It is most likely the dimple version are 5998 since up-specking was common practice , that is where all the parameters exceed the requirement for a given tube spec a substitute is made Very common with rectifiers

Don't overlook the GE 6as7GA it has been the bass king in all the compatible amps I have owned

I think single sided is just a weight reduction thing , maybe cheaper too

It would struggle to provide sufficient current at high demand frequencies Surface-mount op amps with minimum capacitor back up are not ideal for low efficiency

It would have been good to expand the already absurd flexibility of Ultimate Eric builds an excellent parallel 6as7 amp but it must be reserved for headphones with sensitivity 90dB or lower to avoid noise

"Balanced is not better per se unless you are running studio length cables." This is confusing balanced transmission with balanced drive, two different things

All dacs have similar performance so it would be a matter of feature set Uniti will give you an aesthetically pleasing single box solution but with ADI you get the processing features

Another one common on Ebay here in Australia is Dr Nine based in Japan same strategy ridiculous prices for common tubes I messaged him with a low ball offer saying he was embarrassing himself , no reply

I run Erics parallel 6as7g pEar as a headphone amp Currently WE421a matched pair with realistic lifetime GZ34 and 6EM7 Recently I bought the HiFiman HE6se and it is an end game match up, all the character of tubes with the sharp focused power of high end solid state However as mentioned it is a...

Sounds like the insulation on the heaters is worn and they are arcing a little Probably only get worse from there until it shorts out

I recently had a very bad experience with A2A concerning a DOA The matter was not resolved until I requested PayPal intervene A2A were for many years my preferred source Not any more

I use hospital grade mains cables they cost a few dollars more but are rated for interference Remember your home is a matrix of unshielded cables

Yes that is a potential problem Avoid running power and audio parallel

The external noise would need to be very high power to override the noise inherent in ac power No cable can change that