Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Platefire on December 09, 2015, 11:31:02 am
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Seems like what I'm doing these days is going back over my old builds and correcting mistakes and trying to make them better. Since my Bogen's is up at the Church sitting on my Boogie cab, I've been jamming at the house on this one---a Revere Reel to Reel Re-purpose. Attached is the Schematic. When I cut my amps off, I turn the standby switch on first and then turn the power switch off last. That way it will already be on standby when I switch it on for warm up.
When I'm powering down and I switch my standby on I hear a pop followed by a slight humm that fades out gradually. I think I know what to do but figured I need to consult with you guys in order to do it right.
I think what I need to do is add another filtercap or maybe two(like fender) on the rectifier side of the standby switch. Platefire
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Plate, I put a 47K/3W across the standby switch. It gives a "soft" warmup, and no pop.
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Thanks! I have other builds and conversions that have the same setup and they are totally silent. I don't know why this one acts up. Platefire
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Maybe try another switch. Do you really even need a standby switch on that little amp? A mute switch might be a better solution at church.
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I have a better warm and fuzzy when I know my tubes are peacefully resting :icon_biggrin: It may not make a nats hair worth of difference in the life of the tube but that somehow does me good. Platefire
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I have a better warm and fuzzy when I know my tubes are peacefully resting :icon_biggrin: It may not make a nats hair worth of difference in the life of the tube but that somehow does me good. Platefire
But you're still boiling electrons off the cathode with that heater. Only now they have no place to go. They just boil off and fall to the bottom of the tube (like a pot on the stove!) where they make a cloudy mess and eventually muddy your tone!
So, try a new switch. Easy to do and it may stop the pops. Maybe not too.
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They just boil off and fall to the bottom of the tube (like a pot on the stove!)
And this is how rumors become fact. :icon_biggrin:
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Haha! I hope some day I run across someone quoting me on that. Oh, wait! They just did. :l2:
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Your the only one I know that can find words to make someone feel guilty about leaving his amp on standby :l2:
I can almost see a pile of cathode debris accumulating at the bottom of my tube. :offtheair: Platefire
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"Standby" is useful for VERY high-voltage amps. From a cold-start, the rising B+ "rips" electrons from the cathode. This can be especially damaging for hi-volt (>1,000V) tubes with thoriated tungsten bare filaments. It is an issue with oxide cathodes, except all the "Receiving Tubes" (non-professional users) have been designed and specified to withstand any sane number of cold-starts.
Band-amps have standby so you can take a break in total silence, yet get back into action instantly when the bandleader or bartender waves baton or bully-club. For most purposes, it would be sufficient to short the signal somewhere in the signal path (assuming the rest of the amp idles silently-enough). A special trick for pentode/tetrode power tubes is to kill the screen voltage; in most cases the electron flow gets so low that nearly no sound comes out (and the tube idles cool).
I can see how for home-use, where you don't have to shut-up for the sermon yet rock-out for the following blessing, a standby is a frill that offers more trouble than it is worth. Put a NFB selector in that hole.
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Plate, I put a 47K/3W across the standby switch. It gives a "soft" warmup, and no pop.
I use 220K/1w simply because it works well, when off you can't hear the amp when you strum strings (thinking with only 47k you may be able to since more current passes?), and finally - it's the same value as the bleeder and/or "current sharing/equalizing" values used across filter caps, also this is a good choice & type for V1's load resistor. So you can stock this value & wattage for having several duties which is always good. It does limit current to allow the main reservoir cap(s) to charge up slowly when Standby is in the OFF position so that when you power on it doesn't place a heavy current load across your tube recto which helps prevent premature wear or worse, a recto failure as a result of this.
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... Put a NFB selector in that hole.
:hijack1: Sorry about that, I just want to know what NFB does mean!
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... Put a NFB selector in that hole.
:hijack1: Sorry about that, I just want to know what NFB does mean!
negative feedback aka -NB
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... Put a NFB selector in that hole.
:hijack1: Sorry about that, I just want to know what NFB does mean!
negative feedback aka -NB
Many thanks! Hows your amp going?
Did you get that pop fixed? I have similar problem on my amp, but it isn't that obvious to catch up, it is related to a problem in the vibrato circuit, when the V5 is removed the pop is gone, I understand this have nothing to do with or amp, yet it could help to look at the problem from a different point of view. :think1:
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I haven't tried to fix the pop/hummm yet. Wanted to see what everybody says first. Thanks for all the input and consultation. I'm sorry, I love a standby switch and no use trying to talk me out of it. I put it in everything I build.
I might try the resistor across first. If that don't help maybe a new switch or both.