No I have not. From the reaction it seems to be a slightly brighter tube which is not what I need in my system.
Friend of mine is letting me try his Wavac 805M this week. It also has a RCA 805 tube at the output. Even so, the sound is very very different than the LM508IA. Much more refined, incredible amount of detail/clarity/texture, but not as much grunt as the LM508IA. It is also very enjoyable but in a different way. Just another example that the tube doesn't define the amplifier.
Wavac circuit is very different with local feedback around power tube. Thus distortions structure is different too, and that defines the sound. But for all around amplifier you do need grunt. Yesterday I was listening Mahler 2nd, and LM508 almost made it. It excellently handled deep bass (almost subsonic) notes. Only in 2-3 moments of all out forte I felt that it was running out of juice.
@AP1 , are you able to find the schematic for the Wavac 805M? I would love to take a look and learn something. I only managed to find one 805 design by Nobu Shishido but that one has different drivers and it has global feedback. I always thought the more delicate detailed sound is due to the use of a interstage instead of feedback but would love to learn about it. As for the grunt, totally agree. The 508IA is more suited to my type of music which is also mainly larger scale orchestra. Glad to see you have similar taste! I also found that piano and soprano also easily clips the 508IA. One of my test album is this: Album Aida , Various Composers by Aida Garifullina | Qobuz: download and streaming in high quality . On the first track, she easily clips the 508IA (pair with my ~90dB/W Focal Mezzo Utopia, what speaker are you using?). I also find upgrading the power supply capacitor give the 508IA a bit more headroom and I rarely clipping anymore. The Wavac is a really lovely amplifier. I was playing some jazz and to be able to hear so much texture is addicting. Something to aim for when modding the 508IA.
I posted it earlier. You can check out this post and another one a few posts down: New Line Magnetic 508ia Integrated Amp
Hello @jmpsmash Thanks for the info. I'm sorry for my ignorance, but wich cap (code C...) is the 6SL7 power cap on the schematics of the LM508 shared on this thread? On the other hand, can you give us the specific links to where you bought the Mundorf Myltic cap and the Mundorf Aluminum Oil cap? Finally, do you have pictures of your work with this cap? Thank you!
It is C101 right next to the 6SL7. However, I would wait before doing the upgrade. Now that I have listened to the Wavac, I want to see if there is something that can be done to make the 508IA just as powerful but more delicate closer the Wavac.
I found two schematics. One with WE437 tube RE: Wavac MD-805M Biasing? Tube rolling? - Chris O - SET Asylum and one with 5751 tube in he first stage Two teasers...and more - jeffreybehr - SET Asylum Both have global feedback. First also have local feedback - that is how 805 tube is served in many other circuits (but not in LM). My speakers are B&W 802D, their efficiency is around 89dB/W. LM508 works for most music, but not all. For me better sound was achieved when I connected speakers to 4 Ohms output. I have an alternative though - 300W per side Bryston.
I have seen the first one but not the second one. Good find! I don't see local feedback in any of them though. The first one is a simple 437A common cathode stage directly coupled to the 6L6GC. The second one with 5751 in a standard SRPP topology (plus global feedback) direct driving a 6Y6GT and then transformer coupled to 805. SRPP is often used in cases where the designer has the whole dual triode so they need some stage that uses both triodes, as in monoblock. The second looks legit to be the schematic for the Wavac 805M! It does look like Shishido's formula is to have a high gain triode stage direct driving a pentode and then transformer coupled to a 300B or 805.
Local feedback is from additional winding in output transformer to cathode of 805 tube. That is actually a common method to make high gain tube more linear. McIntosh also use it in their amplifiers. What looks like mistake is a capacitor at the cathode of first stage in the second circuit. It should be parallel with upper resistor (like in LM508), not the lower one.
Anyone thought about rewiring the amp? I'm thinking some Mundorf silver gold will take transparency and holography up many notches.
You better start with rewinding transformers. There are thousands feet of wire in them, comparing with dozen feet of all other wires in this amplifier. The more wire changed - the more difference it makes.
One is more feasible and the other is a more technically challenging specialist area to perform. I've had an amp completely rewired in the past and the delta was significant. I'm merely suggesting it as an extra avenue to explore seeing as @jmpsmash is looking to fine tune the amp in areas beyond capacitors.
Hello @jmpsmash I was checking on the mods I did on my LM-508 following Robert Lai's instructions and he made me change the C102 that also goes into the 6SL7 tube, but it's closer to it. Did you try to replace this cap or just C101?
C102 (and C103) are the decoupling caps that carries the sound signal between tubes. I recommend you replace them with some nice film caps like Jupiter Copper. I talked about the film caps here. I plan to change the 2nd one to Jupiter also but I have been so busy these couple of weeks. New Line Magnetic 508ia Integrated Amp C101 is a power supply cap. The 508IA comes with a standard electrolytic. You will be better off upgrading it to something nicer and then bypass it with a small film cap.
It is true that one can probably do a lot better than the stock output transformer in the 508IA. However, a good quality output transformer will go for US$2k+. And the operation is too involved. Might as well buy another amp. For upgrading internal wiring, I suspect upgrading the cable from the input RCA all the way to the 6SL7 will make a difference.
Reading mixed things about placing Isoacoustic Orea Bordeaux under the LM amp ... but might give it try and return them if they don't do anything. I would like to make it look 'clean' so wondering if anyone has removed the stock feet from the LM508/805? I assume that they are just screwed on once the felt pads are removed??
I have done exactly what you're planning to do with mine. The feet unscrew easily, and the Bordeauxs brought an improvement to the sound. One other member on here did so and reported improvements before I tried it out, I just can't remember who.
I've had really nice results using Symposium Rollerblock Jr HDSE's supported by a Symposium Ultra platform. The increase in detail and soundstage is well-noted in my system.
Update on shootout of 805 tubes. RCA 805 made in 60's sounds most transparent but rather lean in balance. RCA 805 vt143 made in 1943 sounds thick without burnin, but after 30 hours of playing time, it sounds excellent with good transparency and nice balance. I had also burnt in United 805 vt143 which sounds close to RCA 805 vt143 made in 1943 with slight less transparency but more warmth. United 805 made in 60's sounds slightly warm and full compared with RCA 805, but not a night and day difference. I sent United 805 made in 60's to one of our member to swap with his RCA 805 tube yesterday. I also ordered National Union vt 143 which will arrive later next week. National Union 6n7 and 6sl7 has a house sound of round midrange. Thus I will see what will happen to National Union vt 143. I will have more than 8 pairs of 805 which may outlast me, since I am 60 years young. I am willing to keep LM 508 for my life unless it get broken since it has nice synergy with high efficient speakers that I have Lansche 4.1, Vaugn Cavernett II and or maybe Scaena 3.2 which need to be assembled yet.
