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5U4GB Rectifiers


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I haven't seen you on here for quite some time. I hope all is going well with you. Are you still teaching? My wife and I are still enjoying my Moondogs, and I only recently came across notes for changing out some parts.


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Teaching is very alive and doing well -- just on Spring Break which gives me some extra time. I hope you and your wife are doing very well, also. Marie and I and our doggie kiddos are all fine. I think it's great you still have your Moondogs -- me too. They are classics, IMO, and I'll never part with them. Those poor things have undergone so many changes and modifications over the years, that this past summer I completely rewired them back to the original design, and just organized for better presentation inside and out. I found some nice Russion PIO capacitors for coupling that were really reasonable compared to the alternatives, and have been very good, not to mention totally reliable. Military grade things that are heavy for their size and built well. I think Craig mentioned these positively some time ago, as well.

Still, there is always that special little grid choke on the 2A3 that I liked so much in the J-F Lessard parallel feed amps I made several years ago. That's the MQ part I mentioned to you. I've found some alternatives to that, but I think the MQ choke is made really well. Very easy mod, too.

Good to hear from you, Bruce.


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Curiosity got the best of me when I read this post.

I've spent the last couple of days doing 5U4 listening tests on 5 Baldwin monoblocks and I'll go with the old clear RCA 5u4G coke bottles, then the Sylvania Smoked glass coke bottles or Raytheon tall boys. Original Baldwin RCA black plates were a little brighter and less desireable after a lot of listening. I have some GE "stubby" 5U4s that I thought were actually a little "lifeless".

I did hear minor differences in the rectifiers. I don't think there were enough differences that I'd really be concerned with confining myself to one brand or type.

Listening was done through an Electrocompaniet SS preamp, Denon CDP, and MC Supex SDX-1000 cartridge on an old KLH X-60 TT.

I tested all 5u4s on my B&K 707 I just went through and restored and calibrated. All tubes tested over 90% and no leaks or shorts. All tubes quiet. I have multiple tubes of the same brand so I listened to the same brands a couple of times and they were very similar or identical in sound.

All Baldwins have been rebuilt or completely modified so they all have different personalities.

I built the Baldwins in matching pair monoblocks with a single 20w mono being the lone monoblock not matched with another. Different caps and even "canned the cans" on the red monos and used Nichicon caps and Mundorf S/O to replace all the caps in the red Baldwins. The most noticable difference was in these amps with the filter cans and all caps being replaced.

I had to switch back and forth numerous times to even notice and appreciate the different personalities of the tubes.

I used Vinyl and CD as sources to see IF it made a difference to MY EARS. I listen mostly to vinyl but do a lot of "quick listening" to CD. Same source material was used for all listening.


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Thanks for the info on the 5U4's, at the advice of Will I am going to try the 5V4's because of the soft start. Anyway for what it's worth with the 5U4's I found the GB's to my liking, Tung Sol sounds about right RCA's were a little laid back GE's were almost bright; and I didn't have any Sylvania's. I think I am going to try some Mazda GZ32's and maybe Sylvania's as well.


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one of my rectifiers

I used these GEC U52 (5U4G) tubes in my 2A3 PP amp for a while finally parked them and I am using a pair of GZ37 Mullards...

these are the mullards:

my mullards

I am not going to say one sounded better than the other, but I stayed with the mullard.

Warm regards, Tony

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