Ampeg SVT VR Head requiring at least 115 volts from wall socket

[MikeyB]

Slick,

You coulda just bought my VR - I already did the mod!

Seriously though... good luck with the mod. I'm SO glad johnk posted that info.

-Mike

 

[Rickles]

Mike,

I did think about it, but the ride was way too long. I'll use the "1 into 2" connector, so it should be pretty easy.

Rick

 

[Rickles]

An addendum: A Loud Tech told me there is also a resistor change (this may have been mentioned on the thread) that service centers will do under warranty if you ask. If the tech at the service center isn't familiar with it, they can call Loud and get the info. on how to do it. Just a thought if you're going in for something else. The point being: Under warranty.

 

[beebassdude]

so this finally happened to my VR at a gig on saturday. i was freaking out but i remembered this building is super old and we'd had problems before there, and my amp was doing exactly what JohnK described in his summary.

my first question is, where can i buy the new connector to do this mod?

 

[Rickles]

...where can i buy the new connector to do this mod?

This is it; scroll down to "2-In-1 Stationary 6.3MM Blade Connector." I got them and they are the way to go.

 

[beebassdude]

could i buy something like that at radio shack or do i need to order it online? and the one that JohnK has, did he make that or can i buy that somewhere as well>?

 

[Rickles]

The link I gave you is the one JohnK gave in a thread. He came across these after he put the mod up using the ones he made. He said these are much easier to use. I don't think you'll find them at Radio Shack, but you can try.

 

[beebassdude]

The link I gave you is the one JohnK gave in a thread. He came across these after he put the mod up using the ones he made. He said these are much easier to use. I don't think you'll find them at Radio Shack, but you can try.

good deal, thanks for the info man, i appreciate it!

 

[bil]

we played at an old club near the beach; all worked ok, but the dread prompted the mod...

found the clip at local PepBoys: Invalid Link Removed (you get 10 in a package for $3.50; takes care of you and nine SVT-VR pals!)

this can be installed without snipping tie-wraps; very clean!

as always, many, many thanx to JohnK

 

[P A U L]

okay. i performed the standby mod this morning and it works PERFECT! i tested it with my variac and i ran it on 95 volts. its going with me to my gig this friday night.

here's a pic of it installed:

View attachment 1416369

rather than post all the pics and info here, i created a page for the mod on my website:

SVT-VR

Many thanks to Jerrold Tiers for the tips on this mod, and thanks to those that were patient enough for me to post it.

regards,

In all the instructions, illustrations, you mention J26 & J27. For some reason, in this, you mention J26 & J28.

I'm going to do this on an amp I'm supposed to pick up tomorrow, that seems to suffer from this.

Is this a typo? or?...

Just want to make sure, that I'm only adding the piggyback to J27 & then unplugging & piggybacking J26 to that. Don't touch J28, right?

 

[johnk_10]

if you refer to the schematic, J27 and J28 are already connected together (are the same thing) so you can use J27 or J28.

 

[Wasnex]

In all the instructions, illustrations, you mention J26 & J27. For some reason, in this, you mention J26 & J28.

View attachment 3948118

I'm going to do this on an amp I'm supposed to pick up tomorrow, that seems to suffer from this.

Is this a typo? or?...

Just want to make sure, that I'm only adding the piggyback to J27 & then unplugging & piggybacking J26 to that. Don't touch J28, right?

I agree the inconsistency is confusing, but I believe it works either way because J27 and J28 are tied together, so electrically they are the same point.

Here's the first example. Disconnect the female spade connector on J26 and connect it to a male end of the Y. Disconnect the female spade connector at J27 and connect it to the other male end of the Y. Connect the female end of the Y to J27.

Here's the second example. Disconnect the female spade connector on J26 and connect it to a male end of the Y. Disconnect the female spade connector at J28 and connect it to the other male end of the Y. Connect the female end of the Y to J28.

The idea is to bypass K1. Normally power from the standby comes in on J26, goes through the contact of the energized relay (K1), and then goes out on both J27 and J28.

When you install the Y cable, J27, J28 and all points on the Y are electrically the same. J26 is just an empty male spade connector...but keep in mind that it is connected to AC through the relay contacts.

 

[P A U L]

ok, J27/J28 are parallel points, tied together... & J26 (wire) is the feed for standby switch....

I just reread Jerrold's post & it makes sense now. That the US version uses both tabs, so you piggyback either one, although it looks like J127 has easier access for the piggyback. EU/220 uses only 1 lug & all they have to do is move J126 to the empty lug...


Thanks guys!

 

[P A U L]

Thanks again guys!

I scored the amp & it took me all of about 5 minutes. I didn't even have to take the chassis out. I just stood the cab, on it's side & leaned it out far enough. It took longer to get the cab mounting screws back in, than everything else combined...

I got the amp, w/ the disclaimer that it wouldn't come out of standby most of the time, or go into standby during a customer's performance.

They are a backline, production company, so it was useless to them, if they couldn't insure it's reliability. Ampeg sure didn't do themselves any favors w/ this brainstorm...

 

[Wasnex]

Thanks again guys!

I scored the amp & it took me all of about 5 minutes. I didn't even have to take the chassis out. I just stood the cab, on it's side & leaned it out far enough. It took longer to get the cab mounting screws back in, than everything else combined...

I got the amp, w/ the disclaimer that it wouldn't come out of standby most of the time, or go into standby during a customer's performance.

They are a backline, production company, so it was useless to them, if they couldn't insure it's reliability. Ampeg sure didn't do themselves any favors w/ this brainstorm...

The same relay circuit is used in the CL, so I don't think the problem is the relay circuit.

If you look at the power amp boards the CL and VR are different. The CL has more extensive bias sense and fault detection capabilities that monitors the tubes individually and puts the amp in standby when a tube is a bad enough to cause damage. AFAIK the VR does not have these features. This is from the VR and I believe it is just a relatively simple 20 second time delay circuit ( 4 components):

I can't find the interconnect diagram for the VR but I am pretty sure the signal goes out on J9 and is fed to Relay Control on J35. Interesting note. The VR is supposedly a modern revisioning of the early Blueline SVTS. The 69 also had a time delay standby feature that did not function properly . So they nailed it !

In the Classic the fault signal goes out on J12 and is fed to Relay Control on J35. See the red rectangle. I am not 100% certain, but I think this circuit is intended to put the amp in standby if massive overcurrent is detected in one or more output tubes.

 

[P A U L]

well, it seems to have fixed it... I'd venture to say, that everyone in my neighborhood knows that there's an SVT in the hood... ...

I found this, that some might find interesting:

Ampeg SVT-VR | Balance Problem

he also has a SVT-CL fix in there.

 

[Wasnex]

I found this, that some might find interesting:

Ampeg SVT-VR | Balance Problem

Yes the VR has a less sophisticated bias sense scheme. It has two bias sense circuits, and each circuit basically sums the cathode current of three tubes and indicates whether it is in the proper range or not. The problem with this simplified setup is it does not detect mismatched tubes are if one or more tubes stops working, it only detects total current.

I believe the Balance circuit monitors the signals at the input of both bias sense circuits and essentially compares them. The bias sense is looking at DC and I believe the balance sense circuit is looking at and comparing AC waveforms.

You drive the amp to an output of 25VRMS and adjust the balance control, which is part of the phase inverter circuit. The Balance sense circuit sort of compares the relative size of the signal generated in each side of the push pull output section. When the output of both sides are about the same, the comparator circuit turns on the Balance LED.

The CL monitors all six tube independently. So if any tubes are over current or not working you will get a fault indication. I believe this is an accurate representation of how the circuit works.

This circuit is for three of the tubes; there is another identical circuit for the other three. All six tubes are also monitored by an additional fault circuit that is attached to the relay control circuit as discussed in post #115.
The CL does not have a balance control.

 

[sonofmt]

Do any of you all know if the more recent SVT VRs have this same issue? I'm assuming so, but perhaps Ampeg changed the wiring over the years.

 

[P A U L]

Do any of you all know if the more recent SVT VRs have this same issue? I'm assuming so, but perhaps Ampeg changed the wiring over the years.

sorry, I never saw this...

I'm not sure when, but Ampeg had, at some point fixed the circuit, they were taking bad ones in for repair too, but IDK the circumstances...

Now Yamaha owns them, so, I'm sure they've got things under control...

 

[Analogeezer]

I have an SVT-CL (made in USA) that has worked down to 92VAC. I got to a gig and plugged in my power conditioner and it showed 92VAC - I was amazed when it clicked out of standby and made noise. When it dropped below 90VAC, (when the guitars started), it cut out...it didn't go into standby, it simply stopped working then came back on when they stopped. Of course, 90VAC is a lot less than 115VAC.

[On a side note, my backup head, a GK 1001RB-II, worked all night long below 90VAC without a hitch.]

Reminds me of decades ago (early 80's) there was this guy who worked at a local music store who also had a large sound company - we used to buy used SM-57's from the guy for cheap.

Anyway at the time our band was being asked to play a lot of "field parties" and I remember turning down this one because they wanted to use a generator.

So I asked this guy about it and he said "NEVER DO A GIG ON A GENERATOR, I don't care if it's the size of a VW you are asking for trouble"

Fast forward about 25 years and our band gets asked to play this outdoor thing at this farm with a bunch of bands on the bill. You guessed it, generator.

Four piece band, a guy who played four keyboards and a module and the guitar player had a digital preamp into my Peavey 50/50 rackmount PA amp.

So we are deep into about the fourth song and the power starts to sag, all of a sudden it's a drum and bass solo.

I look back and the guitar player's preamp is doing the "LED's going in a circle around the knobs thing" it did when you first fire it up. They keyboard player is frantically stabbing at his boards because when the power glitched his rig reset so he had to call up all his programs for that song again.

This happens about 3 or 4 times during the 45 minute set, VERY annoying. Thing was my Ampeg B2-R I was using never missed a beat, so the drummer and I had about four long solos during the set LOL.

Analogeezer