[Xcalibur255]

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As promised, pictures! and dust!
 
 
http://www.head-fi.org/g/a/697715/glenn-otl/
 
 
Teaser!
 

Love that photo wotts.  Whatever shutter settings you used it looks amazing.

 

[wotts]

Thanks SO!
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Love that photo wotts.  Whatever shutter settings you used it looks amazing.

 
Thank you! I used my 18-55mm lens and it was a 10s exposure at f5.6. Some of the really cool ones I forced a flash at the start and then did the exposure to light the amp and still get the tube glow.

 

[rosgr63]

Very nice photos Wotts, I like your album.
 
The glowing tubes look nice.
 
How does your Sylvania 6F8G sound?

 

[Xcalibur255]

It occurred to me it's been a long time since I've heard a 5U4G, so today I've dared to put my Tung Sol 5Z3 w/adapter in the OTL to reference how they sound with the other rectifiers.  So far so good, the tube didn't arc when I started it up so it seems like it will be up to the task for this short test.  This tube is NOS so I'm going to let it run a bit before listening.
 
I pulled my 5V3 out as well and tried it this morning too.  It didn't arc over either, I'm thinking my old listening tests were with the 6AS7s which draw another 20mA a piece, that must put it over the line for these 5U4 family tubes.  I think the 5AU4 is the better choice over this tube.  Honestly the GZ33 and the 5V3 sound very similar, with the latter being more lit up in the upper mids, slightly more edgy, and a bit thinner sounding.  Both sound flat, with a 2-D soundstage presentation, with the GZ33 being the worse offender.  With the 5V3 it is more like notes are lying on top of each other than a lack of Y-axis soundscape. 
 
For fellow owners I do recommend tracking down a fat plate 5AU4, they're a very worth alternative to the 3DG4 and the 5U8C and sound different from either of them.  I'll weigh in on the 5Z3 (5U4G) later on.

 

[Xcalibur255]

I'm going to try out the 5AW4 too.  If the 5U4G doesn't blow up neither will this.

 

[Xcalibur255]

I've given each tube a few hours now and I think I've heard what I needed to from each.  I'm not very impressed with the 5U4G in this scenario.  It has a nice round fullness to notes that is a good thing IMO, but it sounds slow and sloppy.  Everything seems slightly out of focus, the bass is especially bad.  Soundstage is nice and round but doesn't get wide enough and notes get crowded IMO.  I found it to be pretty sibilant in the upper registers and sometimes glassy sounding in the upper mids.  It bears a resemblance to the 3DG4 sound in quite a few ways though, just an out of focus version, which makes sense considering that the 3DG4 was designed to replace 2 5U4G tubes in a circuit.  There is much more voltage sag on a 5U4G though which is where the lazy sound is coming from. 
 
The 5AW4 was a surprise, and a fairly pleasant one.  This doesn't sound too bad.  Again I think there is a bit of a thinness, a lack of fullness to the notes, that I'm finding in a lot of these tubes outside of the "big 3" (3DG4, 5AU4, 5U8C) but it isn't too bad here.  Soundstage is nice and wide but a little flat in front/back depth like some of the others were.  Tonally I thought it was good, balanced and pretty well behaved.  Good bass speed/impact and treble was pretty controlled.  It sounds a lot like a 5R4GY actually now that I think about it, who knows maybe it's a straight bottle version of one.  I was afraid the amp would blow the tube up, the filaments seem like they're a little thinner than those on a 5U4G but the tube seems to handle it and doesn't really sound strained.  I believe mine is made by RCA (branded Philco), I'd like to get my hands on an older vintage Sylvania one.
 
Back to the 3DG4 for a reality check now.

 

[Silent One]

Xcalibur255, with all your testing and feedback, did our amps just become Military Grade? 

 

[rosgr63]

Yes, code CGR-OTL1W.
 
BTW any chance for a photo or list of the adapters necessary for each tube please?
It'll be a good reference source.

 

[Clayton SF]

Quote:

It occurred to me it's been a long time since I've heard a 5U4G, so today I've dared to put my Tung Sol 5Z3 w/adapter in the OTL to reference how they sound with the other rectifiers.  So far so good, the tube didn't arc when I started it up so it seems like it will be up to the task for this short test.  This tube is NOS so I'm going to let it run a bit before listening.
 
I pulled my 5V3 out as well and tried it this morning too.  It didn't arc over either, I'm thinking my old listening tests were with the 6AS7s which draw another 20mA a piece, that must put it over the line for these 5U4 family tubes.  I think the 5AU4 is the better choice over this tube.  Honestly the GZ33 and the 5V3 sound very similar, with the latter being more lit up in the upper mids, slightly more edgy, and a bit thinner sounding.  Both sound flat, with a 2-D soundstage presentation, with the GZ33 being the worse offender.  With the 5V3 it is more like notes are lying on top of each other than a lack of Y-axis soundscape. 
 
For fellow owners I do recommend tracking down a fat plate 5AU4, they're a very worth alternative to the 3DG4 and the 5U8C and sound different from either of them.  I'll weigh in on the 5Z3 (5U4G) later on.

 
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I'm going to try out the 5AW4 too.  If the 5U4G doesn't blow up neither will this.

 
Glenn has made different versions of his amp. Are your rectifier recommendations good for the stock version as well?

 

[Xcalibur255]

Quote:

Yes, code CGR-OTL1W.
 
BTW any chance for a photo or list of the adapters necessary for each tube please?
It'll be a good reference source.

No adapters.  I used one on my 5Z3 because it is a 4-pin version of the 5U4G.  They are the same tube aside from this difference.  These all drop right into the socket.  For the record I don't recommend running the 5U4G, 5V3 or the 5AW4 in the amp long term, they're all pretty maxed out in current draw and will likely fail prematurely in such a state.  This was a one day thing I did to gather impressions.  I have other incentive to gather impressions because all of these tubes would be usable in my future amp you see.
 
I still consider the 3DG4 the best choice.  I'm not sure how else to put it, but the amp just sounds "right" with this tube.

 

[Xcalibur255]

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Glenn has made different versions of his amp. Are your rectifier recommendations good for the stock version as well?

I don't think any of them are safe to use with 6AS7 tubes, in either of the bias settings I know Glenn has used with the amp.  It seems passable with the 5998 because they draw a little less current but long term our only 4 options really are GZ33/37, 3DG4, 5U8C or old style big plate 5AU4.

 

[Silent One]

Perhaps, not your personal choice, but the USAF-596 is an option as well.

 

[Silent One]

 

 
 
I'm 6 hours out from returning home and getting into the listening room. Just temporarily installed my new feet under the 'OTL' to see how they fit. These just came in for my music server. But will get some for the amp in January/February. No idea how it sounds...later tonight.

 
Footers spec'd @ 3"x 3"...6 lbs ea.; Maple platform 18 lbs ea.; 36 lbs under given component.

 

[Xcalibur255]

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Perhaps, not your personal choice, but the USAF-596 is an option as well.

I keep forgetting about it because I haven't used one.  Apologies.

 

[Silent One]

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Perhaps, not your personal choice, but the USAF-596 is an option as well.

I keep forgetting about it because I haven't used one.  Apologies.

 
Man, we're good. I've been trying to kick one out there for your evaluation. 

 Was it Danny DeVito who asked "What's the worst that could happen?!"