[Amps] GU-84B Conversion (Re-thought) (pair of 3-400s on e-bay

[Roger (sub1)]

There are a pair of 3-400s on e-bay at the moment. Item # 170627540860
5 days to go, 6 bids and they are up to $107.50

73

Roger (K8RI)


On 4/13/2011 8:22 PM, Carl wrote:
> Measure the overall height between the 400 and 500 but with the anode cap on
> the 400 and nothing on the 500. If they come in the same Ameritron sells a
> cooler that does not extend above the tubes own cap but is about 3X the
> width of a standard Eimac HR series cap.
>
> If the socket has to be dropped a bit then use a small fan below to keep air
> on the filament pins.
>
> The 4-400A is another choice that often shows up NOS at $20-50 at hamfests.
> It takes a bit more drive for the same output as a 500 but they are rugged
> and stable. Since the Swan grids are grounded its a plug in but you may have
> to diddle with the bias values around K-1
>
> If you can find PL-175A's they will equal a 3-500Z watt for watt..
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "Bill Smith"<ko4nrbs at yahoo.com>
> To:<amps at contesting.com>
> Sent: Wednesday, April 13, 2011 6:23 PM
> 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 at aol.com<RZaepfel at aol.com>  wrote:
>
> From: RZaepfel at aol.com<RZaepfel at aol.com>
> Subject: Re: [Amps] GU-84B Conversion
> To: ko4nrbs at 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 at 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
> _______________________________________________
> Amps mailing
>    list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>