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Re: [Amps] GU-84B Conversion (Re-thought)

To: "Bill Smith" <ko4nrbs@yahoo.com>, <amps@contesting.com>
Subject: Re: [Amps] GU-84B Conversion (Re-thought)
From: "Carl" <km1h@jeremy.mv.com>
Date: Wed, 13 Apr 2011 20:22:27 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
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@yahoo.com>
To: <amps@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@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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