Warming up KT-88's

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Warming up KT-88's

Postby (rickaddict) » Mon Apr 18, 2016 8:03 pm

Hey Greg!

I recently bought a Mesa Prodigy bass amp, which uses 4 KT-88 power tubes. I've read the manual and poked around on the internet and from what I've read, they operate at a higher temperature than some of the other tubes and need a longer warm up time. I've also noticed that it sounds different 5 minutes after the "Standby" switch is flipped than it does 50 minutes after. My normal warm up procedure is to flip on the "Power" switch, but leave it on "Standby" until I'm ready to play (which might sometimes be a half hour or so).

So...My question is: If I turn the power on and wait 3 or 4 min before I flip the "Standby" switch to "On"(without playing through the amp for my hypothetical half hour warm up period), will that help to warm the tubes up? I mean...rather than having it on "Standby" for a half an hour and taking it off of "Standby" right before I play? I don't like the way I'm wording this so far...What I mean is...Will the tubes warm up faster if I take it off of "Standby" for a half hour before I play? Do tubes warm up fully just by the amp being off of "Standby," or do they need some signal going through them in order for them to heat up?

:?
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Re: Warming up KT-88's

Postby (jps) » Mon Apr 18, 2016 8:40 pm

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Re: Warming up KT-88's

Postby (rickaddict) » Tue Apr 19, 2016 1:19 pm

Thanks, Jeff. That was a good read, even if most of it is beyond my electronics comprehension level. I guess what I get out of it is that I don't need to have my amp on "Standby" for very long and that doing so might actually be harmful. The author seems to feel that a "Standby" switch is unnecessary at all, but I've read so many contrary opinions (including in my very well written manual that came with the amp) that I'd be afraid to take his word for it.

Luckily this amp also has a mute switch. I use it often when plugging and unplugging, etc. The store owner kept switching the amp on and off of "Standby" when I was demo'ing it... every time I'd switch basses etc... but that's not how I do it or how I've ever done it with my Ampeg tube amps. I'll either turn the Master down or hit the "Mute" switch when changing basses and leave the amp powered up.
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Re: Warming up KT-88's

Postby (jps) » Tue Apr 19, 2016 8:16 pm

I have read more on this subject than just what I linked, although he has a lot of excellent articles on everything tube amp related, all be it, fairly technical but I do grasp much of the relevant information.

I have a Swart STR_Tremolo amp that has a standy by switch, but I just leave it on all the time (this amp uses a rectifier tube which in low power amps in particular negate the need for a standby switch at all). My old Fender Princeton Reverb Amp didn't have a standby switch, I felt I needed one as that was what I was used to but learned otherwise. As your Mesa uses solidstate rectification a standby switch is good to use for the first 20-30 seconds when you first turn the amp on, after that just leave the amp on and use the mute as you do for changing instruments, or during a break. And, you do not have to put the amp in standby before turning it off, in fact, the high voltages in the various capacitors will bleed off faster that way.
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Re: Warming up KT-88's

Postby (rickaddict) » Tue Apr 19, 2016 10:00 pm

jps wrote: And, you do not have to put the amp in standby before turning it off, in fact, the high voltages in the various capacitors will bleed off faster that way.


Thanks, Jeff. I actually have always put my tube amps on "Standby" for a while when I'm done playing before I kill the power. And I guess that doesn't make any sense since the "Standby" mode is basically there to warm the tubes up before you hit them with the full power.
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Re: Warming up KT-88's

Postby (jps) » Tue Apr 19, 2016 10:07 pm

Exactly! 8)
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Re: Warming up KT-88's

Postby (farace) » Wed Apr 20, 2016 12:01 pm

So if I've read this correctly, am I right in saying that for my Ampegs, a '68 B-15N and a '72 B-15S, the only amps I have with standby switches, I'm better off just leaving the standbys "on" all the time and never use them? (I honestly can't remember if the S has a rectifier tube, but the N has a 5AR4.
--Bob

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Re: Warming up KT-88's

Postby (rickaddict) » Wed Apr 20, 2016 3:44 pm

That's pretty much what my eyes read, Robert. But it is an opinion and, well...you know the old saying...everybody's got one!

8)

I think I'm still gonna warm up my tube amps on "Standby" but only briefly, and once I put the "Standby" switch to "On", I'm gonna leave it that way until the next time I need to power my amp up.
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Re: Warming up KT-88's

Postby (jps) » Wed Apr 20, 2016 6:18 pm

If the amp uses rectifier tube(s) then the standby can be left on the operate/launch position all the time.

The switch with the rocket next to it is the standby switch on my amp. 8)
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Swart STR-Tremolo Tuxedo 003.jpg
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Re: Warming up KT-88's

Postby (rickaddict) » Wed Apr 20, 2016 11:49 pm

That amp is cool as heck, Jeff!

I played through my Mesa Prodigy head tonight. I did a short warm-up and then took it off of "Standby." I had it powered up for at least 2 hours when I went to shut it down for the night. So for the first time, I didn't put it on "Standby" to let the tubes "cool down" for a bit before shutting the power off. And when I flipped the power off the amp let out a loud and unpleasant crackle/pop that it has never let out before (AND...it was on "Mute!"). I turned the amp back on and played through it to make sure nothing was damaged (and it appears that nothing is), but I gotta say...I think I'm gonna be putting it on "Standby" for a few minutes when powering it off (like I did before) from now on. I can't explain in electro jargon why my amp yelled at me when I shut it off like that, but I'm gonna listen to what its trying to tell me.

My Ampeg B-15R that I also played through tonight did not have a similar issue when shutting it down.

But the good news is...When I powered it up, took it off "Standby" after a few minutes and let it warm up for over a half an hour...it was ready to go when I plugged in. So...issue resolved!

8)
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Re: Warming up KT-88's

Postby (rickaddict) » Thu Apr 21, 2016 12:23 am

Here's a gratuitous shot of the amp being discussed...

8)
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Re: Warming up KT-88's

Postby (jps) » Thu Apr 21, 2016 6:53 pm

Perhaps the Mesa dumps power supply voltage through the output, sort of what all SWR amps do, so I suppose placing the amp in standby for a few seconds (which is all it would really need in this case) would be prudent; possibly it is due to it being a fairly high power amp (?).

Here are some more photos of the Swart (not mine). The only photos I have taken are of the chassis, itself.

Swart STR-Tremolo Tuxedo 022.jpg

Swart STR-Tremolo Tuxedo 023.jpg

Swart STR-Tremolo Tuxedo 024.jpg


This is the other basic version, there is a version that is all dark tweed, too.

Swart STR-Tremolo 005.jpg
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Re: Warming up KT-88's

Postby (jps) » Thu Apr 21, 2016 6:57 pm

The Prodigy is a very cool amp; Mesa did a great job on the looks, too. 8)
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Re: Warming up KT-88's

Postby (rickaddict) » Thu Apr 21, 2016 9:25 pm

Very cool little retro tube amp!

I do like the Prodigy. It sounds different from my Ampegs, (a bit brighter) but I'm getting used to it. One nice thing is the weight. A 31 lb head is a whole lot more manageable for me than 80. Plus, my Epifanis are around 35 lbs each vs. (110lbs?) for my 410 HLF. I'm too old and too small to be carrying my SVT and 410HLF around.
:(
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Re: Warming up KT-88's

Postby (jps) » Thu Apr 21, 2016 10:10 pm

The Swart STR-Tremolo is based on a late '50s-early'60s Gibson amp circuit, a GA-17 RVT Scout, IIRC. It puts a very loud 5 watts out of this amp! The casework on mine (Tuxedo) is like a '60 Univox amp.
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