Circuit for a portable 2-valve amplifier - UK Vintage Radio Repair and Restoration Discussion Forum

Pete_kaye · 24th Oct 2014, 4:36 pm

Can anyone point me towards a DIY circuit that will run from batteries and be portable, suitable to add to a crystal set?

I have plenty of D series 1.4 v valves and some Russian EL84s. I also have 45 and 90v batteries.

terrybull · 24th Oct 2014, 5:29 pm

If you look here
http://www.portabletubes.co.uk/sitefiles/downloads.htm
And scroll down to FJ Camm's beginers guide to radio I am pretty sure there is an amplifier stage described that may be suitable.

af024 · 24th Oct 2014, 6:29 pm

That selection, as do others on that website, open up in Notepad and provide nothing more than a load of ASCII characters. Oooh err. Does anyone else get the same?

ThePillenwerfer · 24th Oct 2014, 6:47 pm

A lot of stuff on that site is in DjVu format so you need an appropriate viewer. I use WinDjVu.

- Joe

Pete_kaye · 24th Oct 2014, 8:26 pm

thanks for the idea .I was thinking of something more modern , as a general purpose amp .

Cobaltblue · 24th Oct 2014, 10:01 pm

How about something like this

Came from this forum

Cheers

Mike T

Herald1360 · 24th Oct 2014, 10:50 pm

Looks fine as an amp, but you'd get more gain with the DAF91 used as a pentode rather than strapped as a triode.

Any D*91 series battery set will have a suitable circuit.

Biggles · 26th Oct 2014, 12:23 am

I built one a while ago based simply on the AF amp stages of a battery portable using a DAF96 and DL96. It works very well and is built on a small aluminium chassis, powered by a single D cell for LT and a string of "Poundland" PP3s for 90V HT. I wired the diode section of the DAF96 via a switch so that it can be used as a test amp for IF strips etc.
Alan.

Pete_kaye · 27th Oct 2014, 6:26 pm

Biggles is it the same as the last two stages from a Ultra R825 or similar.I lhave one and could copy that or maybe find a scrap and use the chassis etc.

Biggles · 27th Oct 2014, 8:39 pm

Hi Peter, any generic two stage audio amp from a valve portable will do. Choose a one which uses the DL96/ DAF96 if possible, as your LT battery will last longer, (25mA filaments instead of 50mA for the DL94/ DAF91 combination). I would use a circuit with parallel fed filaments i.e. 1.5V as they tend to be a bit more straightforward. I had a spare battery valve output transformer handy and the whole thing mounts on a small ali chassis made in the shed. I haven't got round to putting it into a case with a speaker yet but I prefer to see "the works" anyway.
Alan.

G6Tanuki · 27th Oct 2014, 9:03 pm

If you want sensible audio-output levels I'd suggest going for a CV807 [also known as the 3A4 or DL93] output-valve.

http://www.r-type.org/exhib/aad0023.htm

It'll drain a bit more in terms of heater-power but is really much more sensible as a 'power' output valve than any of the '96' range.

If you want to get serious, look at the 'Quiescent-push-pull' double-tetrodes/pentodes that were popular in the immediately pre-WWII era: "Quiescent Push-Pull" - http://www.r-type.org/addtext/add019.htm - was the name of the game and you could get over a Watt of output from a single [double-pentode] valve.

24th Oct 2014, 4:36 pm	#1
Pete_kaye Octode Join Date: Jun 2005 Location: Sheffield, South Yorkshire, UK. Posts: 1,227	Circuit for a portable 2-valve amplifier Can anyone point me towards a DIY circuit that will run from batteries and be portable, suitable to add to a crystal set? I have plenty of D series 1.4 v valves and some Russian EL84s. I also have 45 and 90v batteries.

24th Oct 2014, 5:29 pm	#2
terrybull Octode Join Date: Jan 2011 Location: Southwell, Nottinghamshire, UK. Posts: 1,784	Re: Circuit for a portable 2-valve amplifier If you look here http://www.portabletubes.co.uk/sitefiles/downloads.htm And scroll down to FJ Camm's beginers guide to radio I am pretty sure there is an amplifier stage described that may be suitable.

24th Oct 2014, 6:29 pm	#3
af024 Octode Join Date: Jan 2003 Location: Ashby-de-la-Zouch (it's not by the sea) Posts: 1,255	Re: Circuit for a portable 2-valve amplifier That selection, as do others on that website, open up in Notepad and provide nothing more than a load of ASCII characters. Oooh err. Does anyone else get the same? __________________ Now where on earth did I remove that from?

24th Oct 2014, 6:47 pm	#4
ThePillenwerfer Octode Join Date: Mar 2011 Location: Sheffield, South Yorkshire, UK. Posts: 1,453	Re: Circuit for a portable 2-valve amplifier A lot of stuff on that site is in DjVu format so you need an appropriate viewer. I use WinDjVu. - Joe __________________ "Experts are only good at one thing: explaining why something will not work!"

24th Oct 2014, 8:26 pm	#5
Pete_kaye Octode Join Date: Jun 2005 Location: Sheffield, South Yorkshire, UK. Posts: 1,227	Re: Circuit for a portable 2-valve amplifier thanks for the idea .I was thinking of something more modern , as a general purpose amp .

24th Oct 2014, 10:01 pm	#6
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,879	Re: Circuit for a portable 2-valve amplifier How about something like this Came from this forum Cheers Mike T Attached Thumbnails __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

24th Oct 2014, 10:50 pm	#7
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: Circuit for a portable 2-valve amplifier Looks fine as an amp, but you'd get more gain with the DAF91 used as a pentode rather than strapped as a triode. Any D*91 series battery set will have a suitable circuit. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

26th Oct 2014, 12:23 am	#8
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Re: Circuit for a portable 2-valve amplifier I built one a while ago based simply on the AF amp stages of a battery portable using a DAF96 and DL96. It works very well and is built on a small aluminium chassis, powered by a single D cell for LT and a string of "Poundland" PP3s for 90V HT. I wired the diode section of the DAF96 via a switch so that it can be used as a test amp for IF strips etc. Alan.

27th Oct 2014, 6:26 pm	#9
Pete_kaye Octode Join Date: Jun 2005 Location: Sheffield, South Yorkshire, UK. Posts: 1,227	Re: Circuit for a portable 2-valve amplifier Biggles is it the same as the last two stages from a Ultra R825 or similar.I lhave one and could copy that or maybe find a scrap and use the chassis etc.

27th Oct 2014, 8:39 pm	#10
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Re: Circuit for a portable 2-valve amplifier Hi Peter, any generic two stage audio amp from a valve portable will do. Choose a one which uses the DL96/ DAF96 if possible, as your LT battery will last longer, (25mA filaments instead of 50mA for the DL94/ DAF91 combination). I would use a circuit with parallel fed filaments i.e. 1.5V as they tend to be a bit more straightforward. I had a spare battery valve output transformer handy and the whole thing mounts on a small ali chassis made in the shed. I haven't got round to putting it into a case with a speaker yet but I prefer to see "the works" anyway. Alan.

27th Oct 2014, 9:03 pm	#11
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: Circuit for a portable 2-valve amplifier If you want sensible audio-output levels I'd suggest going for a CV807 [also known as the 3A4 or DL93] output-valve. http://www.r-type.org/exhib/aad0023.htm It'll drain a bit more in terms of heater-power but is really much more sensible as a 'power' output valve than any of the '96' range. If you want to get serious, look at the 'Quiescent-push-pull' double-tetrodes/pentodes that were popular in the immediately pre-WWII era: "Quiescent Push-Pull" - http://www.r-type.org/addtext/add019.htm - was the name of the game and you could get over a Watt of output from a single [double-pentode] valve.