1KV DC is not that bad. I've been hit with it (accidentally) in my 211 mono blocks and lived. Granted, only one hand was the entry and exit point. Sure did wake me up though.
It is amazing how many people "fear" 1KV in a tube amp, but will work around 240VAC all day long. I've been hit with that too and prefer 1KV DC.
well ..... I worked on my first insane 800V EL34 PA amp when I had 20 yrs .
then I was even more stupid than today ........ but I knew about "hand behind back " rule
later I worked on various things ..... 4KV tube transmitters - without fear ;
but always with respect .
and that respect goes from mileage , nothing else
then I was even more stupid than today ........ but I knew about "hand behind back " rule
later I worked on various things ..... 4KV tube transmitters - without fear ;
but always with respect .
and that respect goes from mileage , nothing else
those Tango transformers are a real prize.
much (electro) porn here -
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I met up with Stuart today. He figured out that the amp uses 845 tubes. He also figured the smaller tubes as well, 2 6CG7 and 1 12AT7 or 12AU7.
Does anybody have some 845 tubes for sale? I am looking for something inexpensive.
Does anybody have some 845 tubes for sale? I am looking for something inexpensive.
I am still confused about whether my amp uses 845 or 211.
With out any tubes installed the grid voltage is -340 VDC.
With only the 3 driver tubes installed, they are all lit up, The grid voltage can be adjust from +27 VDC to -70 VDC.
Do you guys know whether the grid voltage will change once I install the 845 or 211?
I already ordered the 845. What happens if I put the 845 in my amp and the grid voltage is only at -70 VDC?
With out any tubes installed the grid voltage is -340 VDC.
With only the 3 driver tubes installed, they are all lit up, The grid voltage can be adjust from +27 VDC to -70 VDC.
Do you guys know whether the grid voltage will change once I install the 845 or 211?
I already ordered the 845. What happens if I put the 845 in my amp and the grid voltage is only at -70 VDC?
I thought it was determined that the amp used 845's?
Depending on the plate voltage, you may be underbiased. On my Chinese 845 amp, the plate voltage is about 810VDC and the bias (fixed) is about -104VDC.
Yes, unless the grid voltage changes with the power tubes installed, the amp uses 211. -60 to -70 VDC grid voltage is for 211.
The plate voltage with out the power tube is 1098 VDC
I just learned a way to measure the plate current without opening the plate circuit.
I learned that I could measure the plate current by:
-1st measure the resistance between the center tap and the plate tap on the OPT primary with the amp OFF.
-2nd measure the voltage drop of the OPT (putting the negative probe on the center (50%) tap and the positive probe on the plate (finish) tap of the OPT primary).
-3rd divide the voltage drop by the resistance to get the current.
What do you guys think of this method? How accurate is this method?
It seems like the most accurate way is to open the plate circuit and put the meter in series with the plate circuit to measure the current.
I learned that I could measure the plate current by:
-1st measure the resistance between the center tap and the plate tap on the OPT primary with the amp OFF.
-2nd measure the voltage drop of the OPT (putting the negative probe on the center (50%) tap and the positive probe on the plate (finish) tap of the OPT primary).
-3rd divide the voltage drop by the resistance to get the current.
What do you guys think of this method? How accurate is this method?
It seems like the most accurate way is to open the plate circuit and put the meter in series with the plate circuit to measure the current.
I still think that Stuart (SY) is right.
The range of bias WITH the driver tubes and WITHOUT the power tube is +27 to -70. That range has to be off because neither 845 nor 211 operates in the positive grid voltage. I think that the grid voltage will change once the power tube is installed.
The range of bias WITH the driver tubes and WITHOUT the power tube is +27 to -70. That range has to be off because neither 845 nor 211 operates in the positive grid voltage. I think that the grid voltage will change once the power tube is installed.
You can't accurately measure plate current unless an output tube is in circuit.
Based on your latest information, it would seem the plate voltage and bias are set-up for a 211 tube. I run my 211 amp with about 1080VDC on the plate and -60 bias (cathode bias).
Based on your latest information, it would seem the plate voltage and bias are set-up for a 211 tube. I run my 211 amp with about 1080VDC on the plate and -60 bias (cathode bias).
The real issue is you can't measure plate current that way. The grid bias voltage controls the current through the tube. I don't think you are measuring something correctly if you can adjust the grid bias voltage positive. If the voltage really is -70, then its too low for an 845. Maybe you could get away with -70 if you kept the plate voltage low... But anyhow the driver tubes should have no effect at all on the bias voltage.
The only way to answer any of these questions is to draw out a schematic. The pictures you posted so far look like a hobbyist amp. For all you know this could be a project that never did work.
Interesting. In my amp, the driver tubes do make a difference. However, this could be due to the fact that I have been measuring the grid voltage without the power tube.
If you look at the drawing, the R and L power tube grid voltage wire go to pin 3 and 8 respectively of one of the small socket.
Just to be clear, the bias voltage is the grid voltage right?
I have been measuring the grid voltage by putting the negative probe on the chassis and the positive on the grid of the 845/211 socket.
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