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Balance and bias voltage unstable

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#65
yep, wish this looked better, this is connected to the output, c2 dead flat. So at least we know it is good up to the plate. So for the novice brain (mine) the plate (anode) will begin the flow across the grid to the cathode? And is that were it passes to the next stage, from the cathode (conventional current flow - anode to cathode)?

I guess I am just trying to understand the signal flow in these 7247 tubes, I know they are dual triode but dissimilar, and I know we just checked one side...
 

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#67
okay I guess by output I mean, where the signal comes into the 7247 and where it leaves. I am missing some fundamentals here for sure. I thought in conventional current from the flow will be from anode to cathode. So with the 7247, trying to understand I guess the signal path. I will have to study the schematic here for a sec. To me it looks like from the schematic the signal leaves the, yep, plate (anode) like you said and it goes across the pots for bass and treble and then back to the second triode's grid in the 7247 and i guess the same happens again.
 
#68
In post #63, you measured signals at both plates. But the scope sees no waveform at one plate?

If you connect both probes to the same place, like one output,
do you see the same waveforms on each channel on the scope?
Are you sure the scope is working in both channels?
 
#70
Connect the scope at the exact same place as the DVM probe.
It should be on AC coupling to block any DC present.
You have to measure the same thing if you expect to see the same thing.
If your scope works, you don't really need to use the DVM at all.
 
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#72
No, you've already measured that. Go on the the following circuit block, after the tone controls.
The circuit blocks are all in series. You go forward from the first block to the second block to the third block, etc.

A bad measurement means the previous circuit block is bad.
Obviously one circuit block is bad, since there's no signal at the main output, after all the blocks.
 
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#74
rayma said:
No, you've already measured that. Go on the the following circuit block, after the tone controls.
The circuit blocks are all in series. You go forward from the first block to the second block to the third block, etc.

A bad measurement means the previous circuit block is bad.
Obviously one circuit block is bad, since there's no signal at the main output, after all the blocks.
Click to expand...
okay I will move along that signal path and report back but in theory everything you are saying makes perfect sense, let me just see if I can put it to the test using my brain and find it! Thank you again so much for your time. Let me check the other end of the 7247.
 
#75
Ok, you don't need to adjust the level control any more, that was only for testing the level control tracking.
Just set the level control to give a reasonable level, maybe halfway up, and leave it there.
Only check the signals at the plates. Some of the grids are virtual grounds, and are not data.

You do have to say at which node you are measuring, or the data are meaningless.
This is called "signal tracing", for obvious reasons.
 
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#76
okay sounds good, I appreciate that. So like I saw in the schematic, it looks like signal goes through the bass and treble controls and then back into the grid of the second side of the 7247 and then leaves the anode, would this be the next logical place to repeat?
 
#77
Yes, at the plate (anode is for diodes).
The tone block grid is a virtual ground, and so a measurement is not needed.
This is because it is a feedback tone circuit.

You start at the input plate, and go forward, measuring at each plate, until the signal is gone.
Then the problem is just before or at that node.
 
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