First a big thanks to Stephe for her videos/guides on this A50. There is much work involve making/editing those videos, great work!
I have always wondered about no feedback sound thru my audio journey. Started with Fisher 300/400, progressed to Dynaco, large tube mono blocks, threshold and parasound, most slightly or massively modified. I'd thought it was time to make an effort to sample a SET amplifier. Along comes the Boyuurange A50 mk3 300b. I have followed along Stephe's path, from initial purchase to the full modded version and would like to share my experience. Been doing the audio thing for a long time, almost 50 years. Of course, can't hear as well now. Maybe the reason I don't experience much break-in sensation of parts. However, I've have learned to listen carefully over those years.
My system is made up of sources; Meridian, Oppo modded for 2 channel only, VPI/Dynavector, Tara labs bi-wired Von Schweikert VR-5 HSE(91db). Multiple DIY interconnects (RCA/Eichmann) . Room has been tuned as best I can manage for a non symmetrical arrangement. It very difficult to explain sound as we all experience and prefer a certain presentation. I for one have had a long battle between detail/edgy, warm/blur with the soundstage definition a priority. I'm a low level listener, no 100db level here, and mostly acoustic/folk and light rock.
Stock A50;. I only listen long enough to make sure the unit operated. I only recall the sound was encouraging, and leaning toward my liking which I suppose is "musical", what ever that means to you and me.
Mod #1; As in the videos, I raised the voltages as Stephe advises. Jumper resistor, 5AR4, cap between the chokes, changed 6sn7s to 50s GEs. Now this was a very nice upgrade. I was using the 4 ohm taps to match the impedance of the woofer section of my speakers. The mid/tweeter section is reported to be 8ohms, for an overall 6.5ohm specified impedance. Wow, the ease of the presentation was a nice experience for me. Lacking bass NOT. I can't explain how or why, but musical without having to ramp up volume to get a full picture if you know what I mean. Not perfect, but very surprising, fine detail a little muted. My system, my preference, I could enjoy this for awhile, YMMV.
Cascode mod;. First I have Auricaps(.47 for coupling) and KZ Muse for the 300bs. The first obvious change is the input sensitivity dropping quite a bit. To achieve the same loudness the volume control must be advanced at least a quarter turn or more than previously. Not because loss of power output, just the loss of sensitivity. Overall a cleaner general presentation. Bass also diminished surprisingly but was better defined. The overall presentation had lost it's, say it, it's ease of presentation leaning towards SS. My opinion. What surprised me was the arrival of delicate detail. Can't think of a better explanation, just that. Little delicate details in voices and in the soundstage became apparent. Not forced into the presentation, just floating into the picture.
There is little run-in time on the mods at this time. I will give it an appropriate "break-in". I could be tempted to go back one mod to only raising the voltage. Will see....
I have always wondered about no feedback sound thru my audio journey. Started with Fisher 300/400, progressed to Dynaco, large tube mono blocks, threshold and parasound, most slightly or massively modified. I'd thought it was time to make an effort to sample a SET amplifier. Along comes the Boyuurange A50 mk3 300b. I have followed along Stephe's path, from initial purchase to the full modded version and would like to share my experience. Been doing the audio thing for a long time, almost 50 years. Of course, can't hear as well now. Maybe the reason I don't experience much break-in sensation of parts. However, I've have learned to listen carefully over those years.
My system is made up of sources; Meridian, Oppo modded for 2 channel only, VPI/Dynavector, Tara labs bi-wired Von Schweikert VR-5 HSE(91db). Multiple DIY interconnects (RCA/Eichmann) . Room has been tuned as best I can manage for a non symmetrical arrangement. It very difficult to explain sound as we all experience and prefer a certain presentation. I for one have had a long battle between detail/edgy, warm/blur with the soundstage definition a priority. I'm a low level listener, no 100db level here, and mostly acoustic/folk and light rock.
Stock A50;. I only listen long enough to make sure the unit operated. I only recall the sound was encouraging, and leaning toward my liking which I suppose is "musical", what ever that means to you and me.
Mod #1; As in the videos, I raised the voltages as Stephe advises. Jumper resistor, 5AR4, cap between the chokes, changed 6sn7s to 50s GEs. Now this was a very nice upgrade. I was using the 4 ohm taps to match the impedance of the woofer section of my speakers. The mid/tweeter section is reported to be 8ohms, for an overall 6.5ohm specified impedance. Wow, the ease of the presentation was a nice experience for me. Lacking bass NOT. I can't explain how or why, but musical without having to ramp up volume to get a full picture if you know what I mean. Not perfect, but very surprising, fine detail a little muted. My system, my preference, I could enjoy this for awhile, YMMV.
Cascode mod;. First I have Auricaps(.47 for coupling) and KZ Muse for the 300bs. The first obvious change is the input sensitivity dropping quite a bit. To achieve the same loudness the volume control must be advanced at least a quarter turn or more than previously. Not because loss of power output, just the loss of sensitivity. Overall a cleaner general presentation. Bass also diminished surprisingly but was better defined. The overall presentation had lost it's, say it, it's ease of presentation leaning towards SS. My opinion. What surprised me was the arrival of delicate detail. Can't think of a better explanation, just that. Little delicate details in voices and in the soundstage became apparent. Not forced into the presentation, just floating into the picture.
There is little run-in time on the mods at this time. I will give it an appropriate "break-in". I could be tempted to go back one mod to only raising the voltage. Will see....
Many additional mods later I've come across a rather interesting issue.
First I split the PS feed to the driver tubes so each has it own resistor and cap. Also most of the caps are now DC Link MKPs including the 300b cathode bypass. I played around changing the type(MF, CF, etc) of 47k resistor between 6sn7 plate and ground.
Now for the surprise. I read that someone suggested replacing the red LED/200ohm bias on the 6sn7 to a green/50ohm for more gain. I was in need of that extra gain after doing the above posted suggested mods. It would affect the amount of feedback, but I thought the sound was on the SS side of things with the additional mods.
Well, I did expect was a less "transparent" affect, and yes I got exactly that. But what wasn't expected was the rather startlingly increase in bass response. This isn't due to the lessening of the higher frequency, even though I've been there before. It truly surprised me. The bias point/current through the 6sn7 didn't change, I check that out.
What happened?
First I split the PS feed to the driver tubes so each has it own resistor and cap. Also most of the caps are now DC Link MKPs including the 300b cathode bypass. I played around changing the type(MF, CF, etc) of 47k resistor between 6sn7 plate and ground.
Now for the surprise. I read that someone suggested replacing the red LED/200ohm bias on the 6sn7 to a green/50ohm for more gain. I was in need of that extra gain after doing the above posted suggested mods. It would affect the amount of feedback, but I thought the sound was on the SS side of things with the additional mods.
Well, I did expect was a less "transparent" affect, and yes I got exactly that. But what wasn't expected was the rather startlingly increase in bass response. This isn't due to the lessening of the higher frequency, even though I've been there before. It truly surprised me. The bias point/current through the 6sn7 didn't change, I check that out.
What happened?
Never found the reason for that change. I have since, done an Ultrapath mod using the DC link Caps. Again for me another well worth change in the sound, my preference. I've tried at least 5 other 6sn7s, sylvania " bad boys", chrome tops, RCA, 6sn7wgt, and my preferred Raytheon VT231. Quit easy to hear the subtle differences.