From postmaste–(at)–riodeel.com Sat Oct 2 13:55:38 CDT 1999
Article: 205949 of alt.guitar.amps
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From: Ned Carlson
Subject: Re: Stand-By Switches and Tubes Theory
Date: 2 Oct 1999 01:08:06 -0500
Organization: Triode Electronics
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Kent Pearson wrote:
>
> I’ve heard that it’s best for the amp and/or the tubes to allow the tubes to
> warm up for a minute or two on stand-by before switching to play mode.
This isn’t a bad idea…since you’ve got a standby switch, why not use it.
But lots of tube amps were made that had no standby at all. AAMOF, I’ve got
a couple Bogen MO-100 tube PA amps here, diodes and no standby.
Since Bogens were typically used in places like hospitals and
schools, one can figure they were either run 24/7 or
got hit with a turnon surge every morning.
Directly heated rectifiers like 5U4 and 5Y3 are not a slow
warmup device, despite rumors to the contrary.
A simple voltmeter check will verify this.
Fortunately for most tube amp owners, nearly all
tube amps used in audio frequency service (which includes
guitar amps), either apply a negative voltage to the grid
of the output tubes at the time the power is applied,
or have a cathode resistor to limit current.
Also,
> I’ve heard that it’s best to put the amp on standby for a minute or two before
> powering down. My understanding is that this practice will help to get the
> most life out of your tubes. Can someone elaborate on that a bit? Why is
> that? To Stand-by, or not to Stand-by . . what goes on? That is the
> question!
I would do exactly the opposite, turn off the power then LATER turn off
the standby, so as to drain off the charge in the power supply
capacitors.
I’ve recieved some lengthy missives from certain folks regarding
cathode stripping and possible damage from too fast warmup in tube amps.
>From these I have determined the following:
1.If you’ve got a tube regulated radar power supply on your B52-B bomber,
you’d better use a tube rectifier, as using diode replacements that
slap B+ voltage on cold 6336B tubes can destroy them.
List price on 6336B is $141.00, which ain’t chopped liver, especially
if you have to replace them on taxpayer’s money. So if you are
a 3rd world dictator with some used B52-B’s that need retubing,
call us and get some 5R4-WGB tube rectifiers before you send your
bomber fleet to carpet bomb suspected terrorist sites.
2.if you’ve got an Wurlitzer bubble-tube jukebox, it uses
a fast warmup circuit that jacks the filament voltage to
over 9 volts when someone hits the selection button.
So figure replacing 6L6’s a bit more often than usual in these
units…of course, if you’ve got $10,000 to blow on a jukebox,
a few bucks replacing 6L6’s probably won’t bother you much.
3.Tungsten and thoriated tungsten filaments (not ones you’ll
find in guitar amp) apparently aren’t bothered by this at all,
at least one BE has confessed to slapping thousands of volts
of B+ on a cold 4CX20,000. This is a tube that lists for
over $4500. Yep, a single tube that lists for $4500.
Presumably if he’d screwed up and blown a $4500 tube, he might
not have a job, but major market FM stations don’t think much
about blowing a million bucks for an AM drivetime DJ.
Heck, I think a major market outlet could drum up some major
drive-time cume numbers by hosting a political debate
between me & Lord Valve. I can see it in the Pioneer Press,
“Who the hell is Lord Valve?”.
—
Ned Carlson Triode Electronics “where da tubes are!”
2225 W Roscoe Chicago, IL, 60618 USA
ph 773-871-7459 fax 773-871-7938
12:30 to 8 PM CT, (1830-0200 UTC) 12:30-5 Sat, Closed Wed & Sun
Magnequest Transformers stocked for Dynaco & Sunn!
Order online at:
http://www.triodeel.com/cgi-bin/miva?Merchant/merchant.mv+
