Consider putting a GS-35 in it if you change anything.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of Bill Smith
> Sent: Wednesday, April 13, 2011 6:23 PM
> To: amps@contesting.com
> Subject: [Amps] GU-84B Conversion (Re-thought)
>
> Well thanks to all of you here I have abandoned the idea of using the
> GU-84B. Staying with a Triode is the way to go. As it sets the amp
> needs a Tuned Input and a tank circuit refinement if I stayed with the
> 3-400Z tubes. Not a big deal but the tubes are hard to come by and can
> be quite expensive.
>
> I now will explore using the GS-31B and the 3-500Z. The 3-500Z is too
> tall for my enclosure but it could be modified I guess. The 8877 is a
> great tube but $$$$!!
>
> 73,
> Bill
> KO4NR
>
>
>
> --- On Wed, 4/13/11, RZaepfel@aol.com <RZaepfel@aol.com> wrote:
>
> From: RZaepfel@aol.com <RZaepfel@aol.com>
> Subject: Re: [Amps] GU-84B Conversion
> To: ko4nrbs@yahoo.com
> Date: Wednesday, April 13, 2011, 3:00 PM
>
>
>
>
>
> Bill,
>
> I rarely respond to the list, but will offer a bit of information. I
> have
> in progress a design-build from scratch hf amp using the GU84B tetrode.
> I'm at
> the 85% point in the job. My approach involved solving the initial
> problem of
> the enclosure as a starting point because most commercially available
> amp cases
> are pretty chunky and most are tall to accommodate transformers inside
> the
> table top box. So I chose to use the case and cabinetry from a deceased
> HP 8660
> series signal generator for the table top and the PS is located in an
> old UPS
> box on the floor out of sight. That makes some of the problems a bit
> easier to
> solve. Your thought to go from triode to tetrode may be too big a leap.
> There's
> quite a bit that must be worked out. You must have a well-regulated
> screen
> supply of 360 - 380 volts for the GU84B capable of handling negative
> screen
> current and a well-regulated bias supply of around -70 to -100 volts.
> Both
> are not usual requirements for gg triodes. My solution is to incorporate
> a set
> of Tetrode Boards from Ian White, GM3SEK. Also, you will need a filament
> supply
> of 27 v at about 4 amps. I solved this by having Peter Dahl build a 2
> amp ccs
> transformer for me before he ceased doing business -- weighs 46 lbs as I
> recall.
> It's too large for a table top installation, so the floor is a good
> solution.
> The other big issue is the input circuit. You will need to build a
> swamped input
> circuit with a noninductive 50 ohm load, some inductance to compensate
> for tube
> input capacitance and a way to deliver bias while isolating the bias
> supply from
> RF. Also need to install at the tube base a bleeder resistor for the
> screen
> supply and a simple resistor-inductor combination in the screen to
> secure
> stability. Reading the Tetrode Boards site might be a good idea, as you
> will get
> the steps for designing and installing all this stuff from the "horse's
> mouth".
> There's quite a bit of work here. Staying with triode(s) would be
> easier. How
> about a 8877?
>
> 73,
>
> Bob, K4HJF
>
>
>
> In a message dated 4/12/2011 8:47:41 P.M. Eastern Daylight Time,
> ko4nrbs@yahoo.com writes:
> I'm
> considering converting my old Swan Mark 1 (two 3-400Z tubes) to use
> one
> GU-84B. Some time ago I replaced the panel bandswitch in the Swan
> with a
> Radio Switch Model 86 six position switch with two wafers. At that
> time
> I also replaced the tank coil with one that was made for the National
> NCL-2000
> amplifier. My new bandswitch required me to rearrange the RF
> compartment
> considerably.
>
> The transformer was replaced with a new one from Heyborer
> in Michigan. At that time I had them use the next larger diameter
> wire
> in the HV and filament windings when they wound it. The caps, etc.
> were
> all replaced with snap in type on a circuit board.
>
> Ok that's the
> history of the amp to date. It has a resting plate voltage of 2900vdc
> and 2500vdc or so under load.
>
> Readings with two 3-400Z tubes:
> Plate
> Current Readings on Operate HV Setting (SSB):
> 270ma using a Tuning
> Pulser
> Resting Plate Current is 190ma
> 460ma SSB Peak (Talking in
> Mic)
>
> Plate Current readings using CW Mode(1500vdc)
> Key down
> 660ma
> Resting 80ma
> SSB 320ma Peak
>
> My question is will the GU-84B
> perform satisfactorily with this transformer? I know I'll need
> another
> filament transformer and one for grid voltage.
>
>
> 73,
> Bill Smith
> KO4NR
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