Ordinary Carbon Film works as grid stoper resistor and probably Metal Film / Mox - I had the oscillation beacuse grid stoper was not near enough the socket pin - as soon as i have changed the position to the underside on the socket pin it stoped ( this was with 6S3P-EV tubes ).
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I found a recent data sheet on metal film resistors and the inductance was 10nH. Very low resistances were said to be higher but you wouldn’t want a 10 ohm grid stopper anyhow. For the record I used a calculator and one inch of 30awg wire is 26nH.
IMHO metal film is fine for grid stoppers.
IMHO metal film is fine for grid stoppers.
The late DF96 once wrote on this forum that the parasitic inductance of grid stoppers doesn't matter. It took me some time to realize he was right as long as the grid stopper resistance exceeds the absolute value of the negative input resistance of the amplifier stage that requires stopping. I didn't get the chance to reply to him that I finally understood his remark, as he had deceased by then.
I was "told" that since no current flows through that grid resistor there was no noise generated. Is that correct? Any downside to replacing the CC grid resistors with MF ones? I also used new Allen Bradley CC resistors for the triode strapping of the D3A. Is that appropriate use?
The grid stoppers are truly right against the pins of the sockets. Couldn't be closer.
In principle, with no current flowing through it, a carbon composition resistor produces just as little noise as any other type of resistor of the same value at the same temperature with no current flowing through it. If it didn't, it would violate the second law of thermodynamics.
Nonetheless, you managed to solve your noise issue once by replacing two resistors. Presumably one of them had failed and had become a rotten contact rather than a resistor, and I suspect it was the carbon composition resistor. Hence my suggestion to replace it with carbon or metal film.
An easy experiment to do would be to bypass the string of LEDs in the cathode circuit of the 2nd stage with a good sized 'lytic to see if that does anything. LEDs are normally not noisy, so adding the cap may have no effect.
Hi WnterMute2
Are those LED bias? In any case, try this: Replace them with a resistor of appropriate value and see if the hiss goes away.
I had both LED's and Zeners that hissed. Start with the LED you have on the input tube. That one will be easy to swap out.
Since that experience I went back to regular fool-proof film resistors. Metal films are nice. If you want, by-pass them with a cap but you should check (ie. measure) how this affects your RIAA - ideally with some inverse RIAA network and frequency sweep.
I doubt it's the gyrator.
Best regards
Ian
Are those LED bias? In any case, try this: Replace them with a resistor of appropriate value and see if the hiss goes away.
I had both LED's and Zeners that hissed. Start with the LED you have on the input tube. That one will be easy to swap out.
Since that experience I went back to regular fool-proof film resistors. Metal films are nice. If you want, by-pass them with a cap but you should check (ie. measure) how this affects your RIAA - ideally with some inverse RIAA network and frequency sweep.
I doubt it's the gyrator.
Best regards
Ian
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Very pretty phono btw. Put shields on your tubes/valves if you would like it to be even quieter.
Oh one more thing. I see you use this really cute little toggle switch to go from stereo to mono? I would by-pass that thing after fixing the hiss issue. I bet it will sound better.
Oh one more thing. I see you use this really cute little toggle switch to go from stereo to mono? I would by-pass that thing after fixing the hiss issue. I bet it will sound better.
Some of the larger Jumbo based AKA 50-watter pinch base valves were made with internal inductors in series with the G1s if intended for audio use. They probably had to just accept a fair amount of inductance in the internal filament (also their cathodes) leads and to expect a lot more inductance in external "cathode" circuits.
A lot of common audio circuits could use resistive cathode stops, especially followers with their high feedback level and often capacitive loading at higher frequencies. The valve's cathode output is inductive, and gets excited seeing a capacitive load - just can't help themselves.
All good fortune,
Chris
A lot of common audio circuits could use resistive cathode stops, especially followers with their high feedback level and often capacitive loading at higher frequencies. The valve's cathode output is inductive, and gets excited seeing a capacitive load - just can't help themselves.
All good fortune,
Chris
Yes, noise from LEDs can increase when they are exposed to modern LED lighting.
LEDs work in reverse, to some degree. Put some soft black tubing over them.
I had some cheap LED's that were fantastic and did not hiss. But the voltage drops were inconsistent. Sadly I could not source them anymore, and had to source some slightly more expensive LED's - these had very nice voltage drop but at least 25% of them hissed - and not all at the start - sometimes after a few hours of use or even after a week of use. None were exposed to LED lighting.
Don't get me started on Zeners. As much as I respect Morgan Jones, I will never build another "statistical regulator".
Don't get me started on Zeners. As much as I respect Morgan Jones, I will never build another "statistical regulator".
You can also "modulate" 1N4148's with fluorescent lighting. Discussed in an Analog Devices application note.
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Sorry to ask such a novice question but how do I determine what resistor value to pick for the 5687 as well as the D3A? Do I need a bypass cap for those?