Bassman micro 12au7 planning/build thread

[2L man]

Ok, gotcha. I don’t put standby switches in my amps anymore after learning what KF points out. I’m not sure how the MV would handle being close to the power switch and/or pilot light. I guess it depends on the light but it may be susceptible to more hum there.

When faceplate has a Stby switch hole I always install the switch. I improve it installing a resistor over its contacts and when Mains is switched On there begin to flow low HV current and elecgrolyts pre-charge slightly and this depends of resistor value. Tube cathodes don't "poison" so switch comes true Standby Amp can be played as well but sound is quiet and very distorted. Obviously that Stby switch resistor could be used as a "bedroom brown sound effect" when its value is select so that current floaw comes higher?

When amp does not have a stby switch tubes can produce so bad sounds first minute or so that possibly there is a danger to destroy the loudspeaker but work just fine when they have reach operation temperature. I have been challenged speaking against "Leo" what comes "grounding" but what comes to Stby I think he was right!!! Yes I understand that indirect/delayed heating rectifier tubes were designed but still direct heating rectifiers are often favored and they and stby switches belong to the same phase in tube technology.

 

[King Fan]

I’ll put Merlin's logic and referenced science up against all the received wisdom we see from standby proponents. As Merlin says, they include lots of experts — who have lots of different reasons for their beliefs. As for Leo, Merlin discusses that in his section on standby origins.

The Valve Wizard

In any case, that faceplate doesn’t have a standby hole, it has an MV hole. Rob draws an MV there; it definitely needs to be on the front panel, since it’s just about the most important control on this amp. And mine is totally silent sitting right by the switch with non-shielded wire. @Blueslover88 , where were you going to put your MV?

 

[Blueslover88]

I’ll put Merlin's logic and referenced science up against all the received wisdom we see from standby proponents. As Merlin says, they include lots of experts — who have lots of different reasons for their beliefs. As for Leo, Merlin discusses that in his section on standby origins.

The Valve Wizard

In any case, that faceplate doesn’t have a standby hole, it has an MV hole. Rob draws an MV there; it definitely needs to be on the front panel, since it’s just about the most important control on this amp. And mine is totally silent sitting right by the switch with non-shielded wire. @Blueslover88 , where were you going to put your MV?

I definitely am going to put it in where the standby hole is. I was thinking just putting a washer on each side would hopefully suffice as that's a 1/2 hole I stead of 3/8.

 

[Blueslover88]

I took a crack at making my own faceplate with clear adhesive paper. It has some bubbles and isn't perfect but will work for now. I may just keep it on the white background and drill holes in it next time! I was going to try decal type paper but it seemed to tall a task lol. Also I'm trying my hand at rivets for the tube sockets and Rivnuts for the Other irons

 

[Blueslover88]

Some more weekend progress. PT, OT and choke mounted. Tube sockets and pots as well. Coming along nicely!

 

[Blueslover88]

Spent some more time working on it. Anybody see problems with my primary wiring? Both reds mounted to neutral IEC, both blacks to one side of switch, other side of switch to fuse then to hot on the IEC. Just need ground bolt to mount safety ground and purple shield of PT. Tested for continuity which it has with sitch in and does not with switch off.

 

[mountainhick]

Am I seeing correctly, are your heater wires shorted? It looks like at V4, the outgoing orange and green are attached together on pins 4-5, then the same is repeated at each tube. If you are consistent with the colors, the outgoing green needs to attach to pin 9 with the incoming green

 

[Blueslover88]

Am I seeing correctly, are your heater wires shorted? It looks like at V4, the outgoing orange and green are attached together on pins 4-5, then the same is repeated at each tube. If you are consistent with the colors, the outgoing green needs to attach to pin 9 with the incoming green

I don't think I'm consistent with the colors, but with pins 4-5 jumpered on each tube I am sending the 6 volts to each outgoing tube, correct? I'm not understanding what I did wrong or how it would short any of the heaters. Please help me understand if I'm off, I'm no expert.

 

[mountainhick]

I don't think I'm consistent with the colors, but with pins 4-5 jumpered on each tube I am sending the 6 volts to each outgoing tube, correct? I'm not understanding what I did wrong or how it would short any of the heaters. Please help me understand if I'm off, I'm no expert.

Am I seeing three wires to each pin 4/5 connection, and only one wire to pin 9?

It needs to be 2 and 2 to the alternate sides of the tubes, pins 4/5 jumpered together constitute one side. The other side is pin 9 on each tube.

Using the colors, 2 orange wires (incoming and outgoing) to pins 4/5 and 2 green wires (incoming and outgoing) to pin 9 at each tube. V1 gets only one on each side.

electrically, you need this (the twisted wire routing makes the actual wire layout look different. You need two green wires to cross over the middle of the tube to pin 9).

As far as shorting, my bad, as it looks now, the 6.3V will only reach V4. There is no wire from pin 9 to carry on the parallel connection to the next tube. But I can still say that the outgoing wires to V3 are indeed shorted together, and that pattern is repeated on V3 and V2

 

[Blueslover88]

Am I seeing three wires to each pin 4/5 connection, and only one wire to pin 9?

It needs to be 2 and 2 to the alternate sides of the tubes, pins 4/5 jumpered together constitute one side. The other side is pin 9 on each tube.

Using the colors, 2 orange wires (incoming and outgoing) to pins 4/5 and 2 green wires (incoming and outgoing) to pin 9 at each tube. V1 gets only one on each side.

electrically, you need this (the twisted wire routing makes the actual wire layout look different. You need two green wires to cross over the middle of the tube to pin 9).

View attachment 1109492


As far as shorting, my bad, as it looks now, the 6.3V will only reach V4. There is no wire from pin 9 to carry on the parallel connection to the next tube. But I can still say that the outgoing wires to V3 are indeed shorted together, and that pattern is repeated on V3 and V2

Okay perfect I get what you are saying, I will deff fix it!. I was thinking green to pin 9 and red to 4 which is jumpered, so sending those two down from 4/5 to each tube would work. What do you think about primary wiring? Am I correct on it?

 

[mountainhick]

What do you think about primary wiring? Am I correct on it?

Looks right to me.

Not sure why that rubber pad is inside the box? Those are to pad the TF itself.

 

[King Fan]

If I follow all the above, @mountainhick has it just right. In case it might help, heater wiring example:

PT mount inside chassis (the rubber pads go over and under the PT itself).

For both 1° and 2° wiring, I may have missed it -- do you have a diagram showing the wire colors from your PT?

 

[mountainhick]

Is that teflon insulation? I use PVC, soldering would melt the insulation under the 4-5 jumper. Interesting trick!

 

[Blueslover88]

Is that teflon insulation? I use PVC, soldering would melt the insulation under the 4-5 jumper. Interesting trick!

I know this PVC wire melts so easily, I was just removing heater wires from first three tubes and made a mess, corrected wiring pics to follow. Thank you guys so much for the experienced eyes catching my mistake. I did this at 6 am before work and it shows I still have a lot to learn!

 

[Blueslover88]

Kingfan, hopefully you can read this okay. I only have a pdf of the wiring

 

[mountainhick]

Kingfan, hopefully you can read this okay. I only have a pdf of the wiring

Same one I used on my last build. And same series as @King Fan 's photo. He used the terminal strip though instead of going straight to the switch and neutral on the IEC socket with the twisted pairs.

 

[Blueslover88]

Same one I used on my last build. And same series as @King Fan 's photo. He used the terminal strip though instead of going straight to the switch and neutral on the IEC socket with the twisted pairs.

Yes and being the 12au7 BMM I plan to use yellow and white for 240v to four diode configured rectifier

 

[Blueslover88]

@mountainhick . I was careful not to melt the insulation on these heater wires and even put some shrink tube in first 3 valves. Is this wiring better. I tried flying wires on the jcm800 micro. I think I like that way better, not sure.

 

[mountainhick]

@mountainhick . I was careful not to melt the insulation on these heater wires and even put some shrink tube in first 3 valves. Is this wiring better. I tried flying wires on the jcm800 micro. I think I like that way better, not sure.

You got it! That should work.

I don't do that jumper over the green wires, it is not necessary, but it is a neat trick.

 

[Blueslover88]

You got it! That should work.

I don't do that jumper over the green wires, it is not necessary, but it is a neat trick.

I have a 6 volt marshall style pilot light and dual gang MV pot on the way, I believe I will use three post terminal strip to land the 6 volts secondary, pilot, and heater wires to. I like the way it looks in kingfans build! Kuddos to you kind sir. If I make a artificial center tap with two 100r resistors can I land that to the bottom cathode resistor. I have done so on other builds, just unsure if that will elevate it appropriately, I should read up on it more.