thomasweissbach
Amazing build
You should put the photos on Photo Gallery would be a change from all the 6v6 and EL84 amps.
Amazing build
You should put the photos on Photo Gallery would be a change from all the 6v6 and EL84 amps.
Wow!
Looks much better than Gates transmitter!
Looks much better than Gates transmitter!
An externally hosted image should be here but it was not working when we last tested it.
I am currently struggling with my GU-46 amp. The amp is built as SE amp. The schematic in thread 148 the latest.
The amp blows its grid 2 resistors (100R/3W). Respectively the resistor to reduce the grid 2 voltage after the PSU wich seems to be approx 680V (Not measured due to missing HV Meter >600V), i could not use the intended voltage controller due to the high current drawn by the grid 2 (thread 119).
Facts:
- approx. 1300V Anode (not measured, but approx, since halve wave is approx 650-680V)
- g1: 0V, grid 1 bias: -63V
- grid 2: 530V (measured in front of the 100R/5W grid 2 resistor. The 530V appears after reduction with a 3k3 resistor /25W which blows after 50s, reducing probably 150V under these conditions - which from calculative view seems completely ridiculous)
Grid 2 seems to draw >160mA under these conditions, since the 100R grid resistor blows in the 3W Version, with a 100R 5W it works.
But then PSU output for grid 2 should be in the kV range (with the 3k3ohm resistor in the PSU, 166mA would give 530V drop, which would mean there is full B+ on the half wave…)
The PSU itself workes as intended, for the supply of B1 and B2 since they are well in the range.
Any ideas?
Thanks for your support
The amp blows its grid 2 resistors (100R/3W). Respectively the resistor to reduce the grid 2 voltage after the PSU wich seems to be approx 680V (Not measured due to missing HV Meter >600V), i could not use the intended voltage controller due to the high current drawn by the grid 2 (thread 119).
Facts:
- approx. 1300V Anode (not measured, but approx, since halve wave is approx 650-680V)
- g1: 0V, grid 1 bias: -63V
- grid 2: 530V (measured in front of the 100R/5W grid 2 resistor. The 530V appears after reduction with a 3k3 resistor /25W which blows after 50s, reducing probably 150V under these conditions - which from calculative view seems completely ridiculous)
Grid 2 seems to draw >160mA under these conditions, since the 100R grid resistor blows in the 3W Version, with a 100R 5W it works.
But then PSU output for grid 2 should be in the kV range (with the 3k3ohm resistor in the PSU, 166mA would give 530V drop, which would mean there is full B+ on the half wave…)
The PSU itself workes as intended, for the supply of B1 and B2 since they are well in the range.
Any ideas?
Thanks for your support
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I've been testing the GU46 in SE, both in pentode and triode. I used a 5k transformer, and it is perfect for triode mode but too low for pentode. Not sure how it would turn out in PP, though!
I use a voltage doubler for plate voltage and works perfect, also allows for easier cap voltage. I use a 230 to 425, 475, 525, 600V 2500VA so I can choose the plate voltage.
In the schematic you show you need to use a cap at the gate of the 6SN7 as you are not referencing the gate to ground (the 1M resistor is connected to a point that might have some voltage).
Hi palmas, which shematic do you mean? I am currently using a 12hg7 for input, see the latest shematic. I think you refer to an earlier shematic, the hand drawn one, that i made to open up the discussion at the time. The latest shematic in this thread shows the last version of the amp, which works pretty well. still room for improvement maybe.
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I think there's a mistake in the "GU-46 SE final" schematic in post #148. In it there's a 470uF capacitor between the grid stopper of g1 of the GU-46 and ground, which, if it would realy be there, shunts all signal to ground. I guess that the grid resistor is missing in the schematic (between the grid stopper and the 470uF capacitor).
Hey palmas, the pentode can be adjusted to fit any load( nearly) by changing the g2 voltage. This sets the envelope the load line drives through. Am thinking if 5k SE is good for triode, then it shall be fine for pentode, maybe with a small adjustment to the g2 votlage.
I have a set of sweep tubes running 10k a-a, and another running 5k a-a, and the basic difference is a change to the g2 voltage.
cheers,
Douglas
I have a set of sweep tubes running 10k a-a, and another running 5k a-a, and the basic difference is a change to the g2 voltage.
cheers,
Douglas
Hi,
triode mode 1300V, so I send 1300V dc down the shield, I guess not very healthy. In pentode I used 650V for the shield.
I never worked with power pentodes, just triodes and triode strapped pentodes, so I can use all the help you can give me.
Will lowering the shielding voltage would reduce the impedance? Can you suggest a shield voltage for the GU46 so I get similar response as in triode?
Thanks
triode mode 1300V, so I send 1300V dc down the shield, I guess not very healthy. In pentode I used 650V for the shield.
I never worked with power pentodes, just triodes and triode strapped pentodes, so I can use all the help you can give me.
Will lowering the shielding voltage would reduce the impedance? Can you suggest a shield voltage for the GU46 so I get similar response as in triode?
Thanks
A pentode is never going to have the low plate resistance of a triode. Adjusting g2 voltage to set the operating envelope the load line traverses is quite another story. You would not want the load line hitting the diode line at -10V, yes? Nor would you wanting it crossingV_g1=0V some hundreds of volts before in needs to.
cheers,
Douglas
cheers,
Douglas
