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PostPosted: Fri May 15, 2020 12:42 am 
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The 52.4K resistor is OK. It might help if matched the other 56K in the phase inverter, but it's close enough for a tube guitar amp.

Signal wires are also those running to the tone controls, and anything running to the grid on a tube.

The pine cabinet is starting to look good. Great way to use some old shelving.


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PostPosted: Fri May 15, 2020 10:31 am 
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Wow, thanks for the fast and complete replies !

I've checked the link Han. That's perfect. It's all what I needed. The coax cable is now done and one side soldered on the normal volume control as pictured (I'm very visual and reading the text, I now understand what it meant... sorry :)

I'm going to skip the optionnal 470K since I don't know what it exactly change on the sound.


For the rest I think I'm all good. My next questions will certainly be related to the final testing.


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PostPosted: Fri May 22, 2020 11:41 pm 
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Ok, I've put it aside for a while but finished the build this evening.

I'll do more checks tomorrow but I think it will be ok. I've checked connectivity with my multimeter after each soldering. I've tried to keep wires close to the chassis when possible and keep them away as far as possible from the heater wires. I've put the coax cable is under the eyelets board. Since it has also to be close to the chassis I thought it would make sense. I've taped to it. I was also finally able to twist the yellow wires together from the power transformer, same for the reds. They are tied but I think it's overall better now. I've tried to have an overall neat build and soldering ( and to be able to desolder if necessary).
Oh and yes... I put the screw from the outside to install the board (on purpose, I prefer this way). I'll get 4 nuts tomorrow.

I haven't install the VRM. Maybe later.



Few questions about the final tests...


Point 1, "With no rectifier in place" :
- it's without any tube, isn't it ?
- Rectifier is the V5, right ?


Point 6, install the rectifier (...)
"(...) Check the plate voltages on the tube sockets", ok... can someone explain precisely what I'm supposed to do and check here ? That's would be very appreciated ! I understand I should have something like 400 volts DC as result/measurement but I don't know how I'm supposed to get that result (it's the only check for this step btw ?). I'll google B+ tomorrow since I've seen it at different place but still don't know what it is.


Point 8, "Measure the DC voltages from tube pin to chassis ground and compare to voltage chart"
What the use of the table at the point 8 ? I guess there's a reason why it's shown here. This table doesn't fit with the voltage chart... I'll stick with the voltage chart which is straightforward but the table at the point 8... (???)
(+ in the table there's 4+5 for the V1 and V2 in the Heater column. I'm not sure how to interpret this)


Thanks a lot !!


In the meantime here are some pictures of where I am now.


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PostPosted: Sat May 23, 2020 2:46 am 
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Thanks for the pictures. The build looks good. Nice and neat. Looks like the amp should work well. The only thing I noticed that could be improved is using more solder on some of the eyelets on the board. I like to see them completely filled to make sure the connections are good.

Point 1, "With no rectifier in place" :
- it's without any tube, isn't it?
Yes.

- Rectifier is the V5, right?
Yes.

Point 6, install the rectifier (...)
"(...) Check the plate voltages on the tube sockets", ok... can someone explain precisely what I'm supposed to do and check here? That would be very appreciated! I understand I should have something like 400 volts DC as result/measurement but I don't know how I'm supposed to get that result (it's the only check for this step btw ?). I'll google B+ tomorrow since I've seen it at different places but still don't know what it is.

This means with no tubes in the amp except for the rectifier, measure the voltage at the plate pins on the tube sockets. Plate is another term for the anode on a tube. The plates are pins 1 and 6 on the 12AX7s and pin 3 on the 6V6s. But if they aren't installed, there will be no load to drop the voltage so you should see pretty much the same DC voltage that's coming out of the rectifier. This is the B+ and it should be around 400 volts. Measure it carefully with the meter's negative probe clipped to the chassis and the positive probe on each plate pin. This is all you have to do in this step.

B+ is an old term that used to refer to the positive voltage coming from a battery. But when it's used with a tube circuit it means the DC high voltage coming from the power supply, usually before any resistors drop it down for the various tubes.

Point 8, "Measure the DC voltages from tube pin to chassis ground and compare to voltage chart"
What's the use of the table at point 8 ? I guess there's a reason why it's shown here. This table doesn't fit with the voltage chart... I'll stick with the voltage chart which is straightforward but the table at point 8... (???)
(+ in the table there's 4+5 for the V1 and V2 in the Heater column. I'm not sure how to interpret this)

The table just shows the pins and their names for the various tubes. These are the pins that you should check for the voltage measurements. The table doesn't give the expected voltages, though. Use the voltage chart to find that.

For example, V1 is a 12AX7. Its plates are pins 1 and 6. Its cathodes are pins 3 and 8. Its heaters are pin 9 and pins 4+5 tied together.
V3 is a 6V6. Its plate is pin 3. Its cathode is pin 8. Its heater is pins 2 and 7.

The schematic drawing shows all this too.


Last edited by mitch m on Tue May 26, 2020 9:25 pm, edited 1 time in total.

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PostPosted: Sat May 23, 2020 9:12 am 
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Thanks a lot for your time and patience Mitch. I'm all good now for this evening !

I'll add more solder on few spots on the board as you say (I like/try to think in advance and I was concerned about futur service. I didn't want to put too much to get more easily removed in case pieces need to be changed :) But of course, main and first concern is to get a proper/durable connection ! I'll do it !

About the table at the point 8, I can't believe I didn't pay attention it was a summary of the location of plate/cathode/heater pins. I think I was too much focused on measurements at that time. It's obvious but not enough for me apparently.. ahah.


Alright, so I'll do the test this evening. In good conditions, without my son around for example.. :)

Thanks again !


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PostPosted: Sun May 24, 2020 12:34 am 
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Hi, I've done the measurements. Here are the result :

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As you can see,
- pin 6 of V1 and V2 // pin1 of V2 are smaller than expected
- Pin 8 of V1 is slighty above than expected
- pin 7 of V2 is way off with 2.9 instead of 17


About the sound, the amp plays but it doesn't sound as it should. The interaction between both volume control is weird (increasing hiss when turn the pots but it may not be the right term here..). But anyhow I'll write another time about that. Need to sleep now.


Any comment about the measures would be appreciated Thanks !



Also, I was wondering about the 22K resistor. I've seen it on every build it's a bigger one in size, like the 4K7 just besides. Mine is blue body and smaller, I guess it cannot cause any issue.. They are only two different kind, bothe metal film and doing the same job, right ? it's supposed to be 2W but I was only able to confirm the value of the resistor.

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PostPosted: Tue May 26, 2020 9:23 pm 
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The volume controls do interact. That's normal on 5E3 amps, even the originals.

But if the sound isn't right, check all your connections, looking for bad solder joints. Also make sure all the parts and wires are in the right places. Looks like they are in the photos, but it wouldn't hurt to check again.

As I said earlier, the eyelets on the board should be full of solder to make sure the connections are good. It's easy to take a component out of an eyelet later for maintenance or modifications, even if the eyelet is full.

The 22K resistor looks OK. The one in my Tweed amp looks the same. Sometimes it's hard to tell if a resistor is 1-watt or 2-watt.


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