[Hallicrafters] SR 2000


Jim Liles hallicrafterssr2000 at k9axn.com
Mon Jul 28 19:47:19 EDT 2014


Hi Donato:

I don’t know what you mean by position HT

The plate voltage dropping from 2800 to 2500 is normal.

R316 must be 12K.  the value is chosen to drain the negative screen current that is common in the 8122.  At 45K ohms the negative screen current can draw the screen voltage up to avalanche levels destroying the 8122’s.

If the idle current changes when switching to high power mode, the bias resistors in the P2000 are either out of tolerance or incorrect values.  They should ALWAYS be replaced in the P2000 with metal film resistors.  They will not change and will hold their tolerances.

The radio should deliver 450 to 500 watts to the antenna in low power mode and 900 to 1100 watts to the antenna in high power mode.

NOTE:  The 8122’s have a vast range of bias variations.  This affects the output capabilities in the class AB1 amplifiers used in the SR-2000.

A good rule is to use Burle 8122’s or have them tested not only for a match but whether they will work in the SR-2000.  The Burle 8122’s are color coded to indicate their bias range.  They are Red, Blue, Green, and black.  The Blue tubes will work in the SR-2000 without mods and the Green will work but some need circuit changes to make them work properly.  I have not seen the Red version and know that they will only deliver about 750 to 850 watts out.  The Blue about 950 to 1050 watts out and the Green 1000 to 1150 watts out.

The Black 8122’s will not work in the SR-2000 and exceed the design capabilities of the SR-2000. 

The different output capabilities is a result of the Class AB1 design.

Let me know what the HT position is.

Good luck and Kindest regards Jim K9AXN    


    

-----Original Message----- 
From: Donato Mascia 
Sent: Monday, July 28, 2014 5:39 PM 
To: Hallicrafters at mailman.qth.net 
Subject: [Hallicrafters] SR 2000 

Hallicrafters SR 2000 (serial No. 452000 142001), good conditions + power
supply P 2000.
Low voltage power supply tuning position for approximately 1800 volts. At
the end of tuning by going to the location HT, about 2800 volts read on the
instrument of P 2000, instead of increasing the anode current is lowered
circa 20-40 mA, and a similar reduction also the output power (about 450
watts according in position low voltage is passed to about 300 watts and
less in position HT). Even the plate voltage drops from 2800 to about 2500
- 2600 while the voltage of the screen grid appears normal and stable
300-volt low-voltage and high-voltage 400 volts. Change both 8122 and the
driver no change. Other voltages and currents all normal. At the receiver
nothing to report. Only resistor R 316 on P 2000 (12 kOhm Nominal 25 W) is
about 45 kOhm. Replaced by one with the correct value 12 kOhm no change.
The grid current without signal is sharply negative and goes up to about
10-15 mA with the signal. The rest all normal, proper the bias. Antenna OK.
Could I have some advice for the anomaly ? Perhaps the diodes of the HT ? I
thank you for your kindness and competence to restore the noble and
venerable apparatus.

IZ5URV (former I5MVD) Donato Mascia.
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