Aug 032012

Happy Friday everyone! After drinking a couple cups of coffee this morning, I decided to warm up the Hi-Fi rig and do a little tube rolling in the Fi 300B mono amplifiers, which is a great way to have little fun on a Friday morning!

My Fi 300B monos came with Sovtek 5AR4 rectifiers (far left in the photo above – click on image for a larger version) which are not bad sounding, but it’s hard to resist the temptation to do a little tube rolling! First I had asked Don if he had a favorite rectifier for the 300B mono amplifiers, and he said:

“Probably the old Mullards (or RCA) 5A4/GZ34, but they’re so damned expensive. I’m not sure if they’ll do well with the Tannoys, but I also like RCA 5R4GYs (yes, 5R4, not 5AR4). It’s a lower operating point, but it really sounds good.”

When I went out to check prices on the Mullards at Brent Jesse Recording & Supply, Inc. they came in around $200 each, so they’re spendy, just like Don warned. They also had some of the RCA 5R4GYs in stock ranging from $11 to $25 so I ordered a pair those to try out in the Fi 300B monos instead (the tube to the left in the photo below).

I had a couple of different rectifier tubes laying around that I’ve been using with my Sophia Electric 300B mono amplifiers (the FAA 5U4G & Shuguang 5Z3PA in the photo with the Sovteks above), and with a hankering to order a few more to try as well (like 274Bs et all), I asked Don Garber for a little advice about suitable rectifier substitutions in the Fi 300B mono amplifiers. Don told me:

“I think (with my admittedly limited knowledge) that just about anything will “work”. It’s just got to be a 5 volt rectifier drawing no more than 3 amps of filament current. The primary difference (but not the only one) between rectifiers is the amount of voltage drop across the tube. This affects the operating point of the amp. That said, I’m quite sure that there will be sonic differences between two tubes with the same voltage drop. The 274B is close to identical with the 5U4G, and the 5R4 is close. These amps were originally designed to use a 5AR4 which comes about as close to zero voltage drop as one can. Incidentally, if you’re doing a lot of ‘tube rolling’ you should either have a good tube handbook or use the online references. is an excellent one.”

Be sure to check out Frank’s Electron Tube Data Sheets web site that Don mentioned, it really is an excellent reference.

Shuguang 5Z3PA: The Shuguang 5Z3PA is the rectifier that Richard Wugang equipped the Sophia Electric Model 91-01 300B mono amplifiers with that I reviewed for Positive Feedback Online here, and then purchased after the review.  The Shuguang 5Z3PA is a nice sounding rectifier with an ST-16 bottle shape (I love that shape!). This rectifier is warm and rich sounding, fairly spacious, and very musical. Not the last word in transparency but very easy on the ears, and they have been completely reliable in operation. The Shuguang 5Z3PA are the rectifiers on the right in the photo below. 

FAA 5U4G: The Federal Aviation Administration (FAA) 5U4G is either a Brimar, Sylvania, or Tung-Sol provided to FAA, but there’s no manufacturer markings on them so I can’t be sure which. The internal structure is very different from that of the Shuguang, and almost identical looking to the of the RCA 5R4-GY. The FAA 5U4G is much more transparent than the Shuguang, with more of a sense of space, better imaging, and that sort of thing. Musically the FAA 5U4G is very impressive, kept me riveted with the way the music is unfolded.

RCA 5R4-GY: Don was a little worried about using the RCAs with the Tannoys, but I still had plenty of gain, rarely going above 9 o’clock on the volume control of the Leben RS-100 line amplifier for musically realistic sound pressure levels. The RCA not only looks like the FAA, it also sounds similar to the FAA 5U4G, but is a little smoother perhaps. However, both of these tubes have just a few hours on them at this point, so maybe their individual character will become more obvious in time (a 100 hours is the usual period I allow for the full sonic character to develop for vacuum tubes). I’ll report back when I get some more time on them.

I enjoyed all of these rectifiers and I think I could (and will!) live with any of them. Rectifiers make as much of a sonic difference in the Fi 300B mono amplifiers (or any SET) as do input and output tubes, so it’s really worth trying a few to see which ones complement the sound of your system & tastes – they can make all the difference in the final sound of your system. (while I was writing this post I got all excited and ordered a pair of 274B rectifiers from, so stay tuned, I’ll update this post after I give them a listen).

I can’t really comment about which rectifiers I like best in the Fi 300B mono amplifiers yet, as I want to try some more rectifiers, and the Fi’s are still going through their break-in process, which with the Black Gate capacitors Don uses in the circuit, takes about 300 hours, so I’ve still got months to go before they’ll be done running in.

By the way, the Sophia Electric Royal Princess 300B vacuum tubes that I reviewed for Positive Feedback Online in Issue 57 are still going strong after a year of use, and they impress me as much in the Fi 300B mono amplifiers as they do in the Sophia Electric Model 91-01 300B mono amplifiers – awesome tubes!

Speaking of great sounding Sophia Electric vacuum tubes, the Sophia Electric 6NS7 with its cool looking mini-ST bottle sounds really good in the Fi 300B mono amplifiers, better even than they did in the Sophia Electric Model 91-01 300B mono amplifiers (where I prefer the KEN-RAD 6SN7GT). I really like the Sophia 6NS7 tube, it has even bested the NOS tubes I’ve compared it to (Sylvania & Ken Rad) in the Fi 300B monos, being better in every sonic attribute, as well as sounding more musically natural. An easy recommendation. It’s the tube to the right in the photo below, and I have to say that a 300B amplifier with a full set of ST bottles is a wonderful thing to see!

When Don Garber shipped the Fi 300B mono amplifiers to me he included the Sophia Electric Globe Mesh Plate 300B vacuum tubes (Don really likes the Sophia Electric tubes from Richard Wugang). I have to say those Globe 300B tubes (tubes on the right in the photo below) are really nice sounding tubes, and I think I prefer them to the Sophia Electric Princess Mesh Plate 300Bs that came in the Sophia Electric Model 91-01 300B mono amplifiers for their more relaxed presentation.

I tip my hat to Richard Wugang, he really has done a wonderful job with his Sophia Electric vacuum tubes. The Sophia Electric vacuum tubes I’ve heard have all had excellent build quality, and the Sophia Electric 300B product line provides a spectrum of sonics that will provide something suitable for everyone’s tastes and budget. Thank you for bringing us such great vacuum tubes Richard!

Update August 10, 2012: The Shuguang 274B tubes don’t fit in the Fi 300B mono amplifiers, as the glass bulb is too big to fit in the chassis cutouts. So instead I’ll give them a listen in the Sophia Electric 300B mono amplifiers and report back in a future post.

Well, I guess that’s it for now. Have fun listening!

 Posted by at 11:14 am

  5 Responses to “An On-line Vacuum Tube Reference & A Little Tube Rolling in the Fi 300B Monos – Updated August 10, 2012”

  1. Thanks for an entertaining read, fleshed out with some great photos to illustrate the differences in the rectifiers.

    I was skeptical of the impact different rectifiers could make, until I recently did a little rolling on my own, humble but very enjoyable system: Decware SE 34.I 2+ SET integrated and Blumenstein Ultra Fi Orcas and matching subs. The Decware comes standard wiht 5U4Gs but can use several different types of rectifiers. I was originally running mine with Sovtek 5U4Gs but had a fun day comparing them to some NOS RCA 5U4Gs (non-ST shaped). The difference was not subtle, with the RCAs clearly winning out based on low-level detail, lack of grain and overall musicality. My friend, a solid state kinda dude with no prior tube experience, agreed completely and had a blast hearing for himself what tube rolling is all about (we rolled different driver tubes later in the day, also a HUGE difference in the sound).

    Someday I’ll explore other types (5R4GY, 274B, etc.), but for now I’m really happy with the RCAs. I’m not surprised, based on my limited understanding, that the 5R4GYs would tend to sound “smoother” or more “laid back” given the relatively bigger voltage drop. That’s referred to as “sag” in the guitar amp world, right?

    Anyway, thanks again for the fun post and I’m looking forward to further explorations.



    • Hi Blake,

      Thanks for the kind words my friend – appreciated. I’m going to have to give those NOS RCA 5U4Gs a try.

      Interestingly enough, the humble Chinese Shuguang 5Z3PA has been the most musical of the rectifiers I’ve tried. Crazy thing is you can’t find them anywhere it seems! They’re not as transparent as the NOS valves with the ST bottles, but they really deliver on the musical side of the house.

      Thanks for stopping by and keep me posted on any new discoveries!

      Kind regards,


  2. Yeah, RCA 5U4G is the right tube!
    I use 6X5GT from different brands. Now i’ve had the chance to get 10 NEW UNSED RCA 6X5GT from 1943.
    This is the best. But keep in mind: The great sounding level is only for 2-3 years!!!!!!!
    Then you must replace the tube.



  3. Hi Jeff,

    My few cents worth. I found that any valve change on my 300B monoblocks – driver, final or rectifier changed the sound. Problem is what/which is better? Answer (for me): Use a different amp. In my case a Lyngdorf/Tact semi digital amp does what I want which is to faithfully amplify the input. If that sounds strange use headphones to check. Having said that both of my front ends, Cd and LP, have valves in the path. Which make a difference when changed. It’s all subjective unless you have something to compare the result to.
    Got bored with the subject and now listen to the music!
    I needed something better in the very low bass, sub 20Hz for organ, so I have just finished my variation of a 1/4 wave
    sub woofer. In essence a 600mm X 600mm tube, 6 meters long with 4 X 18″ speakers stuck on one end. Now I can enjoy the 32′ and 64′ octaves at realistic volumes……..
    Quite Mad.
    Are you still having fun with your Westminsters?
    Chris in South Africa

    • Hi Chris,

      Sounds like you’re having fun – very cool!

      I’m still enjoying my Westminsters, they’re sounding better than ever. It probably sounds perverse, but I do enjoying playing around with different tube combinations, and actually for reviewing it comes in handy, because I can voice the system for best synergy with whatever is in for review, so there’s built in flexibility that way.

      Kind regards,


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