I’m Back! Pilot TV37 - Page 5 - Videokarma.org TV - Video

Chris K · #61 12-20-2022, 04:07 PM

Quote:

Originally Posted by bandersen

Check for continuity on the AC plug with the power switch turned on. Also, 60W is pretty low for a TV - you're really starving the set of power. Try 200W or bigger.

Will dp Bob

Chris K · #62 12-20-2022, 04:08 PM

Do not dp!

Chris K · #63 12-20-2022, 05:18 PM

Still nothing. Let me ask a couple of questions about the electrolytic cans. One of them, a double with a 40uf section and a 100uf section is grounded to the chassis. The other 2, an 80uf and a 40uf are insulated from the chassis with phenolic bases and cardboard covers. The schematic shows the positive side of these two going to ground. Is that correct?

Electronic M · #64 12-21-2022, 09:14 AM

Quote:

Originally Posted by Chris K

Still nothing. Let me ask a couple of questions about the electrolytic cans. One of them, a double with a 40uf section and a 100uf section is grounded to the chassis. The other 2, an 80uf and a 40uf are insulated from the chassis with phenolic bases and cardboard covers. The schematic shows the positive side of these two going to ground. Is that correct?

I think that's a typo on the schematic.If the original can is still present on chassis and has a legible label on it I would look for text stating 'can negative' or 'can positive' on the can to confirm.
Schematics have typos and aren't always the same chassis revision, in vintage electronics....An original chassis with original factory parts and wiring is just about always going to be more right than the schematic, so it's wise to recap based on what's actually in the set with the paperwork as an extra guide if you get lost or need a 30k feet view of things.

EDIT: looking at the schematic it looks like those caps form a negative supply fed by the plate of the 35W4 and are positive ground in both Riders and Sam's...I forgot about this, but it does look correct in documentation. The label on the can should help confirm.

Chris K · #65 12-21-2022, 09:40 AM

Quote:

Originally Posted by Electronic M

I think that's a typo on the schematic. If the original can is still present on chassis and has a legible label on it I would look for text stating 'can negative' or 'can positive' on the can to confirm.
Schematics have typos and aren't always the same chassis revision, in vintage electronics....An original chassis with original factory parts and wiring is just about always going to be more right than the schematic, so it's wise to recap based on what's actually in the set with the paperwork as an extra guide if you get lost or need a 30k feet view of things.

Thanks Tom...yes I'm beginning to understand the typo issue. I do have the Sams and the Radiomuseum schematics and despite being 2 different versions, they do agree on the chassis grounding of the positive side of the 2 paper/phenolic electrolytic caps. I've attached the Sams here and earlier in the thread I attached the RM version, so if you have some time in the next few days (yeah right Chris...Christmas. Who has time!), can you take a quick look and see if they do agree? As always, thanks for your help!

Electronic M · #66 12-21-2022, 09:51 AM

Quote:

Originally Posted by Chris K

Thanks Tom...yes I'm beginning to understand the typo issue. I do have the Sams and the Radiomuseum schematics and despite being 2 different versions, they do agree on the chassis grounding of the positive side of the 2 paper/phenolic electrolytic caps. I've attached the Sams here and earlier in the thread I attached the RM version, so if you have some time in the next few days (yeah right Chris...Christmas. Who has time!), can you take a quick look and see if they do agree? As always, thanks for your help!

If you look at the edit in my previous post I went to the ETF and looked up the schematics quick and it looks like the positive ground on the cans is correct. I'd still read the can labels to confirm things, but the odds of both Riders and Sam's having it wrong are much lower than only one of them getting it wrong.

bandersen · #67 12-21-2022, 03:41 PM

You say the filament strings have continuity all the way through but are not lighting up? Then the problem must lie in the AC power cord, switch and so on. Start at one end of the AC plug and check for continuity at every point along the way to the other side of the plug. Something must be open somewhere.

Chris K · #68 12-23-2022, 03:33 PM

Quote:

Originally Posted by bandersen

You say the filament strings have continuity all the way through but are not lighting up? Then the problem must lie in the AC power cord, switch and so on. Start at one end of the AC plug and check for continuity at every point along the way to the other side of the plug. Something must be open somewhere.

OK...I'm missing something very basic here I think. I have 117v AC going through a 300w bulb so at the first filament pin in the string, I've got around 110v AC...the last pin in the filament string I've got...110v AC. What am I not seeing??????

init4fun · #69 12-23-2022, 03:57 PM

Quote:

Originally Posted by Chris K

OK...I'm missing something very basic here I think. I have 117v AC going through a 300w bulb so at the first filament pin in the string, I've got around 110v AC...the last pin in the filament string I've got...110v AC. What am I not seeing??????

That the open circuit is between the last pin and whatever wiring it normally uses to complete the circuit ....

Chris K · #70 12-23-2022, 04:42 PM

Quote:

Originally Posted by init4fun

That the open circuit is between the last pin and whatever wiring it normally uses to complete the circuit ....

Correct, the last tube in the string, the ratio detector 6AL5 was open. I replaced it and brought up the variac and dim bulb and it started red plating. The filament didn't burn up so the tube might be OK but there's something else going on. All of this started when I powered it up a few weeks ago and the 3 ohm resistor between the filaments of the second to last tube, the sound IF 6AU6 and the 6AL5, the last tube in the string burned up. I replaced it and had nothing since but that was because of the open 6AL5. With a good 6AL5 in the last socket, I'm back to the same resistor/tube frying problem all of this started with.

jr_tech · #71 12-23-2022, 05:37 PM

Are v1 v2 and v3 lit up normally?

jr

Chris K · #72 12-23-2022, 06:19 PM

Quote:

Originally Posted by jr_tech

Are v1 v2 and v3 lit up normally?

jr

I haven't left it on long enough to tell but what I can tell you is in the earlier, resistor/6AL6 frying incident, V2 of the 12AT7 run that's the other grounding part of the string also opened.

Chris K · #73 12-23-2022, 06:41 PM

I brought it up slowly to about 85 volts on the variac dim bulb so the 6AL5 didn't cook too long and none of the other tubes got warm including V1, V2 and V3. It looks like the 6AL5 is getting straight AC power and is the only tube lit.

jr_tech · #74 12-23-2022, 08:32 PM

“It looks like the 6AL5 is getting straight AC power and is the only tube lit”

Did you happen to measure the voltage applied the 6AL5 heater (across pins 3 &4)?

jr

Chris K · #75 12-24-2022, 11:54 AM

There is something odd here. There's a coax cable coming off the on/off/volume control pot. If the cable is traced all the way to its other end, both the shield and the center wire connect to a 4 terminal terminal strip near the 6AU6 and the 6AL5. But back up at the volume control, the shield isn't connected to anything. The insulation is stripped back and the weave is exposed and twisted but it's not soldered to anything. I've checked the schematic briefly but I can't find it.