Thank you for this glimpse into an old Lahey. Even though aspects of the construction techniques were disappointing, the sound of these was astounding back in the day. I'm unlikely to ever see the real thing, so this will have to do...
Yet another thing I agree with you on. If you need a resistor between the cathode and ground to measure your bias in a fixed bias amp, you don’t need to be inside your amplifier. Get a bias probe. I have absolutely nothing against them and they are accurate enough for musical instrument amplifiers.
Great work overall in this amp and the many other amps you have worked on :-) You mention reliability a lot. I´m holding my breath to see how you will go about this aspect with EL34s running at close to 600 Volts on their screen grids in these old Laneys.
Can you explain more about why you don't bias power tubes using a 1 ohm resistor from cathode to ground because the measured bias current has screen current? I'm not understanding why this is considered a bad biasing measurement.
Do you suppose there's a purpose for the 10 ohm resistor, other than just measuring the cumulative cathode current? That value is about ten times what should be necessary for that purpose. Also, it would make more sense to provide the ability to measure the current independently on each cathode. Making it obvious if the tubes were poorly matched. I have to wonder if the intention was also to mitigate the effects of tubes that were slightly mismatched.
Thank you for this glimpse into an old Lahey. Even though aspects of the construction techniques were disappointing, the sound of these was astounding back in the day. I'm unlikely to ever see the real thing, so this will have to do...
Yet another thing I agree with you on. If you need a resistor between the cathode and ground to measure your bias in a fixed bias amp, you don’t need to be inside your amplifier. Get a bias probe. I have absolutely nothing against them and they are accurate enough for musical instrument amplifiers.
At the end of the day other then reliably the tone that comes out of the speaker is what’s important. But neatness counts
Thanks again! Happy New Year as well. My favorite channel on RUclips.
Thanks so much!
Great work overall in this amp and the many other amps you have worked on :-) You mention reliability a lot. I´m holding my breath to see how you will go about this aspect with EL34s running at close to 600 Volts on their screen grids in these old Laneys.
I use the 1 ohm resistor to ground , didnt think it was wrong
It's not wrong per se, just not accurate for a tech and most amateurs have no business poking around inside a live amp. So I don't see the point.
Can you explain more about why you don't bias power tubes using a 1 ohm resistor from cathode to ground because the measured bias current has screen current? I'm not understanding why this is considered a bad biasing measurement.
Do you suppose there's a purpose for the 10 ohm resistor, other than just measuring the cumulative cathode current? That value is about ten times what should be necessary for that purpose. Also, it would make more sense to provide the ability to measure the current independently on each cathode. Making it obvious if the tubes were poorly matched.
I have to wonder if the intention was also to mitigate the effects of tubes that were slightly mismatched.
IKR? Yet it's also too small a value to do anything of note regarding bias.
@@PsionicAudio Definitely a head-scratcher.
How did you wind up getting the knob set screws to loosen? Were they just overtightened and stuck in place?
Hours of soaking with WD40. Combination of rust and some kind of glue.