Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joesatch on September 13, 2021, 09:21:33 am
-
I was all ready to follow Rob's method for adding Tube/SS rectification (with switch center as standby) when i came across Valve wizard stating. "If you have a valve rectifier then the standby switch must be placed after the reservoir capacitor so the cap can charge up slowly as the tube warms up. Leaving the valves totally cut-off, while heated, encourages interface resistance. A simple way to discourage this is to add a resistor in parallel with the switch to allow a trickle current to flow at all times, while still keeping the amp more-or-less muted. A 47k 2W device is a reasonable compromise."
How would i incorporate the standby with Valve Wizard's recommendations to this switching scenario?
(https://robrobinette.com/images/Guitar/Bassman/Rectifier_Switch.png)
(http://www.valvewizard.co.uk/standby3.jpg)
-
Put standby switch between the 5000 ohms and first filter cap : red arrow.
https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Rectifier_Switch
-
Put standby switch between the 5000 ohms and first filter cap : red arrow.
https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Rectifier_Switch
That would seem appropriate and consistent with Valve wizard but i cant see where the rectifiers would be
-
I can only show you with schematic. It say all for me.
Robinette picture is incomplet to show you more.
-
Is this help you ? Click on picture.
-
Is this help you ? Click on picture.
ok i cannot place the rectifier where valve wizard wants the standby. i will need a dpdt switch
-
I dislike disagreeing with Merlin, but IIRC "interface" was from leaving tubes idle for days, not set-breaks.
-
Is this help you ? Click on picture.
ok i cannot place the rectifier where valve wizard wants the standby. i will need a dpdt switch
I don't understand why you can't install the standby switch.
Show us a picture or a drawing of your amp wiring
-
Is this help you ? Click on picture.
ok i cannot place the rectifier where valve wizard wants the standby. i will need a dpdt switch
I don't understand why you can't install the standby switch.
Show us a picture or a drawing of your amp wiring
Because the standby switch will be spdt center would be standby and outer selections would be for SS or tube rectification. Moving the standby switch past a capacitor nixes this rectifier switching as the rectifier cant go there. I'll need two switches (one for standby and one for rectifier selection) or I will need to wire up a https://www.grainger.com/product/CARLING-TECHNOLOGIES-Toggle-Switch-2X594 (https://www.grainger.com/product/CARLING-TECHNOLOGIES-Toggle-Switch-2X594)
-
after some pondering, i'm going to use separate switches. I will wire Rob's switch then a separate standby switch after the cap.
-
Now I understand, it is because you don't use "standard switch" and non standard wiring.
It is not about where you can incorporate stanby switch, it is how can you do all your mod with this Carling switch
-
… IIRC "interface" was from leaving tubes idle for days, not set-breaks.
Indeed, but musicians can be somewhat forgetful, and I recall queries raised by folks that arrive back home from a trip away and find their amp has been on standby for a week or 2 :sad2:
-
... i cannot place the rectifier where valve wizard wants the standby. ...
Do you really need/want a standby switch?
The tubes don't really need a standby, and they're sometimes more trouble than they're worth.
-
.....their amp has been on standby for a week or 2 :sad2:
Yes. And did the amp still work? We used to leave Fishers and Bogens running 24/7 for years.
Also by the late 1950s, sleeping sickness was cured by more testing on cathode metal. Tubes were very fussy customers, yet were very small customers to the Nickel Cartel, yet were critical to national security. The deal worked out was that several melt-ingots would be submitted for testing by all tube makers, and the one they liked best became THE cathode nickel for the next few years. So the problem was fixed, all tubes, not long after vacuum tube computers discovered it.
-
.....their amp has been on standby for a week or 2 :sad2:
Yes. And did the amp still work? We used to leave Fishers and Bogens running 24/7 for years.
…
Almost invariably, the amps are fine.
I’m not aware of any concerns about valve amps being on for prolonged periods / permanently?
My understanding is that due to the build up of interface resistance, the eventual operational life of valves may be lower if they spend, eg, 100 hours of it in standby, rather than 100 hours in normal use / idling.
It’s probably indicative of nothing, but I’ve noticed that in standby, there a small voltage (<-1VDC) can appear on the anode etc, presumably from electrons migrating from the cathode’s electron cloud out to the other electrodes.
Also by the late 1950s, sleeping sickness was cured by more testing on cathode metal … the one they liked best became THE cathode nickel for the next few years. So the problem was fixed, all tubes, not long after
I wonder if modern valve production uses the same spec nickel :icon_biggrin: ?
It seems that Tomer considered interface resistance build up in zero HT current conditions was still a thing when he published his book in 1960; if it wasn’t a problem for, eg 1958 onwards production, that should have been mentioned? Perhaps in a 2nd edition, it might have been.
I suppose there was a heap of valves produced with non ideal nickel still in circulation.
And the remnants of those are still being sold NOS as premium quality. And when eventually put into use, they may well then be put into standby at every opportunity, in the false belief that’ll extend their operational life :icon_biggrin:
https://frank.pocnet.net/other/docs/Tomer_1960_Getting_the_Most_Out_of_Vacuum_Tubes.pdf
-
Interface had been observed before but not consistently.
In digital computers, one byte (tube section) might have normal B+ (so not our case!) with heavy grid bias to cut-off (making a "0") for long periods of time. When the bit finally changed to a "1", nothing actually happened. The interface between metal and oxide had gone non-conducting. If you are calculating gunnery or orbits, or billions of dollars in your bank, this matters.
I think Tomer was a worry-wart and a scandal-monger. He's not wrong but makes mountains out of ant-hills.
-
Trying to make sense of this diagram from Torres Eng. The center of the SS/Tube DPDT switch is a "standby" . There is normal standby in the circuit as well. Trying to understand what occurs with the switch in the center position and what is the effect of switching it back n forth while the amp is on.
(https://i.ibb.co/fSvQXTH/rectsw.png)
It is best to use a dpdt “center off” switch in this application, as it will provide a secondary “standby switch” in the center position,eliminating the need to, or chance of forgetting, to use the existing standby switch when
switching rectifiers
-
> Trying to understand what occurs with the switch in the center position
Nothing is connected to nothing. Nothing much to "understand". Video (https://youtu.be/IX2bE-OBtwk)
-
> Trying to understand what occurs with the switch in the center position
Nothing is connected to nothing. Nothing much to "understand". Video (https://youtu.be/IX2bE-OBtwk)
:l2:
Yay; Billy Preston, the 5th Beatle.:icon_biggrin:
-
switching it back n forth
the rate of switching is key, once nothing cares, 200 times a minute, bad things happen
there are a pile of caps and an inductor that hopefully were put there to mitigate the switch action and provide decent filtering of AC
-
I realize the OP wants a three-way switch with standby in the middle, but is there any electrical reason not to leave the tube rectifier connected at all times and use a switch to connect the SS diodes around it, effectively bypassing the tube?
-
> leave the tube rectifier connected at all times and
Does that save any time or money? I don't see how.
-
> leave the tube rectifier connected at all times and
Does that save any time or money? I don't see how.
My point was that by bypassing the tube instead of disconnecting it, the tube can remain connected to the filter caps at all times, preventing the current surge through the tube caused by hot switching.
-
Not sure if this is what you're looking for, but worth a look:
https://s3.amazonaws.com/tubedepot-com-production/spree/attached_files/jtm45plus_schematic_v4.pdf?1391458123
I would not use the standby switch as drawn . . .
-
Trying to make sense of this diagram from Torres Eng. The center of the SS/Tube DPDT switch is a "standby" .
Its a 3-way switch with centre off. but the switch can be thrown to connect the centre pole(s) to either of the other poles, making the circuit SS diode rectified, or tube rectified (when not centre-off)
-
Not sure if this is what you're looking for, but worth a look:
https://s3.amazonaws.com/tubedepot-com-production/spree/attached_files/jtm45plus_schematic_v4.pdf?1391458123 (https://s3.amazonaws.com/tubedepot-com-production/spree/attached_files/jtm45plus_schematic_v4.pdf?1391458123)
That schematic sort of shows the type of scheme I was asking about (and tried to draw). The rectifier switch doesn't remove the tube from the circuit, it just connects the Si diodes in parallel to bypass it. I don't know if there's any reason not to do this.
I would not use the standby switch as drawn . . .
Yeah, the standby switch is positioned to hot-switch the rectifier, defeating the benefit of leaving the rectifier connected to the filter caps at all times.