okay everything is cleaned and I swapped the pre-amp and tone tubes, same with the phase inverter tubes. Will check again now and report back.
The cleaning may have helped! I will let it get warm for maybe 30 min and try again because i do remember before it got worse with temp and time but let's see. Will report back.
We'll see. If the problem is really a bad resistor, it would have cooled down.
Try biasing the output tubes while you're waiting.
Try biasing the output tubes while you're waiting.
okay, yep, it has been running, It says in the manual to make sure the balance is set first, that is good and now I moved to the bias. Both channels are bouncing between about 0.382 and 0.389 which is MUCH better than before!
Question, would it be considered good practice to change the bias resistors for good quality Vishay ones, as a matter of maintenance? Like people do with recap jobs? Or just leave them if they are fine.
Let's leave things as they are now, until you've used it for a while.
This way you will know that any further glitches are from pre-existing problems, not from new work.
Later on, better resistors are good.
This way you will know that any further glitches are from pre-existing problems, not from new work.
Later on, better resistors are good.
Okay thank you! And in this case for work like this, after you set the amp up, would there be other standard things you would do like put a signal in, check the output on a scope? Check the power out and clipping? Just new to this and wanted to get an idea of standard procedural "check" type things when a service is done.
Thank you!
Thank you!
Once things seem stable, you could input a low level (~0.1V) square wave input to check general operation.
This amp should have a good square wave from 100Hz to 10kHz.
I'm not a fan of full power testing for tube amps. But do take pains to get the output tube DC balance correct.
Use a 1kHz triangle input to both channels to check for channel balance and general volume control behavior.
This amp should have a good square wave from 100Hz to 10kHz.
I'm not a fan of full power testing for tube amps. But do take pains to get the output tube DC balance correct.
Use a 1kHz triangle input to both channels to check for channel balance and general volume control behavior.
Very cool, okay so:
Square wave to check general operation, for this test you are just looking that the square wave remains square or are you looking at changes in amplitude too?
Triangle wave into both channels for balance and volume, same here, looking for remaining triangle or also amplitude too?
Will research this more and perform, thank you!
Square wave to check general operation, for this test you are just looking that the square wave remains square or are you looking at changes in amplitude too?
Triangle wave into both channels for balance and volume, same here, looking for remaining triangle or also amplitude too?
Will research this more and perform, thank you!
Remember to keep amplitudes low, and always use a resistor 8 ohm load.
Never run tube amplifiers without a load. Output voltage should be around 2 - 3V to avoid undue stress.
Never run tube amplifiers without a load. Output voltage should be around 2 - 3V to avoid undue stress.
You can use interdental brushes for cleaning tube sockets. I dip them in a little contact cleaner and brush the contact. Seems to work well. Inserting the tube a couple of times also helps.
https://www.amazon.com/GUM-Proxabru...hvlocphy=&hvtargid=pla-4584276318460623&psc=1
https://www.amazon.com/GUM-Proxabru...hvlocphy=&hvtargid=pla-4584276318460623&psc=1
0.389 / 0.382 = about a 2% difference
If the mains power changes from 120VAC to 122.4VAC, that is also a 2% change.
That will cause the bias voltage to change by 2% too.
Steady current that does not change more than 2%?
Lots of things can cause that.
Again, power mains voltage changes enter into the equation because the B+ voltage changes along with power mains voltage changes:
Those 7591 tubes are operated in Beam Power mode.
If the B+ changes, then the screen voltage changes, and that will change the plate current.
Tube current with Self bias, is generally more steady than tube current with fixed adjustable bias.
If the mains power changes from 120VAC to 122.4VAC, that is also a 2% change.
That will cause the bias voltage to change by 2% too.
Steady current that does not change more than 2%?
Lots of things can cause that.
Again, power mains voltage changes enter into the equation because the B+ voltage changes along with power mains voltage changes:
Those 7591 tubes are operated in Beam Power mode.
If the B+ changes, then the screen voltage changes, and that will change the plate current.
Tube current with Self bias, is generally more steady than tube current with fixed adjustable bias.
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Hey everyone, one quick follow up. I connected the amp to some no value to me speakers (just in case) and first thing I noticed is there is static noise at low and slightly higher volume. Next, balance does not work. Third, the loudness switch, when put ON, almost kills the sound, acts more like a mute.
I was going to approach each of these obviously separately but was curious if anyone could put an order of operations on them or just pick one a dig in.
Thank you!
I was going to approach each of these obviously separately but was curious if anyone could put an order of operations on them or just pick one a dig in.
Thank you!
Go through and clean and exercise all the switches and pots. Often they are seldom used and corrode.
Clean the rest of the tube pins and sockets too. Check for bad looking solder joints.
Clean the rest of the tube pins and sockets too. Check for bad looking solder joints.