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Post subject: Blues Jr Standby switch?
Posted: Sat Apr 03, 2010 5:38 am
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Could anyone tell me why Fender have not incorporated a standby switch in the Blues Jr? My understanding is, when you switch on the amp from cold, the valves get a surge of power which can reduce their life span. Is not having one going to cause a problem. I have fitted a new switch to my 600 Champ which offers Off, Standby and On options in one switch, has anyone done this mod to the BJ?


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Posted: Sat Apr 03, 2010 6:18 am
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I personally haven't but check the link: http://billmaudio.com/wp/?page_id=327

I intend to do several of the mods but am working on my soldering skills before I work on something a don't want to mess up.


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Posted: Sat Apr 03, 2010 10:09 am
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The BJ does not technically need a standby switch as discussed by Billm in his website. However, he offers one, which I installed in my amp (very easy to do and inexpensive) only for the convenience if switching guitars and not needing to shut the amp down or lower the volume.


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Post subject: Re: Blues Jr Standby switch?
Posted: Wed Dec 05, 2018 4:35 pm
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Would you mind telling me how to install the standby switch onto Fender Champ 600?
I have the new switch already but I'm not really sure about the wiring.
Help Please !!!


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Post subject: Re: Blues Jr Standby switch?
Posted: Thu Dec 06, 2018 9:59 am
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s_susanto wrote:
Would you mind telling me how to install the standby switch onto Fender Champ 600?
I have the new switch already but I'm not really sure about the wiring.
Help Please !!!


Witch switch do you have ?
Show a picture.

You need this one ;

https://www.tubedepot.com/products/carl ... ff-stby-on

I do this mod on some amps.
If you don't have any skill and experience on tubes amps, don't do this mod, there is lethal voltage there

ImageCapture d’écran 2018-12-06 à 09.04.26 by [url=https://


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Post subject: Re: Blues Jr Standby switch?
Posted: Fri Dec 07, 2018 6:17 am
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I've always wondered why the Blues Junior AND Pro Junior was never given a Stand-By switch as well. Would be nice.


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Post subject: Re: Blues Jr Standby switch?
Posted: Fri Dec 07, 2018 7:16 am
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White Dog wrote:
I've always wondered why the Blues Junior AND Pro Junior was never given a Stand-By switch as well. Would be nice.



Cost cutting, what else .


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Post subject: Re: Blues Jr Standby switch?
Posted: Fri Dec 07, 2018 7:42 am
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stratele52 wrote:
White Dog wrote:
I've always wondered why the Blues Junior AND Pro Junior was never given a Stand-By switch as well. Would be nice.



Cost cutting, what else .
True!


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Post subject: Re: Blues Jr Standby switch?
Posted: Fri Dec 07, 2018 9:07 am
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New post is about Champ 600 .
Blues Junior is a 2010 post

Champ 600 manual and schematic here;

https://www.schematicsunlimited.com/f/fender


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Post subject: Re: Blues Jr Standby switch?
Posted: Tue Dec 18, 2018 4:01 am
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stratele52 wrote:

...If you don't have any skill and experience on tubes amps, don't do this mod, there is lethal voltage there



Indeed so. If you don't know how to dissipate the capacitors there can be very serious stored high voltage lurking there even when switched off.

I fitted a standby switch on mine as part of a kit off eBay. The instructions were extremely well written and easy to follow.

The PCB format of the 600 does not readily lend itself to fitting a standby switch and IIRC requires you drill into one of the traces to create a new connection point and break one of the other traces. So, as noted above, not one of the easiest jobs to undertake as the board is quite congested and (dependent on who you listen to) of little or no real practical value.

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Post subject: Re: Blues Jr Standby switch?
Posted: Tue Dec 18, 2018 8:02 pm
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John Sims wrote:
of little or no real practical value.

This.
Like the Blues Jr, the Champ doesn't have one because it's really not something that's needed.
It's not truly needed on larger amps, but it prevents hitting a chord before the tubes are warmed up if you follow the normal ritual, and provides a convenient way to silence the amp between sets.

For a bedroom amp, it's not like you're heating it up, playing a 30 minute set, then shutting it down for 30 minutes 4 or 5 times a night 3 times a week.
Under those conditions, I can understand the concern about thermal cycling, but how most <15w amps are used? Absolutely not needed.

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Post subject: Re: Blues Jr Standby switch?
Posted: Wed Dec 19, 2018 2:25 am
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CB91710 wrote:
John Sims wrote:
of little or no real practical value.

This.
Like the Blues Jr, the Champ doesn't have one because it's really not something that's needed.
It's not truly needed on larger amps, but it prevents hitting a chord before the tubes are warmed up if you follow the normal ritual, and provides a convenient way to silence the amp between sets.

For a bedroom amp, it's not like you're heating it up, playing a 30 minute set, then shutting it down for 30 minutes 4 or 5 times a night 3 times a week.
Under those conditions, I can understand the concern about thermal cycling, but how most <15w amps are used? Absolutely not needed.



I desagree .

No stanby switch because ;

1- For a champ or other low power ( budget ?) amp, it is a cost cutting for parts + need more room in the chassis.
2- Tubes set are cheap on a small power amp. More expansives to replace on a "high" power amps.
3- Usefull for a gigging amp as explain. Why can't you gig with a low power amp with a microphone on sound system ?

I can't find where Bilm audio explain why Champ do not need stanby switch. Too much stuff to read


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Post subject: Re: Blues Jr Standby switch?
Posted: Wed Dec 19, 2018 8:23 pm
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the true question is : why to provide a standby switch ? The reason is that to apply the high voltage when the cathode of the power tubes are not sufficientely warm can be destructive for the power tubes. Then, the electrons are litteraly ripped out the cathode and the grids.
The amplifiers you are talking are equipped with EL84 tubes types. These tubes are frequently used in "automatic bias" also called "self-bias" circuits . Shortly, the negative grid voltage (and therefore the bias current) increases progressively when the cathode current begins to increase. Result : the current trough the tube never reaches a destructive value. Thus : no reason to employ a standby switch.
A second reason to save a switch is that in some of these amplifier, the H.T.rectifier is not a solid state rectifier but a tube rectifier. This tube heats at the same time of the another tubes and so, the high voltage appears progressively and reaches his maximum value approximatively when the others tubes are also heated.

(sorry to talk about "tubes", in G.B. , the exact word is "valve" i thing...but it's another subject.)


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Post subject: Re: Blues Jr Standby switch?
Posted: Thu Dec 20, 2018 3:40 am
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1- Blues Junior use a fixed Bias not automatic bias.

2- When stanby switch is set to standby, you are basically telling your amp to not send the full available voltage to the tubes immediately- rather, just enough to get them warmed up.

3- With no stanby sw you send 329 volts ( for BJ) on a cold tube's cathode, automatic bias or fixed bias.


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Post subject: Re: Blues Jr Standby switch?
Posted: Thu Dec 20, 2018 6:25 am
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stratele52 wrote:
3- With no stanby sw you send 329 volts ( for BJ) on a cold tube's cathode, automatic bias or fixed bias.

It actually goes to the plate/anode. The cathode is grounded and the grid is tied to the plate of the PI.
If the tube is not up to temperature, no voltage flows.
I do not believe in the "cathode stripping" idea. That is something that was never discussed in the 70s, 80s, and 90s.

TV, audio amplifiers... no consumer electronics in history other than guitar amplifiers and HAM radios have ever had standby switches.

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