6G6-B Bassman pre, parallel 6AK6 build thread

mountainhick

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I finally feel ready for this project in large part to the great help I've had here on the forum. Thanks to everyone who answered my questions and helped me sort out the circuit, power supply design and a few other things. I learned a ton, and am ready to go now. Parts will start arriving tomorrow!

I did a little chassis work today. This is a Regency MR-10 radio chassis. The top was so riddled with holes, I figured why not make it a nice new surface for the new layout. I cut out the top leaving just a bit of the rolled over edges, deburred everything, spot welded a new top on, leveled the welds and did a rough sanding. I think I'll paint the exterior after drilling/cutting all the holes. I'll clean out the welding garf from the inside as well.

chassis-1.jpg
chassis-3.jpg
chassis-2.jpg
 

pbenn

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Good idea on the inside cleanup (in a body shop, this would be where the estimate doubles!).

But if you use a high speed grinding disc, beware the "scoop" of the radius... it can make the weld weakest in the center.

Bigger disc is going to be shallowest radius... but won't get into the corners.

Maybe one of those pointed stones... but sometimes body of motor conflicts with upper sides of container.

Maybe stone on a long extension to clear sides?
 

mountainhick

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Good idea on the inside cleanup (in a body shop, this would be where the estimate doubles!).

But if you use a high speed grinding disc, beware the "scoop" of the radius... it can make the weld weakest in the center.

Bigger disc is going to be shallowest radius... but won't get into the corners.

Maybe one of those pointed stones... but sometimes body of motor conflicts with upper sides of container.

Maybe stone on a long extension to clear sides?


Thanks.

I purposefully added welds inside the box. They will not be ground flush. Just want to clean up the oxidation.

Dremel with wire brush, toothbrush and abrasive slurry. Blown dry with compressed air.
 

mountainhick

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I am playing with transformer's relative position with headphones. of course the lowest hum is with them furthest apart. Would placing the OT right by V1 and V2 induce hum on the tubes, or no because it receives filtered DC?
 
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NTC

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Love those uncapped wires near that metal housing. Looks like an accident waiting to happen, though I must admit that I have done similar things.

I would worry about wire routing if the ot wires go past the preamp tube wires. That could induce positive feedback and squeals. Routing the wires outside the chassis could be a safety issue. Tough problem.
 

mountainhick

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Love those uncapped wires near that metal housing. Looks like an accident waiting to happen, though I must admit that I have done similar things.

I would worry about wire routing if the ot wires go past the preamp tube wires. That could induce positive feedback and squeals. Routing the wires outside the chassis could be a safety issue. Tough problem.


Thanks, Certainly would be safer to use all possible precautions. The glare in the photo is deceptive. The wires are no where near the chassis nor my hands when working and it's hooked to a 15W bulb current limiter. I'll model better behavior next time.

Thanks for the warning about OT wire routing! I'll use a happy medium that hopefully doesn't induce too much hum.
 
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printer2

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Thanks, Certainly would be safer to use all possible precautions. The glare in the photo is deceptive. The wires are no where near the chassis nor my hands when working and it's hooked to a 15W bulb current limiter. I'll model better behavior next time.

Thanks for the warning about OT wire routing! I'll use a happy medium that hopefully doesn't induce too much hum.
I saw the wires and they did not worry me all that much, the upside down transformer did a little.
 

mountainhick

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I am moving along with layout. I dismantled a couple hammond organ modules and one of the boards can be adapted for this preamp with a little layout tweaking. If anyone is so inclined, I'd love to have this checked.

I had to do a mirror image for my amp's layout.

Point "A" on original layout went to a mxing resistor to join the other channel, but my amp has only this one channel, so goes to .022 coupling cap and master volume

Original:

6G6B-bass-channel.jpg



My layout:

my-pre-board.jpg
 
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