vt-22 half power switch/mod

[meexiko]

Hi to everyone, I'm new in the forum.

I have a master volume vt-22 model and I would like to know if I can mod the amp to run at half-power. I know that any good tech could do that, but I'm asking because I don't want to damage the amp. So, is it possible? I'm thinking to replace the polarity switch with a half-power switch, could be a good idea?
Thanks in advance!

[Hangman]

This is a pretty common question with the v4/vt22. can't say I blame you since they are so darn loud. But there are two things to keep in mind. First, the amp doesn't get much quieter. Many people confuse half power and half volume. With only two tubes the vt22 will still be really loud, volume reduced 10% or less.

Second thing is that the half power switch on so many amps just disconnects the cathode on two of the power tubes. This doesn't make sense because that changes the output impedance of the amp. The speaker load is then fully carried by two tubes instead of four. It's like running an 8 ohm out into a 16ohm cab.
You can pull two tubes run switch the impedance to 4 ohms and run a 8 ohm load, or switch to 2 ohms and run a 4 ohm load. That would keep the ratios correct and not overwork your tubes. But again, for what gain? As I mentioned above the amp doesn't get much quieter.

I don't mind pulling tubes and changing the output impedance to correctly match the amp to the speakers. It's also super easy and doesn't require a switch rewire.

[meexiko]

Thanks Hangman, you're right, 10% is nothing. Maybe using an attenuator could be a better choice...

[Hangman]

Thanks Hangman, you're right, 10% is nothing. Maybe using an attenuator could be a better choice...

yeah, there are a lot of great attenuators out there. My friend uses a V2 and its still way too loud.

[Liquids]

Thanks Hangman, you're right, 10% is nothing. Maybe using an attenuator could be a better choice...

yeah, there are a lot of great attenuators out there. My friend uses a V2 and its still way too loud.

I say, pull two tubes and change the impedance "permanently" in order to save two tubes and buy the best good pairs instead of quads (or cheap pairs x2 instead of a cheap quad), unless you are running out of bass headroom. Then again it's "only" 3db of bass headroom - the output transformers (and power transformers) make low frequency headroom and power possible, even with 2 tubes. I think with amps like Marshalls and such, if I'm not mistaken, the 2 power tube models have OTs that weren't as hefty as the 4 power tube models, which is why it can make a lot of sense to properly run pairs and adjust the speaker output impedance on a 4 power tube model rather than run 2 power tube model--more low end girth that way. On the ampegs, the bigger benefit may be that the V4 type run lower voltage than the V2 type do...

But whatever the case may be, you save 2 tubes if you don't need the extra headroom if nothing else, and only lose 3db...

[Hangman]

Thanks Hangman, you're right, 10% is nothing. Maybe using an attenuator could be a better choice...

yeah, there are a lot of great attenuators out there. My friend uses a V2 and its still way too loud.

I say, pull two tubes and change the impedance "permanently" in order to save two tubes and buy the best good pairs instead of quads (or cheap pairs x2 instead of a cheap quad), unless you are running out of bass headroom. Then again it's "only" 3db of bass headroom - the output transformers (and power transformers) make low frequency headroom and power possible, even with 2 tubes. I think with amps like Marshalls and such, if I'm not mistaken, the 2 power tube models have OTs that weren't as hefty as the 4 power tube models, which is why it can make a lot of sense to properly run pairs and adjust the speaker output impedance on a 4 power tube model rather than run 2 power tube model--more low end girth that way. On the ampegs, the bigger benefit may be that the V4 type run lower voltage than the V2 type do...

But whatever the case may be, you save 2 tubes if you don't need the extra headroom if nothing else, and only lose 3db...

hey! welcome to the Forum liquids! Glad to see you.

I agree with you, the attenuator wouldn't be my first choice. pulling a pair of tubes would. But if its still too loud at 60 watts, there are good attenuators out there that can help take the edge off a little.

-steve

[meexiko]

Thanks guys for the advice, but I need the headroom.

Yesterday I run the amp at high volume. I set the knobs on my vt-22 with Volume One at 11:00 (rocker switch on 0db), High at 03:00 (high switch on), Medium Freqs at 02:00 (300hz), Bass at 01:00 and Master Volume at maximum. With that settings i like the color, the tone very much.

It was loud, very loud, but in a good way. What i noticed is that the sound was distorted, maybe too much distorted. The only pedal i used was a Boss SD-1 set as a boost. If i turn up the gain on the pedal there was almost no difference in the sound coming from the amplifier. Is that normal (the pedal works perfectly on any other amp)? It was like if the amp can't put out more sound, more fuzzyness. I noticed that, also without the pedal on, sometimes the sound was bad, like the sound of something frying. That happens expecially when I hit hard the strings on the guitar.

So, does the amp need a recap job? Maybe a tubes change? Maybe both? I'm asking because I know that with the settings I use, the amp is supposed to sound overdriven, but in good way, with a lot of headroom, dynamics etc etc... Yesterday was no headroom (no real difference with the pedal engaged or not), no dynamics at all.

It's all original inside & outside, caps, tubes, cones, everything.
Thanks if you can help because here in Italy I think I'm the only one with that amp, so I can't visit some friend that have the same amp.
Sorry for my bad english.

[Liquids]

These ampegs typically have no grid stoppers. You might be hearing blocking distortion.

with the volume knob at 10 - there is no grid resistance on the following tube stage in this circuit other than the impedance of the previous stage. You might find it has less of that frying sound if you back it down the slightest bit, and won't loose much distortion.

You might also be hitting the first tube very hard and causing it to flex in it's grid bias significantly - especially with a boss pedal that has a buffered signal when the pedal is on or off. This might be added to the frying sound, in addition to the nature of all that high end and the amp at 10. And it may be that if there is significant blocking distortion, any OD the pedal is producing might be negligable.

First try turning the volume knob down just a tiny little bit, then a bit more, see how that compares. Then, if it makes little to no difference in regard to the frying sound, try plugging straight into the amp and see what that does.

Adding grid resistors is doable and might be an improvement on the sound of these amps when run so hard for better driven sound, but not sure if you are handy and know how to work these things safely.

Otherwise, I suppose it could be the tubes, but probably not the power filter caps.

I suppose it's possible you have a leaky coupling cap...I reccomend replacing them all anyhow--because, why not(?) here, and they're not 30-40 year lifespan parts, nor do they have vintage value as being stock, and mainly it saves time and headache since they'll inevitably drift and leak and blow one by one over the years and cause issues, and replacing them all with new quality parts is far easier and safer than testing them all to find out which leak and which don't...but that is far easier if you're handy.

In this case, you are running the amp pretty hard, why not pull two tubes and change the output impedance? You'll save two tubes that are being driven hard as it is, instead of four, even if you only get -3db less volume. You don't need headroom unless you are playing live with it cranked to 10 - which should be loud enough for, say, Royal Albert Hall. Otherwise, 2 power tubes running at or near full out is more than plenty loud for most people. If it seems quiet, something might be very wrong.

[Hangman]

Yeah, it does kinda depend on the guitar you are using etc... but once you hit the full output of the the amp it will distort pretty heavy and it wont respond as much to changes in the the input.

one thing to remember is that the volume control is a linear taper pot. Not an audio taper. So it seems to reach almost full output very quickly. setting it to 11 actually much like setting an audio taper to 3 o'clock or beyond.

so its as though the amp was cranked. not a bad way to run the amp, but it does make it more one dimensional.

these amps take pedals really well in general, but if they are cranked, they can get really mushy or undefined when using other pedals.

if I was getting my distortion from a pedal, and needed the amp to be clean sometimes, i would run the amp kind of on the edge of distortion (for me around 9 o'clock with my guitar) which was great because it was nice and clean when I wasn't laying into it... but went strait into that ampeg distortion if I played a little harder.

very reactive amps.

[meexiko]

Thanks a lot guys!
I didn't know that the volume is linear. That explains a lot about how the amp works.
It seems that could be that and that grid stoppers lack. I will try to pull out two tubes and soon as I can I'll do a recap job.
Thanks again.

P.S.: the amp it's not quiet at all