GSB-201 Reborn

[WU2D]

That GSB-201 Thread from a few weeks ago is messed up. Done broke.

[WU2D]

Let me try to post the original schematic.

[WU2D]

I took the schematic and greatly reduced the resolution. Hopefully it uploads. The 1.5M file would not go.

[WU2D]

Wow that worked.

[W4AMV]

Thanks Mike for a re post. I was curious about their design.

So observe neutralization used on GG. Improved IMD?

And no cathode match, even 4 // 811A's might benefit again for IMD reduction?

Alan

[Steve - K4HX]

Al, N2SHG (SK) used to run one of these on AM. Seemed to work pretty well. IIRC, he had 572Bs in his.

[MikeKE0ZUinkcmo]

Hi Mike, thanks for re-posting.   I tried several times to open the other thread without success.  

Glad to see another of these old war horses on the air.   Was the refurbishing of the amp the specific intent of your original post?   Do you have more pics?   

GSB-201 is a good amplifier, I've had mine for about 6 years and it just keeps on keeping on.  There were 3 somewhat different versions of the amplifier.







I installed a Carrier operated relay in mine simply because I have so many different boat anchors that trying to mix and match various exciters/amps is at best, difficult.  Its the small  perf board on the right.

[WU2D]

Showing the Recap and New Cord and Fuses.

[WBear2GCR]

I ran this linear in 1970/71 as a college student, from the amateur radio club shack at NYU uptown campus, W2DSC.
Driven by a Drake T4X and the matching receiver... on 40m into a dipole on top of McKracken Hall.
At the time I'd often take a daytime turn as ECARS net control...

The NYU campus, now Bronx Community College, sat at the highest land point in NYC. Quite a view from
that QTH!

                     _-_-bear

At the time the radio club was housed in the basement of the Victorian, square private house at the left of
this pic. The large light tan building to the left did not exist. You can get a sense of the elevation... to the
bottom of the pic, the land dropped quickly down a hill to the Harlem River... note how the apartment buildings,
6 story high, seem to be lower than the edge of the campus - they are, the hill goes down there...

[WU2D]

I ran this linear in 1970/71 as a college student, from the amateur radio club shack at NYU uptown campus, W2DSC.
Driven by a Drake T4X and the matching receiver... on 40m into a dipole on top of McKracken Hall.
At the time I'd often take a daytime turn as ECARS net control...

I first saw a College station when I left SUNY Canton with an associates degree and transferred into EE program at RIT. They had a fine station consisting of the Drake R4 T4 twins and a Henry 2K with a Tribander on the roof and a couple of Dipoles. Man that R4B was a slick receiver for SSB. They also had a novice station with the Drake 2B.  

[WU2D]

Thanks Mike for a re post. I was curious about their design.

So observe neutralization used on GG. Improved IMD?

And no cathode match, even 4 // 811A's might benefit again for IMD reduction?

Alan

Neutralization of GG Amps? Yes because the 811 and 572B tubes are crudely constructed; reminiscent more of 1920's design techniques, so they have a lot of stray capacitance.  See this W8JI link: https://www.w8ji.com/neutralizing__amplifier.htm

The reverse winding on one of the filament chokes in the GSB201 to produce the 180 degrees phase reversal is clever. The Gimmick cap in the GSB201 is primitive. A small variable would have allowed the neutralization to be done more accurately, targeting 15 and 10 Meters, where things are prone to go kittywampus.

So improved IMD? Better Drive? Less Loading on the Exciter? More Stability when unloaded - untuned - mistuned - keyed with no drive etc... YA.     

[N4ZAW]

I took the schematic and greatly reduced the resolution. Hopefully it uploads. The 1.5M file would not go.

I know this is an old thread, but thank you for it! VERY COOL! I've had a GSB-201 under my bench for almost 30 years, threatening to bring it into the 21st century... Well, I'm retired now, and have it ON that bench now, completely gutted.
I just found this via a link while searching for bias schemes for mine. I've already gotten a lot of inspiration from you and this thread.
The "before" pic;

[WD5JKO]

Hi all,

  I too have a GSB-201. Got it about 20 years ago from a Dale, KW1i.

My issues with the amp were many, but two big issues:

1.) one side of the tube filaments is grounded. This creates 60hz cathode modulation. The fix is to make a artificial centertap with resistors, or use a LV winding of another filament transformer that has a CT.

2.) The input SWR was < 2:1 on bands 40-10m, but 8:1 on 80m. Something was wrong with the filament choke. After replacing the choke with one designed for 160-10m, the 80m SWR issue was fixed. I lost the neutralization winding, but using a remote tuner on the input (about 12" RG-8 to tuner), working 15, and 10m is fine. There is a slight offset between plate current dip, and maximum RF output.


I made some changes to the bias circuitry. I kept the -100v cutoff bias during idle, and added two bias circuits selected by a added switch. I use a string of 1N4005's to get -4.5v for SSB (class B), and a 12V 50W zener for AM (class BC, biased at cutoff). The diodes complete the path from filament CT to ground.

Running 811A's with 12v bias at 1500v B+ is pretty much right at cutoff. That lowers the gain about 3-4 DB, and by boosting the drive, the modulation positive peaks climb up there nicely. The output modulation is slightly greater than the input modulation. I can run 180w carrier output with headroom for > 120% positive peaks. Efficiency when run this way is higher, high 30's%. Just remember to switch bias to -4.5v for SSB!

The GSB-201 is the most reliable linear I have ever owned.

Jim

[Pete, WA2CWA]

There were 4 versions of the Gonset GSB-201 in its life cycle.
There was the GSB-201, GSB-201 Mark II, GSB-201 Mark III, GSB-201 Mark IV.
Gonset only manufactured the first model GSB-201. The 201's with suffixes were manufactured by Aerotron.
The GSB-201 and 201 Mark II used four 811A's.
The GSB-201 Mark III and IV used four 572B's.

With each passing model, there were more features and enhancements.

Good info to have available for idle hit-chat at your next amateur radio cocktail party.