standby use with tube rectifier?

[plexitone]

I've read Merlin's (Valve Wizard) page about standby switches and would like some input from experienced builders/techs, please.
http://www.freewebs.com/valvewizard1/standby.html

I have a Blockhead 18w, which is a Marshall 18w clone. The standby switch is positioned:

EZ81 cathode > standby > first filter cap > OT center tap

Questions:
1. Should I let tubes warm up in standby when turning it on? (according to the article, this is more damaging than leaving the standby in "play")

2. Should I move the standby to AFTER the filter cap or just not use the standby when powering on?

3. Should tube amps with solid state rectifiers still be warmed up in standby? I've always done this and now I'm wondering how important it is.

Thank you!

[Kagliostro]

Belive to Merlin

use a resistor in parallel with the SW

if you want put the SW after the first reservoir capacitor

at last don't use standby it isn't indispensable

Kagliostro

[plexitone]

I've read a lot about this today, including searching this forum. I've come to these general conclusions:

• It's better to NOT use standby for warm up in a tube rectified amp.
• Warming up in standby doesn't really extend tube life (regardless of rectifier type).

Anyone disagree with these? I dare ya!

For solid state rectified amps, I'll continue to warm up in standby just because I've done it that way for 25 years and it apparently doesn't matter much either way. I don't want to modify my 18w if simply not using standby when powering on has the same benefits.

Opinions are still welcome.

[analog_stud]

hmmmmm..........apparently, the inrush from SS recto anode is still shitty on your caps? I would agree to throw a resistor in parallel with the switch. Pretty simple mod with some benefit.

[ampdoc1]

Here's a good read on the value of a Standby switch. This guy also has a great site with lots of other information.

[Structo]

I have read that it depends on what kind of rectifier it is.

A directly heated cathode where the filament is the cathode and the indirectly heated cathode that has a separate heater and cathode.

The directly heated tube will heat up faster therefor the B+ will come up faster.

Some say that with a indirectly heated cathode that you don't need to use the standby switch.
And some argue with audio amps you don't need a standby switch at all.

The finicky Vox AC30 (GZ34) amps with rectifier tubes are said to perform better if you leave the standby off, and just let it warm up normally.

[xtian]

I love that Lamkins post. Here's a link to the same post on his site:

http://psg.com/~dlamkins/lamkins-guitar ... dby-switch

[Merlinb]

The most important thing is to avoid 'hot switching'- valve rectifiers DO NOT like it!

'Hot switching' happens when the standby switch is between the rectifier and first cap (reservoir). In this configuration the rectifier warms up during standby, but then gets subjected to the massive inrush current to the reservoir when the switch is closed This stresses the cathode and can lead to shortened life and arcing.

If you do want to use a standby (for reasons unknown...) then make sure the reservoir can charge up at the same time as the rectifier warms up, either by putting a resistor in parallel with the switch, or by moving the switch after the reservoir.

[plexitone]

Thanks for the info everyone. I've decided to avoid the standby in tube rectified amps.

If I still wanted to use standby in a solid state rectified amp (100w Marshall for example), simply adding a 100k 2w resistor across one side of the AC standby switch (DPST) should work, right?

Thanks again.

[plexitone]

I added a 100k to one side of the DPST AC standby on my 100w Marshalls and it seems to work okay. It allows the filter caps to partially charge up to around 60 VDC while in standby and sends some voltage to all the plates. It's completely muted when in standby. Maybe it will save some wear and tear.?

[Merlinb]

I added a 100k to one side of the DPST AC standby on my 100w Marshalls and it seems to work okay. Maybe it will save some wear and tear.?

Highly likely!

[plexitone]

Highly likely!

Thanks for your help Merlin. I have your preamp book and I'm still learning.

[renshen1957]

I've read Merlin's (Valve Wizard) page about standby switches and would like some input from experienced builders/techs, please.
http://www.freewebs.com/valvewizard1/standby.html

I have a Blockhead 18w, which is a Marshall 18w clone. The standby switch is positioned:

EZ81 cathode > standby > first filter cap > OT center tap

Questions:
1. Should I let tubes warm up in standby when turning it on? (according to the article, this is more damaging than leaving the standby in "play")

2. Should I move the standby to AFTER the filter cap or just not use the standby when powering on?

3. Should tube amps with solid state rectifiers still be warmed up in standby? I've always done this and now I'm wondering how important it is.

Thank you!

Hi,

The stand-by switch was installed to prevent Cathode Stripping back in the day. Standby switches are used on high voltage applications (B+ 1000 Volts), High Wattage amps (and since most amps are 50 Watts to 100 Watts), transmitting tubes, expensive tubes (WE 300B), etc.

Stand-by switches on some vintage amps are one reason we see them still on production amps, but not all. Vintage Vox AC30, Tweed Deluxe, Champs, and hi-fi amps from the 1950s-1960s, (The Fisher), dont have stand-by switches.

The 5F6-A Tweed Bassman possesses a stand-by, and so does the Traynor Bassmaster and Marshalls that copied the Bassman. The Tweed Fender Bassman came equipped with a death switch (polarity) which was copied, but the Champ did not have this feature.

Standby-Switches were considered fire hazards by Swedish safety agencies, ergo the Fender's distributor in Sweden had to modify the amps by removing the the switch.

Best Regards,

Steve

[Andy Le Blanc]

I tried a cathode bias that used the heaters of the pre tubes in series in
place of a resistor, irregardless of rectifier type, it worked great, but the
series heaters really did provide the controlled warm up period for the amp,
it was just like turning on the old tubed TV, it took a noticeable period to
warm up, and thats just it, the feature of a instant on, and the feature of a
standby, are for the consumer. Stand by was used to be to keep the hum
and buzz to a minimum when you weren't playing more than any thing else.

Its not the case so much any more, If you know that your rig is properly biased
the tubes will fine after warm up, should we be looking for a soft start up
rather than a stand by switch?

[Structo]

Some Hi Fi guys use the inrush current limiter devices.

They are called a thermistor.

What it does is limit the current at startup, then as it heats up it passes more current.
Like a negative temperature coefficient.

If you choose the right one, it can behave like a standby switch in the sense that it wouldn't pass the B+ until the tubes were warmed up.

They look like a ceramic cap.


The only real drawback would be if you cycled the power on, off then on again before the thermistor cooled.
Then it would not limit the current.

I have a 6A 5 ohm CL-40 sitting here on my desk that I was going to try on a smaller amp I have.


http://www.electronics-manufacturers.co ... r-254.html