Location of Standby switch - before B+1 or after????

[JammyDodger]

Tonegeek,

You are certainly correct. I was looking at a schematic by Odourboy dated Jan 2008. It shows B+1 BEFORE the standby switch. I guess I should re-title this post 'Location of B+1'.

Thanks to everyone.

[talbany]

There are several advantages and dis-advantages to the standby break going between B+1 & B+2.. Advantages are you don't get a loud thump when you turn it off and it does relieve some of the voltage stress applied to the switch with the inrush of voltage..The disadvantages being if your caps are rated @ 500V and say you have 470 on the plates when operating, when you hit the standby your plate voltage will increase and put you near the 500V rating (especially on a 100w Power trans)..
If the amp has a tube rectifier you can normally break it between the rectifier and the plates.. The slower reaction time of the tube does help relieve the stress on the switch as well as you getting a loud thump...If your doubling up on your caps and have some headroom there I prefur the break between plates and screens...
It's not the amount of voltage that stresses the switch but the sudden in-rush that takes them out..Hope this helps...


Tony VVT

[Structo]

Hmm, I don't get any thump when I turn my standby to play.

Could be the balance (bleeder) resistors prevent that?

[Sonny ReVerb]

The disadvantages being if your caps are rated @ 500V and say you have 470 on the plates when operating, when you hit the standby your plate voltage will increase and put you near the 500V rating

Also, would a bleeder resistor provide enough of a load in this situation, to prevent some of the voltage increase when on standby? I know it's usually just a few milliamps across the bleeder, but that would drain some of the charge it seems.

[talbany]

Yeah!! I dont know.. If the screen caps hold the charge it won't thump...
normally in the chain of events you want----from rectifier--- to plate caps--- to standby---- to plates & choke ---Other side of the choke feeds screens...

Here ya go Ampeg B-15N.. Pretty cool!!! what they do is w/full wave they lift the CT on the power Trans.. also have it so if the speaker jack comes un plugged also lifts the CT turning the amp off.. Nothing wrong with this method... Just check to be sure when in standby your not exceeding the voltage on the caps...




Tony VVT

[Tonegeek]

Tonegeek,

You are certainly correct. I was looking at a schematic by Odourboy dated Jan 2008. It shows B+1 BEFORE the standby switch. I guess I should re-title this post 'Location of B+1'.

Thanks to everyone.

Not to derail this thread, but its possible Odourboy's schematic is correct. I know there are mistakes in the hand drawn schematic of #124 that came to light after much analysis. One of them is the voltage doubler circuit for the relay supply IIRC.

[odourboy]

Tonegeek,

You are certainly correct. I was looking at a schematic by Odourboy dated Jan 2008. It shows B+1 BEFORE the standby switch. I guess I should re-title this post 'Location of B+1'.

Thanks to everyone.

Not to derail this thread, but its possible Odourboy's schematic is correct. I know there are mistakes in the hand drawn schematic of #124 that came to light after much analysis. One of them is the voltage doubler circuit for the relay supply IIRC.

If that's the schematic I think it is, the location of the B+1 before the standby switch was an error which was corrected and the schematic replaced by a subsequent version dated Mar. 6, 2008.

[Tonegeek]

What is in question I think is not the B+ but whether the main caps should be on the hot or cold side of standby for #124. Your #124 schemo in the files section shows OT plate caps on the hot side, B+ on the cold side, and the original hand drawn drawing shows it all on the cold side. I seem to remember Funk once saying that HAD put his main caps on the hot side like your drawing, but I trust my memory about as far as i can heave a 100 watt head.

[Structo]

On the schematics I have filed, #124 shows the caps first before the Stby switch.
Although the 101 ODS has the switch before the caps.
The early 80's has the caps first.
The Hybrid has the switch first.
Two Rock Custom Reverb has the caps first.

So for bleeding the whole works down you would have to have the standby switch in the play position.

[butwhatif]

fyi the primary bleeders are attached to the primary caps, they are always bleeding, and generally, it's not ever bled down, unless it's on your bench. if u really think it's an issue, add extra bleeders

[heisthl]

When in doubt, do it like most Fender's (especially the old reliable ones). Main filter caps are charged and the standby switch powers everything else (including the OT). Use a .01 disc cap across the switch to prolong the switch life (although a lot of the old ones didn't have the cap).

[JammyDodger]

Heistl,

I've noticed a lot of builds using that .01uF cap. I'm guessing at least 500V. Does this effect the 'pop' any when you turn it off?

Does anyone use this across the power switch as well?


Cheers, Mike

[tictac]

Here's the way I do it, no thump @ turn on...
When you put the standby before all filter caps the switch sees all the current charging the power supply; put the switch after the first filter cap (the largest value in the amp) and you eliminate the current charging those large caps, the switch is less stressed in this position...

TT

[heisthl]

Heistl,

I've noticed a lot of builds using that .01uF cap. I'm guessing at least 500V. Does this effect the 'pop' any when you turn it off?

Does anyone use this across the power switch as well?


Cheers, Mike

Not sure - I've never had a "pop" problem - the cap stops the arcing so the switch lasts longer. Not needed for AC (like the power switch).

tictac - change that drawing to show where the OT gets it's B+ - there is no point in having a standby if the plates have full power on them.

[talbany]

fyi the primary bleeders are attached to the primary caps, they are always bleeding, and generally, it's not ever bled down, unless it's on your bench. if u really think it's an issue, add extra bleeders

If your referring to the 2 220k resistors on the primary caps (or plates) those are balancing resistors not bleeders which is why they don't bleed off (helps keep the voltage balanced between the 2 caps while operating)..The bleeder caps are normally 220k's going directly to ground from the + side of the cap (as in the precision PS) or Scott's infamous fet load resistor is technically a bleeder, I cannot think of any purpose these resistors serve accept for safety reasons or in the fet case simulate a load or drains them while in standby.. As far as altering frequency response in some way...It may but I seriously doubt you can hear it..Anybody got an opinion on what purpose bleeder resistors serve other than safety bring it on love to hear it..

Here's the way I do it, no thump @ turn on...
When you put the standby before all filter caps the switch sees all the current charging the power supply; put the switch after the first filter cap (the largest value in the amp) and you eliminate the current charging those large caps, the switch is less stressed in this position...

Tictac..
is there a particular reason why you want to keep voltage on the choke or the sag resistor when in standby..

We should change the thread subject to 101 ways to wire a standby switch!! LOL


Tony VVT