to get it.

#### Rahulk70

Joined Dec 16, 2016
521
Probably you will not find a tester for the cold-cathode regulator tubes. The purple-blue glow is OK, the orange glow I don't believe is OK. My guess is way too much current. Check the voltage across the tubes, a schematic should tell you which pin is positive and which is negative. Given that it is a kit there is no assurance that all is OK. And the capacitor substitution you mention is fine, just don't go less than the original voltage specification.
And good luck! I wish you success.
I agree with @DickCappels. The color is due to the gas filled in the tube. I asked a senior colleague of mine who has experience in these and he told me that the orange glow is due to the neon gas inside these gas regulator voltage tubes. The purple glow is due to argon gas inside the OA2 tube. They operate in the glowing discharge region, where a minor increase in voltage directly results in increased currents.

As the tubes should glow steadily when working normally, rather than flicker it seems. It could be due to aging where the pressure of the gas reduces due to absorption into the electrodes or into the glass shell due to sputtering. As pressure drops, the glow discharge voltage goes up. He said the flickering could be either the OA2 has aged or the electrolytics are leaky. But in this case it was the aged OA2 regulator.

#### DickCappels

Joined Aug 21, 2008
7,702
Remember that you can put capacitors in parallel and series to get the values you need. For the series connections include high value bleeder resistors to keep the DC voltage evenly distributed among the capacitors.