I received my A50 2 days ago and started playing with it. Here are my initial impressions and progressive improvements (I have not started on the Skunkie modifications yet). The initial sound of the amplifier was very "thin" and not at all dynamic. I replaced the rectifier with a 5AR4 and heard a significant improvement overall. I then switched out the 6SN7s for USA Sylvania and the 300B for a Sophia mesh plate. Each of these swaps resulted in a much cleaner, crisper, dynamic and fuller sound. Overall I would say it made a 300% improvement to the sound to my ears at least. I did no THD testing yet as I was more interested in the sound and did not want to be swayed by numbers.
I will do the Skunkie recommended mods one at a time and listen to the results. Once I am satisfied with the amps I will run thru a full series of performance tests and publish the results on this forum. Prior to this, the other thing I will be looking at is converting the tube supply to a solid-state design. I know this will raise many eyebrows and I do not wish to get into an extensive debate about the virtues of one vs the other. I will share how I feel about the sonic difference. There are at least four highly regarded amplifiers, the McIntosh 240 and 275 as well as the Marantz Model 8B and 9, all use solid-state rectification. I have not read any suggestions regarding converting them to tube rectification.
Joe in Virginia
So far completed just two modifications.
47uf 500v ripple cap and bypass that other cap.
waiting on coupler caps.
notice the top end is lacking and using my Schiit Lokius fixes the lack of liveliness.
What stinks I didn't watch the entire series and purchased the first set of .33uF coupler caps.
For the front end I had to teach myself how to read the diagram and draw a mock representation of the sockets wired up.
I became confused about the two resistors that look connected to the left tube I think they are little 100 ohm units attached to the black cables which come from rear and connect each tube and guessing that's power? Figured out from the other diagram that's where they are exist.
I swapped tubes and that improved the the performance by fixing the noise the drivers made and the GZ33 I am using did something but not sure how to describe it.
Waiting on Parts Connexion
If I upgrade the couplers from the Mundorf .33uF MKP's I purchased, are Jantzen Superior Z-caps any good for the price? If not is there a sub that can be recommend for less?