Jump to content
Hamer Fan Club Message Center

Archived

This topic is now archived and is closed to further replies.

  • 0
GusS

Explain when standby switches are not needed in tube amps

Question

Most tiny tube practice amps don't have them.. Princetons don't but Deluxe Reverbs do.. Most Ampeg blue diamond guitar amps (eg Gemini, Reverberocket etc) don't but the B15 does. Tell me about controlled warmup rectifiers. Should all amps w/ solid state rectifiers, or with rectifier tubes without a separate cathode have them?

Share this post


Link to post
Share on other sites

13 answers to this question

Recommended Posts

PS: I have a Kalamazoo Reverb 12 w/ a solid state rectifier powered by two 6BQ5s I'm working on which was humming like crazy. Two culprits: bad filter caps (60 hz hum) and the power switch being on the back of the treble knob inducing 120hz hum. Took the power wires away from the tone stack and the amp is quiet. Will move it to the back panel in place of the courtesy two-prong outlet. Debating on whether to use an on-off toggle or with a on-off-standby one.

Share this post


Link to post
Share on other sites

I never use the standby switch on tube amps. I always leave the standby off and just use the power switch. It helps the filter caps to last a lot longer. To avoid the "pop" when unplugging guitars, etc. I just partially remove the cord from the input of the amp, switch guitars, and push the cord back in and go.

Standby switches are for pussies... LOL...

Share this post


Link to post
Share on other sites

Brewmaster would probably know...he's a very experienced amp tech from what I've seen of his posts, but I haven't heard anything from him on the HFC lately.

Not sure about 'controlled warmup' rectifiers, I've heard that a proper GZ34/5AR4 is a 'slow' warm up tube rectifer, also the less common GZ37, but they are the only two tube rectifiers that I've ever heard of with this property...there may be more. From what I understand, a SS rectifier pretty much sends voltage straight to the tubes without a 'warm up'. Also a standby switch allows the heater filiaments to have power without engaging the entire tube.

Why some tube amps have standbys and some don't is a mystery to me, my guess is that the larger, bigger amps get left on for longer periods of time (like when they're used in gigs), and the standby is handy to keep them ready to go without full current being applied to the tubes, and without waiting for them to warm up...after all, a tube that's on full power all the time without it being used is kinda wasteful on tubes, IMHO. The small 'practice' amps, at least early on, may not have had standby switches as the designers figured that those smaller amps would normally be shut down and unplugged if not in use, and therefore were unnecessary...but that's just a guess. That being said, I once had a '61 Fender Tremolux blonde/brownface head that came from the factory without a standby switch, but later Tremolux heads did.

Share this post


Link to post
Share on other sites

It helps the filter caps to last a lot longer.

Please explain.

Share this post


Link to post
Share on other sites

The only reason I can think of is that they've got more voltage on them with no DC going to the tubes.. Not sure why this would make them wear out quicker if they're rated high enough to handle these voltages. By doing so you're hitting cold tubes with high tension which I was under the impression would reduce their life.

Share this post


Link to post
Share on other sites

Applying high voltage to the plates of the output tubes before they warm up to full operating temperature causes a condition known as "cathode stripping" which shortens the life of the tube. They we're left out of smaller amps simply as a cost-cutting measure to meet a particular price point.

Share this post


Link to post
Share on other sites

I don't know if any of you have read Merlin Blencowe's (very sharp dude) web site or books. He explains pretty well why a standyby switch is usually not necessary. They were popularized by Fender, who were using under-rated caps in their amps, and Marshall of course copied the bassman...boom, everyone starts using standby switches. Cathode stripping doesn't happen in receiving tubes.

This is a good read:

http://www.freewebs.com/valvewizard1/standby.html

Share this post


Link to post
Share on other sites

Yep! Just as I said... "Standby switches are for pussies!"

Share this post


Link to post
Share on other sites

Have seen this debate rage on in amp-geek forums before. At the operating range of guitar amps, cathode stripping does not appear to be an issue.

FYI, the standby switch usually only allows electricity to the tube "heaters", which is the -good- glow you see. The heaters raise the temp of the tube cathodes to a level that results in the formation of an electron "cloud" around the cathode. This cloud is the source of the electrons that are drawn to the plate (anode>>positive) when the rest of the amp gets power (standy switch or not). In higher power tubes, if the electron cloud isn't allowed to form (takes a while to heat up), the plate will just suck electrons off of the surface of the cathode, "stripping" it.

Regardless, I like having the standy switch. Much easier than having to reconfigure everthing to avoid unwanted noise. Let em cook for a while. Sound -much- better after a few mins.

Share this post


Link to post
Share on other sites

Regardless, I like having the standy switch. Much easier than having to reconfigure everthing to avoid unwanted noise. Let em cook for a while. Sound -much- better after a few mins.

This is my opinion as well. Back in the bar days (about 25 years ago - man, i'm old...), i would leave the amp on and hit the standby between sets. So the amp is quiet, but the tubes stay nice and cozy warm.

These days, my "gigs" are church services (3 services every other Sunday, yo.) I do the same thing now - leave the amp on and hit standby between music sets (when, like the preacher guy is talking and stuff). The sound guy appreciates the lack of noise coming from the amp at those times.

Opinions vary - trust your ears.

Share this post


Link to post
Share on other sites

I've never heard that the use of a standby switch will kill filter caps. I don't see how having the amp on without voltage applied to the plates would do that.

I do have one tube amp without a standby switch, and it takes a good 30 seconds before it actually starts making noise. with a standby switch amp, you get only a 1-2 second delay when taking the amp off standby.

Share this post


Link to post
Share on other sites

I don't think the stanby switch would threaten the filter caps in any way. It might threaten a rectifier tube if it was placed before the first filter cap, which would overtax the rectifier tube when that cap first wanted to charge itself. However most amps these days put the standby switch after the first filter cap in the case of a tube rectifier.

Share this post


Link to post
Share on other sites

It's not that the standby switch damages filter caps, it's the way it's used when turning off the amp. Most players stop playing, turn on standby switch, turn off power switch. That process is what stores voltage in the filter caps and causes them to not last as long over time.

To bleed off the stored voltage in the caps try this process - Stop playing, turn on standby switch, immediately start playing until sound completely fades out, turn off power switch.

Share this post


Link to post
Share on other sites

×
×
  • Create New...