Phantastrons and high voltage valves - UK Vintage Radio Repair and Restoration Discussion Forum

dominicbeesley · 23rd Aug 2016, 5:32 pm

Hello,

Instead of doing what I'm supposed to be doing (packing up my workshop into storage) I've been playing with CRTs. Just sorting out the valves don't you know.

Anyway I've been playing with phantastron oscillators I found an article here http://www.hanssummers.com/images/st...hantastron.pdf do any of you lads know of a good book on valve oscillators?

I've been using small russian 6.3V pencil valves for this but need something with a bit more poke for the timebases as they need around 300V p-p and the pencil valves are only rated up to 250V. What would you use, preferably cheap, plentiful and small.

At present I have phantastrons followed by common cathode buffers for amplification but I was wondering if there were any small-signal pentodes that could bear about 1000V on their anodes that I could then use direct from the CRT anode supply...

No centering circuitry yet, but not a bad picture for 405 lines on a 1" screen...(DH3-91)

D

G6Tanuki · 23rd Aug 2016, 5:43 pm

You need a pentode with all three grids available, rather than one in which g3 is internally connected to the cathode.

Something like an EF50, which would be rather historically appropriate - should survive +300V on the anode even though _officially_ it's only rated for 250.

ms660 · 23rd Aug 2016, 6:17 pm

ECL80?

Lawrence.

Ed_Dinning · 23rd Aug 2016, 9:44 pm

Hi Dom, most of the classical work on this type of oscillator was by OS Puckle of timebase fame.
Also Parr & Davie "The cathode ray tube and its applications"

Ed

dominicbeesley · 24th Aug 2016, 10:31 am

Thanks lads,

I was hoping for something small that would take >1000V on its anode but not be expensive, mainly to allow DC coupling of the deflection plates without having to have the cathode floating at -500V or split heater supplies.

Thanks Ed for the pointers, I've just treated myself to those two books and the missing three volumes of Amos and Brikinshaw...should give me something to read while all my toys are packed away!

D

ionburn · 25th Aug 2016, 8:38 am

Perhaps not small signal but would something like an EL81 work? They seem to be readily available.

dominicbeesley · 25th Aug 2016, 11:17 am

Good idea, I might have a look through my box of telly valves to see if I have a line output pentode. I'd still be over its rated 550V but under it's pulse limit of 7,000V. Not sure how linear it will be near cut-off but it should be possible to use quite a bit of cathode degeneration...only down side is that it will eat a huge amount of current.

D

23rd Aug 2016, 5:32 pm	#1
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Phantastrons and high voltage valves Hello, Instead of doing what I'm supposed to be doing (packing up my workshop into storage) I've been playing with CRTs. Just sorting out the valves don't you know. Anyway I've been playing with phantastron oscillators I found an article here http://www.hanssummers.com/images/st...hantastron.pdf do any of you lads know of a good book on valve oscillators? I've been using small russian 6.3V pencil valves for this but need something with a bit more poke for the timebases as they need around 300V p-p and the pencil valves are only rated up to 250V. What would you use, preferably cheap, plentiful and small. At present I have phantastrons followed by common cathode buffers for amplification but I was wondering if there were any small-signal pentodes that could bear about 1000V on their anodes that I could then use direct from the CRT anode supply... No centering circuitry yet, but not a bad picture for 405 lines on a 1" screen...(DH3-91) D Attached Thumbnails

23rd Aug 2016, 5:43 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,005	Re: Phantastrons and high voltage valves You need a pentode with all three grids available, rather than one in which g3 is internally connected to the cathode. Something like an EF50, which would be rather historically appropriate - should survive +300V on the anode even though _officially_ it's only rated for 250.

23rd Aug 2016, 6:17 pm	#3
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Phantastrons and high voltage valves ECL80? Lawrence.

23rd Aug 2016, 9:44 pm	#4
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,195	Re: Phantastrons and high voltage valves Hi Dom, most of the classical work on this type of oscillator was by OS Puckle of timebase fame. Also Parr & Davie "The cathode ray tube and its applications" Ed

24th Aug 2016, 10:31 am	#5
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: Phantastrons and high voltage valves Thanks lads, I was hoping for something small that would take >1000V on its anode but not be expensive, mainly to allow DC coupling of the deflection plates without having to have the cathode floating at -500V or split heater supplies. Thanks Ed for the pointers, I've just treated myself to those two books and the missing three volumes of Amos and Brikinshaw...should give me something to read while all my toys are packed away! D

25th Aug 2016, 8:38 am	#6
ionburn Heptode Join Date: Dec 2014 Location: Lincoln, Lincolnshire, UK. Posts: 583	Re: Phantastrons and high voltage valves Perhaps not small signal but would something like an EL81 work? They seem to be readily available.

25th Aug 2016, 11:17 am	#7
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: Phantastrons and high voltage valves Good idea, I might have a look through my box of telly valves to see if I have a line output pentode. I'd still be over its rated 550V but under it's pulse limit of 7,000V. Not sure how linear it will be near cut-off but it should be possible to use quite a bit of cathode degeneration...only down side is that it will eat a huge amount of current. D