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TEXAS STAR 1600 AS A BASE
- Thread starter TonyV225
- Start date
Shadetree Mechanic
Delaware Base Station 808
Shadetree Mechanic
Delaware Base Station 808
You are looking for an answer. You want the best voltage. Best means different things to different people. We told you what we do. The best should be whatever the manufacturer says. Why is that not good enough?
Shadetree Mechanic
Delaware Base Station 808
Shadetree Mechanic
Delaware Base Station 808
You're right, I don't know anything. But apparently, you know less.
You're not making friends with this approach.
As many have explained, the amplifier is made to work at typical automotive voltages...13-14.5, or so.
If you want to know the max voltage before you run into problems...get a pen, paper, and start increasing voltage until you blow it up....then back it off a hair.
As many have explained, the amplifier is made to work at typical automotive voltages...13-14.5, or so.
If you want to know the max voltage before you run into problems...get a pen, paper, and start increasing voltage until you blow it up....then back it off a hair.
Ok...so here’s a question now that the thread is cleaned up.
Do you (or anyone) think that the power wire modifications that are often made on these amplifiers have a significant impact on the bias circuit as a result of reducing the internal voltage drop?
I have no need to go changing power wires to chase a little change in the wattmeter, but I also don’t like the fuse arrangement(DX500 in my case) and will likely change that setup (I imagine there’s a bit of voltage drop there, too).
OK what is with some people anyway? The idiot was given a three ban to smarten up. Obviously he was triggered and went apeshit over it. No idea what he was really wanting in the way of EXACT voltage. Perhaps if he was told 13.813984165386143 volts he would have been happy. Either way he had a second chance and didn't want it so his wish was granted. He is gone..
BJ radionut
Supporting Member and 6m addict
For future reference, 90% of the bias problems and voltage limitations they present, can be eliminated with the addition of 1N4007 diodes in Texas Star amplifiers. In the case of this DX-1600, we have four PA stages combined. Each has its own pair of resistors forming a voltage divider to feed bias into the stage. They are 1.6 ohm small 1/4 watt and 25 ohm wire wound resistors.
The 1.6 ohm resistor is the one that has the direct bias voltage across it. The four resistors in question with this amp are R9, R15, R21 and R27. They are fed through RF inductors with bypass caps. Because we want to make use of the existing RF bypassing, each diode should be added across the resistors RF bypass cap. Those caps are C9, C20, C31, and C42.
Connect the anode side of each diode to the ungrounded side of each capacitor listed above. That is the side connected to the ferrite bead and the 25 ohm wire wound resistors. The cathode side of each diode can be soldered to the shortest ground available. The trick is to place each diode directly on top of the closest RF output transistor with heat sink compound under it.
Now the diode can track thermal changes and reduce bias voltage to stabilize current as temperature increases. This prevents over bias and thermal runaway. The diode also offers some regulation to the bias circuit, making it able to handle a wider range of input voltage. Even with these features, the improved bias circuit would still be considered rudimentary at best. The stock one simply sucks.
Keep in mind there is still no way to adjust the bias current. The modification is dependent on having matching diodes with equal forward voltage drop. They should be pulled from the same lot and matched with a DVM on the diode check scale. They are temperature sensitive so hold them by the lead and not the body when testing.
Further improvement could be had feeding the entire bias circuit through an adjustable regulator. That would stabilize the voltage prior to the diodes and offer precision adjustment of forward bias current. This secondary mod would require removing the 1.6 ohm resistors (replace them with .1 uf RF bypass caps) in order to produce enough forward bias from the lower, regulated input voltage. Start with the bias all the way down and slowly bring it into the AB specification for the transistor in use. Do not remove any resistors if your are only installing the diodes without adding a voltage regulator too.
No real experience is needed to just add the diodes since no adjustment or alignment is needed. If you can solder a mic plug on, you can solder the diodes in here. Even if you disregard the performance improvements, the safety aspect of protecting the transistors alone makes it worthwhile because those little 1.6 ohm resistors are stressed without a diode and have been known to open with age, burning out transistors. Adding the adjustable regulator is a job best done by a professional since setting or building the regulator incorrectly, can destroy all output transistors instantly.
The 1.6 ohm resistor is the one that has the direct bias voltage across it. The four resistors in question with this amp are R9, R15, R21 and R27. They are fed through RF inductors with bypass caps. Because we want to make use of the existing RF bypassing, each diode should be added across the resistors RF bypass cap. Those caps are C9, C20, C31, and C42.
Connect the anode side of each diode to the ungrounded side of each capacitor listed above. That is the side connected to the ferrite bead and the 25 ohm wire wound resistors. The cathode side of each diode can be soldered to the shortest ground available. The trick is to place each diode directly on top of the closest RF output transistor with heat sink compound under it.
Now the diode can track thermal changes and reduce bias voltage to stabilize current as temperature increases. This prevents over bias and thermal runaway. The diode also offers some regulation to the bias circuit, making it able to handle a wider range of input voltage. Even with these features, the improved bias circuit would still be considered rudimentary at best. The stock one simply sucks.
Keep in mind there is still no way to adjust the bias current. The modification is dependent on having matching diodes with equal forward voltage drop. They should be pulled from the same lot and matched with a DVM on the diode check scale. They are temperature sensitive so hold them by the lead and not the body when testing.
Further improvement could be had feeding the entire bias circuit through an adjustable regulator. That would stabilize the voltage prior to the diodes and offer precision adjustment of forward bias current. This secondary mod would require removing the 1.6 ohm resistors (replace them with .1 uf RF bypass caps) in order to produce enough forward bias from the lower, regulated input voltage. Start with the bias all the way down and slowly bring it into the AB specification for the transistor in use. Do not remove any resistors if your are only installing the diodes without adding a voltage regulator too.
No real experience is needed to just add the diodes since no adjustment or alignment is needed. If you can solder a mic plug on, you can solder the diodes in here. Even if you disregard the performance improvements, the safety aspect of protecting the transistors alone makes it worthwhile because those little 1.6 ohm resistors are stressed without a diode and have been known to open with age, burning out transistors. Adding the adjustable regulator is a job best done by a professional since setting or building the regulator incorrectly, can destroy all output transistors instantly.
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