So, I just recapped, new tubed and adjusted balance and bias. Also did 2 dexoit sessions on the pins and sockets of tubes and all wipers and switches. At the 0 volume there is this white noiseish coming through the speakers and as I turn up the volume and at max (with nothing playing) it actually goes mostly away but is very faint. When music is playing I cannot hear it, just when there is no signal. Inserting shirted RCA plugs has no affect neither does changing to any other inputs or selections on the Stereo, mono, L, R.
It is a beautiful amp, very pleased with how it has turned out so far and would love to determine if this is normal (doubt it) or there are some usual players I can look at.
More cleaning? Maybe check other components along signal path? Ground? Any suggestions, thank you!
It is a beautiful amp, very pleased with how it has turned out so far and would love to determine if this is normal (doubt it) or there are some usual players I can look at.
More cleaning? Maybe check other components along signal path? Ground? Any suggestions, thank you!
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It may be a thing. After a bit of googling I fell over this: https://audiokarma.org/forums/index...restore-and-mods.1034313/page-2#post-16505009
But from what I've read it may be worth persevering.
But from what I've read it may be worth persevering.
I have already encountered a similar problem once and it was just the potentiometer stop which was worn/deformed with time and use, the skate was leaving the carbon track. It's worth checking out.
Can you post the schematic?
In general if the volume pot grounds the input, there is still a chance that the ground at the pot is not exactly the same as the ground at the amplifier, so you really just say to the amp: 'Amplify the difference between this ground and that one'.
To elminate this possibility, I suggest you short out the input to the power amp (on the PCB), so the input signal is exactly 0V, and see if the noise is still there. Perhaps disconnect the input wire too, to isolate it completely.
I doubt it's the caps TBH, if stereo, are both channels the same?
These are all great suggestions, @huggygood , @Globulator , @StevenCrook
I have nothing to do today and will put this guy back on the bench and see what I can come up with and post back!
Thank you!
I have nothing to do today and will put this guy back on the bench and see what I can come up with and post back!
Thank you!
would you consider taking it out and apart? The odd thing is how it actually almost goes away when the volume pot is increased.
I should mention that I did use new 7247s (JJ electronics) becuase I could not identify the ones that were in there, all markings were gone. Reused the phase inverter tubes and the 12ax7s, rectifier tube, but also installed NOS matching quad RCA 7591a tubes, all tubes tested good on a go no go tester, maybe I should look closer into the tubes, the ones that just tested good on go no go, worth noting i suppose.
Also, wanted to point out, I didn't do any mods, I left everything intact as far as how the amp was originally designed and wired. Here is a photo of my board after the work I did. There were some carbon comps that I replaced with Yaego Metal Film if there were near a cap I was replacing, or, if they looked like they had gotten hot. Also, i am pretty anal when it comes to values so I matched all cap values to what was being removed. The only thing that changed were voltage ratings and I only replaced with higher values.
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Could you elaborate a little? In my service manual V8 is the Ch2 power output tube and V2 is the Ch2 preamp tube.
This is a characteristic of poor design choices EICO made - there's just too much gain after the volume control. And the feedback around the line amplifier stage is grounded when the volume control is at zero, which increases the stage gain to maximum. The modifications suggested at http://tronola.com/ will help, a further reduction in gain as suggested in the link above will help more.
That link above is great, I definitely want to keep it as original as possible but the mods they do certainly do make improvements, makes sense from reading it.
As in the tronola mod document:
"Adding R33A stabilizes the gain of the stage at low Level-control settings, reducing hiss and hum."
That is what I meant for a grid stopper.
"Adding R33A stabilizes the gain of the stage at low Level-control settings, reducing hiss and hum."
That is what I meant for a grid stopper.
Honestly, I found the fault by chance, I just unsoldered the wires and soldered a temporary 500k potentiometer (in the air) and the white noise disappeared.
Tom above hits the nail on the head, the volume setting affects the nagative feedback - ironically the wrong way around... so the gain moves from a controlled amount to the maximum tube gain at volume zero: so perhaps the max tube gain per channel is not quite equal (for that tube).