Start my LA-2A BUILD

[ZHOUJUN]

I gathered some accessories and started the building process of my LA2A,I have a friend's original LA-2A from the 60's which might save me some time.

 

[thomasdf]

Curious to see how it turns out. Maybe consider using metal film resistors in some specific places ? Plate resistors for instance ?

 

[ZHOUJUN]

Curious to see how it turns out. Maybe consider using metal film resistors in some specific places ? Plate resistors for instance ?

Thank you, I will try it, When I use these carbon core resistors, I also want to get as close to the original electrical performance as possible, I think the special tone of LA2A may be produced by these old-fashioned resistors,I selected a large number of carbon core resistors, and they The accuracy of most is not good, but they are very cheap and cost me a lot of time to get the accuracy to within 3%.

 

[ZHOUJUN]

To further reduce interference from the tubes and transformer on the circuit board, I added a layer of nickel foil to the back of the case that was left over from wrapping the transformer.

 

[beatnik]

where did you get those turret boards ? They seem nice and sturdy

 

[soapfoot]

Great selection of transformers!

 

[GrannyGremlin]

Thank you, I will try it, When I use these carbon core resistors, I also want to get as close to the original electrical performance as possible, I think the special tone of LA2A may be produced by these old-fashioned resistors,I selected a large number of carbon core resistors, and they The accuracy of most is not good, but they are very cheap and cost me a lot of time to get the accuracy to within 3%.

I think the lore that carbon comp resistors sound gnarlier is mostly BS (and the part that isn't is mostly due to bad things), what they are is less reliable, with wider tolerance as noted, and bigger. They are also more susceptible to heat damage (important in a tube device) and can drift in value significantly over time. They also cost double, sometimes triple what 1% metal films do. The only really good reason to use them is when you need something with better pulse endurance (not the case here) or when they are dual purpose as a fuse (like the screen resistors on the 6550s in Sunn amps - but even then I replaced those, which died from overheating BTW, with metal oxide - just don't up the wattage like some folks recomend online because it's better for the resistor to fail than to blow the tube - NOS 6550s be expensive).

 

[soapfoot]

It can be difficult to prove a negative, and there is at least some empirical evidence that the high voltage coefficient of carbon comp resistors can manifest as arguably-significant harmonic distortion in certain situations (which makes it a lot less tenuous than many other things touted in audio)

I’d say if they make you happy, use them. They worked fine in audio gear for decades, in many items that are still in service and widely-sought, so at least their use is unlikely to have massive downsides

My own experience and point-of-view has led me away from them over time, but everyone’s pathway is (and should be) their own

 

[Migs 31]

large number of carbon core resistors, and they The accuracy of most is not good, but they are very cheap and cost me a lot of time to get the accuracy to within 3%.

@ZHOUJUN
Save yourself some time, effort & money (if they go bust in HT). As Thomas said, use the Metal film resistors (1% tolerance) in general.

But for the resistors directly in the Audio path, use the Carbon core ones for that “vintage” sound we all (almost all) love. I have learned this the hard way.

M

 

[ZHOUJUN]

These were cut from some scrap antique insulation board and just needed to be re-drilled。

 

[ZHOUJUN]

For these carbon core resistors, I think the original choice should be respected when they are easily available, because we need to restore their sound as much as possible，I have measured my friend's original LA2A, and those carbon core resistors are still in good condition, no Deviation.







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[ZHOUJUN]

I completed the circuit part of my Vintage LA-2A circuit. After a simple test, the voltages of each point to point are OK. This is thanks to my friend's original LA-2A from the 1960s. I refer to it bit by bit. During the construction, I found that the layout of the lines has a great impact on the noise floor, so I adopted a winding method, which is not so messy. Next, I will test the audio.

 

[ran]

I think the lore that carbon comp resistors sound gnarlier is mostly BS (and the part that isn't is mostly due to bad things), what they are is less reliable, with wider tolerance as noted, and bigger. They are also more susceptible to heat damage (important in a tube device) and can drift in value significantly over time. They also cost double, sometimes triple what 1% metal films do. The only really good reason to use them is when you need something with better pulse endurance (not the case here) or when they are dual purpose as a fuse (like the screen resistors on the 6550s in Sunn amps - but even then I replaced those, which died from overheating BTW, with metal oxide - just don't up the wattage like some folks recomend online because it's better for the resistor to fail than to blow the tube - NOS 6550s be expensive).

Not to mention that, due to their construction (graphite mixture, etc.), they are definitely noisier over time compared to modern film resistors.

 

[ran]

Not to mention that, due to their construction (graphite mixture, etc.), they are definitely noisier over time compared to modern film resistors.