DPST standby switch

[Boone]

Hello everybody, I have a 5F2-A clone. I purchased a standby switch from Tubedepot.www.tubedepot.com/p-dpst-3way.html The layout shows 2 black wires for AC mains and two red for B+. I will assume the B+ on my Princeton PT are the two yellow wires to pins 2,8 on rec. Please see the link and tell me if I am right track with this so as to avoid a BBQ in the power section. I plan to run the blk wire from fuse and the other blk wire from stock switch to right lugs on DPST. I plan to remove ONE of the yellow PT wires from V3 pin 2 and run it up to other set of lugs on DPST ( top left lug) and then run another yellow from (bottom left lug) back down to pin 2 at V3. Is this correct according to link I have provided? Thanks for the help everyone!

[eleventeen]

Pins 2 & 8 on the rectifier tube is the filament or heater, depending upon your chosen terminology. While it is true that the B+ to the amp is taken from one of those two terminals (recommend pin 8 in case you ever decide to try out an indirectly heated rect tube...it doesn't matter on a 5Y3 or a 5U4) the usual practice is to interrupt the B+ itself. That means, the switch cuts the wire that is taken from the rect tube----not one of the two yellow transformer wires. This leaves the rectifier heater/fil lit up and ready to rock as soon as you flip the stby switch. Theoretically, one should try to avoid supplying full AC to the rect tube when the heater is cold....this is supposed to cause cathode stripping which is a life-shortening thing in tubes. But let's face it, this has been done since the dawn of tube time.

Short answer: Most people would not interrupt (using your switch) the heater for the rectifier...Most people would interrupt the B+ power takeoff which COMES FROM one of those tube pins. Most people would also like to see any bleeder resistor (if your amp is so equipped) remain IN CIRCUIT, meaning still connected to the filter caps when you flip the amp into standby so that the HV on the filter caps bleeds off a little faster. Makes for a little safer situation for servicing.

[Boone]

I am new to amp building and am still in newbie class. This is complicated. I have 2 red wires from PT going to rec pins : 4,6 . I have two yellow wires going to 2,8 . Pin 8 has B+ lead to first 16uF cap. Please refer to link. Please water this down for me. Which wires should I use and where to place switch? I followed the std Fender layout in initial build. Them layout per tubedepot DPST switch has black AC mains and (red B+) from the PT. please try to keep this simple for me.

[Boone]

Excuse the mix up on my part with terminology . I assumed yellow was B+ due to pin 8 going to first filter.

[eleventeen]

OK, no problem. Conceptually, it is quite the weird thing for newbs to understand that high DC volts in a tube rectifier comes off a filament wire/pin. It's just so...unintuitive. But it does.

You were proposing to place the stby switch (electrically) by cutting one of the yellow filament wires for the 5Y3 rectifier.

My suggestion is not to touch any of the wires in the red box, and to place the stby switch where the red arrow points. Meaning THAT is the wire you cut.



THAT wire, the one I'm suggesting you cut, is physically soldered to one of the rectifier tube pins, either 2 or 8, but is NOT one of the yellow wires that comes out of the tranny.



It appears, from the schematic, that where I am proposing you cut your wire is "a dot in the air" that you probably recognize as an electrical connection, but I assure you, the actual place where that "dot" is, is upon either pin 2 or 8 of your rectifier tube. The OTHER filament pin, nothing is connected there but the single yellow wire from the tranny. Forget that one. You want to cut the non-yellow wire connected to the OTHER filament pin and place your stdby switch in the middle of that wire.  

AND BY THE WAY, DO NOT TOUCH ANY OF THESE PARTS until power has been shut off to the amp for a good 5 minutes...even better, MEASURE the DC volts on either pin 2 or 8 of your rect tube relative to ground (chassis) and don't touch anything until that reading is in single digits.

[Boone]

Not to complicate matters but on a side note: I have an indirectly heated 5Y3 it's a Bendix 6101. I ran that in the amp for awhile but it allowed more voltage than I would like to see. I ran the Bendix with rec wired per Fender layout. Should I have re wired for Bendix? NOTE: I do want to understand the correct way to wire the DPST though.

[Boone]

Ok, so I place switch inline with wire from pin 8 to first filter cap? Would this method eliminate 5Y3 from the standby wiring? In other words the 5Y3 never gets to pre heat...but is blasted with high voltage when cold?thanks for the patience!!

[eleventeen]

Those are actually "6106". They are considered to be the same thing as 5Y3s except super rugged and they take about 2 minutes to warm up. Like other indirect rectifiers, they would rather you take your B+ from pin 8 rather than pin 2 but it is not that important and it won't break or burn anything if you get this wrong. And they usually output more volts than a vanilla 5Y3.

[Boone]

I think I am getting a handle on this. When switch is in standby mode:black AC mains preheat ALL three tubes and when switched to ON the wire that goes to first filter connects applying power to all three tubes. Correct?

[eleventeen]

There is no "pre heat", a zillion Princetons and Champs were built with no stby switch...they never cared. Even amps that DO have a stby switch...Bassman, Super, Twin, Deluxe...98% of users flipped both switches up at the same time for 50 years. The stby sw was used to quiet the amp on gig breaks....people didn't think about "cathode stripping" or anything arcane like that. We are talking about a theoretical "best practice" (eg; allow tubes to warm up before applying B+) but in low power applications it's kind of a nothingburger.

I can assure you, with or without a stby switch on your Prince, your 5Y3 will outlast your 6V6 and 12AX7 at least 2.5 : 1.

[eleventeen]

Yep, you got it. Light up the tubes, THEN apply B+ (if it makes you feel better)

It's still not an optimized design...because at the moment you turn from "stby" to "on" you get a big current pulse to charge up all the caps....and when you go to stby, there's nothing (other than the residual conduction of the tubes) to discharge the filter caps...because there's no bleeder resistor.

What we'd REALLY like to see happen is, (waving magic wand) 1: reduce inrush current the first time caps are charged 2: hasten discharge of caps (for service safety) when amp is turned off. Neither is achieved by a stby sw in this case.

But it's not worth worrying about! 1: usually achieved by a choke (which is there for other purposes, too) and 2: bleeder resistor. As I said, It's not worth obsessing over these things in these little amps.

[stratele52]

I don't read all the asnwer but my opinion is a 5Y3 is slow start rectifier and don't need standby switch .

If you want one I suggest keep the first filter cap with the rectifier an put your switch's contact BETWEEN the first AND second filter cap.

Keeping one cap in the circuit will save the rectifier from a big current surge when put standby switch in play position. This cap will help the rectifier.

[Boone]

What value is bleeder resistor and where should it be placed?

[stratele52]

It's still not an optimized design...because at the moment you turn from "stby" to "on" you get a big current pulse to charge up all the caps....and when you go to stby, there's nothing (other than the residual conduction of the tubes) to discharge the filter caps...because there's no bleeder resistor.

 
But it's not worth worrying about! 1: usually achieved by a choke (which is there for other purposes, too) and 2: bleeder resistor. As I said, It's not worth obsessing over these things in these little amps.

Why do you want to discharge filter caps on stanby ? No need  to.  They are ready to work when you put standby to play and save your rectifier.

The purpose of a choke is not to bleed and it do not bleed filter caps anyway.
Show us a amp schematic  with bleeding resistor .

To bleed you need a resitor between B+  to ground . This is more load to the rectifier.

[eleventeen]

You know, I'm guilty of misreading posts too, or, as you said, not reading the posts. But then you point out what you think are errors in what you haven't read.

So I will draw it out for you.

[stratele52]

You know, I'm guilty of misreading posts too, or, as you said, not reading the posts. But then you point out what you think are errors in what you haven't read.

So I will draw it out for you.

Yes I read but am I understand what you write ?   

[Boone]

Gentlemen, I would rather just flip the damn stock switch and be done with the standby issue. Is this cathode stripping thing a load of bull? I run my (inherited) NOS tubes in the.......RCA,Raytheon,TS's etc....vac tubes are not 2 dollars anymore.

[Boone]

Clarify: I run (inherited) RCA, Raytheon and Tung Sol etc...in this amp. These tubes are not 2 bucks anymore and was curious if the stripping thing is a load of bull or not.

[Willabe]

98% of users flipped both switches up at the same time for 50 years. The stby sw was used to quiet the amp on gig breaks....people didn't think about "cathode stripping" or anything arcane like that.

I don't think that 98% is right. All the guys I knew always used the standby switch if they had one.

It was nice on a gig to have the amp ready to play when you came back from break on a gig. It made the band leader look bad to have to wait for the other guitar player and bass players amp to warm up. Hit the stage, flip the switch and go. All the old blues guys I played for and have seen used the standby switch too.

You can just turn down the volume and leave the amp on to quite it but then all the tubes are idling which is helping to wear them out.   

These tubes are not 2 bucks anymore and was curious if the stripping thing is a load of bull or not.

Kevin O'Connor has said many times that the standby switch came from the old power triodes that had 1000+ dcv on their plates. That it was a hold over from the old circuits and Fender and others left them in. When you have that high of a dcv on the plates you can/will get K striping but under 500/600dcv and most music amps are less then 500dcv you wont strip the cathodes.

I still like to have 1 on an amp, but that's just me.


            Brad     

[eleventeen]

I am sure it will reduce the life of your tubes by at least...2-3%. It's honestly not worth worrying about, in my opinion, on small amps. Note that it really only applies to the the 5Y3...because you are not hitting the other tubes with full-on B+ because the 5Y3 is itself warming up slowly and thus delivering a ramping B+ to the other tubes anyway. As I said, I would expect the 5Y3 to massively outlast the other tubes anyway so in the end...this is just a big fat nothing. In practical terms, you don't get the last 10 or 20% of the life out of a tube anyway, because by that time, it's acting funny or making noises or both, and you go and change it for a new one and then the old one sits on your shelf for the next 20 years or gets sold as "vintage" "tested" "carefully matched" "special rectangular Mohegan getter loops" on ebay for big bucks. Or gets thrown out.

[stratele52]

I am sure it will reduce the life of your tubes by at least...2-3%. It's honestly not worth worrying about, in my opinion, on small amps. Note that it really only applies to the the 5Y3...because you are not hitting the other tubes with full-on B+ because the 5Y3 is itself warming up slowly and thus delivering a ramping B+ to the other tubes anyway. As I said, I would expect the 5Y3 to massively outlast the other tubes anyway so in the end...this is just a big fat nothing. In practical terms, you don't get the last 10 or 20% of the life out of a tube anyway, because by that time, it's acting funny or making noises or both, and you go and change it for a new one and then the old one sits on your shelf for the next 20 years or gets sold as "vintage" "tested" "carefully matched" "special rectangular Mohegan getter loops" on ebay for big bucks. Or gets thrown out.

+1000   

I agree

[Boone]

That ends that. I will stock up on some 5Y's and be done with it. Thanks for all the input. I hear you on the eBay bullshit........my ears are not as keen as the guys who can hear one getter tone from another .....what a load.

[eleventeen]

"I will stock up on some 5Y's and be done with it..."

You don't even have to do that. If yours are newish, it's not at all uncommon for 5Y3's to last 20+ years. And there are billions of them out there. You'll replace your 6V6 and the 12AX7 long, long before you need a new 5Y3....which is the cheapest tube in the lot anyway, and your amp stresses the 5Y3 at maybe 1/3rd its ratings. Fuhgeddaboutit.

[stratele52]

"I will stock up on some 5Y's and be done with it..."

You don't even have to do that. If yours are newish, it's not at all uncommon for 5Y3's to last 20+ years. And there are billions of them out there. You'll replace your 6V6 and the 12AX7 long, long before you need a new 5Y3....which is the cheapest tube in the lot anyway, and your amp stresses the 5Y3 at maybe 1/3rd its ratings. Fuhgeddaboutit.

+10000