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.

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

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;

Thanks for those links, Pete.

73DG

Ken, W2DTC built 2 3CX3000F7s, (the F designation doesn't require a socket). He did a helluva job on them too.

http://w2dtc.com/

Ebsolutly!

Vee shore Dat Dat is lady?  Jess?

--Shane
WP2ASS / ex KD6VXI

Of course, we also have one here:
http://amfone.net/Amforum/index.php?board=45.0

And, if you do visit QRZ, they also have a "Tips and Tricks" forum:
https://forums.qrz.com/index.php?forums/tips-and-tricks-share-yours.135/

very nice.. I have no advice for you as I have never grid driven a 3x3 tube....  I would like to try a grid driven 4x5 tube if I can get around to it.   
   Did you wind the plate choke?  .. What are the sPecs on the parasitic plate suppresor?  Is it standard for a low band 3X3? 
  Again     very nice ..good luck ...I hope to hear you on this rig..  Steve

Even if you are "On the Zed", you may not have found this:

https://forums.qrz.com/index.php?threads/w7tfo-hints-kinks-fear-loathing-in-the-land-of-engineering.525303/

I try to post useful info for those of us that build gear. 

73DG