[Amps] GS-35B; Best choice Int'l shipping?

[Bill, W6WRT]

On Tue, 27 Apr 2010 11:27:41 -0700, Patrick Barthelow
<apolloeme at live.com> wrote:

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>RE GS 35 B Possible choice for Homebrew Amp:
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>Thanks Bill for your comment on the GS-35B  The efficiency may become important, if it means that you cannot get 1.5KW out of the GS 35B with 100 watts drive.  Whether the efficiency sucks more watts out of the wall socket/power supply  is less important than if we can get full output with a solid state 100 watt TX exciter.   

I was able to get 1500 watts out with about 85 watts drive, no problem
there. But to do that I had to drive it to about 1000 mA plate current
at 2900 VDC. I have two GS-35b's and the results were the same with
each.  In both of the amps I built with a GS-35b, I replaced the tube
with an 8877, replaced the heater transformer, changed the bias diode
from 24 V to 8.,2 V and was then able to get 1500 watts out with only
830 mA plate current. Drive with the 8877 was about 50 watts. Other
than the DC plate current difference, the two tubes worked fine. 
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>Some more questions about the GS35.  
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>Are all about the same reliability, independent of source?  what percentage random DOA?   Best purchase source?  USA dealers?  Eastern Europe hams?  New?  Used?  NOS?  I have seen suggestions for conditioning which recommended all newly acquired GS 35bs be operated at reduced B+ and heated for some time to Getter out any residual gas before applying full B+ for operations.

I bought mine (two of them) from a dealer on eBay. He has a Texas
address but ships direct to you from Russia. No problems there. I ran
the tubes with heater voltage only (and cooling fan) for 24 hours
before applying HV. I don't really know if that was necessary but it
was cheap insurance and the tubes worked fine right away. They never
did arc as some new tubes do. 
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>One of the first GS 35B Amps I looked at some years back used very simple clamps of the grid ring directly to the chassis, with a hole punched for access to the cathode/filiment power.   Almost no "Socket" per say.  And simple drilled holes around the base to allow cooling air to be chimnied. or ducted up through the anode cooler fins.
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>Also I recell a lot of backpressure, and flow reqts to the tube.  Is a GS 35B amp properly cooled, noisy, esp when compared to a typical 3-500Z pair which requires far less pressure to get the flow?

I mounted mine directly to the chassis, as you state above with no
problems. By the way, a replacement glass from a Coleman lantern fits
perfectly for an air chimney. I mounted it to the chassis with a few
dabs of silicone RTV and also put a few dabs between the top of the
chimney and the GS-35b fins to keep the spacing constant. Works great.
There may be more than one size of Coleman glass so be sure to measure
the diameter before you buy. I used a 91 CFM EBM-Papst blower, which
is overkill, but it was not too noisy at all. I highly recommend that
blower for overall quality and freedom from vibration, but it is a bit
expensive, about $140 USD. 

73, Bill W6WRT