[Hallicrafters] Hallicrafters HT-33A

[Carl]

Here is a 4CX1000A conversion, the 4CX1500B is almost identical. A stock 
33B is shown for comparison.

http://www.hollowstate.ca/HT33B.html

http://www.isquare.com/personal_pages/ht33b.htm

The FCC 2000W PEP SSB rule was in effect when the B model was out and Id 
suspect that it was capable of meeting or exceeding that. Unfortunately 
I do not have a manual or an ad handy to confirm.

I had considered the current AC line voltage when I commented about the 
8122's.

Carl
KM1H


----- Original Message ----- 
From: "Glen Zook" <gzook at yahoo.com>
To: <hallicrafters at mailman.qth.net>
Sent: Friday, September 19, 2008 5:38 PM
Subject: Re: [Hallicrafters] Hallicrafters HT-33A


>I joined the amps group about an hour ago and have already sent the 
>person advertising the 8295A an E-Mail.  Am waiting for his reply.  If 
>I can obtain the 8295A then that will make things MUCH easier!
>
> One thing that I have been thinking about is the actual power that the 
> HT-33A is capable of without any problems.  Of course the unit was 
> manufactured when the maximum INPUT was 1000 watts and the tuning 
> instructions in the manual are for that value on CW.  The instructions 
> are to use the amplifier with a cathode current of 390 mA which 
> supposedly equates to 370 mA of plate current.  At 2700 volts this 
> makes a plate input of right at 1 kW.  They also say for SSB operation 
> to tune up to 520 mA of cathode current which equals 500 mA of plate 
> current.  That equals 1350 watts input.
>
> Now "typical operation" of the PL-172 is shown at plate voltages of 
> 2000, 2500, and 3000.  At a plate voltage of 2500 volts and a plate 
> current of 960 mA this shows the PL-172 giving 1870 watts output. 
> This is for CW and represents an efficiency of almost 78%.  In Class 
> AB-1 (which the HT-33A is capable of running) at 2500 volts at an 
> average input current of 400 mA (but a "peak" input current of 1.6 
> amps) the "typical operation" of the PL-172 shows to be 2310 watts 
> output.
>
> In the "real world", with the circuit losses in the final tank, etc., 
> the efficiency is probably going to be more in the 65% range.  Maybe a 
> little better, maybe a little less.  But, assuming that 65% is the 
> efficiency then to get 1500 watts output would require right at 2300 
> watts input.  At 2700 volts this would require a plate current of 
> pretty close to 850 mA and a cathode current of 870 mA.  At 2300 watts 
> input and 1500 watts output the plate dissipation is going to be 800 
> watts which is well within the ratings of the tube.
>
> Another thing to take into consideration is the higher line voltage 
> that is common today.  My line voltage generally runs pretty close to 
> 127 volts at my breaker box and the breaker box is located about 3 
> feet from my main operating console.  Therefore, for all practical 
> purposes, the voltage drop due to the conductors can basically be 
> ignored.  Assuming that 2700 volts is the output from the 3B28 
> rectifiers then the additional input voltage of 127 volts (which is a 
> little over 8.5%) should produce a voltage of around 2930 volts. 
> Then, I am planning on replacing the gas rectifier tubes with 
> solid-state devices.  Now the voltage drop across the 3B28 tubes when 
> compared to solid-state should result in an increase of maybe 25 volts 
> to 50 volts, probably closer to 25 volts than 50 volts.  The main 
> reason for replacing the tube rectifiers is to get the B+ off of the 
> filament winding on the power transformer with a slight increase in 
> voltage being a potential
> "bonus".  This should result in a plate voltage of around 2960 volts 
> which is within the ratings of the tube.
>
> The maximum scale of the meter in the cathode current position is 800 
> mA.
>
> Assuming a plate voltage of 2950 volts and a plate current of 750 mA 
> this would result in an input power of a little over 2200 watts.  Then 
> assuming an efficiency of 65% this means an output power of just under 
> 1450 watts.  At this point the plate dissipation of the PL-172 would 
> be right at 775 watts.
>
> After all this reasoning actually comes my question.  How "hefty" is 
> the power supply in the HT-33A?  The physical size of the high voltage 
> transformer is considerably larger than in my Tempo 2001 amplifier 
> that can put out 1400 watts.  In fact, there is only a single 
> transformer in the Tempo linear which provides heater and control 
> voltages as well as the high voltage.  Now the Tempo has solid-state 
> rectifiers from the "get go".  The high voltage transformer definitely 
> weighs considerably more than the entire Tempo amplifier including 
> cabinet.
>
> My concern is not with the capabilities of the r.f. portion of the 
> amplifier but in what is a safe level to run the power supply.  Since 
> the instruction manual states that 520 mA of cathode should be run to 
> comply with the old 1000 watt "average" input regulations of the past 
> and that is a very conservative rating.  Therefore, I am looking for 
> ideas from those who have run the HT-33A or HT-33B as to what to 
> expect.
>
> Glen, K9STH
>
> Website:  http://k9sth.com
>
>
>
> ______________________________________________________________