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[AMPS] YC-156

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Subject: [AMPS] YC-156
From: (Bob Marston)
Date: Tue, 23 Feb 1999 20:22:16 -0800
At 01:50 PM 2/21/99 -0500, wrote:

>>Secondly they have a fairly high output 
>>(36pf) So even though they have a max freq spec of 110Mhz your not 
>>going to
>>match them up with a pi-network on 10 Meters.
>And why not?
>Details please.

OK Carl

I dug out my W6SAI Amateur Service Newsletters just for you. And all the
subscribers to the Amps List. BTW  These notes are a treasure trove of
amplifier design info. From Pi Pi-L Networks to Intermodulation Distortion
to Forced Air Cooling to the Original Article on the Stanley Steamer Bill
Orr has packed quite abit into the 49 Notes that I have. I'm missing a few,
AS-13 Understanding Tetrode Screen Current, AS-22 Reference Index-- Eimac
Tubes in Amatuer Service, and AS23 External Anode Tetrode Tubes. If there
is interest I would consider obtaining permission to reprint them from
Eimac/W6SAI and posting them on the net.

To the matter at hand. First what has to be determined is the input
resistance at the desired operating voltage.

R=  Plate Voltage
   2x Plate Current   

Assuming 50% efficiency 1500 watts out yields 3000 watts in.

At 3kv this yields 1 Amp of plate current  > 1500 ohms  

At 4kv this yields .75 Amps                > 2700 ohms

At 5kv this yields .60 Amps                > 4100 ohms

at a tank Q of 10 the Capacitive Reactance for the Tuning Cap is  Figure 3
page AS-30-4

150 ohms   for     1500
270 ohms   for     2700
410 ohms   for     4100

this yields   a TOTAL  Cin of

38 pf
20 pf
13 pf

Cin = Ctube + Cstray + Ctuning cap

Ctuningcap = Cin - (Ctube + Cstray)

Ctube is 36pf
Cstray is 5pf

Ctuningcap = 38  - (36 + 5)
Ctuningcap =  -3pf

Well that rules out a design Q of 10

Now to a design Q of 20

the capactive reactance for the operating conditions sited above are:

75  ohms
135 ohms
205 ohms   respectively

and a capacitances of

80 pf
40 pf
25 pf

3kv is easily do able if you don't mind retuning every 20 khz. The best
Vacuum Variables have a minimum capacitance of 5 pf + 36pf + 5pf = 46pf.
4kv and above ain't going to work.

Initial reports from some who have worked with this tube on 10 indicate an
efficiency on the order of 40%.

That's marginal to poor in my book

Is that enough details???


Bob K1TA  

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