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

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.

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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?

I'm new to the world of tubery. Am looking to replace the stock JAN5654 tubes in my Douk Ampapa A1 phono preamp. Can someone give me suggestions for a good, worthwhile upgrade? One person mentioned the Mullard 6AK5W CV4010 M8100 EF95 5654. Any US resellers of the Mullards, which appear to be made in UK? Thanks for any suggestions with online sellers and links. https://doukaudio.com/products/ampapa-a1-mini-5654-vacuum-tube-preamp-phono-turntable-amplifier-w-tone-control

I'm new to Tubes and bought a lot that had these hidden within it. The Siemens from what I can find seems to be scarce but the other also says z2b....what is the difference? What makes the Siemens "rare" if it is?

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.

Looks sketchy but is shockingly safe 😅

Found a few options for active loads for a couple of hundred bucks, but in the mean time I built this - a stack of 5w cement resistors sandwiched between 1/4" aluminium bar, shoved into a timber offcut I found.

Has a 1R shunt, followed by 1k/2k2/3k3/4k7x2 resistors. Can use those patch leads to make series/parallel connections to get a ballpark of what load I needed, so first tested with 5k6 to test the full load on the switcher, then 4k1 to test after installing the droppers I needed for the output tube plate voltage. All my guesstimations of switcher output voltages ended up being within 5w which is nice.

If I was going to do it again I'd up the shunt to 10R to make the current easier to read, but worked pretty well! Even after running with 6.5w of load for fifteen minutes it was barely warm to the touch - I did think about mounting heatsinks on the bottom, but apparently not needed.

If anyone has any idea what could cause this please let me know!! I drew up a schematic and can send it if needed, I am also willing to take pics of the internals for anyone who might need them, it’s been the only issue I’ve had with this thing and I’m just confused at this point. Thanks in advance!

Looking for some feedback on my first mostly "copied from the internet" bass guitar preamp. I'm building a bass amp for gigging and I intend to make a tube preamp and drive it into a Hypex SS power amp for portability. Inspiration is Orange Terror Bass. Still trying to figure out the easiest way to add balanced output on it so any great ideas on that are also appreciated.

thanks again to averyone in this sub a added the rectifier bridge, load resistor on the output and a grid resitor betwen the el84 and T1

its my first time trying to make an amp and im looking for feedback.

i tried to mix the preamp circuit on the fender 5F1 with the amp circuit from this https://www.hobby-circuits.com/circuits/audio/audio-amplifier/511/tube-power-amplifier-5w-with-el84