UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Reply
 
Thread Tools
Old 18th Oct 2021, 8:58 pm   #21
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

It takes me a few days to do the metalwork and build up the parts for these projects, but the next stage has been completed to a point. The EHT unit is working and provides approx 3.8kV for the final anode, 250 to 260 Volts for g2 and down to -42 volts for the control grid.

I have used a EL91 7 pin valve to drive the LOPT, a few component changes to get it up near 10KHz frequency, but it seems to be be working OK. seeing how long the EL91 will last as it is not meant to handle the voltage spikes but the one in the home made TV is still OK.

Click image for larger version

Name:	EHT.jpg
Views:	37
Size:	83.5 KB
ID:	243709

Short video

https://youtu.be/el3mzvLhkHc

Be safe.

Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve
AdrianH is offline   Reply With Quote
Old 22nd Oct 2021, 7:52 am   #22
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

Just wondering about adding an iron wire wrap over the focusing coil, does anyone know if it makes an improvement in that it may need less current through the coil?
Was thinking of two layers of 1.2mm, would it have any adverse effect?

Cleaned up an old Radar frame and started to mount parts in it to save all the mess.
Click image for larger version

Name:	frame.jpg
Views:	33
Size:	61.1 KB
ID:	243929

Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve
AdrianH is offline   Reply With Quote
Old 22nd Oct 2021, 8:49 am   #23
dalekmoore2007
Pentode
 
Join Date: Aug 2008
Location: Melbourne, Australia
Posts: 169
Default Re: 5FP7 project starting with the focusing coil.

Quote:
Originally Posted by AdrianH View Post
Just wondering about adding an iron wire wrap over the focusing coil, does anyone know if it makes an improvement in that it may need less current through the coil?
Was thinking of two layers of 1.2mm, would it have any adverse effect?

Cleaned up an old Radar frame and started to mount parts in it to save all the mess.
Attachment 243929

Adrian
Looking good Adrian

Yes the Focus coil was always a problem to me in 1990 mainly didn't want to wind a new coil or add to what i had .
You would think a round permanent magnet would be a easier fix .

Magnetic Focus
In early television tubes and in some high quality tubes such as tubes for film scanning, the focus lens takes the form of an electro-magnet or permanent magnet producing, over a short region, a magnetic field parallel to the axis of the tube. This magnetic field acts to bend the electron paths towards the axis and by correctly adjusting the strength of the field, the point of focus may be made to occur at the fluorescent screen

Iron wire sounds like it would help i would try it .
Attached Thumbnails
Click image for larger version

Name:	R.jpg
Views:	34
Size:	50.7 KB
ID:	243931  
dalekmoore2007 is offline   Reply With Quote
Old 22nd Oct 2021, 9:07 am   #24
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

I do have a permanent magnetic focus unit as well, but would like to be able to do it electrically. I may still have to get hold of some magnetic rings to centre the spot, unless I find a way of using the deflection coils for this as well as scanning. I believe doing the 400 scan lines will be OK with valves, just not sure about the 6Hz frame rate, that seems very slow, even when compared to 50 Hz frame rates.

The mains power supply will be next together with some drivers to get a raster, but, it could be some time as it is a holiday half term here and the wife is now at home.

Forgot to say I have a MW6/2 scan unit and that uses iron wires over the deflection coils, I guess it may do two things: -

1) Possibly concentrate the magnetic field lines into a more compact area as not as much tray magnetic field outside the scan assembly and
2) Lessen the effect of other magnetic fields from power transformers etc.

Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve
AdrianH is offline   Reply With Quote
Old 22nd Oct 2021, 9:23 am   #25
jayceebee
Heptode
 
jayceebee's Avatar
 
Join Date: Jun 2007
Location: Durham, County Durham, UK.
Posts: 543
Default Re: 5FP7 project starting with the focusing coil.

Quote:
Originally Posted by AdrianH View Post
I also picked up some gear with another 5FP7 in it yesterday, it has an old LOPT in it which I am trying to figure out what it is from and it's connections.

Everything seems to be connected, as in everything has a resistance from one pin to another, so no separate transformer winding to go to the scan coils It looks as though it would have used pins to plug into the LOPT originally.

I was thinking that I may be able to add windings to it on the other leg of the ferrite to get 250 and -50 Volts?

So if anyone recognises the transformer i would be grateful.

Adrian
Looks very similar to the LOPT in this Rediffusion Mk7 TV thread. https://www.vintage-radio.net/forum/...54#post1416354

John.
jayceebee is offline   Reply With Quote
Old 22nd Oct 2021, 9:30 am   #26
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

Indeed it does, i will have to keep an eye on that thread to see if a circuit comes available.
Many thanks

Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve
AdrianH is offline   Reply With Quote
Old 22nd Oct 2021, 9:46 am   #27
jayceebee
Heptode
 
jayceebee's Avatar
 
Join Date: Jun 2007
Location: Durham, County Durham, UK.
Posts: 543
Default Re: 5FP7 project starting with the focusing coil.

https://www.radios-tv.co.uk/communit...2/#post-108145 Circuit of the cable version in this thread over on Vrat.

John.
jayceebee is offline   Reply With Quote
Old 22nd Oct 2021, 10:01 am   #28
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

Thank you John appreciated.

Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve
AdrianH is offline   Reply With Quote
Old 22nd Oct 2021, 10:08 am   #29
dalekmoore2007
Pentode
 
Join Date: Aug 2008
Location: Melbourne, Australia
Posts: 169
Default Re: 5FP7 project starting with the focusing coil.

Quote:
Originally Posted by AdrianH View Post
Just wondering about adding an iron wire wrap over the focusing coil, does anyone know if it makes an improvement in that it may need less current through the coil?
Was thinking of two layers of 1.2mm, would it have any adverse effect?

Cleaned up an old Radar frame and started to mount parts in it to save all the mess.
Attachment 243929

Adrian
Looking good Adrian

Yes the Focus coil was always a problem to me in 1990 mainly didn't want to wind a new coil or add to what i had .
You would think a round permanent magnet would be a easier fix .

Magnetic Focus
In early television tubes and in some high quality tubes such as tubes for film scanning, the focus lens takes the form of an electro-magnet or permanent magnet producing, over a short region, a magnetic field parallel to the axis of the tube. This magnetic field acts to bend the electron paths towards the axis and by correctly adjusting the strength of the field, the point of focus may be made to occur at the fluorescent screen

Iron wire sounds like it would help i would try it .
Attached Thumbnails
Click image for larger version

Name:	R.jpg
Views:	17
Size:	50.7 KB
ID:	243936  
dalekmoore2007 is offline   Reply With Quote
Old 27th Oct 2021, 8:47 pm   #30
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

I wound the Iron wire around the focus coil just to see if it improved things, the result is, basically not a lot.

Previously with a EHT of 3K5 Volts, it took 82 mA to focus the beam now at 3K6 volts EHT it is now taking 81 mA to do the same. So I guess that there has been little to no improvement down the axis of the coil, perhaps I have stopped some tray field but nothing to really have much of a gain.

I used 1.6mm iron wire which was probably to thick, it was certainly a pain to wrap the coil with and I have done two layers. Oh well.

Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve
AdrianH is offline   Reply With Quote
Old 28th Oct 2021, 11:50 am   #31
dalekmoore2007
Pentode
 
Join Date: Aug 2008
Location: Melbourne, Australia
Posts: 169
Default Re: 5FP7 project starting with the focusing coil.

Thats a pain ! have a look at the link below
Richard lab guy looks to have found better way in this link
https://labguysworld.com/5FPn_CRT_Tester.htm
dalekmoore2007 is offline   Reply With Quote
Old 28th Oct 2021, 12:09 pm   #32
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

I do have a magnetic unit, obtained when I got the chassis which was after the project started. If I need to use it I will, but still like the idea of using the focusing coil. Basically I have as per 'a' in the page an open field, unless I can machine some iron to fit the coil I have, it will have to stay that way.

I have been working through some used EL84's I have on my home made static tester, varying the screen volts from 250 down to 150 volts and mapping the anode current against grid voltage with Va at 250 volts and plotting the results.
Click image for larger version

Name:	EL84plots.jpg
Views:	11
Size:	48.7 KB
ID:	244451

I have also wound a single ended transformer to try and drive the scan coil. I had a spare EI core and bobbin that quick calcs showed it should be capable of approx 25VA and EI-60 with a stack height of 30mm. I have assumed the ra of the EL84 to be 4k5 Ohm and done a 9:1 n ratio to drive the existing wound scan coil. If I have it correct approx 23mA should give me the 204 mA required in the coil with approx 14 Volts across the scan coil and 126 Volts sawtooth.
Click image for larger version

Name:	scandrivertfmr.jpg
Views:	13
Size:	63.8 KB
ID:	244452

With a few pot's in the cathode resistance of the EL84, I may be able to vary the shape of the scan or even add a bit of negative feedback?

I used a figure of 14 TPV for the windings and stacked all the E's together and used a bit of High temp masking tape used for powder coating as an insulator between the E's and the I's on the end. I managed to completely fill the bobbin which either means I have gone way OTT or that I am crap at winding a bobbin.

Next is to work building up a small test board.

Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve

Last edited by AdrianH; 28th Oct 2021 at 12:14 pm.
AdrianH is offline   Reply With Quote
Old 28th Oct 2021, 10:31 pm   #33
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

Been pottering with components again, just using copper clad, just the EF91 as a Miller-Transitron, or what ever it is called, saw tooth generator. At present the sweep would be around 2.8mS and the flyback 0.22mS. The next stage is to try and drive the EL84 and drive the transformer, that for another day as fast running out of time for today.

Click image for larger version

Name:	miller1.jpg
Views:	14
Size:	48.7 KB
ID:	244503

Click image for larger version

Name:	miller2.jpg
Views:	19
Size:	79.8 KB
ID:	244504

Have to search my junk bits for a suitable variable Pot. Fingers crossed.

Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve
AdrianH is offline   Reply With Quote
Old 29th Oct 2021, 12:10 am   #34
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

Just had a thought on this, I believe I am going to need to reverse the waveform if I am driving the grid of the EL84. The grid needs to be higher at the end of the trace to make the current through the transformer and anode highest before I cut back to have any chance of fly-back moving the trace to the opposite side of the screen. Does that seem correct?

Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve
AdrianH is offline   Reply With Quote
Old 30th Oct 2021, 10:39 pm   #35
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

I have added a second stage EF91 as a reversal of the original sawtooth, basically using the circuit that would normally drive an electrostatic CRO symmetrically. But with a change of cap values I have reduced the output of the waveform to approx a 50 Volt peak, it may also provide a little bit less loading on the first stage.#

Next step is to add the EL84 driver for the transformer and keep my fingers crossed it will work.

Click image for larger version

Name:	miller6.jpg
Views:	16
Size:	95.5 KB
ID:	244641Click image for larger version

Name:	miller4.jpg
Views:	16
Size:	54.3 KB
ID:	244642Click image for larger version

Name:	miller5.jpg
Views:	20
Size:	86.7 KB
ID:	244643

Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve
AdrianH is offline   Reply With Quote
Old 6th Nov 2021, 12:19 am   #36
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

I stuck the EHT section and added a mains power supply to an old chassis from a forum member, the chassis was part of a BC1151 display section off a radar unit.

With the CRT and line transformer fitted, I could progress with more tests on the line deflection, It meant a bit more planning and plotting response curves with a used EL84. The project is certainly bringing up topics I have probably never dealt with before with electromagnetic deflection and is definitely interesting to see things work even if not perfect. Just takes me time to cram things on the chassis.

https://youtu.be/zOtp6PBUKA8

Just wondering if I can find a CRT with a similar footprint to fit the chassis, one that is electrostatic deflection for later so I do not have to listen to the transformer, perhaps it will end up getting varnished.


Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve
AdrianH is offline   Reply With Quote
Old Yesterday, 4:59 pm   #37
AdrianH
Heptode
 
AdrianH's Avatar
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 890
Default Re: 5FP7 project starting with the focusing coil.

The project has been tidied up slightly, fitted the scan pcb within the front of the case, protected fingers by using some aluminium panels to keep finger tips out of HT. A small 50Volt mains transformer, bridge rectifier and cap used to supply the focus coil, fed via a variable resistor.

Lastly started with some horizontal scan coils for the frame side of NBTV and a bit of testing deflection with the bench power supply.

5FP7 Part 5 video

Still a long way to go.


Adrian
__________________
Asking questions and learning, or trying to!
Youtube EF91Valve
AdrianH is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 11:55 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.