Kolster Brandes RV 10 (Crown)

[sexton_mallard]

I swapped the connections as suggested and get the following results - a horizontal deflection/line this time with the line/horizontal coil connections disconnected. I went further and connected the line/horizontal coil connections to the frame/vertical coils.The EHT does not come up as before which appears to rule out the scan coils. So it looks like a dud LOPT. If there are no more tests/checks to try I will open a thread in the wanted section. I feel this set is worth getting going and will try any suggestions.

[sexton_mallard]

I've posted a new thread in the 'Wanted' section. http://www.vintage-radio.net/forum/s...d.php?t=138864

[sexton_mallard]

I have been extremely fortunate to obtain a NOS LOPT, more about this later. Upon returning to this telly, I decided to try the NOS valves I obtained recently. I now realise a PY81 was fitted in place of a PY83. A NOS PY83 has been fitted. In addition, the new PL81 appears to have a different electrode structure (see pic). A quick image google pf PL81s seems to show some variation in electrode design. To be honest, the valve markings have all but disappeared and that valve might be something else! The envelope appears to be slightly different in height.

Replacing the valves unsurprisingly did not make a difference. I will next remove the old LOPT and treat the new one to a 'warm up' by slowly passing a current through it to minimise any chance of any moisture absorption.

[1100 man]

I will next remove the old LOPT and treat the new one to a 'warm up' by slowly passing a current through it to minimise any chance of any moisture absorption.

Good plan! What are the chances of finding a NOS LOPT? I've just re- read the thread and will be very interested to see if the LOPT cures the problem!
Strangely enough, I bought the identical Mazda PL81 to yours at Harpenden today and noticed the construction was different to the older type I'm used to.
I don't doubt it will work just as well though.
Best of luck
Nick

[sexton_mallard]

The new LOPT went in and... no difference. Both time bases seem to be running as before with a purring noise from the frame output transformer and a weak 10kc/s whistle from the LOPT. I will run back over the same steps again as I done before. I did double check all replacement caps and wired connections for any cock-ups and replaced the temporary bunch of 5 0.1 X rated caps with a single .47mfd cap. All components were checked for shorts and resistances. I will get my 'scope out and. attempt to 'scope the line drive waveform out of curiosity. Watch this space

[sexton_mallard]

Tonight I got my scope out and connected to the on the grid/pin 2 of the PL81, attached is a pic of the waveform. The scan coils are disconnected and a vertical line is displayed on the screen as before. Twiddling the horizontal hold shortens and lengthens the waveform as expected as the line frequency goes up and down. I calibrated the scope lead beforehand and have it set to x10. Again, I have -45 volts on the grid/pin 2 of the PL81. The heater glow of the U26 is barely visible, my gut feeling the EHT being generated is weak and the extra loading of the scan coils damps what little EHT is getting generated. Should I be getting more of a sawtooth waveform?

[crackle]

Hi
Did you ever get hold of a service manual for the KB RV10. TV's are not normally my thing but I have the service manual here, which I could scan if you are still looking.

Mike

[FERNSEH]

"I have -45 volts on the grid/pin 2 of the PL81." That's about the right figure. The sawtooth drive waveform supplied to the grid of the line output valve is typically 100 volts. As the waveform is AC coupled to the valve, conduction takes place on the latter part of the scan. The valve functions as a switch. The first part of the scan is derived from the reclaimed energy in the scan coils.

DFWB.

[sexton_mallard]

Thanks Mike for your offer of service data. I have J.P Hawker's 1960/61 Radio and Television servicing manual. If you have a different manual that would be great.

Thanks FERNSEH for the explanation. I now realise I am running the system with a part of it missing - the disconnected scan coils. I will reconnect and repeat the test and look at the trace.

[sexton_mallard]

The story continues... I have still not been able to get a raster.

As a recap ('scuse the pun) at this point I have:

1. Checked and measured all components and work done back to V6, the PCF80. One or two resistors that had gone 2x high have been replaced including R68, the PL81 screen resistor. Vertical and horizontal controls tested and are OK..

2. Replaced the boost cap C63 and C60 cap (cap in series with scan coils) once again.

3. Changed the PCF80, PL81, PY83 and the U26 EHT rectifier for all NOS ones. Valve holders checked.

4. Removed, examined and replaced the scan coils, removed checked the line and frame coil wiring harness for damage.

5. Run the set with the line deflection coils disconnected, boost voltage comes up to about 680volts and a tiny weak spark can be produced between the top cap lead and the cap of the U26 EHT rectifier. Vertical line on the screen (frame deflection coils still connected). Frame timebase working fine.

6. Line drive (with line whistle) appears to be OK with a reasonable scoped waveform and about -45v on pin 2 of the PL81.

7. With all connections restored, on switch on, the line whistle comes up, the boost voltage starts to rise to beyond 300v and the line whistle is loud, the line whistle then goes quieter but still audible and the boost voltage falls back to about 230V, no light on the screen and the PL81 start to red plate.

8. NOS replacement LOPT fitted which included NOS high voltage caps C62 and C64.

My gut feeling is a high voltage breakdown somewhere possibly in the deflection coils. I might try and 'ring' them but I doubt I will find the problem as it appears to be a high voltage breakdown.

Is there anything else I have overlooked?

[1100 man]

7. With all connections restored, on switch on, the line whistle comes up, the boost voltage starts to rise to beyond 300v and the line whistle is loud, the line whistle then goes quieter but still audible and the boost voltage falls back to about 230V, no light on the screen and the PL81 start to red plate.

Hi Dom,
Glad to see you are having another battle with this thing!

I wonder if the above statement occurs as the U26 starts to conduct? Have you tried running it with the top cap of the U26 disconnected and monitored the boost? Does it still die?

This is certainly proving to be a tough one to solve.

Cheers
Nick

[sexton_mallard]

Hi Nick,

I disconnected the connector as suggested and the boost voltage fails to rise as before. I disconnect the line coils and the boost voltage comes up to 680v.

I forgot to mention that I previously swapped the frame coil wire connections in place of the line coils and got a horizontal line (with the line coils disconnected). But probably as the boost voltage climbs, the insulation breaks down. I might try holding a small AM radio close to the deflection coils to pick up any arcing. There is a faint rustling noise from the sound but that could be a noisy volume pot. The PL81 coupling cap C39 was also replaced.

[1100 man]

That still implies that the scan coils could be faulty. I've just re-read the entire thread from the beginning and it would seem that absolutely everything has been tried! Even substituting the frame coils for the line coils!

I can't believe the line coils are faulty, but it would be nice to try some different ones.

Hmm....

[sexton_mallard]

Originally Posted by Techman

"...It could be that both the transformer and the scan coils had dampness in them...."

From seeing this thread about a pye V4 I think I will try treating the scan coils (and the LOPT as a precaution) to a bit of warming.

[sexton_mallard]

After 'trickle' warming the LOPT and the scan coils over a few days each I still have no success. I tried ring testing the scan coils using my 'scope but I can't get any meaningful results. Can some suggest a reliable method of testing the scan coils with a 'scope? Thanks in advance.

[sexton_mallard]

Looks like then I will be posting for a yoke/deflection/scan coils in the wanted section. Would the yoke from a set with a Mullard AW43-80 tube also work or is it matched to the set?

[sexton_mallard]

A request for a yoke as been posted in the wanted section: https://www.vintage-radio.net/forum/...d.php?t=156551

[Heatercathodeshort]

The RV10 employs a 90 degree tube. The AW43-80 is a very similar 90 degree tube and providing the scan coils are a reasonable match they should work OK. Well worth a try. John.

[sexton_mallard]

This probably should be going in the 'wanted' section but I posted here instead to give some background and context to the problem. Is there a way I can 'ring' the scan coils to prove they are the problem? I have a scope, AF, RF, and sweep generators. The breakdown is probably at high voltage pulse but I just wanted to explore any more possible tests.

[Heatercathodeshort]

Unfortunately no tests other than hooking up a set of replacement coils will definitely prove the coils are faulty. It's a bit like testing eggs to prove they are not rotten. The stink when you break one open proves the fact!

I have had some time on my hands recently due to a health problem. It has given me some time to sort through boxes of unbelievable junk in an attempt to fill the green scrap bin..
[It's slowly filling with PX4s PX25s and those round Ekco contraptions]
I found this set of what looks like 90 degree scan coils. They are new but I have no idea of the model they belong to. The frame coils read 6 ohms, the line coils 22. It's my guess they will fit your RV10 Crown.

They are yours FOC but I am not driving at the present time and it will be a few days before a mate can take me to the local PO and shops. Suggest you PM me with your details and I will pack them up. Your most welcome.
Regards, John.