Peavey Valveking 112 Design Weirdness.....

[jrfrond]

I was working on a Valveking 112 combo, and I have never seen another amp that has the Standby switch in this location. The VK places the Standby switch AFTER the first filter cap and dropping resistor, before the screen grid supply.

?????

There are THREE other places where I would have put the Standby switch: in series with the AC feeding the B+ bridge, in series with the DC output of the B+ bridge, and in the ground on the B+ bridge.

I was thinking that they might want to eliminate a slight turn-on thump, but the PSU uses no bleeders and will hold a charge for a couple of days! Plus the filter caps are a healthy 100uF.

So, the plates at the output are always ON, and I can't think of ANY good reason for this. WTF am I missing here?

[Jazz P Bass]

That would be a good one to ask Glen at Peavey.

[jrfrond]

Do you have Glen's contact info?

The ONLY practical reason I can figure out, after chewing on this for awhile, is that, by placing the Standby switch between two DC nodes that differ by only a couple of volts, you pretty much eliminate arcing, therby extending the life of the cheap Chinese switch.

[Enzo]

Don't service Peavey's much, John?

Peavey has put the standby switch there on their tube amps for years. The Mace/Deuce/Artist VT from 1978 is that way. In fact so is the earlier ARtist. Encore 65 1983, Butcher 1985, Rock Master 1983. Classic 50, JSX, Triumph, Ultra, Windsor, Triple XXX.

Even their big old Classic 400 head did it that way, though the screen and plates had totally separate supplies, the screen supply switched on/of.

The VTX stuff did it differently, but they used the standby switch as a voltage selector for hi/lo power.

As to CHinese switch, this circuit goes way back before CHina came along. Besides, when first turned on, the hot side of the switch charges up to 450-500v, but the screen side is still at zero until you flip the switch. You do bypass any potential inductive kick from the OT, I'd imagine.

[mooreamps]

I was working on a Valveking 112 combo, and I have never seen another amp that has the Standby switch in this location. The VK places the Standby switch AFTER the first filter cap and dropping resistor, before the screen grid supply.

So, the plates at the output are always ON, and I can't think of ANY good reason for this. WTF am I missing here?

Really ? I would have thought you would have known this one....... First of all, it's a perfectly valid point for a stand-by. . But, there are a couple of things going on here....

1. Passed the first filter cap, the current load through the switch is very low... Perhaps less arcing on the contacts...But it still puts the power tubes and preamp tubes into a stand-by mode. . . .Plate current through the power tubes will idle back to a very low value without having to control all of that power through a switch. . .
2. It does manage to keep a charge on the first filter cap ; on my drawing labeled C202.. Keeping an electrolytic cap charged like this does tend to help it live a longer service life. . .

-g

[txstrat]

1. Passed the first filter cap, the current load through the switch is very low... Perhaps less arcing on the contacts...But it still puts the power tubes and preamp tubes into a stand-by mode. . . .Plate current through the power tubes will idle back to a very low value without having to control all of that power through a switch. . .
2. It does manage to keep a charge on the first filter cap ; on my drawing labeled C202.. Keeping an electrolytic cap charged like this does tend to help it live a longer service life. . .
-g

Those were the reasons (read it somewhere) why I changed the location of the std by switch in one of my amps. I thought the arcing in the switch and therefore the stress on the contacts would be less. I noticed a slight thump when I switched into play mode and a rather heavy thump when I switched from play back into std by mode. Eventually I changed the std by switch back to right after the bridge and all switching is quiet again.

[jrfrond]

Don't service Peavey's much, John?

Peavey has put the standby switch there on their tube amps for years. The Mace/Deuce/Artist VT from 1978 is that way. In fact so is the earlier ARtist. Encore 65 1983, Butcher 1985, Rock Master 1983. Classic 50, JSX, Triumph, Ultra, Windsor, Triple XXX.

Even their big old Classic 400 head did it that way, though the screen and plates had totally separate supplies, the screen supply switched on/of.

The VTX stuff did it differently, but they used the standby switch as a voltage selector for hi/lo power.

As to CHinese switch, this circuit goes way back before CHina came along. Besides, when first turned on, the hot side of the switch charges up to 450-500v, but the screen side is still at zero until you flip the switch. You do bypass any potential inductive kick from the OT, I'd imagine.

Actually Doug, Peavey tube amps are NOT very popular in the NY area (SS seems to be more popular), and never have been (then again, neither is Boogie, thankfully). Ironically, I used to own an Artist. They do show up once in awhile (last one being an old Butcher, which I liked for it's "Marshall-ness), but the bulk of what I see is Fender, Marshall, Vox and Ampeg (vintage and new), with the occasional Hiwatt, Orange or something else. I never usually take notice of the Standby switch location, but in this case, with the amp having a bad filter cap, I was wondering why I heard hum even with the Standby switch off, so I took notice.

It must be a regional thing with amp popularity, because my two other guys here who have been servicing amps for many years thought it was strange as well. I guess we are deprived here on the East Coast!

I would still love to hear the rationale of the design from Peavey engineers though.

[Enzo]

Oh well, I didn't mean it to be snotty.

WHy don;t you drop the engineers at Peavey a line and ask them? I occasionally have some discussion with one of them.

Oh I have no doubt about the regionality of amp popularity. You probably don;t have near the interest in country up there as we do in the midwest or down south. And wherever you see pedal steel being played, there is probably a big PV solid state amp with a 15 nearby.

[jrfrond]

Oh well, I didn't mean it to be snotty.

WHy don;t you drop the engineers at Peavey a line and ask them? I occasionally have some discussion with one of them.

Oh I have no doubt about the regionality of amp popularity. You probably don;t have near the interest in country up there as we do in the midwest or down south. And wherever you see pedal steel being played, there is probably a big PV solid state amp with a 15 nearby.

Snotty??? I didn't get that at all Doug.

We've all been mainstays in our respective regions, it would seem, so it makes sense that some of us don't see as much of a particular product as others. I mean, GC and Sam Ash sell them, we just don't see them. I've never asked at either store how many Peavey tube amps they sell, but I KNOW they sell sh*tloads of Fender.

[Enzo]

But serious, ask them. Worse they can do is ignore us.




(Just didn;t want to seem disrespectful)

[jrfrond]

Peavey Valveking 112 Design Weirdness.....a redux (aka DUHHHHH!!!)

OK, I'm an idiot (hey, don't agree so quickly!).

After wondering just WHY Peavey placed the Standby switch after the first filter (B+), I got back one of my old amp builds for service (shorted power tube; you know the drill), I saw that I had wired this early design version EXACTLY like that. The NEWEST schematic version didn't show it that way, but this was an early version, just past prototype, that I sold this way. DUHHHH!!!

Hey, it was over 10 years ago folks! Sometimes remembering breakfast is a challenge. So sue me.

Yes, I rewired it.

[Gregg]

Not only Peavey uses this type of standby switch. In newer amps I've seen this in Marshall JVM410 for example but there all preamp tubes + power tubes plates get the high voltage when power is turned on. Standby switches only the screens and the PI on. This way you can use your amp as preamp only.

[Enzo]

I been seeing that more lately, they run separate B+ rails for preamp only, so the amp can have "silent mode" play.

[jmaf]

I unconsciously always thought this placement of standby after the first reservoir cap was meant to keep the amp's largest current path always on for some reason. During the amp's function there is no larger current than that reservoir cap charging spike.

Coincidentally, on the first amp I ever built, I did this by accident and recall being worried that I'd screwed my power supply up. I left it like that in the end.