Two different preamps (one octal and one regular) in a Tweed Delux "clone"

[Jerry garrcia]

@andrewRneumann and @printer2
Finally after many hours of de and resoldering. I went with a combination of your layouts to minimise the work since everything was already put in place. Now just to connect the fuse, S1 and S2 and wall current.
Took the sag resistor and diode connection and CT from Andrew and the C3, c5 with 4,7M resistors (quite tight to get them on the ground bus due to the jacks) from Printer and also printers R16, 17, and 18.

Will connect the shielded wires to S2 to a common chassi ground. Hopefully done tomorrow

I’ll include some pictures and the newly built cabinet.
Please shout if you se something strange.

 

[printer2]

I would separate the bypass cap from the cathode resistor just a little to keep it cooler. Even a little air space helps.

So your next project will be building a ship in a bottle?

 

[BB]

Beautiful looking amp JG! If it sounds half as good as it looks, you got a winner.

 

[Jerry garrcia]

Beautiful looking amp JG! If it sounds half as good as it looks, you got a winner.

Hopefully it works… if so, I need it to be as good looking inside.

 

[Jerry garrcia]

I would separate the bypass cap from the cathode resistor just a little to keep it cooler. Even a little air space helps.

So your next project will be building a ship in a bottle?

Haha. It was more distance between them from the beginning but had to resolder almost everything so on the picture it was not separated. In the retrospect I should have uncoupled the eyelet board from the chassi when I did the rewiering from your and @andrewRneumann layout. It would have saved me a couple of hours work. If this thing even remotely delivers any sound I will redo the whole mounting board according to your last help with the layout.

 

[printer2]

Haha. It was more distance between them from the beginning but had to resolder almost everything so on the picture it was not separated. In the retrospect I should have uncoupled the eyelet board from the chassi when I did the rewiering from your and @andrewRneumann layout. It would have saved me a couple of hours work. If this thing even remotely delivers any sound I will redo the whole mounting board according to your last help with the layout. View attachment 943005

Heck no. If the thing works with no problems button it up and play. You may find you need to adjust something, a new build that is going off the beaten path is not guaranteed to be perfect out of the box. Keep our fingers crossed. I would vacuum the crap off the board while using a small paint brush to get in places. Maybe a splash of alcohol if needed.

 

[Jerry garrcia]

Heck no. If the thing works with no problems button it up and play. You may find you need to adjust something, a new build that is going off the beaten path is not guaranteed to be perfect out of the box. Keep our fingers crossed. I would vacuum the crap off the board while using a small paint brush to get in places. Maybe a splash of alcohol if needed.

I have a bottle of 99.7% ethanol at home. Nothing survives that.

 

[andrewRneumann]

Just a quick reminder... let's leave the tubes out and go through each socket with the ohmmeter to make sure we can explain the resistance on each pin. We can measure plate and screen resistance back to their respective power supply node. Grid and cathode resistance can be measured back to chassis. Refer to your tube data sheets and make sure every pin is correct--plate is plate, grid is grid, cathode is cathode, ground is ground, etc. In some cases you will have a parallel capacitor that has to charge up (to the voltage of your ohmmeter) before the resistance reading stabilizes.

It's going to be hard for us to visually spot hidden errors given the cramped nature of the layout. Using the ohmmeter helps find hidden mistakes.

Once we are satisfied that the resistances are correct, we can power the amp on with no tubes installed. Then go back through the sockets with the voltmeter and check you have B+ on the plates and screens ONLY and nowhere else. If you have a light bulb limiter, I suggest you use it continuously in this phase. Check for 6.3vac across the heater pins. Be extremely careful with the probe. Keep one hand behind your back, use your steady hand for the probe. Don't touch the chassis with your other hand. Also very important--don't create a short with your probe. For example, pin 2 on 6V6 is a heater terminal, pin 3 is plate (B+). If you accidentally touch pin 2 and pin 3 at the same time with your probe--short circuit. This is one reason why LBL is good.

Getting excited about seeing if this works? I am.

 

[Jerry garrcia]

Just a quick reminder... let's leave the tubes out and go through each socket with the ohmmeter to make sure we can explain the resistance on each pin. We can measure plate and screen resistance back to their respective power supply node. Grid and cathode resistance can be measured back to chassis. Refer to your tube data sheets and make sure every pin is correct--plate is plate, grid is grid, cathode is cathode, ground is ground, etc. In some cases you will have a parallel capacitor that has to charge up (to the voltage of your ohmmeter) before the resistance reading stabilizes.

It's going to be hard for us to visually spot hidden errors given the cramped nature of the layout. Using the ohmmeter helps find hidden mistakes.

Once we are satisfied that the resistances are correct, we can power the amp on with no tubes installed. Then go back through the sockets with the voltmeter and check you have B+ on the plates and screens ONLY and nowhere else. If you have a light bulb limiter, I suggest you use it continuously in this phase. Check for 6.3vac across the heater pins. Be extremely careful with the probe. Keep one hand behind your back, use your steady hand for the probe. Don't touch the chassis with your other hand. Also very important--don't create a short with your probe. For example, pin 2 on 6V6 is a heater terminal, pin 3 is plate (B+). If you accidentally touch pin 2 and pin 3 at the same time with your probe--short circuit. This is one reason why LBL is good.

Getting excited about seeing if this works? I am.

Hi and thank you for your concerns.
As I have written before you need to think of me as a totally newbie. Learning a bit as everything proceeds.
Regarding the resistance measurements I’ll do that. Need a bit of guidance though. How can I find to what I should measure the resistance between? Like for pin 1 on V1 and so on. Is there a easy way to see that?

Then I might have to get a new multimeter. The one I have does not have clips. Hard to do the measurements with one hand on my back.
I’m so eager to power this thing up so I’m about to explode! A good behaviour therapy this amp thing

 

[printer2]

Your tips look fine. There are other probes that have a lot of exposed metal to accidentally touch other parts. Ask to see any electrician's probes and you have a good chance of seeing where they touched what they should not have and a piece burned away. Thankfully we have lower current in our stuff, but stuff still happens. Maybe you could practice a little.



Just kidding. What I do is while holding the probe place one probe where I want it. If I have it firmly positioned that it will not slip I place the second probe on the other point I want to measure. What you can also do is use an alligator lead and put it on a ground point when the amp is powered off and heave the other end of the lead clipped on the end of the probe. Then turn the amp on and measure with the other probe with only one hand. Don't worry too much on the capacitors charging up, as long as you see it happening you have a good idea that you are measuring somewhere that there is a capacitor attached to. Otherwise measuring the pin which should have the 1.5k or 100k resistor should read right when you are across the other side of the resistor. The tube side of the resistor will be a short to the tube pin. Check the pins to ground also, other than the cathode of the input pentode there should not be a short to ground.

Also very important, when going to measure resistances, make sure the amp is off and the caps discharged. Also make sure you are on resistance or voltage when measuring either. Yes, it is easy enough to switch it over and forget which you are on when you are figuring out what you are doing next.

I think Rob has an amp start up page you can use to help out.

 

[Jerry garrcia]

Your tips look fine. There are other probes that have a lot of exposed metal to accidentally touch other parts. Ask to see any electrician's probes and you have a good chance of seeing where they touched what they should not have and a piece burned away. Thankfully we have lower current in our stuff, but stuff still happens. Maybe you could practice a little.



Just kidding. What I do is while holding the probe place one probe where I want it. If I have it firmly positioned that it will not slip I place the second probe on the other point I want to measure. What you can also do is use an alligator lead and put it on a ground point when the amp is powered off and heave the other end of the lead clipped on the end of the probe. Then turn the amp on and measure with the other probe with only one hand. Don't worry too much on the capacitors charging up, as long as you see it happening you have a good idea that you are measuring somewhere that there is a capacitor attached to. Otherwise measuring the pin which should have the 1.5k or 100k resistor should read right when you are across the other side of the resistor. The tube side of the resistor will be a short to the tube pin. Check the pins to ground also, other than the cathode of the input pentode there should not be a short to ground.

Also very important, when going to measure resistances, make sure the amp is off and the caps discharged. Also make sure you are on resistance or voltage when measuring either. Yes, it is easy enough to switch it over and forget which you are on when you are figuring out what you are doing next.

I think Rob has an amp start up page you can use to help out.

Thanks. Will do tomorrow. Luckily I have a case of Covid (again, even after 3 doses of vaccine), quite an exposure at work…

Another question as usual. What’s the best way of grounding the shielded signal wires going to S2? Can I twist the copper shield from all “A” connections to S2 and do the same with the three “B” connections and twist the six shields and solder them together with a ground wire to be attached to a separate chassi ground?

 

[printer2]

I hope you only suffer temporary effects. I retired a few months pre-covid, do not regret missing it.

Six together might be a handful but yes. Careful not to overheat the insulator around the center wire.

 

[Jerry garrcia]

Finally!!!!
The whole thing is put together. A true PITA but fun. Haven’t started to measure yet. Checked all grounds and the sound fine anyway…
The 240 VAC from PT is resting on the R 270 ohm, 10W. Might have to move those wires. The shielded signal cables were not fun to work with inside this huge chassi. It all looks like an old Gibson amp with wires all over the place.
Anybody have any concerns by looking at the pictures? Except that it looks like a crows nest.
After the pictures I cleaned it with brush, vacuum and bottled air.
I just want to put in the tubes, speaker, guitar and power it up!
The wait…….

 

[andrewRneumann]

The 240 VAC from PT is resting on the R 270 ohm, 10W. Might have to move those wires.

Yeah--that is tight. I think you are right to be concerned. We need to make sure that resistor isn't melting any insulation or overheating any nearby components.

I don't have time to sit down and explain each and every resistance measurement. Measure from plate to the appropriate power supply capacitor and make sure you get the plate resistor value you have on your layout. For the power tubes, you should get a small amount of resistance from the OT primary. The screens back to their capacitor should reflect the screen grid resistors your installed. The grids and cathodes should be measured to the chassis. You should get the cathode resistance according to the cathode resistors you installed. The grid resistance to chassis should be the grid leak resistors / volume pot you installed. (Keep volume and tone controls on 10 for this.) Verify the grids resistances are proper depending which channel you have selected. You should get 0Ω for any pins that are supposed to be grounded.

You should also check the power supply B+1, 2, 3 nodes for proper resistance to each other, and that they have a very large amount of resistance to the chassis. The PT secondary (prior to the diodes) resistance to chassis can be checked too. It should be around 320Ω taking into account the resistance of the PT secondary winding and the 270Ω sag resistor on the HT C/T.

A spreadsheet with a row for each pin on each tube is valuable for keeping track and communicating to us what you are seeing. You can have a column for resistance measurements, and then a column for voltage measurements once the amp is up and running.

That's all I got for now.

 

[Cosmic Cowboy]

Hi all. I would like to have the possibility to shift between two preamps in one combo speaker cabinet, Tweed Delux, 5E3. One octal preamp (1x6SL7, 2x6SJ7) and one 12AY7+ 5751 preamp. Then 2x6V6 power tubes and a Weber 12A125 or a Jensen P12R Speaker.
1) Is that possible?
2) will it fit in a Tweed delux cabinet? If not, what is the minimum required tweed cabinet size?
3) if so what is the best solution to shift between the preamps? A switch?
I don’t want any external preamps even if it easier or cheaper.

Does anybody have a nice schematics/layout for this construction from a previous build?

Despite the fact that this is not a 5E3...This amp is quite a chameleon. I was super blown away when I got to play one. Two tone stacks, two power sections, and covers everything from Brad Paisley (EL-84 cleans) cleans to Marshall grunt with EL34's Goes back and forth from EF86 and 12AX7 tone stacks.

With this amp, my pedal board would be paired down to a tuner, a volume pedal, and maybe a tremolo.

 

[Jerry garrcia]

Yeah--that is tight. I think you are right to be concerned. We need to make sure that resistor isn't melting any insulation or overheating any nearby components.

I don't have time to sit down and explain each and every resistance measurement. Measure from plate to the appropriate power supply capacitor and make sure you get the plate resistor value you have on your layout. For the power tubes, you should get a small amount of resistance from the OT primary. The screens back to their capacitor should reflect the screen grid resistors your installed. The grids and cathodes should be measured to the chassis. You should get the cathode resistance according to the cathode resistors you installed. The grid resistance to chassis should be the grid leak resistors / volume pot you installed. (Keep volume and tone controls on 10 for this.) Verify the grids resistances are proper depending which channel you have selected. You should get 0Ω for any pins that are supposed to be grounded.

You should also check the power supply B+1, 2, 3 nodes for proper resistance to each other, and that they have a very large amount of resistance to the chassis. The PT secondary (prior to the diodes) resistance to chassis can be checked too. It should be around 320Ω taking into account the resistance of the PT secondary winding and the 270Ω sag resistor on the HT C/T.

A spreadsheet with a row for each pin on each tube is valuable for keeping track and communicating to us what you are seeing. You can have a column for resistance measurements, and then a column for voltage measurements once the amp is up and running.

That's all I got for now.

I understand you fully for not having the time to explain it all. Everything you have helped med with is more than anybody would expect from a fellow human.
I’m taking time off building tonight (since I’m done, hopefully) and dedicating this evening in an awful weather, to read Rob Robinette and the brilliant book “Vacuum Tube Amplifier Basics”.
Will move the wires touching the resistor. Have a concern nagging in the back of my head. I didn’t have any unshielded ground wires left after the ground bus so I used regular black ground wire for connection between C11-C12-C13. And also regular black ground wire to all connections from the board to the ground bus. Seems like good connections but the visual appearance is not that great. Like it matters in this nest of a build .

I will act on your comments and report back.

 

[andrewRneumann]

I didn’t have any unshielded ground wires left after the ground bus so I used regular black ground wire for connection between C11-C12-C13. And also regular black ground wire to all connections from the board to the ground bus.

You mean uninsulated plain wire? Insulated is totally fine.

 

[Jerry garrcia]

Are the diodes placed with the right polarity?

 

[andrewRneumann]

Are the diodes placed with the right polarity? View attachment 944409

Yes. If you measure resistance from the junction of the two diodes to chassis you should a get small number that rises quickly to >>100K.

 

[Jerry garrcia]

Yeah--that is tight. I think you are right to be concerned. We need to make sure that resistor isn't melting any insulation or overheating any nearby components.

I don't have time to sit down and explain each and every resistance measurement. Measure from plate to the appropriate power supply capacitor and make sure you get the plate resistor value you have on your layout. For the power tubes, you should get a small amount of resistance from the OT primary. The screens back to their capacitor should reflect the screen grid resistors your installed. The grids and cathodes should be measured to the chassis. You should get the cathode resistance according to the cathode resistors you installed. The grid resistance to chassis should be the grid leak resistors / volume pot you installed. (Keep volume and tone controls on 10 for this.) Verify the grids resistances are proper depending which channel you have selected. You should get 0Ω for any pins that are supposed to be grounded.

You should also check the power supply B+1, 2, 3 nodes for proper resistance to each other, and that they have a very large amount of resistance to the chassis. The PT secondary (prior to the diodes) resistance to chassis can be checked too. It should be around 320Ω taking into account the resistance of the PT secondary winding and the 270Ω sag resistor on the HT C/T.

A spreadsheet with a row for each pin on each tube is valuable for keeping track and communicating to us what you are seeing. You can have a column for resistance measurements, and then a column for voltage measurements once the amp is up and running.

That's all I got for now.

Damn!!!!!!!
I just realized that the two 2 W resistors between B+1-B2 to B3 were wrong. They were 18 Ohm and 5,1 Ohm. Not 18k Ohm and 5,1K Ohm. There have been a lot of resoldering at those three points. Can I cut them and twist the new ones around the caps "legs" or or is it better to cut them out close to the resistor and make a small hook to attach the new one or do I need to resolder the whole eylet?
I'm a bit uncertain that i have the proper 2W values resistors at home. What's the closet value that is OK? Must it be 2W?
Measurments of the resistance is done. Plates and screens measured against closest power cap connection and all other values are measured against chassis ground. Too bad I realized the wrong value on the resistors after...
Need to measure again? And the main question is should I prioritize sleep, family, work, dog or amp?
Specs for the tubes:

https://www.evatco.com.au/assets/images/12ax7%20pin%20out%20configuration%20ecc83.jpg

6SJ7 @ The Valve Museum

6SC7 @ The Valve Museum

6V6GT @ The Valve Museum

V1 V2 V3 V4 V5
Pin 1 0,5 0 17,5M O.L O.L
Pin 2 32K 49 0,6 50 50
Pin 3 814 0 4,68K 155 149
Pin 4 49 4,7M 416K 464 464
Pin 5 49 0 0,2 227K 223K
Pin 6 0,5 0,4 0,983K 227K 223K
Pin 7 0,973M/32,3K 49,5 49 49 49
Pin 8 814 0,5 49 270 270
Pin 9 49

Regarding Pin 7 on V1 the resistance changed with the S2 switch.
All values are in Ohm unless it states anything else.