RCA 8PCS41 from CL update

[cwmoser]

What does "blooming" look like?
I've heard this term but never really knew what it means.

Thanks

Carl

[jmetal88]

Originally Posted by cwmoser

What does "blooming" look like?
I've heard this term but never really knew what it means.

Thanks

Carl

If it's being used the way I use it, it's when the picture gets larger due to increased brightness.

[old_coot88]

'Blooming' occurs when the high voltage drops signifigantly. Static attraction from the front of the CRT decreases, allowing sweep angle to increase or "bloom". The raster progressively dims and goes out of focus as it blooms.

The most common cause is a weak HV rectifier. Or excessive CRT beam current can lug the HV supply down (eg., from the brightness control being turned too high).

[jmetal88]

Originally Posted by old_coot88

'Blooming' occurs when the high voltage drops signifigantly. Static attraction from the front of the CRT decreases, allowing sweep angle to increase or "bloom". The raster progressively dims and goes out of focus as it blooms.

The most common cause is a weak HV rectifier. Or excessive CRT beam current can lug the HV supply down (eg., from the brightness control being turned too high).

I feel like I'm getting off-topic (sorry), but thanks for that explanation. That might actually help me with the blooming on my set. The 1K3 rectifier was dead when I got the set, so I replaced it with a 1B3 I had lying around, thinking it would be 'close enough'. If it's outputting on the weak side, that might explain the weird blooming pattern I've been seeing lately.

[earlyfilm]

Originally Posted by Eric H

This set uses three 1B3's by the way, not 8016's, maybe a different version?

My 1949 made 8PCS41 cabinet sticker calls for the 8016.

Between it and the other 1949 9PC41 I had one 8016 (probable replacment) and two RCA branded 1B3/8016. The rest were replacment 1B3.

Originally Posted by John Folsom

The 8016 is just the developmental number for the 1B3. Same thing.

Usually interchangable, but:

8016 = PIV 10,000 max, Ip = 7,6 max ma, average 2 max ma (1942 data)
1B3/8016 = PIV 30,00 max, Ip = 17 max ma, average 2 max ma (1949 data)
1G3/1B3 = PIV 33,000 max, Ip = 35 max ma, average 1.1 max ma (1965 data)

As the tubes improved the PIV increased, the short-flow current increased, but the average-flow current decreased. I would not put a 1G3 in an RCA projection set.

James

[Eric H]

Did some resistor checking tonight and replace a few high ohm resistors that had drifted out of tolerance. Not badly out but like a 2.2m that measured 2.8m, 1.0m drifted to 1.4m, it seems to have improved the sync and vertical lock, they were all in those sections.

The Contrast control was having no effect except a slight increase in Contrast all the way at one end, I opened up the Pot and found this:

It's a 1000 Ohm Pot and it's stacked with the Brightness control, according to the schematic it's not the same as used in the 630, I had hoped it might be since I have some spare parts for one of those.

Hopefully I can find a good Carbon in something else and transplant it to this control.

[cbenham]

Originally Posted by old_coot88

'Blooming' occurs when the high voltage drops signifigantly. Static attraction from the front of the CRT decreases, allowing sweep angle to increase or "bloom". The raster progressively dims and goes out of focus as it blooms.

The most common cause is a weak HV rectifier. Or excessive CRT beam current can lug the HV supply down (eg., from the brightness control being turned too high).

Here's 4 pages from the RCA HB-3 Tube Manual showing the specs. for the 5TP4 CRT.
The limiting factor for this tube is that it can only dissipate 5.4 watts. This is determined by multiplying the Ultor operating voltage ~~27,000 volts by the beam current ~~200 microamps.

If this value is exceeded for a long time the heat developed can crack the faceplate. This results in what RCA laughingly calls a "catastrophic failure" of the CRT.

You can measure the beam current by connecting a 1000 ohm resistor in series with the cathode lead to ground and measuring the DC voltage across it. 200 microamps [0.2MA] would show a voltage of 0.2 volts.

It is always gratifying to see these projection sets restored because they represent an important step in the development of television.
Your restoration is specially interesting because you have done so much work
and very well to make this set look and operate like new again. Congratulations.

[Eric H]

I have spent hours over a period of days trying to figure out why the Audio Amp in this set wasn't working, it was dead silent except for a very faint bit of static if you touched a screwdriver to the plate of the output tube.

I poured over the schematic, checking wiring, checking resistors, checking voltages, convinced I'd wired something wrong, I tried jumping the field coil in the speaker and using a PM speaker, I tried different sources and not a peep, voltages all looked good enough that it should be working but it wasn't!.

I had subbed the 6J5 where the signal comes in but I didn't test the 6F6 output tubes because no way could they be dead enough for it to be completely silent.
They had a nice getter and looked fine, anyway it's a push pull amp so if one is bad it'll still work on the other, and no way could they both be dead enough to kill the whole thing, could they?

Both 6F6 output tubes were completely dead, heaters lit, no shorts, no apparent gas, just absolutely no emissions at all. I couldn't find any 6F6 tubes handy so I stuck the first somewhat similar audio tube I could find in the amp, a 6L6 and viola, it worked fine on one tube. I dug up a couple 6V6's and plugged them in and the Amp is alive, of course now the TV chassis is somewhat dead waiting on a contrast control but one thing at a time.

[Einar72]

I've had 3 or 4 of those amps, and I've never seen one where the green power resistors didn't look like they'd run hot. I finally got another 8PCS41 last year, and it came with a newer pair of 6K6's in it. Got a fair amount of audio while the plates were glowing! I'm assuming the owner who had it serviced used it this way for years.

[Eric H]

One of the big green resistors was open, I don't think it was originally since they were all running hot to start with so maybe I blew it open while tinkering. I subbed it temporarily with a 2.5k @ 5 watts.

I'll have to look for some 6F6's, not sure I have any.
Will the 6V6 sub it on a permanent basis or do I need 6F6's? I tried a 6L6 also and it worked.
I'd like to get some in an ST bottle like it shows in the Sams picture.

[Boobtubeman]

Didnt hurt my 37 Delco subbin the f6 with a v6....

SR

[kvflyer]

I believe that a 6V6 is a good substitute for a 6F6. The heater current of the 6V6 is .45 amps vs 6F6 which is .7 amps. So, you can use two 6V6s until you get a pair of 6F6s or keep the 6V6 in there.

[Einar72]

They have the same 315 volt maximum plate supply voltage, but the 6V6 grid bias at maximum rating is only -13, while the 6F6 is -22, so there's less danger of it running too hot when biased for a 6F6. Values are similarly safe for push-pull configuration...

[Einar72]

BTW, is there -21 volts on the Grid #1's?

[Eric H]

Originally Posted by Einar72

BTW, is there -21 volts on the Grid #1's?

Yes, all the voltages on the 6F6 sockets were in the ballpark.