MY one and only ORANGE Super Bass JMP 100 Mk 2

chilipeppermaniac said:
The amp does work now and makes music with the new tubes in. So now I plan to continue to improve the amp with new reliable filter caps, and make it safer and more reliable than how I received it. Then a few fixes of some half shortcut type repairs and undoing a mod and cleaning up a few sloppy bits and she should be ready to rock.
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YEE HAW... :woohoo:
 
chilipeppermaniac said:
OK Sysco, Your info is SIGNIFICANT. THIS is a very important detail I must log into my memory bank.
WHEN calculating the numbers to bias an amp, do we need to use the higher value voltages or the lower ones with the power tubes installed?
Also noted,,,,,,,, the difference between a PIN 5 voltage between my 6550 ones and an EL34 one like in the chart.
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I’ve always run my bias calculations based on “tubes in place” voltage readings.
 
chilipeppermaniac said:
WHEN calculating the numbers to bias an amp, do we need to use the higher value voltages or the lower ones with the power tubes installed?
Click to expand...
Higher. Pin 3 of the power tubes connects to the tubes plates. This is where the B+ is measured.

6550 tubes are rated for 36 watts of plate dissipation (EL34's are rated at 25 watts).
A nice bias range is 50% to 70% of the tubes rate dissipation.
50% to 70% of 35 watts equals to 18 watts to 25 watts.

Now you're going to take the 18-watt-minimum to the 25-watt-maximum and break them down to millivolts. 18(watts) divided by your B+ will give you the minimum (50%) value you'll be looking for on your meter. 25(watts) divided by the amp's B+ will be your maximum (70%) value.
If your measured B+, for example, is 450vdc:
18 / 450 = .04 = 40 millivolts
25 / 450 = .05 = 55 millivolts
The range you would want to be in is: 40mV to 55mV

It's all going to depend on after you install the fresh caps and fresh tubes. Then you'll get the proper B+ measurements for a proper bias.
 
chilipeppermaniac said:
WHEN calculating the numbers to bias an amp, do we need to use the higher value voltages or the lower ones with the power tubes installed?
Click to expand...
.....and this is another “I misread his question” thing, I guess....

Thatbastarddon said:
I’ve always run my bias calculations based on “tubes in place” voltage readings.
Click to expand...

....and took for granted that “plate voltage” (pin 3) would be used in the equation, as it should be.

syscokid said:
Higher. Pin 3 of the power tubes connects to the tubes plates. This is where the B+ is measured.

6550 tubes are rated for 36 watts of plate dissipation (EL34's are rated at 25 watts).
A nice bias range is 50% to 70% of the tubes rate dissipation.
50% to 70% of 35 watts equals to 18 watts to 25 watts.

Now you're going to take the 18-watt-minimum to the 25-watt-maximum and break them down to millivolts. 18(watts) divided by your B+ will give you the minimum (50%) value you'll be looking for on your meter. 25(watts) divided by the amp's B+ will be your maximum (70%) value.
If your measured B+, for example, is 450vdc:
18 / 450 = .04 = 40 millivolts
25 / 450 = .05 = 55 millivolts
The range you would want to be in is: 40mV to 55mV

It's all going to depend on after you install the fresh caps and fresh tubes. Then you'll get the proper B+ measurements for a proper bias.
Click to expand...

This ^^^^^^^^^^^^^ is a nice, concise answer! With the math even!
 
Thanks both of you. I got 446vdc with my new Tubes in prior to Sysco mentioning difference with or without tubes in. I used the 6550c spec sheet from Svetlana that shows 35 plate dissipation. I based things off 35x 60% =21 for the math. Got .047 from Center tap to pin 3. Multiplied .047x2 for each pair. .094 x15.9 and .094 x 14.6. after taking readings on each side of the output transformer, to get bias setting of -1.4946 for v4 and v5 and - 1.3724 for v6 n v7. That is it as best as I can remember and type in my smartphone.

If I missed something, let me know. I don't do as well on that little screen vs my 17 inch Laptop one.
 
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chilipeppermaniac said:
I used the 6550c spec sheet from Svetlana that shows 35 plate dissipation.
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Yeah, I need to correct something about what I said about the specs on those 6550's. The 6550C is rated for 35 watts... no problem here. But, I just found that there's a difference between a 6550, 6550A, and a 6550C. The C is rated for 35w, but the other two are rated for 42w! That will change the calculations depending which variant of 6550 you have, or will have.
 
chilipeppermaniac said:
It is now,,,, thanks to all my friends here, and to some who aren't.
Also want to give a big shout out to a really nice guy from ebay who I just met Friday. I found him on ebay and he is local to me. He sells tubes and tests every one on his modern tester and provides the readings on each tube box. He had a set of 5 Svetlana 6550's that I offered to buy from him without knowing if the 3 Ruby and one Sovtek ones that were in my amp were any good or not. Having asked if he'd be open to allowing a local pickup and even to test my tubes for me, I was in luck when he said yes and the testing showed a dangerously bad tube and only one good 6550 out of 4, plus a bad 12ax7 in the V3 Phase Inverter position.

Now, from my visual, Multimeter testing of Voltages, readings of the Output transformer, Resistor tests, plus running the amp with only the preamp tubes in and not blowing fuses, the signs pointed to the wisdom of suspecting a tube issue. The eventual testing confirmed this.
The amp does work now and makes music with the new tubes in. So now I plan to continue to improve the amp with new reliable filter caps, and make it safer and more reliable than how I received it. Then a few fixes of some half shortcut type repairs and undoing a mod and cleaning up a few sloppy bits and she should be ready to rock.
Click to expand...
That's awesome! Such a cool amp!
 
Hey when I see Orange in the heading , I thought Orange amps, this is false advertising, you will hear from my Lawyer Chilli.... Where's Ray.
 
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