The Old Standby Switch Chestnut!

[valvewhiz1]

Hi all,

Back to the old standby switch chestnut:

I just decided while my AC30's back is off to measure the inrush
current when turning the amp as per the Vox instructions.

I inserted a peak reading DVM on amps across the HT fuseholder,
(fuse removed) and followed the "switch on wait two minutes and
turn on standby") routine, the measured peak current was 400mA
according to Mullard the maximum current for the GZ34 is 250mA.

No wonder using the standby damages them!

[Ikeburner]

Wow, good job!

I really wonder why Vox put something in this amp that's so bad for it and will easily result in damaging the tubes and possibly other parts... I guess it really is just about customer demand these days - people hear a standby switch is a good thing -> people demand it in an amplifier -> Vox puts it in -> customers are happy (until their amp burns down and someone who knows what he's doing tells them it's the standby switch that did it).

[freakboy]

Where is Lyle Caldwell?

[P-Dawg]

Hi all,

Back to the old standby switch chestnut:

I just decided while my AC30's back is off to measure the inrush
current when turning the amp as per the Vox instructions.

I inserted a peak reading DVM on amps across the HT fuseholder,
(fuse removed) and followed the "switch on wait two minutes and
turn on standby") routine, the measured peak current was 400mA
according to Mullard the maximum current for the GZ34 is 250mA.

No wonder using the standby damages them!

Huh? According to the RCA manual which I trust with my life, the 5AR4/GZ34, peak plate current that the GZ34 is capable of taking is 825ma per plate. The hot switching transient plate current (whatever that is) is 3.7 amperes per plate. These are design maximum values.

Your average output current with choke input is, indeed, 250ma in typical operation but of course these are yanqui tube ratings.

[valvewhiz1]

Hi P-Dawg,

I got the info I posted from the European Valve "Bible" A Mullard Data Book from the mid 60's.

Obviously Mullard believed in rating them more conservatively.

Who's right or wrong I dont know - Vive La Difference as the French say!

I'm certainly not going to fall out over it - life's too short!

[blackba]

So what is the current spike if you turn on the amp without using the standby switch?

[P-Dawg]

So what is the current spike if you turn on the amp without using the standby switch?

You're not going to get a spike, because your GZ34 is an indirectly heated device that gradually raises your B+ or HT if you prefer, over a period of about 10-15 seconds.

Now. If you had a running amp, shut it off and switched it back on real fast before the tube cooled down and the capacitors were fully charged you would get a current spike-doing that was enough to shoot purple lightning bolts in the Chicom 5U4 in my Princeton Reverb.

Hi P-Dawg,

I got the info I posted from the European Valve "Bible" A Mullard Data Book from the mid 60's.

Obviously Mullard believed in rating them more conservatively.

Who's right or wrong I dont know - Vive La Difference as the French say!

I'm certainly not going to fall out over it - life's too short!

I think i have the answer. I was able to review the Phillips and Telefunken data sheets on a couple of sites and they give typical operating values only.

The JJ data sheet for their GZ34 gives the typical values which are indeed 250 ma, and limiting values of 750ma.

My RCA RC28 manual is pretty consistent with that. What I get from it is that the device can take a short high current surge that exceeds the typical operating parameters, but I still wouldn't do it unless I had to.

So we're both right.

these folks have some great information.

http://tubedata.itchurch.org/more.html

[musicman]

From the above, am I right in reading that the AC30CC shouldn't be switched off then straight back on again now ?
If so how long should it be left before it's switched back on please ?
I beginning to think we should leave them permanantly switched on !

[Vortexion]

I'm beginning to think we should leave them permanently switched on !

Ahhh, if only. If we were all able to do that, our valves would last for donkey's years.

[musicman]

But think of the environment (& the electricity bill !)

[Vortexion]

But think of the environment (& the electricity bill !)

Haven't you heard? Someone else is doing that for us. Having already forced us to abandon incandescent lightbulbs in favour of those hideous low-energy things, the UK authorities are now spreading the net to include thermionics. As of 2015, the importation and sale of any electronic equipment that uses "non-essential" thermionic devices (i.e. anything whose basic function can more efficiently be undertaken by a non-thermionic equivalent) will be BANNED. Trading in second-hand equipment and NOS valves will be still be permitted, but no new products will be allowed to be manufactured in this country or imported from abroad.









Naaa. Just pulling your leg, mate. I wouldn't put it past 'em, though.

[musicman]

You very nearly got me then.
I was just about to start typing furiously then read the last line of your post.
Suggest this entire post needs to be deleted, digitally shredded then eaten with a nice Chianti before someone thinks what a good idea that would be, save all that wasted heat, light etc.

[valvewhiz1]

Vortexion,

I just hope no one from our government sees your post, you know what they are like
for getting ideas!

Actually they would probably introduce a "Thermionic Tax"

[T.G.3-55]

If we can stay serious for a min...this is troubling or I need to change my ways:

My Germino Club40 lets me change tube types and rebias to get different tones. The trannys are strong enough to allow on-the-fly impedance changes within reason to get diffrent tones or if I'm running KT66s and 1/2 normal impedance. Of course I always power off the amp.

But usually I quickly flip the impedance knob and power up again, all within say 5-6 seconds - is this damaging ?

[P-Dawg]

If we can stay serious for a min...this is troubling or I need to change my ways:

My Germino Club40 lets me change tube types and rebias to get different tones. The trannys are strong enough to allow on-the-fly impedance changes within reason to get diffrent tones or if I'm running KT66s and 1/2 normal impedance. Of course I always power off the amp.

But usually I quickly flip the impedance knob and power up again, all within say 5-6 seconds - is this damaging ?

If I understand what you're saying, you power down, change the impedance, and power up again in 5-6 seconds? If that's the case you will get surges. Whether that's bad, who knows? It certainly can't be good, but without more knowledge of how the circuit's constructed it's impossible to say whether it's a great idea.