----- Original Message -----
From: "Patrick Barthelow" <apolloeme@live.com>
To: <dezrat1242@yahoo.com>; <amps@contesting.com>
Sent: Tuesday, April 27, 2010 2:27 PM
Subject: [Amps] GS-35B; Best choice Int'l shipping?
>
> RE GS 35 B Possible choice for Homebrew Amp:
>
>
>
> 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.
>
>
>
> Some more questions about the GS35.
>
>
>
> 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.
"Gettering" procedures are online at W4ZT's (SK) site GS35b.com via
UR4UL. That said, I personally run the heater for 24-48 hours & then full
B+ for another day, 0 issues on 3 tubes so far. Hipot them though- I got a
few duds in my purchases (they were represented as NOS but were obviously
used- pics available). Everything from UR & RU has been fine, so far...
Email me privately if you want names of whom I bought from.
>
> before applying full B+ for operations.
>
>
>
> 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. 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 do this with two 6m amps- the first has a low cfm blower & will drift
if hit hard for over 15 minutes, otherwise 1.2 kw all day with a reduced
67cfm. My primary amp (2nd GS35b HB) uses a slow-speed 137cfm Dayton
blower- under the bench it is quieter than my SB220 conversion. Just do the
math with your holes- you need at least 7-8 cubic inches of airflow (I
recall 96 cfm is the required airflow). With my current amp, I use a 4" PVC
chimney (no problem unless tube anode close to chassis, obviously). To get
the required cfm thru the anode cooler, I used hot-air (like plumbers do) to
expand the base of my 4" PVC to 4 1/2" or better. Simplifies the whole
thing, pics available if you like, just email me. I used the K7IUV approach
(including the HB grid-ring clamp aluminium "blocks") but after in-situ
testing the airflow wasn't enough, so I enlarged the 1/2" holes with a
dremel & expanded the diameter of the PVC via a torch & "mold" (base of a
Spackling can). Viola, no more problems, key-down for loooooong periods if
I like. No need for a socket at all.
Use a separate bias choke (like W4ZT's site describes). Didn't use one
on my 1st project, and had some issues. 2nd amp uses one (not trifilar in
my case, separate completely from bifilar filament choke)... 0 issues or
bad reports with that config. The old amp, with no bias choke, got a few
comments at times re "AC hum".
>
>
>
> Also on a more practical level, I plan to ship various KW RF components,
> for this project, to Uruguay, proabaly only the lighter ones...chokes,
> tubes, band switches, meters, etc. What is the best (Cheapest) choice
> for an international shipping company between USA and Uruguay?
>
>
>
> Thanks to those who have replied to earlier queries about sourcing the QRO
> power supply pieces. I am hoping to find a sympathetic Radio Station
> engineer in Montevideo, or Salto, that may source a suitable, surplus to
> their use, B+ transformer.
If you run the tube at the supposed 3kv max, expect a BIG current draw
at full output (at 50 MHz it is about .9 amps). My 1st 6 meter amp drew
almost an amp at 2800VDC & did well over legal limit. My 2nd HB amp, with
4450 VDC on the plate, I get .550 amps for plate current- efficiency between
54 & 57 % depending on the "power-added" or "new" measurements & legal limit
Plus up to 100w with full drive (on a good day). You can do better than
50%, just remember the Mu is 13 as compared to 20 for an Eimac tube. That
said, I don't even measure grid current- no need with the GS35b unless you
drive it with 200w. Can't hurt them, or at least I can't with a ProII....
With a PiL tank you can increase efficiency a lot- properly tuned a 100w
exciter can get full-out with 50-60w, though the curve isn't linear so don't
expect too much more with 100w drive (on VHF anyway).... I use a variable
transformer on both amps for filament VAC- the filament V is crucial, so I
check the voltage via test-points built into the amp with my Fluke & adjust
the filament V accordingly if my B+ is low (and hence 240 line VAC).
Doesn't matter much in Spring but is critical in local summer for the last
few 100w output when the pole pig is being taxed. It is worth the extra
work.
>
>
>
> Thanks guys,
>
> Best Regards,
> 73, de Pat Barthelow AA6EG
GL, 73 Dave N3DB
>
>
>> From: dezrat1242@yahoo.com
>> To: amps@contesting.com
>> Date: Tue, 27 Apr 2010 09:20:46 -0700
>> Subject: Re: [Amps] Helping a Uruguayan Ham build an Amp.
>>
>> ORIGINAL MESSAGE:
>>
>> On Sun, 25 Apr 2010 10:15:47 -0700, Patrick Barthelow
>> <apolloeme@live.com> wrote:
> Then even the possibility of choosing a GS 35B tube as as the basis of the
> amp.
>>
>> REPLY:
>>
>> I would recommend against using a GS-35b. Their efficiency is low
>> compared to other types. I and several others have obtained
>> efficiencies in the range of about 50%, compared to about 60% for an
>> 8877 and other comparable tubes.
>>
>> Aside from poor efficiency they do seem to work well so that is not
>> necessarily a show-stopper, just something to consider.
>>
>> 73, Bill W6WRT
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