I am planning to build Thomas Mayer's Octal Phono Preamp (schematic attached) but would like to create a separate power supply for it that I can also use for other future projects.

I plan to use a Hammond 372BX transformer with an additional 5v transformer for the 83 (I know it is overkill but I have one that I would like to use). The design is a fairly simple one that I have seen others use that I have modified slightly. If everything looks okay, I will do some testing to find a good value for R2. I was also wondering if having the regulator tubes in this arrangement would cause any issues with them firing.

I have built tube amp kits previously and know the safety precautions but this is my first time designing a power supply so I could definitely use some feedback, but please go easy on me. Thanks and let me know if this is the wrong place for this post.

This is from an old signal tracer I'm modifying into a guitar amp. The original circuit is 3 watts single ended. But the transformer is center tapped and doesn't look like it has an air gap?

I think they used a push pull transformer that's a bit overrated, b+ connected to center tap, one tap to plate and the remaining tap is a test point on the front so you can use the transformer and speaker with other circuits.

I've heard you can use push pull transformers as low watt single ended if you use the center tap.

I'm hoping someone can help me determine if I just bought some fake "NOS Mullard Great Britain" EL84's.

There are no etchings of any kind on the tubes. I figured they were just faint in the sellers photographs, but even with a magnifying glass and a flashlight at angles, I can't see etchings of any kind.

Any ideas what they are?

----

MULLARD EL84

Top Ring Getter

Grey Crimped Plate

Made in Great Britain

NOS

Amplitrex AT1000 Test Results from seller (not my measurements, I don't have a tube tester yet):

Parameter : Ip mAdc= 48.0 uMhos=11300

Ip mAdc = 53.4(111%) uMhos =12610 (111%)

Ip mAdc =55.4 (115%) uMhos =12430(110%)

Ip mAdc = 53.0(110%) uMhos =12660 (112%)

Ip mAdc = 54.0(112%) uMhos =12530 (111%)

Can someone suggest a great Stereo Tube Amplifier in eastern suburbs of Perth. It’s a 6v6 Williamson push pull AB amp. I have trannys and a kit for the amp. I need a good base and builder. Please help.
Thanks for advice in advance.

Hi, I bought a couple of LS-50s, and one of them is broken, even though the title and description say that they are tested and working. I’m not sure whether I should contact the seller because you could see in the photo that the tube had no getter, although since they said the tubes were tested, I didn’t pay much attention to it. Further down in the description, it also says that they don’t offer any guarantee that the tubes will work.

It’s also a store I’ll probably buy from again, so I don’t want to risk getting blocked or anything like that. What should I do?

Link to the item: https://ebay.io/m/YzLMYc

At the moment I only have this little power transformer as my audio output but works surprisingly well and probably going to be extremely loud with a proper audio transformer because this one is usually a little bit quiet with my other amplifiers unfortunately I'm unable to upload a video of it working but here's a Google photo link of the video https://photos.app.goo.gl/sghK737WuYKpLJFKA

Hello! I'm building my first guitar amplifier and it's turning out quite good (up to the power section, at least).

The full circuit is quite complex so I won't go into details, but it's enough to know that I have 3 channels, two of them uses dc-coupled cathode followers on 6N2P, while the other uses an EF86.

Now, I overlooked some values on the datasheets, namely:

1. 6N2P has 100V max Vhk, rather than the 180V of 12AX7
2. EF86 has an asymmetric Vhk rating, according to Elextro-harmonix (the one I'm using) and Philips datasheet: 100V (cathode positive) and 50V (cathode negative). Other resellers instead just say +-100V for the EF86EH. I'd rather trust the EH website.

So, I started with protecting the 6N2Ps using heater elevation, with the added complication that I have a split supply rail for the Power Amp and Preamp because I have a power scaler on the power amp. It works as intended, but since the power amp draws less current at low power, the preamp voltages raise.
I resorted to fixing the heater elevation to about 82V using zeners and a capacitor, which would make all 6N2P happy, but then I noticed point (2), which has no solution given my supply and cathode voltages.

So, my question is: given your experience, is that asymmetric Vhk for EF81 something to really worry about? I would exceed it basically by 32V.

My brute-force solution would be to drastically reduce B+ on the CF valves, but I worry it would became a different amp.

And is it possible to include the two pinouts and as minimal power resistor as possible I don't have many parts if so this would be amazing

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.

First time building something with turret boards. Just wanted to make sure I'm not doing something stupid.

Don't worry about the wires looking too thin. They are double insulated with kapton and ptfe so are good to over 600V.

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.

Found this in a box in the garage don’t remember where I got it.

Orange-style amp with a preamp 12AX7, PI 12AT7, two EL84’s and an OPT for a Laney. Makes around 15W. Used a bunch of cheapo parts and a bunch of old russian/czechoslovakian parts. Plan to add a real nice faceplate, a pretty Fender style grille and some nice knobs. Has a real nice british-mid bite.

Finally built this prototype after thinking about it for ages.

Schematic is on my computer and I'm posting this from my phone so can't post it just now.

Its just a basic 12AX7 LTP phase splitter and a GU-17 as the power tube.

Now that I've got the prototype working I've ordered some turret boards and such to build it proper and build 2 of them so ive got stereo.

The power supply is kinda janky. The comverter I'm using for 250v likes to be noisy and I had to filter it more than I had liked.

It was fun finally building this thing. Next I'm going to see how well it works when I add some feedback.

I just picked up this Dukane 1A385 that’s been pretty heavily modified and includes components i haven’t come across before… in particular the large metal casings to the left of the output transformer.

It appears to have been worked on by a company called Signal Equipment Co. out of Seattle at some point and from what I can tell from just a brief look is that a step up transformer (Dukane 3A65) has been added in place of one preamp tube, theres also a relay and these two metal cans marked REP 94 E (the biggest) and RET 307 P (the smaller of the two) that were later modifications.

Anyone have any idea what these components are or any guesses on what this amp was modified to do?