Q1/5 diode- What is it? - UK Vintage Radio Repair and Restoration Discussion Forum

1100 man · 10th Apr 2017, 10:04 pm

Good evening,
As part of the interlace filter on my Pilot Pt650, there is a diode which according to the circuit is type Q1/5, about 1/2 inch long, 3/8 wide with a green and a black band. It measures open circuit.
I am guessing that it is probably a germanium type and that an OA91 would be a suitable replacement? But does anyone actually have any info on it?
Many thanks
Nick

AC/HL · 10th Apr 2017, 10:42 pm

It's a Brimar metal rectifier, Selenium, 120v RMS, 0.25 mA.

1100 man · 11th Apr 2017, 12:09 am

Is it indeed!: that's interesting, I hadn't thought of that! I've just found a forum thread by Alan Stepney (RIP) showing some data tables for metal rectifiers. Unfortunately they are a bit too small to read all the information, but it would seem that a Q1/5 consists of 5 plates of No 1 size in a 'Q' type package. I'm not sure I'm any the wiser for knowing that though

Does anyone know what the forward voltage is and what the 'on' resistance would be?
More importantly, what would be a suitable substitute?
Very interesting, this is not a technology I know much about and I imagine silicon very quickly made it obsolete.
Many thanks
Nick

Terry_VK5TM · 11th Apr 2017, 3:43 am

1958 Brimar data book here:-

https://frank.pocnet.net/sheets/155/...fo/Brimar7.pdf

Page 277 for the Q1/5

Terry

1100 man · 11th Apr 2017, 9:04 am

Brilliant, many thanks for that

There's some good bedtime reading there!!
Cheers Nick

ColinTheAmpMan1 · 12th Apr 2017, 1:23 pm

Quote:

Originally Posted by 1100 man

Q1/5, about 1/2 inch long, 3/8 wide with a green and a black band.

Going by the data book, the bands are green and brown....

Selenium diodes are stinky when they fail, so it must have died some time ago. I don't advise opening it up to see the innards, selenium isn't the nicest stuff. Mind you, it is a useful mineral for the preservation of memory, which I know that some of us are beginning to lose. Now where was I? Oh yes, a good source is brazil nuts, but I don't think they make very good diodes...or do they?

Colin.

Cobaltblue · 12th Apr 2017, 3:00 pm

I Don't have the circuit to hand but these selenium diodes were often used in such things as the sync circuits.

It may have too high a reverse voltage for an OA90 or similar.

I think I would try someting like a pair of common diodes such as 1N4148's in series with say 470K in parallel with each of them (to share the reverse volts).

You might even be able to hide it in the original plastic tube.

Cheers

Mike T

AC/HL · 12th Apr 2017, 3:37 pm

Circuit here: https://www.vintage-radio.net/forum/...6&postcount=10

julie_m · 12th Apr 2017, 8:51 pm

Try a 1N4007UF, the ultra-fast recovery type?

You can rob fast diodes from an old SMPSU -- look for a chequered, rather than solid, band around the business end.

10th Apr 2017, 10:04 pm	#1
1100 man Octode Join Date: Apr 2016 Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK. Posts: 1,377	Q1/5 diode- What is it? Good evening, As part of the interlace filter on my Pilot Pt650, there is a diode which according to the circuit is type Q1/5, about 1/2 inch long, 3/8 wide with a green and a black band. It measures open circuit. I am guessing that it is probably a germanium type and that an OA91 would be a suitable replacement? But does anyone actually have any info on it? Many thanks Nick

10th Apr 2017, 10:42 pm	#2
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Q1/5 diode- What is it? It's a Brimar metal rectifier, Selenium, 120v RMS, 0.25 mA.

11th Apr 2017, 12:09 am	#3
1100 man Octode Join Date: Apr 2016 Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK. Posts: 1,377	Re: Q1/5 diode- What is it? Is it indeed!: that's interesting, I hadn't thought of that! I've just found a forum thread by Alan Stepney (RIP) showing some data tables for metal rectifiers. Unfortunately they are a bit too small to read all the information, but it would seem that a Q1/5 consists of 5 plates of No 1 size in a 'Q' type package. I'm not sure I'm any the wiser for knowing that though Does anyone know what the forward voltage is and what the 'on' resistance would be? More importantly, what would be a suitable substitute? Very interesting, this is not a technology I know much about and I imagine silicon very quickly made it obsolete. Many thanks Nick

11th Apr 2017, 3:43 am	#4
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,342	Re: Q1/5 diode- What is it? 1958 Brimar data book here:- https://frank.pocnet.net/sheets/155/...fo/Brimar7.pdf Page 277 for the Q1/5 Terry

11th Apr 2017, 9:04 am	#5
1100 man Octode Join Date: Apr 2016 Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK. Posts: 1,377	Re: Q1/5 diode- What is it? Brilliant, many thanks for that There's some good bedtime reading there!! Cheers Nick

12th Apr 2017, 3:00 pm	#7
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,878	Re: Q1/5 diode- What is it? I Don't have the circuit to hand but these selenium diodes were often used in such things as the sync circuits. It may have too high a reverse voltage for an OA90 or similar. I think I would try someting like a pair of common diodes such as 1N4148's in series with say 470K in parallel with each of them (to share the reverse volts). You might even be able to hide it in the original plastic tube. Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

12th Apr 2017, 3:37 pm	#8
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Q1/5 diode- What is it? Circuit here: https://www.vintage-radio.net/forum/...6&postcount=10

12th Apr 2017, 8:51 pm	#9
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Q1/5 diode- What is it? Try a 1N4007UF, the ultra-fast recovery type? You can rob fast diodes from an old SMPSU -- look for a chequered, rather than solid, band around the business end. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.