That's the 1k resistor, for grid stopper I believe, to go on the side of the power tubes. The stupid thing keeps deleting my text, so I added it on again in my second follow-up
Do you have a resistor or diode inline with this cap?
Question on 1959 Crown SXA tube amp power supply, switching noise from half wave rectifiers?? 120hz hum.
The grounding I believe, is of some concern, as the micalex sockets don't have the same grounding ring, so I have some small terminal posts to ad to a central place in there to ground the bias pots and tubes from the same ground strap.
A question: in what setup would the screen voltage be in contact with the speaker?
Thanks!
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If the speaker output jack is an octal, any situation where someone lands the wire on the wrong pin. I just don't like the idea of high voltage even being an option in the event of a simple mistake. I try and stupid proof things to save myself tears later when i screw up.
Definitely! It should be a DIN jack or a Molex, something not Octal. To avoid any possibility of confusion.
yeah I wouldnt' really want an octal speaker output either, just too inconvenient. My Rauland-Borg amps used one, it remains on the chassis for hole-fill reasons and I'm using it for the bias test points. The speaker outputs are on a pair of binding posts on the side.
Thanks, I don't think it was like that in the schemo.... but the output for phase inverter is coming from the outputs. Is that typical? Seemed odd to me. And do you understand the schemo for the heater windings? I'm always a little bit in the dark about the heaters on these... the tubes are 12, heaters... But in variably they seem to be getting six volts.... Is that per heater? Because it is too basic amps or pre amps... And I can't seem to figure out if these are getting both sides used or not, As the preamp level seems to be a single stage.... But then there is no phase inverter tube, But rather the old fashioned PI... So maybe that's getting a side as well of that same tube? As I look at the schematic it looks as though both sides are getting heater... And all of the relative pins are being used... So I'm thinking it does. Use the entire 12at7.... I'm just not sure how to hook up the heaters... 6v on either side and ground in the middle? I actually looked it up, but I didn't get the information that would tell me specifically... I understand what's being said, i'm just not sure in this instance. Mainly because this amp is old enough to to have exceptions to a lot of rules. Sorry if i'm making this more difficult!
OH, and I got a call from a major boutique speaker manufacturer... that he needs a Leslie cab, and can get me some matched mullard EL37's for this. And his speakers won within the top ten speakers this year, using the dipole design for the bass speakers in the new manepans. Killer connect!
I just got out of the hospital from getting my leg sliced open by a Revox A-77 tape recorder and Swiss army knife! Lol.
Crazy$:%#@^&^
Ow! I used to perform warranty service on Revox, but never had one attack me.
The 12AT7 (like others in that series) can be operated on 6.3V or 12.6V, depending on whether the two halves of the filament are wired in parallel or in series. Most hi-fi gear has the center (pin 9) grounded with pins 4,5 connected together for a 6.3V filament.
Jack
The 12AT7 (like others in that series) can be operated on 6.3V or 12.6V, depending on whether the two halves of the filament are wired in parallel or in series. Most hi-fi gear has the center (pin 9) grounded with pins 4,5 connected together for a 6.3V filament.
Jack
Correct. The input and gain stage duo-triode tube heaters are wired to use 12.6VAC, and the output tube is wired to use 6.3VAC off the same power transformer heater tap.
What they said about the 12a*7 heater stuff
not sure what you mean about the phase inverter. This definitely has one, its the second half of the first triode. This is basically a classic Williamson design. Slightly different tubes than typical but tons of amps were built from this basic arrangement with various tubes.
C5 is the input from the input jack. Pretty straightforward.
The connection to R10 is coming from the speaker terminals through a resistor. This is the negative feedback connection that flattens out response and reduces distortion.
Output from the plate (pin 1) is direct coupled to the second grid (pin 7)
This is called a split load, cathodyne, or concertina inverter depending on who you ask. All the same thing. It has one input on the grid, and an output on the plate and cathode. The output is equal in voltage but opposite in phase so long as the plate and cathode resistor values are identical. Plate side is inverted relative to grid, cathode side is in-phase with the grid.
The 6SN7 sections after this are just a voltage gain stage to drive the output tubes.
not sure what you mean about the phase inverter. This definitely has one, its the second half of the first triode. This is basically a classic Williamson design. Slightly different tubes than typical but tons of amps were built from this basic arrangement with various tubes.
C5 is the input from the input jack. Pretty straightforward.
The connection to R10 is coming from the speaker terminals through a resistor. This is the negative feedback connection that flattens out response and reduces distortion.
Output from the plate (pin 1) is direct coupled to the second grid (pin 7)
This is called a split load, cathodyne, or concertina inverter depending on who you ask. All the same thing. It has one input on the grid, and an output on the plate and cathode. The output is equal in voltage but opposite in phase so long as the plate and cathode resistor values are identical. Plate side is inverted relative to grid, cathode side is in-phase with the grid.
The 6SN7 sections after this are just a voltage gain stage to drive the output tubes.
I guess what I'm asking is, the 12at7 in this schematic... is it showing both heaters energized?? I see the pins out, but I don't see pin 9 grounded, and the schematic for the heater shows what appears to be four connections... and in all the pics I took, none of them are showing me exactly the wiring of the heaters explicitly... nor can I find any pictures on line.
Also, the phase inverter section I referenced, was only because it was drawn from one of the output transformer taps... which I guess would be from a plate, like you were saying. It goes through that small mica cap and 100k resistor parallel combo, which are using the open pins on the outside power tubes to wire them, where the wire heads back to the preamp. I only mentioned it because you previously mentioned not grounding the parts of the power tube to the outputs, but this isn't the ground, however just was making sure it wasn't a hazardous practice as well.
It's difficult to read the numbers in the partial schematic in #131 above. It appears that (maybe) pins 4 and 5 both connect to "W" in the power supply, but that won't light that side of the filament. Pin 5 is (maybe) connected to "Z". Looks to be an error.
It has to power both sides, but i didn't study it close to see how they did it. I'm just assuming the usual setup with 4 and 5 connected to one side of the heater supply and 9 to the other. Whether or not they drew it or did so correctly doesn't usually matter much.
Its not even that uncommon to see the heaters not even drawn, with the assumption that anyone working on it knows they have to be powered and how that is usually done.
Its actually one of my gripes with modern schematics, they draw all that to the tube rather than just drawing a group of heaters out of the way or indicating a connection to some point without the lines. Makes it all very messy even if its more technically accurate.
Its not even that uncommon to see the heaters not even drawn, with the assumption that anyone working on it knows they have to be powered and how that is usually done.
Its actually one of my gripes with modern schematics, they draw all that to the tube rather than just drawing a group of heaters out of the way or indicating a connection to some point without the lines. Makes it all very messy even if its more technically accurate.
I always draw filaments as part of the PS. That's where they belong unless there's a compelling reason to do otherwise (maybe if they were elevated using a nearby cathode connection).
These were all 6V-only. If they had center taps, I would have included pin numbers.
Jack
Ok, so basically, since both sides are being used, wouldn't I use a 6v for 5&6 and then just ground 9 to get them both powered, since 9 is the ground point for both as far as I know?
or run 4&9 with 6v taps and ground 5... same thing basically?
most of the time the heater circuit isn't grounded on one end, but sometimes it is.
When its grounded, you can tie 9 to ground and 4+5 to the heater line.
If its not grounded, 4 and 5 go to one side of the heater, and 9 goes to the other.
doesn't really matter how its done, to run on 6v pins 4 and 5 connect together and 9 connects to the other side of the supply to make it all go.
if you tie 4 to 9, only half of the tube is going to light.
When its grounded, you can tie 9 to ground and 4+5 to the heater line.
If its not grounded, 4 and 5 go to one side of the heater, and 9 goes to the other.
doesn't really matter how its done, to run on 6v pins 4 and 5 connect together and 9 connects to the other side of the supply to make it all go.
if you tie 4 to 9, only half of the tube is going to light.
Does this help?
The Valve Wizard
www.valvewizard.co.uk
I'm not sure what you're saying here. For 6.3V use, pins 4 and 5 must be connected together. How you apply power between 9 and pins 4/5 is a different issue, because it doesn't matter which node is grounded. In fact, how you maintain the AC zero-crossing at ground potential is also not necessarily relevant to the flow of heater current. Everything could float, including the transformer winding, although that generally induces noise into the tube.
Jack