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You can make a significant change to the sound of the 15 by using a 5U4GB rectifier instead of the standard 5AR4.
How does it affect the sound?


The 5U4 manifests itself in less compression and the amp sounds cleaner. If you want more clean headroom, then try it. The 5AR delivers the classic Matchless sound. Very different and very noticeable and compressed. Its great to be able to easily swap a rectifier and get a noticeably different sound.

Lawrence Bethune has done some listening with various 5U4GB's vs. the JJGZ34/5AR4. He report:

"The 5U4's are give the amp a crisp and immediate response. You can dial in jagged if you want. Some styles demand this kind of snap and twang. It is really nice with a strat and a silver bell. Like Coco said there is a good deal of clean headroom with the tranny I have in mine.

The JJ5AR4 changes the character of my amp quite a bit. It is very much softer in terms of note attack. The sound overall is more compressed, smooth and less twangy. Some may say less harsh. I liked humbuckers better this way. Keep in mind though, there is a fairly large OT in my amp (>15 watts I think?) so there is pretty much no saturation going on in there. But with the 5AR4 there is this smooth singing thing going on. It's funny though. I found it hard to get a really clear clean sound.

If you decide to stick with the 5U4GB, it would be a good idea to put in a standby switch. This is because the 5AR4 has a controlled warm-up before high voltage is applied to the tubes while the 5U4GB does not.

Depends on what sound you're after.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Have you measured the B+ voltage with both rectifiers? I've always been under the impression that the 5U4 has more voltage drop across it than the 5AR4/GZ34.

Yes, it's in the 340 volt range, which is about 10V less than the 5AR4. That expalins some of the cleanliness at least, but the 5AR4 really compresses the sound and the 5U4 opens it up. I know of one person who liked that sound better that way in his 15 than his stock DC-30.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I like the spank of the 5U4GB but I keep a 5AR4 in the kit bag for a (much) more compression.

That sounds a bit backwards to me. Usually lower voltage means more overdrive. I'll have to check the currents through the tubes with the funny primary impedence to see if I can explain what you are talking about.

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--s2
www.s2amps.com
www.category5amps.com

Yeah, I know it sounds backwards.
The 5AR4, has less internal resistsnce, therefore less voltage drop and should therefore compress more. Right?

But the 5U4GB really does sound cleaner, with more headroom, even though it has more resistance and more votage drop.

If you get a chance, put 5U4GB in there and let us know what you think.

I think, the operating range of the EL84s is maxed out at the higher voltage, in combination with the 4K impedance, and that's the main reason for the cleaner sound with the lower voltage 5U4s.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I agree that the 5U4 is cleaner sounding and a little stiffer. Have you tried a 5Y3? That is my current favorite rectifier in the Lightning.

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--s2
www.s2amps.com
www.category5amps.com

Really? I have my 15 at the rehursal hall right now. I will have to bring a 5Y3 and see what changes it makes.

How would you characterize the change in sound/feel s2?

Remember if you want to keep using non-5AR4s, that a Standby switch should be used to save the tubes. Although, come to think of it, I do use a 5U4GB and no standby...

lbet, what's the verdict on te 5Y3?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

My 15 has west labs trannies in it. I thought i needed to install a filaments trans to use 5U3. Is that correct?

The West Labs tranny has 5V tap and I confirmed with Dave that it can handle 3A, so the 5Y3, 5U4 can be substitued for the 5AR, no problem (except maybe the stand-by in the long term).

Try it and let us know how it sounds.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I just used a 3 way switch in a Blues Jr conversion to slide a standby into a single hole. It is an on-off-on DPDT wired so that down is standby, center is off (obviously) and up is on. Pretty cool as it turns out. I might do the same thing with my Lightning if I ever actually open her back up. This is a very nice and very simple modification that doesn't require any modifications to the chassis or face plate.

_________________
--s2
www.s2amps.com
www.category5amps.com

Cool idea indeed. Going through the Off position on the way to Standby is not a concern?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Nah. Standby only powers the heaters, which can be thought of as light bulbs. It is no more dangerous than flipping a light switch off and back on.

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--s2
www.s2amps.com
www.category5amps.com

Westlabs sell a double pole triple throw progressive (DPTTP) that does the standby/power in the one switch. They're super heavy duty (20amp) rated, a bit expensive, but very good. I've got one in my Lightning clone. In the bottom position both circuits are off; middle position has one circuit on and top position has both circuits on ... perfect ..

REGARDS

Barry M

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Barry M

5U3? Not necessasy for the 5U4, 5Y3. The West Labs 5V rectifier tap is good for up to 3A.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Carling makes a similar switch in on-off-on configuration (slow make, slow break progressive toggle). You can buy it from Mouser for $6.79 PN 691-2GM51-73.

_________________
--s2
www.s2amps.com
www.category5amps.com

That's an On-OFF-ON configuration. Barry was talking about ON-ON-OFF I think.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

An ON-ON-OFF would certainly make it a lot more painless to put a PPIMV in an 18. Currently I've been moving the Power switch and drilling a new hole for the pilot light.

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Richard Johnson
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Playing an insturment doesn't make you a musician, listening does

Just to throw another rect into the mix, try a JAN 5R4. More voltage drop than the 5U4 (about the same as 5Y3) but only two amp heater draw, and DC ouput current to spare, so it's barely breaking a sweat in a 2xEL84 amp, and neither is the westlabs PT. (Also works great at high altitudes CraigB