VHT gig review

[jgcable]

I loved the ease of setup, but missed tube amp 'feel' with the vetta. Sure was a great sounding amp though, and I'll probably get another one eventually. The VHT really has some tricks in it though that the Vetta can't touch tone/feel wise, but it certainly isn't as versatile either.

Pete

My Stiletto has some of the features that your VHT does. It has a variac, I can run 50 or 100w on either channel and I have my choice of Rectifier or Silicone Diodes on either channel. Running the amp with the variac on and at 50w with the Rectifier big bottle tubes activiated really does do a nice convincing brown tone. Much better than a 5150.
I agree about the feel of a Vetta compared to the feel of a good tube amp. I like the way tubes feel much better than how the Vetta feels. Sound wise... I like the Vetta better than any of my tube amps for both clean and high gain tones.

[Twisteramps]

The thing that I forgot about the VHT that no other amp I've played does is the clarity thing. I can have raging dimed out mayhem levels of distortion and play diminished chords - each note rings out fine. I can hear the difference in how hard I pick with full distortion, or if I hammer... what you give up is the ability to coast, or just kinda let your hands get pretty close to the notes you want and for them to come out ok. The VHT is just a strange beast, people either love them or hate them. There's nothing like them IMHO... and the Ultra Lead is even worse. At least the 50/CL has a little bit of give to it - the UL is so stiff you could use it to shore up a skyscraper.

Pete

[akoch]

"The tube rectifier drops voltage by quite a bit - it can be thought of as a built in variac of sorts. "

Sorry, wrong statement. It does not.

What happens though is that under heavy load its efficiency is not as high as of the solid state rectifier, so it sags the voltage. And you get this natural compression in sound, the feel of the amp becomes more sloppy. The thing is, one tube rectifier is still plenty for a 50W amp, so no sag really detectable. For all intends and purposes, solid state rectifier is by far a better choice. Using the tubes for this is basically a trend, marketing, you name it. Has little to do with the sound and music. All IMHO of course.

[akoch]

the Stiletto is more "saturated", thicker and compressed sound-wise, I actually love it. VHT is more transparent, quick, tight and precise. Subjectively I percieve it as a more complex sound.

[Twisteramps]

"The tube rectifier drops voltage by quite a bit - it can be thought of as a built in variac of sorts. "

Sorry, wrong statement. It does not.

What happens though is that under heavy load its efficiency is not as high as of the solid state rectifier, so it sags the voltage. And you get this natural compression in sound, the feel of the amp becomes more sloppy. The thing is, one tube rectifier is still plenty for a 50W amp, so no sag really detectable. For all intends and purposes, solid state rectifier is by far a better choice. Using the tubes for this is basically a trend, marketing, you name it. Has little to do with the sound and music. All IMHO of course.

Sorry, you don't know what you're talking about.

A variac can be used to drop plate voltage. A tube rectifier *will* be less efficient/not have as much voltage for the amp compared to a solid state one. This is a fact. I've built amps with tube rectifiers and solid state ones, using the same transformers. However, the ones with solid state rectification have a higher B+ voltage since they are more efficient. Also, solid state rectifiers are going to react faster to current demands - meaning you won't get as much sag with one. Careful selection/substitution of rectifier tubes can tweak your amps' plate voltage and sag characteristics at high volumes. Some amps have power supplies that are saggier... I haven't been able to sag the VHT yet, but I can tell a difference between SS and tube rectification in the amp.

Here's an example of voltage drop, from a 3rd party so you don't have to believe my word: Page 121 and 122 of the tube amp book by aspen pittman (this is the huge coffee table book, well worth the $ imho):

Same amp, with different rectifiers. He has a nice graph showing how quickly they went to full voltage, etc, which isn't really germane to this thread. Note the numbers - SS was the highest, and it dropped according to different rectifier tube types. This is the same amp being measured, ALL they are changing is the rectifier type:

Solid State - 449.08 volts
5AR4 - 413.9 volts
5U4G - 357.06
5R4-GYB - 330.93
5Y3GT - 303

FYI, you are *always* going to lose some voltage with tube rectification in a guitar amp. Just the nature of the beast. Note there was nearly a drop of *150* volts in the most extreme example. I'd have to go take a peek at the back of my 50/CL, but I'm betting it probably uses a 5U4G or variant - so rough guestimating, it probably loses 90 or so volts in tube rectifier setting vs solid state. You should be able to notice this - the amp will 'brown out' more (more distortion) and lose a little volume compared to the solid state setting. If you don't believe me, measure plate voltage on your power tubes with the amp set to SS and then tube rectification. One of these days when I get a chance I'm going to do just that, I'll be glad to share if you're unable to check your amp voltages.

Keep in mind you just can't toss different tube rectifiers in an amp at will - there are many factors you have to think about for a safe substitution. Just because it fits physically doesn't mean it will be able to supply the amp properly.

Pete

[Twisteramps]

Bump for interesting rectifier info

[hippietim]

I think somebody was...

[akoch]

"Sorry, you don't know what you're talking about."

OK, if I don't know what I am talking about, here is my quick test: my 50cl, 1kHz sine wave from the generator, measuring current and voltage on the 16Om load, master volume at 3pm, channel volume at 12pm for both red and green channels.

Results:
- green channel - identical readings on SS and tube rectifications, plate volrage 419V, output power readiing has not changed
- red channel, 5% reduction in power overtall in relation to the green channel, 6% reduction to for the tube rectifiction setting, but - no detectable plate voltage variation.

I don't observe any voltage and current drop on neither output, nor plate voltage.

What I will agree though, I will see a certain reduction under dynamic load while on the tube rectifier. You are correct about the lesser efficiency of the tube recto. My point was that this is by far difficult to tell in a 50W amp, it has more scientific interest than practical. I still don't see a reson to use the tube recto other than nostalgia.

[akoch]

No comments on Pittman and other coffee table books, here is the spec on 5U4G installed in my amp (Ruby):

Typical Conditions:
DC output voltage 470Volt
Total rectified current 225mA

If you use Sovtec or some others, the max current can even exceed 250+ mA. As you see a single 4UG can 'amost' handle 100+W of power rating. Almost but not quite. For our discussion lets say that it is more than enough for the 50W (or less in class A) 50CL amp.

[Spivonious]

Pete....pwned back!?!?!?!?!?!?

[Twisteramps]

No comments on Pittman and other coffee table books, here is the spec on 5U4G installed in my amp (Ruby):

Typical Conditions:
DC output voltage 470Volt
Total rectified current 225mA

If you use Sovtec or some others, the max current can even exceed 250+ mA. As you see a single 4UG can 'amost' handle 100+W of power rating. Almost but not quite. For our discussion lets say that it is more than enough for the 50W (or less in class A) 50CL amp.

here, from aikenamps website:

If a vacuum tube rectifier is used, sag is generated because of the internal resistance of the tube. Unlike a solid-state rectifier, a tube rectifier exhibits a fair amount of voltage drop which varies with the amount of current passing through the tube. In a class AB amplifier, the current drawn from the power supply is much greater at full power output than it is at idle. This large change in current demand causes the voltage drop across the tube rectifier to increase, which lowers the available plate supply voltage to the output tubes. This lowering of the supply voltage lowers the output power slightly in opposition to the larger input signal, making it act like a compressor. The lowered supply voltage also tends to decrease the available headroom, increasing clipping and changing the operating point of the tube dynamically. This type of sag can be emulated artificially in an amplifier with a solid-state rectifier by adding a series resistance, typically around 100 ohms or so..

Also, the 'output voltage' is going to be predicated by how much voltage goes in. A rectifier isn't a device that automagically creates power. Please understand this - your rectifier will handle up to 470volts. This doesn't mean it's going to output 470volts no matter what is fed into it. It changes AC (alternate current, the stuff in your walls) to DC. A tube rectifier is going to lose more power than the Solid State rectifier. Are you understanding this yet?

Again, get your meter out and measure your amp's voltage with the solid state rectifier setting and then the tube rectifier setting. See for yourself - you WILL lose voltage on the tube setting. you WILL get more sag with a tube rectified amp than a solid state one unless it has added series resistance to imitate tube sag.

If you want to discount the tube amp book, go for it... but it's a good resource for amp builders and hobbyists. It's also filled with spec sheets like the one you quote above.

I feel like I'm trying to teach my cat algebra.

Pete

[hippietim]

here, from aikenamps website:

If a vacuum tube rectifier is used, sag is generated because of the internal resistance of the tube. Unlike a solid-state rectifier, a tube rectifier exhibits a fair amount of voltage drop which varies with the amount of current passing through the tube. In a class AB amplifier, the current drawn from the power supply is much greater at full power output than it is at idle. This large change in current demand causes the voltage drop across the tube rectifier to increase, which lowers the available plate supply voltage to the output tubes. This lowering of the supply voltage lowers the output power slightly in opposition to the larger input signal, making it act like a compressor. The lowered supply voltage also tends to decrease the available headroom, increasing clipping and changing the operating point of the tube dynamically. This type of sag can be emulated artificially in an amplifier with a solid-state rectifier by adding a series resistance, typically around 100 ohms or so..

Also, the 'output voltage' is going to be predicated by how much voltage goes in. A rectifier isn't a device that automagically creates power. Please understand this - your rectifier will handle up to 470volts. This doesn't mean it's going to output 470volts no matter what is fed into it. It changes AC (alternate current, the stuff in your walls) to DC. A tube rectifier is going to lose more power than the Solid State rectifier. Are you understanding this yet?

Again, get your meter out and measure your amp's voltage with the solid state rectifier setting and then the tube rectifier setting. See for yourself - you WILL lose voltage on the tube setting. you WILL get more sag with a tube rectified amp than a solid state one unless it has added series resistance to imitate tube sag.

If you want to discount the tube amp book, go for it... but it's a good resource for amp builders and hobbyists. It's also filled with spec sheets like the one you quote above.

I feel like I'm trying to teach my cat algebra.

Pete

[Twisteramps]

Pete....pwned back!?!?!?!?!?!?

Not in this thread.

[akoch]

"I feel like I'm trying to teach my cat algebra."

Thank you for the comment I'm afraid in this case the cat has a masters degree in electronics. OK, Pete, I have nothing to respond. I gave you the test results obtained from my amp, with both SS and tube rectification using a fairly good lab equipment. I showed you performance ratings and specs of the equipment. Hope you understand how to obtain the power ratings from these numbers. I also gave my subjective opinion on playing this amp for a few years by now, not theorizing about it. There is very little I can do other than refering you to some obscure gurus on the net or to your cat.

I recall me and a few guys had a discussion with Steve Friette on the very same subject a few years ago. He was very blunt about it. In his own opinion there is a very subtle difference in the amp feel when switching the rectos on the 50C. But this was the amp where he at least tried to implement it, as it was pointless on a 100W version - two 5U4s required to handle a 100W version would never give the sag.

[Twisteramps]

There is no way you're going to get the same voltage from a solid state rectifier and a tube rectifier. Unless the VHT has some compensating circuitry, the amp is going to lose voltage running through a tube rectifier. End of story. The amp is going to exhibit more sag, whether detectable to your golden ears and fingers or not, with a tube rectifier. Where were you measuring plate voltage from?

I'll put a meter on my VHT in the next day or so and report my findings. Again though, you aren't going to find a tube rectifier that is as efficient as a solid state device.

BTW, a master's degree is well and good. Unless your degree was obtained several decades ago however, I'm doubting you guys spent much time or any with tubes. What tube-specific courses did you learn? How many tube amps have you built?

Pete