[Moon-net] [Mw] Pre-Tuning a 8877

[W2DRZ Thomas Mott]

Hi,

For filament voltage I use a 35 to 50 ohm rheostat at 25 to 50 watt in the 
110-120 AC input primary to drop the filament voltage,
 this will sage the inrush voltage upon start application of voltage with 2 
things,
 protect the tube inrush current and allow adjustment of the filament 
voltage (5.0v " +or- 5%") after tube is heated and stabilized.
 Bring out to test terminals of the filament voltage to allow metering 
during operation as you wish to meter filament.

The power supply at 400 mills is very short of current,
 the idle current with a cathode (8-9) volt zenier will idle at ?? 100+ to 
200 or so mills plate current,
 no drive yet.

The tube will easily do 800 to 1 amp of plate current (2900 volts) during 
operation with 30+ to 60 watts of drive for up to (1.5-2+) KW output as 
tuning is done on unit with a efficient input circuit.
 Grid current will vary up to 100 ma with the PA loading affecting that 
value,
 finished tunning drive grid current about 10 to 60 ma is expected???,
 just be careful with drive at start of tuning.
would start with 5 to 10 watts at start up tunning.
The higher the plate voltage 2900 to 3500 dc, the lower the grid current 
when tuned.


tom W2DRZ


http://www.w2drz.ramcoinc.com/
----- Original Message ----- 
From: "Edward Cole" <kl7uw at acsalaska.net>
To: "W2DRZ Thomas Mott" <w2drz at madbbs.com>; "Moon-Net" 
<moon-net at list-serv.davidv.net>
Cc: <microwave at echo.valinet.com>
Sent: Friday, July 25, 2008 12:56 AM
Subject: Re: [Mw] Pre-Tuning a 8877


> Thanks Tom, and all who replied.
>
> I will be testing the input tuning parameters with a MFJ-269 antenna
> analyzer which outputs around 10mw, so will not be running any
> HV.  Since I am interested in the full power input impedance (R+jX) I
> will use 54-ohms across the cathode-grid.  That ought to help make
> any gross adjustments to the input coils.  After sufficient burn-in
> on the filaments, then will try applying some HV looking for arcs and
> setting bias without drive.  Hopefully, in a few days I can report
> success in achieving some power.  My HV supply provides 2500-vdc at
> 400-mA so hoping to get about 600+ watts with 25-30w drive.  I have a
> QRO HV supply (2900-vdc at 900-mA) that needs some TLC before
> applying power, but hopefully it will be ready by this fall before
> the ARRL EME Contest (I have to wire 240-vac to the radio room for that 
> one).
>
> As far as the filament in-rush circuit, I am using the design given
> in G3SEK's Triode Board Manual.  It operates on the primary side of a
> transformer and uses a simple RC time delay circuit with diode
> rectifier to drive a 12-volt relay.  The relay shorts out the current
> limiting resistor after the delay time.  I am going with a 4-second
> time constant (1750-ohm x 2200mfd).  My 5-volt transformer is rated
> for 12-amps and runs 5.15 vac open circuit.  It has multi-tapped
> primary coil.  I am selecting the full primary of 126-vac to step
> down to run at 4.9 volts (my line voltage is 120-vac).  I understand
> that running about 4.75-4.95 volts will extend tube life.
>
> 73 Ed - KL7UW
>
> At 07:02 AM 7/24/2008, W2DRZ Thomas Mott wrote:
>>Hi,
>>
>>Use a 54 ohm for tube impedeance.input, output is 2,000 ohm.
>>
>>tom W2DRZ
>>
>>http://www.w2drz.ramcoinc.com/
>>----- Original Message ----- From: "Edward Cole" <kl7uw at acsalaska.net>
>>To: "Moon-Net" <moon-net at list-serv.davidv.net>
>>Cc: <microwave at echo.valinet.com>
>>Sent: Thursday, July 24, 2008 10:48 AM
>>Subject: [Mw] Pre-Tuning a 8877
>>
>>
>>>I recall hearing that one can use something like a 6K reisistor
>>>across the cathode-grid on a gg 8877 to resemble input impedance
>>>for pre-tuning the input ckts using a small signal from a MFJ-269
>>>antenna analyzer.  Can anyone confrim the input impedance for a
>>>8877 (144-MHz)?  Should I have the tube inserted to include
>>>inter-electrode capacitance?  This is with HV off, of course.
>>>*****************************************************
>>>73, Ed - KL7UW              BP40iq, 6m - 3cm
>>>144-EME: FT-847, mgf-1801, 4x-xp20, 185w
>>>http://www.kl7uw.com     AK VHF-Up Group
>>>NA Rep. for DUBUS: dubususa at hotmail.com
>>>*****************************************************
>>>_______________________________________________
>>>Microwave mailing list
>>>microwave at lists.valinet.com
>>>http://www.valinet.com/mailman/listinfo/microwave
>
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