[Hallicrafters] SR 2000 |
Jim Liles
hallicrafterssr2000 at k9axn.com
Tue Jul 29 10:27:34 EDT 2014
Good morning Donato:
The drop in high voltage is a result of the doubling circuit design used in the high voltage power system. Ignore it, it is normal.
The problem that you have is inadequate drive to the 8122’s.
A good way to check the drive is to remove the heat dissipating shield from the 12BY7A driver, wrap a copper sleeve around the tube, attach a scope probe to it and measure the voltage when in transmit mode as you tune the pre-selector and increase the transmit RF drive. You don’t need to enable the high voltage. It should measure 18 to 25 volts on the 15 and 20 meter bands. That level will fully drive the 8122’s.
It is quite common to find an SR-2000 behaving as yours does because of inadequate drive. Do a full alignment beginning with measuring the output of the VFO, Heterodyne, and Carrier oscillators. The VFO should be approximately 1.5 to 2.0 volts PP at V2AP7, the Heterodyne as stated in the manual, and Carrier approximately 5 volts PP at V9AP8.
Let us know what you find.
Kindest regards Jim K9AXN
-----Original Message-----
From: Donato Mascia
Sent: Tuesday, July 29, 2014 5:36 AM
To: Jim Liles
Cc: Hallicrafters at mailman.qth.net
Subject: Re: [Hallicrafters] SR 2000
Good morning Jim (11:30 AM Local), you are very kind
1) I have some valves is 8122 RCA Burle some red and others black, or a pair of new red Burle. For now I have only been rehearsing with RCA, I do not want to take risks with new valves Burle, the 8122 are very delicate!.
2) HT position corresponds to the P 2000 High Voltage.
3) Today I replace the R316 with a new 12 K 25 Watt came from Nebraska Surplus.
4) The power antenna is a wattmeter-automatic tuner 1 KW.
5) in low power about 350-400 watts max; in Hight power drops to about 250-300 W max. always with the screen grid current stable on 15 mA.
6) after the maximum screen current of 15 mA does not have any increase in power beyond the limits given above is that in LV & HV lowvoltage.
7) in normal conditions rightly plate voltage HV may drop in relation to the greater absorption of the valves, but in my case, the voltage drop is also associated with a decrease of plate current (!) And output power. How is it that a voltage drop is also associated with a decrease in current? It seems to me an inconsistencythat suggests an alteration in the chain of rectifier-capacity-resistors.
8) correct and stable bias current to 200 mA in both LV & HV.
9) screen grid voltage correct and stable to 300 Volt LV & 400 Volt HV.
10) the voltages are measured on the output of P 2000 on the connection plug, and both the point of measurement of the transceiver shown in the manual.
11) no smoke or odor even in prolonged operation with HT applied.
I think to a fault in only P2000. Maybe a short in one of the capacitors 90 uF or alteration of the diodes?
Please excuse my verbosity, thanks and regards, Donato Mascia IZ5URV
mascia.donato @ gmail.com
2014-07-29 4:35 GMT+02:00 Jim Liles <hallicrafterssr2000 at k9axn.com>:
Hello again Donato:
How much power out can you get from the radio in low and high power mode with 15 ma of screen current?
After tuning the radio for maximum 15ma of screen current, further increases in transmit RF drive should cause the anode current to drop. What do you observe when you do that?
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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