Mid 70's Peavey VT Classic 50 - Standby Switch help

[Hendershot2009]

Hey guys,
I have a mid 70's Peavey VT Classic 50 that has only the stock power switch & doesnt have a standby; I want to have a standby (possibly) on the stock 3-way on switch so it would then work as "OFF-STANDBY-ON" so I don't have to drill and extra hole in the chassis, unless I need to. The amp still has the factory Peavey Super 6L6's, and still works fine without any issues. However, it is biased sort of on the cold side, and when I order a set of JJ's I am going to heat up the bias to proper spec or a little more. While I have the amp open, I am also going to take out the old filter caps and get some sprague, JJ's, or Ruby caps to replace them. I know Peavey still has amps that do not have standby switches, but I absolutely want this addition in my amp also to prolong tube life and to prevent cathode stripping.
Has anyone else done this?
Anyone have photos, or instructions?
My model has bias pots on each tube, not sure if they are factory or not. With a standby on this amp, it will also make biasing a little easier. Please let me know if you have any information.

[selloutrr]

Don't these amps use a Thermoster to mute the amp until the tubes are warm?

[selloutrr]

http://www.singlecoil.com/docs/standby.pdf

[Hendershot2009]

I don't think that they do - I will double check to be sure.
Thanks for the switch diagram! I thought that I could still use the old switch, I just wasn't sure.

With the way this amp is built, I'm just unsure of where to insert the standby; just in between the B+ and the tube(s)?

[selloutrr]

AC should already be at the switch the B+ can be tapped just after the rectifier.

[gingertube]

Standby Switches are for transmitter tubes running 1500 Volts plus.

Cathode Stripping simply does not occur in tube amps with typical tube complements and voltages. I'm not quite sure why we haven't managed to put a stake through the heart of this ancient piece of missinformation.

Minor tube life extensions are possible with "full bore" standby circuits which include reduction in heater voltage as well as High Voltage removal, otherwise its best just to leave the amp on.

Amps using cathode bias and in particular amps using cathodyne phase splitters stress tubes much worse when a standby switch is used as in both cases you get large current spikes in the output tubes when switching out of standby to the extent that I've seen amps which pop their HV fuses when the HV is reapplied with heaters already up to operating temperature.
EXPLANATION: In cathode biased amps you get a current surge until the cathode bypass cap(s) charges up and establishes correct bias voltage, with the cathodyne splitter you get a high positive going pulse on the output tube grid connected to the anode side of the cathodyne when HV is applied, this causes a high current pulse in that side of the Push Pull Output Tubes.

SO Standby Switches CAN introduce serious reliability problems.

If you simply want to mute the amp during band breaks at gigs then a circuit to remove signal (but NOT bias) from the oputput tube grids is a far better approach.

If someone askes me to design and build an amp for them and wants a standby switch I do my best to talk them out of it, if they persist I offer them an output tube grid mute function instead. If they still insist I add $150 - $200 to the price so that it can be done properly and safely with a heater voltage reduction circuit included and a slow HV turn on.

Cheers,
Ian

[Hendershot2009]

Thanks Ian! Basically I was wanting a standby because all of my other amps do, and this Classic is one of my favorite amps that I like to use. I know with amps that use EL84's dont have to have standby switches and operate fine that way, but every 6L6/ EL34 amp (other than this Classic) that me or my friends have had always ends up having issues when switching the amp fully on (leaving the standby switch on, so only flipping the "on" switch turns the amp on) with either a tube that goes bad, redplates all of a sudden, etc. even with somewhat new tubes. However, JJ's seem to be pretty tough in this kind of use. I guess if this amp has been working fine for the past 30+ years, it's most likely going to continue working fine (although, the caps are for sure getting replaced and upgrading the wattage on the screen resistors).

I have actually got rid of the original combo cab because it had some moisture damage on the bottom, and I didn't have room for a combo anyways; so I built a head cabinet, and bought white chickenhead knobs to get rid of the butt ugly colored ones (bugged me because they weren't all the same color), I built a tube "support" with springs to hold in the 6L6's better and reduce vibration. The back has a panel with a metal screen to protect the tubes, etc. and vent the heat (instead of the small board/ panel that had tolex and fabric on the back of it that surprisingly didnt catch fire). The only bad thing about the amp is that the previous owner removed the footswitch jack, and not sure why. I'd never use it anyway, but is always good if its there. I'll post a few photos.