GA-16/18T in a Stout chassis?

[Blooze]

I do like me some blinky lights 

Bought these for the standoffs. They’re pricier than straight nylon, but have the brass inserts so they can’t strip out.

[Blooze]

Does the output jack need to have a separate wire to ground in this instance?

[bmccowan]

Probably not. If there is unexplained noise, worth a try. Getting the ground right can be an exercise of try this/try that. But this amp is simple and medium gain. I love the sound!

[Blooze]

Probably not. If there is unexplained noise, worth a try. Getting the ground right can be an exercise of try this/try that. But this amp is simple and medium gain. I love the sound!

Did you ever find NFB values you liked?

[bmccowan]

Where did you buy those standoffs? If wanting non-metallic standoffs, I have gone really cheapo for no particular reason: nylon spacers; outside casing from a power cord; or a trick learned from Sluckey, cutoff pieces of a cheap ballpoint pen casing. All with a #6 bolt through them. I can't help it - my Mom grew up in the depression - she used butter wrappers to grease a skillet, balanced the old ketchup bottle upside down on top of the new one to drain every drop, and saved soap bar remains in a big mayo jar of water and used the slurry to wash the car and the dog!
NFB - Well I was happy with the stock NFB, but wanted to tinker. Following PRR's advice, worked well too. That's how I have it now with a 2.2K resistor following a 5K pot. It was fun and I learned a bit, but for improved sound over stock  As PRR said, there is very little NFB in the stock circuit, so changes are subtle. I do not like the sound with the NFB completely off, as the noise floor increases. If wanting a gain boost (I don't) I would go another route, such as switching in a different different bypass caps, etc. But I think Gibson got the circuit right on this one.
OK - now I am just procrastinating because its 14 below 0 here and 45 in my basement workshop.

[PRR]

....its 14 below 0 here and 45 in my basement workshop.

We touched -15F, same as you. The cellar rarely goes to 55 but yesterday it was 50. (I think one of the sealed windows came unsealed, but it's mostly a lot of uninsulated concrete.)

I'm waiting to see if the Pine Tree Camp egg run happened.

[bmccowan]

Great event for a great camp. Do you sled? I've done about 20 charity bicycle rides, but never been a snowmobiler.

[AlNewman]

Great event for a great camp. Do you sled? I've done about 20 charity bicycle rides, but never been a snowmobiler.

You'd love sledding.  Some of the best and most expensive fun you can have with lots of clothes on.

[Blooze]

Would this be the best place to add a toggle switch for the trem? If so, where would be the best place to ground it? 

I’ve also intended to ground the trem footswitch jack to the ground point of the V2B cathode resistor, but it’s gonna have to be ran about 8-10” across the OPT wires and V3 wires. So maybe there’s a better place there as well.



Still learning as I go 😁

[shooter]

I'd put it either side of MV

[sluckey]

I'd like to offer a few suggestions. Refer to attached schematic...

I don't think your NFB will work with that bypass cap. I suggest removing the cap.

Your MV can be simplified, eliminating two coupling caps and two resistors.

Put the trem on/off switch as shown. Only need a SPST switch.

Move the F/S to be parallel with the trem on/off switch. The F/S works as you had it drawn, but, the tremolo will be slow to start up. Moving it as shown allows the trem oscillator to run continuously, avoiding any slow start up issues.

[Blooze]

Thanks Sluckey. That schematic (sans trem toggle) was just a redraw of the original I did with some mods to the caps in the trem circuit to slow it down a bit.

I don’t have the switches or anything hooked up yet. This is as far as I’ve gotten, but I’m not sure I like the location of the impedance rotary switch.

[bmccowan]

Sluckey, The original schematic shows a .01 cap for that bypass cap. So small that it seems like it would boost frequencies that only dogs can hear. Or was it there for noise reduction?
Blooze - nice job on the plate for mounting the PT.
Also - your question on grounding the trem switch. You only have two ground points in the amp, right? The preamp buss and the power amp ground. I would think it should join the other preamp grounds on the buss, but I bet it does not make much difference.
Project is coming along nicely.

[Blooze]

Sluckey, The original schematic shows a .01 cap for that bypass cap. So small that it seems like it would boost frequencies that only dogs can hear. Or was it there for noise reduction?
Blooze - nice job on the plate for mounting the PT.
Also - your question on grounding the trem switch. You only have two ground points in the amp, right? The preamp buss and the power amp ground. I would think it should join the other preamp grounds on the buss, but I bet it does not make much difference.
Project is coming along nicely.

I have a ground lug at the input jacks (which aren't insulated) at one end of the buss. The input jacks and buss attach together there.  The PT high voltage center tap attaches to the other end of the buss, bot directly to the chassis. The 6.3V filament doesn't have a center tap. I have a virtual center tap with two 100R resistors on the 1st 6V6 and elevated by attachment to the 6V6 cathode.

On the switch, I could just put it in parallel with the footswitch though, correct?  Run a couple of jumpers from the footswitch jack?

[bmccowan]

Grounds - I am not quite sure what you meant. So I'll just describe typical practice nowadays.
A ground buss that takes all the preamp grounds and sends them to a ground point near the input. I think you have that.
A second ground point that is not connected to that buss, bolted to the chassis near the PT and it collects the power tube cathode grounds, the PT center taps, and the filter cap grounds. I think you might have that.
There are variations of all sorts, but that's what a lot of builders do.
What did Gibson do? Like a sailor lost at sea; any port in a storm. Grounds are all over the place.

[Blooze]

So if I parallel the trem toggle switch with the trem footswitch jack I have layout #3 currently.  If I swap places of the jacks, toggle, and rotary switch on the back panel I can have layout #2. Problem is the hole for the tiny toggle switch is gonna be pretty oversized (it was for the rotary). I’d need to drill a new hole for the rotary too. It’s too close to the 6V6 sockets for my liking in the other holes.

You can see that the PT center tap is attached to one end of the buss by the first filter cap.  The cathode grounds go up to the buss as well. I could split the buss wire between the 250R 6V6 cathode resistor and the 1st 16uF filter cap, then tie the end at the first filter cap (22uF) to a chassis lug.

[bmccowan]

I could split the buss wire between the 250R 6V6 cathode resistor and the 1st 16uF filter cap, then tie the end at the first filter cap (22uF) to a chassis lug.

I think that is easily done and a good way to go.

[Blooze]

Well, it’s all wired, fwiw. I need to rebuild my light bulb current limiter before I mess with it. I did check the filament wiring voltage and unloaded PT voltage (sans rectifier) just to make sure. Soldering to the tops of turrets sucks. I’m not worried about the connections though.

Not happy with having to run some of the OPT wiring where it is, but hopefully won’t give me any grief.

Any suggestions I’d appreciate.




Edit: Poop, I have a filter cap backwards. DOH! Don't solder while you're tired.

Fixed. That sucks getting them out of the top.

[bmccowan]

I thought I saw that backward cap just as I headed to friends for dinner. You caught it - good.
Did you decide to not divide the grounds?
Very neat work. I was confused by the PT colors but then remembered that Matt uses non-standard color schemes.

Soldering the tops of turrets takes a bit of practice - you think you are done and then the solder sinks into the hole and you are like Lassie looking for Timmy in the well. I have taken to a two step process - first solder a secure connection, wait a few seconds and top it off. It gets easier.

[Lectroid]

Blooze,

It looks like you made your schematic with DIYLC.  Would you be willing to share that file?  I want to tweak my version.  Of course.

Also, a toss-up for the Wizard Council:  would a pre-PI master volume work with a cathodyne PI?

[Blooze]

Blooze,

It looks like you made your schematic with DIYLC.  Would you be willing to share that file?  I want to tweak my version.  Of course.

Sure.

[Lectroid]

Blooze, et al.,

Please take this for whatever you think it's worth.  I took Blooze's .diy file and opened it with DIYLC, ver. 4.35, the latest as of 2/23/23.  The program ran glacially slow in updating changes to the file.  Every command and change worked, but they  took 15-20 seconds to update the screen.  All of my other personal files were fine, they ran as quick as ever.  Just this one made DIYLC run so slowly.

I wrote to bancika about it.  He requested a copy of the .diy file for analysis, which I sent.

[Blooze]

Blooze, et al.,

Please take this for whatever you think it's worth.  I took Blooze's .diy file and opened it with DIYLC, ver. 4.35, the latest as of 2/23/23.  The program ran glacially slow in updating changes to the file.  Every command and change worked, but they  took 15-20 seconds to update the screen.  All of my other personal files were fine, they ran as quick as ever.  Just this one made DIYLC run so slowly.

I wrote to bancika about it.  He requested a copy of the .diy file for analysis, which I sent.

Interesting.  I haven't opened that file for a while now.  I typically do schematics in Diptrace most of the time, because I use it for pedals.

[Blooze]

Success! Partially at least.  Brought it up in bits and pieces with the final through a lightbulb current limiter.  No shorts. Wired my Gain and tone pots backwards, but I don't care at the moment as they still work. Sounds pretty decent through the generic 16 ohm Jet City combo speaker. I hear no difference with the 48K feedback resistor in or out of circuit.
But, the tremolo doesn't work for nothing.  If I turn the depth knob full on it will trem what little hum there is in the amp (which is practically none until you ramp the MV up 3/4 the way). When I can hear the trem working it's sporadic at best.  The Frequency does seem to adjust the speed from about 1-2 oscillations per second to really fast. It won't work at all that I can notice, then if I move the depth control a little bit after a minute of it sitting in one spot it'll work for a couple seconds then nothing. Maybe the way I have the trem switch wired. Maybe that 10uF cap that differs from the original?

Here's what I have so far. On the schematic the voltages I've measured are in red. Picture from a couple posts ago is the finished product as it stands now.

[Blooze]

Trying to digest Aikens explanation of this circuit, but it might take me a bit with everything else I have going on right now.

Edit:  I’m going to start with the original values. See what that brings which is what I should have done to begin with. If that works but it’s too fast I may try the LED and upping 1-2 of the caps at that point. Either way I have to order parts 🙄

How much effect could the length of my wires cause?  Also, I don’t see that my switch does anything as I can get it to intermittently work with it the ground connected or not.