I have only seen one other that was modded this way and that was in the 1990s... Vintage Ham Radio Amplifier Scottsbluff Nebraska | eBay
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Modded Mv 250. Interesting,.
- Thread starter Staybolt
- Start date
And that will chernobyl the final tubes in quick order. That's way too much drive from the driver tubes. Whoever modded it needs to get slapped upside the head. It doesn't make any logical sense to mod up a MV 250 that way, you'd have to add some sort of padding in between the driver stage and final stage to make it work to where you're not going to overdrive the final tubes. *sigh*
Sorry about the rant.... just seems like a waste to me.
~Cheers~
Sorry about the rant.... just seems like a waste to me.
~Cheers~
I actually had one just like this on the bench last weekend.
Guy bought it local and said it did 1kw Bird watts.
He was talking on it and then the tube flashed and some started turning red.
I found 6 of the 8 tubes dead on the B&K tube tester.
The bias PS was toast.
So there is at least two of them around, the one on ebay and the one local here in North Florida.
Guy bought it local and said it did 1kw Bird watts.
He was talking on it and then the tube flashed and some started turning red.
I found 6 of the 8 tubes dead on the B&K tube tester.
The bias PS was toast.
So there is at least two of them around, the one on ebay and the one local here in North Florida.
Just adding more tubes will not make the amp do more power. Power output has more to do with stage gain, drive power available to that stage and the current available from the power supply. Four of the same tubes in parallel has the same stage gain as two. Therefore, with the same radio driving the amp we should not expect an increase in power. If it does show more power, it usually means the original tubes were weak and would not support full emissions.
If your power supply is weak, adding more tubes can actually reduce the power output. Each tube is going to use more bias and filament current before it even begins to produce RF. If that cause the voltages to sag from lack of current, power output will likely drop off too. Power does not come from the tubes. The tubes simply have to handle the power being passed through them.
If your power supply is weak, adding more tubes can actually reduce the power output. Each tube is going to use more bias and filament current before it even begins to produce RF. If that cause the voltages to sag from lack of current, power output will likely drop off too. Power does not come from the tubes. The tubes simply have to handle the power being passed through them.
Shockwave,
I just woke up and am still having the first cup of coffee.
If the tube is not the component in the amplifier design that is responsible for amplifying the input signal then just what component is responsible.
If I recall ALL amplifier designs the rf has to be input to the tube, the output comes from the tube.
It is the design of the associated circuitry that determines the efficiency of the tube.
Agreed, the HV PS and any bias PS should be designed around the valve.
6jg6a requires 6.3 volts at 1.6 amp filament voltage.
6lq6 requires 6.3 volts at 2.3 amps.
With this info I would be concerned if thae two transformers have enough amperage for the filaments.
Maybe the filament voltage is 12.6 and just wire two tubes in series.
Regardless it is a waste to have a two stage amplifier with four tubes going into four more tubes of the same type.
I repaired the amp and I only seen 450 watts with a small amount of drive. I think the bench radio has a 3 watt dead key with 12 watts pep output.
Owner said he has some galaxy radio that swings 45 watts.
He picked up the amp and I wished him best of luck and not to bring it back when he blows up the NOS tubes he paid an arm and a leg for to get it back working.
6jg6a requires 6.3 volts at 1.6 amp filament voltage.
6lq6 requires 6.3 volts at 2.3 amps.
With this info I would be concerned if thae two transformers have enough amperage for the filaments.
Maybe the filament voltage is 12.6 and just wire two tubes in series.
Regardless it is a waste to have a two stage amplifier with four tubes going into four more tubes of the same type.
I repaired the amp and I only seen 450 watts with a small amount of drive. I think the bench radio has a 3 watt dead key with 12 watts pep output.
Owner said he has some galaxy radio that swings 45 watts.
He picked up the amp and I wished him best of luck and not to bring it back when he blows up the NOS tubes he paid an arm and a leg for to get it back working.
The tube is the active component between the power supply and tank circuit. It is not the source of the power. Output power depends on what's available from the power supply and how hard the amp is driven. The resonant load impedance of the tubes is what determines how much current will be drawn from the supply. That impedance is dependant on drive power more than the number of tubes.
Doubling the number of tubes does not double the current drain or make a significant difference in output since it has little effect on resonant load impedance on the output of the amp. Doubling the drive on the other hand can cut the resonant load impedance by approximately half and double the output power. The tubes have to handle the power but the source is the power supply.
