When you're working with high voltage, there is no such thing as a dumb question. Please use this thread to ask about practical or conceptual things that have you stumped.

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As always, we are built around education and collaboration. Be awesome to your fellow tube heads.

Sitting on a box of tubes. Open to suggestions on what to build.

Assuming that I want to use the miller capacitance of a 12AX7 to make a low pass filter with 20kHz cutoff frequency, that means I’ll have a 40k ohm resistor with a 200pF miller capacitance approximately.

Now, if I have a passive guitar that has a 20k ohm output impedance, does that mean that my actual filter shall consider that impedance too? If so, my grid stopper would be 60k, and my cutoff frequency would go down to about 13.2 kHz.

Is that how it works?

Sorry for the dumb question.

Just wanted to share this beauty I scored today, a Neuberger WE238 tube tester, made in Berlin, Germany ca 1930.

Cosmetic condition is almost like new. Electrically I have not tested it yet.

I had given up on getting myself a tube tester due to their prices. But I kept an eye open both here and there and I could finally purchase this one for an almost unbelievable $30. (The seller knows exactly what it is and had set the price as a part of a bigger clearance.)

Even if it would be completely fried in the inside it is well worth its price as a workshop decoration. But I fully expect it to be as well kept on the inside as on the exterior. I'm really looking forward to the restoration!

When you're working with high voltage, there is no such thing as a dumb question. Please use this thread to ask about practical or conceptual things that have you stumped.

Really awesome answers and recurring questions may earn a place in the Wiki.

If you'd like to nominate a comment to be included, just reply [Wiki] (with the brackets)! The mods will be automatically notified that something awesome just happened.

As always, we are built around education and collaboration. Be awesome to your fellow tube heads.

Anybody have any thoughts on this PCB that includes Gillespie's EFB enhancement and eliminates the single 7247 per channel and swaps in a 12ax7 and 12au7 sharing duties?

Link to eBay listing - Dyna St-35 clone

When you're working with high voltage, there is no such thing as a dumb question. Please use this thread to ask about practical or conceptual things that have you stumped.

Really awesome answers and recurring questions may earn a place in the Wiki.

If you'd like to nominate a comment to be included, just reply [Wiki] (with the brackets)! The mods will be automatically notified that something awesome just happened.

As always, we are built around education and collaboration. Be awesome to your fellow tube heads.

Hi all,

I run 100s of dual triode tubes through the Project Ember headphone amp I have to listen for microphonics, general quality, noise, etc. That is a lot of wear and tear on the socket. I had to fix a broken socket pin recently, but it got me wondering if there are any lever-based sockets that are similar to a pin based CPU socket. Anyone ever see something like that?

Here’s the latest iteration of my PP KT88 Stereo Power-Amplifier. See what you think.

i am an electronics grad,very new to the vacuum tube audio! (Enthusiast,) Currently reading books about designing vacuum tube amps.. I am serious about getting into designing tube amps! But so far accomplished fever amp diy kit. I know tubes are voltage driven,if the secondary windings of the OPTs is wound with very less power rating ,would that be safe to drive the low impedance loads??! Need guidance! Thank you 😊

I'm restoring this receiver. The mica caps in the tuner look like a ceramic coin and are filled in the bottom with a paste. The paste has unfortunately cracked revealing the metal wafer underneath. My first thought was to just toss them out and replace but 616pF isn't gonna be an easy match. I'm aware RF isn't you guyses speciality but I would just like a second opinion. Is there even any point in trying to fill it back in with silicon or epoxy, or even leaving it exposed as is. I'm thankful for any thoughts. 😊

When you're working with high voltage, there is no such thing as a dumb question. Please use this thread to ask about practical or conceptual things that have you stumped.

Really awesome answers and recurring questions may earn a place in the Wiki.

If you'd like to nominate a comment to be included, just reply [Wiki] (with the brackets)! The mods will be automatically notified that something awesome just happened.

As always, we are built around education and collaboration. Be awesome to your fellow tube heads.

I recently picked up the reissued MIG-50 mkII. Only problem is... it's exceedingly loud. My first thought to make it workable for when I'm at home and not in Madison Square Garden was to mod it to put in an FX loop and run a volume pedal. I can't find much information about people modding these online, or a schematic. Lots of stuff about modding the old Sovtek versions. Anyone have any experience of this? Or alternate recommendations?

edited to add pictures, because everything is better with pictures

https://preview.redd.it/ftpdahvqu3zd1.jpg?width=4032&format=pjpg&auto=webp&s=2c3f956f0c0fd41525e411df9a7e9247e3344f52

https://preview.redd.it/az171pvqu3zd1.jpg?width=3024&format=pjpg&auto=webp&s=e3bd6785315234531619ab797f76984fcf62bdeb

Whats the best contact cleaner for heavy corrosion, rust, oxidation on electrical components, pcb boards, and plastics?

Hi,

I had a friend borrow my amp, and they blew it up. They plugged in a guitar going through a pedal (EHX canyon) and heard a "pop" and a small amount of smoke appeared.

I want to start fiddling with the unit, but I want to be careful. I'd like to try some things on the cheap before I take it to a tech, though I'm not against having it looked at (I'm just cheap). I'm hoping someone can point me in the right direction.

Is the first step to order a new set of tubes and replace the current ones? That sounds cheaper than going straight to a tech, especially if I can send it later to a tech with the tubes (will this cover parts, or will someone want to order their own set?).

The tubes themselves don't look dark (I'm thinking of how a lightbulb gets darkened when it goes).

Should/can I open the back to reveal the guts, transistors, etc? I don't have much proper electronics gear beyond a soldering iron and multimeter.

As for how to unit behaves, it turns on as usual, but never produces any noise (beyond a very slight hum) when I plug into it.

I'm happy to describe anything else needed or I can take pictures of whatever. Thanks in advance!

When you're working with high voltage, there is no such thing as a dumb question. Please use this thread to ask about practical or conceptual things that have you stumped.

Really awesome answers and recurring questions may earn a place in the Wiki.

If you'd like to nominate a comment to be included, just reply [Wiki] (with the brackets)! The mods will be automatically notified that something awesome just happened.

As always, we are built around education and collaboration. Be awesome to your fellow tube heads.

Does anyone have a reference schematic for a KT170. If someone has made an amp around it. Have been struggling to find some reference.

Wondering if anyone has built the RoeTest tube tester?

http://www.roehrentest.de

Wondering how much of a pain it is. I have been as looking at vintage testers on eBay. A lot of the testers that come "calibrated" I still question it how well they will work. For the ones I am looking at I could build the RoeTest for around the same price.

Hey guys, I am new to this subreddit and I am looking for some help with my little amp. I've had it for a good while, but broke down right when the pandemic hit, and just recently I have been able to find a stable job and have money to potentially throw at this thing in order to fix it.

The rundown of my problematic 6505mh:

• Bought it back in 2017ish/2018ish used
• Had a weird buzzing sound, similar to a ground loop sound even when the guitar wasn't plugged in. This sound wasn't noticeable when plugging into the headphones in the back
• Took it to a local shop and had it repaired, but they returned it to me with the TSI lights red
• I found that it doesn't have a normal 115v/230v switch but a 100v/115v one instead

The amp still produces sound, but like I said, it is very weak compared to a normal operating 6505mh. Less perceived oomf from my friend and I alike. I have ordered a new pair of EL84s for this amp, and the lights are still red, so at the very least the power tubes weren't the problem. I was hoping that maybe I could get some insight on this sub for so easy to do at home troubleshooting before I consider taking it to another shop, because I no longer trust my local one. I have no experience biasing amps, I have pulled the fuse and I get an audible reading from my multimeter that it is intact. Lastly, while perusing other forums, a user mentioned taking note of the resistance over the mains. At 100v I got a reading of 23ohms and it almost doubled to 44ohms at 115v; I have a Marshall JTM60 that currently works fine and the measured resistance across the mains reads 2.5ohms. Once again, I do not know if this is normal but it was mentioned and easy enough to perform. Any thoughts?

When you're working with high voltage, there is no such thing as a dumb question. Please use this thread to ask about practical or conceptual things that have you stumped.

Really awesome answers and recurring questions may earn a place in the Wiki.

If you'd like to nominate a comment to be included, just reply [Wiki] (with the brackets)! The mods will be automatically notified that something awesome just happened.

As always, we are built around education and collaboration. Be awesome to your fellow tube heads.

I’ve recently gotten into replicating Lemmy’s bass rig. Dont feel like spending $3k for a legit super bass and I’ve always wanted to build an amp.

https://www.mojotone.com/British-Style-100W-Lead-Bass-Head-Amp-Kit

Anyone built one of these? Anything I should know going into it? Is it solid as is or are there some minor tweaks and upgrades I should be looking into?

Looking forward to it thanks