[Moon-net] Gain of a tetrode (TH347)

[dfaessler at bluewin.ch]

hi Peter

interesting question. There seems to be an optimum Ua for these tubes on 23cm which is considerably below maximum rating. I could not go beyond the 3.35KV due to transformer settings. Therefore this was our highest Ua in the Plisch system. Therefore reference is made to the TH308 types of Thomson tubes. I however found out with the TH308/th328 families that arcing inside the tube between anode and grid was critical at the higher end of operating conditions. Therefore I personnally prefer somewhat lower Ua and thus a notch higher Ic.

 

I have another TH347/TH327 amp using much harder power supply. (same as I delivered to ON7UN and ON4BCT). Eddy has fired it up already and may comment on his working parameters. He apparently sucks about the same RF out as I do with the small amp.

 

Interesting stuff though.. Will have more time for all these topics in a year after retiring from day-to-day going into Zurich for qrl...

73

HB9BBD Dominique



 

Dominique Fässler
HB9BBD
+4179400218



----Ursprüngliche Nachricht----
Von: df3kv at t-online.de
Datum: 02.10.2007 15:43
An: <Moon-net at list-serv.davidv.net>
Betreff: Re: [Moon-net] Gain of a tetrode (TH347) - corrected

Hi Dominique,

On your tests, what was the upper usable limit of the anode voltage on 23cm
with the Plisch cavity?
I usually try to get screen currents low with tetrodes by raising the EHT

73
Peter

  _____  

From: dfaessler at bluewin.ch [mailto:dfaessler at bluewin.ch] 
Sent: Dienstag, 2. Oktober 2007 15:00
To: df3kv at t-online.de; Moon-net at list-serv.davidv.net
Subject: Gain of a tetrode (TH347) - corrected



This is just to clarify my earlier statement re TH347 TH327 tube operation.

The operating data as stated are the result of many tests some 10 years ago.
I brought up some Plisch linear amplifiers using these fine tubes. Late
Peter, OE9PMJ got one amp as well as OE9ERC. We all tried out how to get
full throttle on 23cm and the results are as they are. Importantly we
realized that the original design of G2 current supply was delivering some
30mA only. This apparently limited the amplifier to deliver 10dB gain at the
maximum operating environment.  By allowing this current to peak
approximately 70mA we found 10dB of gain with 250W of drive in linear mode.

Thats all gentlemen. Just be very careful in fingering into the power
supply. Early listing in silent key columns are to be definitely avoided.

73

HB9BBD Dominique 





Dominique Fässler
HB9BBD
+4179400218





----Ursprüngliche Nachricht----
Von: df3kv at t-online.de
Datum: 02.10.2007 02:01
An: <Moon-net at list-serv.davidv.net>
Betreff: [Moon-net]  Gain of a tetrode (TH347) - corrected

Hi Günter and the group,

Generally for linear service 0,5A of idle current is just right which means
less negativ voltage on the grid.
With a given drive the bias voltage has to be overcome by the rf voltage for
full output.
So with more negative bias the rf voltage needed will be higher.
With too less drive maximum power will always be higher at higher idle
current.
Running the tube in class B or closer to class C always requires more drive
but efficiency will be higher because the load line gets longer.
With plenty of drive there will be no problem with power output, but  the
actual gain will alsways be lower then with true class AB.
At the given idle current gain will not vary much until the compression
point is reached.

73
Peter


-----Original Message-----
From: moon-net-bounces at list-serv.davidv.net
[mailto:moon-net-bounces at list-serv.davidv.net] On Behalf Of Koellner,Guenter
(NSN - DE/Germany - MiniMD)
Sent: Montag, 1. Oktober 2007 20:31
To: moon-net-bounces at list-serv.davidv.net; moonbounceboard
Subject: [Moon-net] Gain of a tetrode (TH347) - corrected


Hello,

back to a technical question:

On 23cm, my amp is using a TH347. I have about 75W drive (from a GSM
amplifier) and am getting about 950W output from it. While tuning and
optimizing, I found that the gain increases when I am increasing the idle
current, so this situation is at 300mA idle current.

I am now going to get more drive power, the plate current might become too
high and the plate loss too much. In order to compensate here, I may reduce
the idle current. But, how much less gain may I get when I for example
reduce idle to 50mA. Not that I now drive it with 3dB more and on the other
hand loose 3dB of gain, so that at the end the output is equal.

73, Günter (dl4mea)


corrected: was 300mA drive power -> 300mA idle current

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