Replacing valves with FET's. - UK Vintage Radio Repair and Restoration Discussion Forum

Mach One · 19th Oct 2005, 12:08 pm

Hello...

Has anyone thought of / tried as an experiment, replacing the valves in a valve radio with FETs (with the obvious change in HT supply)? To my mind, this ought to be possible.

Yours ignorantly...

Biggles · 19th Oct 2005, 12:18 pm

Hi, I remember a detailed article in a magazine from the early eighties to "upgrade" a valved communications receiver by replacing the valves with fets and altering supplies etc. If I remember correctly, the new devices were mounted on "plug-ins" which plugged into the vacant valve bases. Strange idea. Wouldn't recommend it.

Biggles.

Aerodyne · 19th Oct 2005, 12:33 pm

It's not radio, but I recall being supplied with a so-called 'solid state valve' to fit in place of the apparently then scarce to obtain output valve. I think it was the field output, usually a PCL8XXX in the rental Fergie chasses I worked on. There may have been one designed to replace one of the bottles in the line output stage, too, but I'm not sure about that. I believe they functioned adequately - but everyone preferred the valves!
-Tony

Rod H · 19th Oct 2005, 12:42 pm

Yes, I recall such devices, they were known as "Fetrons", and were contained in tubular metal cases that plugged in as a direct valve replacement.

I tried a Google search which came up with quite a few links, here is the first one up: http://www.sigtel.com/tel_tech_fetrons.html

Rod H

Sideband · 19th Oct 2005, 12:46 pm

There was also a solid-state version of the PL802 luminance amplifier valve(PL802T I think). We used these in the old Pye hybrids when they became difficult to get. They worked OK and the picture was more stable. The PL802 had a habit of running into grid current. That did wonders for the picture!!

With regard to vintage radio's though it would be a no-no....at least from my point of view. I could not imagine replacing the PEN4DD in my Philips 470 radio with a FET......heaven forbid!!

Rich.

Ed_Dinning · 19th Oct 2005, 12:50 pm

Hi Gents, the Fetron details appeared in a 1980 WW article and I think they were targetted at communications sets. They were touted as being lower noise and designed to be plug ins with no changes to circuitry.
The TV solid stae device was I think a PL504 T (?), a plug in for a particularly short life video OP valve. It lasted a lot longer than the hollow state type it replaced and was a compination of a small signal bipolar and a plastic power bipolar I think.
I did some experiments some time ago to see if I could produce a UL41 (T), these were moderately successful, but needed more work.

Ed

Biggles · 19th Oct 2005, 12:59 pm

Hi all, I remember solid state replacements for valve rectifiers being used at a previous workplace, they looked just like octal metal cased valves, and presumeably had two diodes in with a current limiter inside?

Biggles.

Neil Breward · 19th Oct 2005, 1:24 pm

As an emergency measure, pending the location of a proper replacement, I've used a solid-state valve consisting of a FET and npn RF bipolar transistor in a cascode circuit to replace a missing IF valve. The FET is the lower, input, device and the bipolar the upper 'grounded grid' amplifier. Its performance was pretty good, with about 20 volts supply via a resistor and zener diode.

Cheers,
Neil

(I used a 2N3819 FET with BF194 or similar I think).

jim_jobe · 19th Oct 2005, 1:32 pm

In the RSGB book, "Amateur Radio Techniques" (1970's editions)by Pat Hawker he mentions someone successfully replacing valves with FETs in communications receivers without changing component values and gives some circuitry.
Jim

Jeremy M0RVB · 19th Oct 2005, 1:35 pm

Just so you can see these beasties, http://www.tubecollector.org/nonvalve/fetron.htm - the heatsinked one is the PL802T (if I remeber!), there is a plug in 2x transistor thing, and the one with the chip is an actual 'fetron'.

brunel · 19th Oct 2005, 3:47 pm

Slightly off topic.

I still have two of the solid state PL802's. (see pics)

Used by the hundreds in the Tandberg 1-90 series

brunel

GMB · 19th Oct 2005, 5:17 pm

Could we have it's circuit?

ratiodetector · 19th Oct 2005, 8:02 pm

There was a short article in Electronics World about 3 years ago where someone had replaced a valve with a FET (in a valve radio)
I'll see if I can dig it out.

YC-156 · 19th Oct 2005, 8:23 pm

So how does one go about making a solid state replacement for a beam deflection mixer like the 7360 say??

SS plug-in replacements for 4CX250Bs and 7289s would be handy too. Not to mention 3-500Z and...

Regards

Frank N.

roger_a · 19th Oct 2005, 9:25 pm

This site fully details a valve to semiconductor conversion on the Zenith range.

http://www.antiqueradios.com/marc/1l6.html

Roger

joe · 20th Oct 2005, 11:15 am

Roger

Thanks for that interesting link. I have three Zenith Transoceanics waiting in the loft and its odds on that at least one will be without a functioning 1L6 heptode. If I ever get round to trying a home made "Fetron" replacement I'll post it & let you know what happens.

Joe

Andy Day · 20th Oct 2005, 7:45 pm

My experience of fets in the 70s was not good, they went short if you looked at them - mind you these were fet switches used as part of the switching matrix in automatic test equipment. However, it was enough to make us lads in the test lab sceptical when we heard of attempts to replace hot bottles with fets. (This was 1973 - 74).

Later experiences of switch mode PSUs and monitors showed that fets had indeed become quite robust, but I would still back a valve against a Fet in terms of ability to withstand operation outside it's spec.

FrankB · 21st Oct 2005, 6:37 pm

Here in the states we had many of the "plug in" replacements for tubes available years ago. The rectifier types are still available. Diode & triode types were the most common.

My old ham Elmer, Bill Ward, W7SS (SK) converted an entire Collins receiver to FET's, with circuitry of his own design.
I still have a few of the "solid state tubes" as they were called, for the TV HT & focus rectifiers, dampers, and HV rectifiers for industrial/ham equipment snoozing in my junkbox.

Skywave · 10th Jun 2006, 11:05 pm

Quote:

Originally Posted by jim_jobe

In the RSGB book, "Amateur Radio Techniques" (1970's editions)by Pat Hawker he mentions someone successfully replacing valves with FETs in communications receivers without changing component values and gives some circuitry.
Jim

Yes, I know that article too! The set in question was an Eddystone S640. The article continued to report that the RF alignment needed no adjustment after this mod! Now some might say this was vandalism, but . . .

Skywave · 10th Jun 2006, 11:08 pm

Quote:

Originally Posted by FrankB

Here in the states we had many of the "plug in" replacements for tubes available years ago. The rectifier types are still available. Diode & triode types were the most common.

My old ham Elmer, Bill Ward, W7SS (SK) converted an entire Collins receiver to FET's, with circuitry of his own design.
I still have a few of the "solid state tubes" as they were called, for the TV HT & focus rectifiers, dampers, and HV rectifiers for industrial/ham equipment snoozing in my junkbox.

He did WHAT to a COLLINS RX, for God's sake!

19th Oct 2005, 12:08 pm	#1
Mach One Heptode Join Date: Sep 2005 Location: Shoreham-by-Sea, West Sussex, UK. Posts: 611	Replacing valves with FET's. Hello... Has anyone thought of / tried as an experiment, replacing the valves in a valve radio with FETs (with the obvious change in HT supply)? To my mind, this ought to be possible. Yours ignorantly...

19th Oct 2005, 12:18 pm	#2
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Re: Valves Out, FETs In Hi, I remember a detailed article in a magazine from the early eighties to "upgrade" a valved communications receiver by replacing the valves with fets and altering supplies etc. If I remember correctly, the new devices were mounted on "plug-ins" which plugged into the vacant valve bases. Strange idea. Wouldn't recommend it. Biggles. Last edited by Biggles; 19th Oct 2005 at 12:20 pm. Reason: Additional text.

19th Oct 2005, 12:33 pm	#3
Aerodyne Octode Join Date: Jun 2004 Location: Hampton Vale, Peterborough, UK. Posts: 1,698	Re: Valves Out, FETs In It's not radio, but I recall being supplied with a so-called 'solid state valve' to fit in place of the apparently then scarce to obtain output valve. I think it was the field output, usually a PCL8XXX in the rental Fergie chasses I worked on. There may have been one designed to replace one of the bottles in the line output stage, too, but I'm not sure about that. I believe they functioned adequately - but everyone preferred the valves! -Tony

19th Oct 2005, 12:42 pm	#4
Rod H Triode Join Date: Jan 2004 Location: Flitwick, Bedfordshire, UK. Posts: 47	Re: Valves Out, FETs In Yes, I recall such devices, they were known as "Fetrons", and were contained in tubular metal cases that plugged in as a direct valve replacement. I tried a Google search which came up with quite a few links, here is the first one up: http://www.sigtel.com/tel_tech_fetrons.html Rod H

19th Oct 2005, 12:46 pm	#5
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,566	Re: Valves Out, FETs In There was also a solid-state version of the PL802 luminance amplifier valve(PL802T I think). We used these in the old Pye hybrids when they became difficult to get. They worked OK and the picture was more stable. The PL802 had a habit of running into grid current. That did wonders for the picture!! With regard to vintage radio's though it would be a no-no....at least from my point of view. I could not imagine replacing the PEN4DD in my Philips 470 radio with a FET......heaven forbid!! Rich. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

19th Oct 2005, 12:50 pm	#6
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Valves Out, FETs In Hi Gents, the Fetron details appeared in a 1980 WW article and I think they were targetted at communications sets. They were touted as being lower noise and designed to be plug ins with no changes to circuitry. The TV solid stae device was I think a PL504 T (?), a plug in for a particularly short life video OP valve. It lasted a lot longer than the hollow state type it replaced and was a compination of a small signal bipolar and a plastic power bipolar I think. I did some experiments some time ago to see if I could produce a UL41 (T), these were moderately successful, but needed more work. Ed

19th Oct 2005, 12:59 pm	#7
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Re: Valves Out, FETs In Hi all, I remember solid state replacements for valve rectifiers being used at a previous workplace, they looked just like octal metal cased valves, and presumeably had two diodes in with a current limiter inside? Biggles.

19th Oct 2005, 1:24 pm	#8
Neil Breward Retired Dormant Member Join Date: Aug 2005 Location: Keyworth nr. Nottingham, UK Posts: 140	Re: Valves Out, FETs In As an emergency measure, pending the location of a proper replacement, I've used a solid-state valve consisting of a FET and npn RF bipolar transistor in a cascode circuit to replace a missing IF valve. The FET is the lower, input, device and the bipolar the upper 'grounded grid' amplifier. Its performance was pretty good, with about 20 volts supply via a resistor and zener diode. Cheers, Neil (I used a 2N3819 FET with BF194 or similar I think).

19th Oct 2005, 1:32 pm	#9
jim_jobe Heptode Join Date: Nov 2004 Location: Ripon, N.Yorkshire, UK. Posts: 782	Re: Valves Out, FETs In In the RSGB book, "Amateur Radio Techniques" (1970's editions)by Pat Hawker he mentions someone successfully replacing valves with FETs in communications receivers without changing component values and gives some circuitry. Jim

19th Oct 2005, 1:35 pm	#10
Jeremy M0RVB Hexode Join Date: Jul 2003 Location: Leeds, West Yorkshire, UK. Posts: 458	Re: Valves Out, FETs In Just so you can see these beasties, http://www.tubecollector.org/nonvalve/fetron.htm - the heatsinked one is the PL802T (if I remeber!), there is a plug in 2x transistor thing, and the one with the chip is an actual 'fetron'.

19th Oct 2005, 3:47 pm	#11
brunel Heptode Join Date: Sep 2005 Location: LEEDS.......North of the River Aire. Posts: 872	Re: Valves Out, FETs In Slightly off topic. I still have two of the solid state PL802's. (see pics) Used by the hundreds in the Tandberg 1-90 series brunel Attached Thumbnails

19th Oct 2005, 5:17 pm	#12
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,093	Re: Valves Out, FETs In Could we have it's circuit?

19th Oct 2005, 8:02 pm	#13
ratiodetector Retired Dormant Member Join Date: Oct 2005 Location: Horsham, West Sussex. Posts: 8	Re: Valves Out, FETs In There was a short article in Electronics World about 3 years ago where someone had replaced a valve with a FET (in a valve radio) I'll see if I can dig it out.

19th Oct 2005, 8:23 pm	#14
YC-156 Retired Dormant Member Join Date: May 2005 Location: Aarhus, Denmark Posts: 281	Re: Valves Out, FETs In So how does one go about making a solid state replacement for a beam deflection mixer like the 7360 say?? SS plug-in replacements for 4CX250Bs and 7289s would be handy too. Not to mention 3-500Z and... Regards Frank N.

19th Oct 2005, 9:25 pm	#15
roger_a Retired Dormant Member Join Date: Sep 2003 Location: Croydon, London, UK. Posts: 40	Re: Valves Out, FETs In This site fully details a valve to semiconductor conversion on the Zenith range. http://www.antiqueradios.com/marc/1l6.html Roger

20th Oct 2005, 11:15 am	#16
joe Rest in Peace Join Date: Apr 2003 Location: Edgware, North London. Posts: 307	Re: Valves Out, FETs In Roger Thanks for that interesting link. I have three Zenith Transoceanics waiting in the loft and its odds on that at least one will be without a functioning 1L6 heptode. If I ever get round to trying a home made "Fetron" replacement I'll post it & let you know what happens. Joe

20th Oct 2005, 7:45 pm	#17
Andy Day Pentode Join Date: Aug 2005 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 154	Re: Valves Out, FETs In My experience of fets in the 70s was not good, they went short if you looked at them - mind you these were fet switches used as part of the switching matrix in automatic test equipment. However, it was enough to make us lads in the test lab sceptical when we heard of attempts to replace hot bottles with fets. (This was 1973 - 74). Later experiences of switch mode PSUs and monitors showed that fets had indeed become quite robust, but I would still back a valve against a Fet in terms of ability to withstand operation outside it's spec. __________________ The older I get, the faster I was!

21st Oct 2005, 6:37 pm	#18
FrankB Heptode Join Date: Oct 2005 Location: Olympia, Washington, USA. Posts: 664	Re: Valves Out, FETs In Here in the states we had many of the "plug in" replacements for tubes available years ago. The rectifier types are still available. Diode & triode types were the most common. My old ham Elmer, Bill Ward, W7SS (SK) converted an entire Collins receiver to FET's, with circuitry of his own design. I still have a few of the "solid state tubes" as they were called, for the TV HT & focus rectifiers, dampers, and HV rectifiers for industrial/ham equipment snoozing in my junkbox.