Restoration and modding a vintage Yaesu FT75B. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Osvaldo LW1DSE · 13th Dec 2022, 7:50 pm

The original shield for the output stage was missing before I owned this rig. Thus I made a new one from holed thinker. The large hole brings access to the neutralizing trimmer.

Cruisin Marine · 14th Dec 2022, 11:22 pm

Again, nice work! I remember that perforated sheet used to be common in old Pye equipment, I wonder where it may be readily available from now- at an affordable price?

Osvaldo LW1DSE · 16th Dec 2022, 12:11 pm

I used a piece of it saved during several years from an old PC monitor. More than 10 years stored. I cut it to the desired size with a thinker scissors and made the holes for screwing it to main chassis and neutralizing cap with a Dremel machine. The sheet is made of steel, but easy to home working. Thanks for your comments.

Cobaltblue · 16th Apr 2024, 8:49 pm

Thread opened at OP's request

Cheers

Mike T

Osvaldo LW1DSE · 16th Apr 2024, 9:08 pm

Many thanks to mods to re-open this thread.

During this time I had doing some reworks on the set. This time, the first mixer, originally a JFET 2SK19 had been replaced by a DGMOSFET 3SK45. The LO previously injected into the source, now comes to G2 actualy at 0V DC bias. Source of MOS is now grounded by a 120R resistor and a .01uF disc capacitor. This result in a much bigger gain, as the 1.7mS of JFET now is about 13mS. But I read an interesting article where the author suggest to bias the G2 at about 1.2 to 1.3DCV. Soonly I'll try this too.

Below, pics of parts involved. 3SK45 is rescued from a vintage FM tuner, the same from I got the gang condenser for the VFO.

Peter-29 · 17th Apr 2024, 5:19 am

Quote:

Originally Posted by Cruisin Marine

Again, nice work! I remember that perforated sheet used to be common in old Pye equipment, I wonder where it may be readily available from now- at an affordable price?

I have seen it in b&q and wickes.

Peter

Cruisin Marine · 17th Apr 2024, 11:39 am

What do you mean by
as the 1.7mS of JFET now is about 13mS

?

Osvaldo LW1DSE · 17th Apr 2024, 12:26 pm

The transconductances of the devices.

Here are the datasheets. Not very clear unfortunately.

Cruisin Marine · 17th Apr 2024, 2:25 pm

Thanks. DG MOSFETS are wonderful devices

Osvaldo LW1DSE · 17th Apr 2024, 2:53 pm

I'm tube enthusiast, and as JFET and MOSFET's behaves like tubes, I like them very much too.

Osvaldo LW1DSE · 17th Apr 2024, 2:56 pm

Quote:

Originally Posted by Cruisin Marine

Again, nice work! I remember that perforated sheet used to be common in old Pye equipment, I wonder where it may be readily available from now- at an affordable price?

There are some local manufacturers of those experimental PCB's.

13th Dec 2022, 7:50 pm	#21
Osvaldo LW1DSE Tetrode Join Date: Jan 2022 Location: Barrio Garay, Almirante G. Brown, Buenos Aires, Argentina Posts: 76	Re: Restoration and modding a vintage Yaesu FT75B. The original shield for the output stage was missing before I owned this rig. Thus I made a new one from holed thinker. The large hole brings access to the neutralizing trimmer. Attached Thumbnails __________________ Enjoying high heel sandals, shoes or boots when I can.

14th Dec 2022, 11:22 pm	#22
Cruisin Marine Octode Join Date: Jul 2018 Location: Worthing, West Sussex, UK. Posts: 1,003	Re: Restoration and modding a vintage Yaesu FT75B. Again, nice work! I remember that perforated sheet used to be common in old Pye equipment, I wonder where it may be readily available from now- at an affordable price? __________________ "Behind every crowd, there's a silver Moonshine"

16th Dec 2022, 12:11 pm	#23
Osvaldo LW1DSE Tetrode Join Date: Jan 2022 Location: Barrio Garay, Almirante G. Brown, Buenos Aires, Argentina Posts: 76	Re: Restoration and modding a vintage Yaesu FT75B. I used a piece of it saved during several years from an old PC monitor. More than 10 years stored. I cut it to the desired size with a thinker scissors and made the holes for screwing it to main chassis and neutralizing cap with a Dremel machine. The sheet is made of steel, but easy to home working. Thanks for your comments. __________________ Enjoying high heel sandals, shoes or boots when I can.

16th Apr 2024, 8:49 pm	#24
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,879	Re: Restoration and modding a vintage Yaesu FT75B. Thread opened at OP's request Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

16th Apr 2024, 9:08 pm	#25
Osvaldo LW1DSE Tetrode Join Date: Jan 2022 Location: Barrio Garay, Almirante G. Brown, Buenos Aires, Argentina Posts: 76	Re: Restoration and modding a vintage Yaesu FT75B. Many thanks to mods to re-open this thread. During this time I had doing some reworks on the set. This time, the first mixer, originally a JFET 2SK19 had been replaced by a DGMOSFET 3SK45. The LO previously injected into the source, now comes to G2 actualy at 0V DC bias. Source of MOS is now grounded by a 120R resistor and a .01uF disc capacitor. This result in a much bigger gain, as the 1.7mS of JFET now is about 13mS. But I read an interesting article where the author suggest to bias the G2 at about 1.2 to 1.3DCV. Soonly I'll try this too. Below, pics of parts involved. 3SK45 is rescued from a vintage FM tuner, the same from I got the gang condenser for the VFO. Attached Thumbnails __________________ Enjoying high heel sandals, shoes or boots when I can. Last edited by Osvaldo LW1DSE; 16th Apr 2024 at 9:15 pm.

17th Apr 2024, 11:39 am	#27
Cruisin Marine Octode Join Date: Jul 2018 Location: Worthing, West Sussex, UK. Posts: 1,003	Re: Restoration and modding a vintage Yaesu FT75B. What do you mean by as the 1.7mS of JFET now is about 13mS ? __________________ "Behind every crowd, there's a silver Moonshine"

17th Apr 2024, 2:25 pm	#29
Cruisin Marine Octode Join Date: Jul 2018 Location: Worthing, West Sussex, UK. Posts: 1,003	Re: Restoration and modding a vintage Yaesu FT75B. Thanks. DG MOSFETS are wonderful devices __________________ "Behind every crowd, there's a silver Moonshine"

17th Apr 2024, 2:53 pm	#30
Osvaldo LW1DSE Tetrode Join Date: Jan 2022 Location: Barrio Garay, Almirante G. Brown, Buenos Aires, Argentina Posts: 76	Re: Restoration and modding a vintage Yaesu FT75B. I'm tube enthusiast, and as JFET and MOSFET's behaves like tubes, I like them very much too. __________________ Enjoying high heel sandals, shoes or boots when I can.