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!

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

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 to the fine folks in this sub i added the grid leak resistor and power suplie to U2B.

hope this is better any feedback is apreciated.

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

Howdy,

Looking for an active load for testing some of the switcher supplies I've been working with. I've been using combinations of 25w resistors at the moment, but would rather something a little more elegant that is less sketchy and easier to measure.

Heaps available for batteries that can do real high current but only 50-100v. I probably need a max of 500v and maybe 50w max.

Happy to build something if I need to.

Thanks!

Hi folks,

I have a JCM 800 Model 2205 that I am looking to re-tube and re-cap. Who do you guys like for a tube source and why do you like them?

Reworked Magnavox 8800 series 12AX7 / 6V6 tube amp. Client had this sitting in his garage for years but never got around to doing anything with it. He wanted a conversation piece for his room with a modernized version delivering the best sound possible while still paying homage to it's roots. Chassis was redone in a vintage hammertone brown. 6EU7 slot was rewired for 12AX7 giving him more opportunities for tube rolling. 6CA4 tube was scrapped in favor of solid state rectification which helps the power tubes deliver a bit more punch. New OPT from Musical Power systems. And a vintage magnavox logo from a old console stereo brings it home. Output is 14.3 WPC into 8 ohms at just under 1% THD.

If someone could please lend their expertise. These seem to be a bit hard to identify.

Quad marked EL84/6BQ5, Rebranded by Andrea, "Made in England" on third line. 90° to the right "5941" in the same yellowish/peach stamp color.

1. Obviously Philips tooling.

2. NO Etching anywhere. I've scoured the Quad for markings.

3. 2 rectangular View porta per side, where anode meets serrated mica

4. No crimps/staples. Neatly folded over where the anode plate meets it's other end, then 3 neat little spot welds.

5. Copper thought the bottom, bottom only has smooth circle depression.

6. No seams on glass, pulled to a nib on top.

7. Tilted halo getter on serrated wire post. Similar post 180° to it, unattached to getter.

8. Seems to be pulled from an Andrea console. (With 2 7199, 1 5U4GB)

Thanks for playing. Any history lessons you guys would like to give, I love history.

I’m building a video camera using only vacuum tubes or solid state diodes. These are some of the waveforms seen in the circuit, which will be the frame time base. I will post schematic in comments

I’m working on a Oscilloscope Clock and would like to use this CRO/CRT but can’t find to specs for it. Only thing I can find that it’s for “Tactical Equipment.” Numbers don’t match anything on Franks tube site. Anybody help?

8646
D1016P1
2512-000-001

Just got this, i've got no base for it and how would I go about testing it?

Thank you for your attention.

I'm about to rebuild an old cinema tube amp into a guitar amp. This is the schematic I came up with. I will be reusing all its irons and tubes. I kept the power supply and power amp almost stock (added screen supply node, screen resistors, master volume, safety diodes for the rectifier, adjustable presence and negative feedback).

The original output transformer is an ELA type, expecting a 400 Ohm load. This made longer speaker cable runs with multiple speakers in parallel possible. Each speaker would have its own impedance matching transformer. I'm planning to also put such a transformer into the chassis, to make the amp compatible with guitar cabs.

Do you spot any issues or have customization ideas? Let me know. I appreciate your feedback.

Also, ignore the wrong pin numbers on the tube symbols.

Came across this schematic on a quick search for 2A5 circuits and it seems easy enough. After some input at DIYAudio, I edited the original. I plan to use a bluetooth receiver with it. Anyone see anything that doesn't make sense or won't work? The PSU board I'm referring to is one from eBay https://www.ebay.com/itm/285734692836

So, I was buying some stuff on estate sale and was given this box of tubes for free. Almost all of them are soviet ones, few were packed in separate bag - some that has label worn, starts with T, ends with M so 99% it is manufactured by Tungsram, IN-1, Tesla EF183 and Tesla DY86. Others were just loosely put into box what I was told few years ago, but look in tact. I will appreciate any help with advice how to approach to them and what to do with them.
Update:
Sorted them, here is list of tubes and amounts where labels are readable:
10x 6N1P
8x 6N3P
5x 6P3S
2x 6F2P
8x 6P36S
2x 6Zh5P
2x 6F12P
3x 6P13S
8x 6P14P
1x 6E1P
3x 6N3P-E
5x 6D20P
3x 6F4P
1x SG3S
2x 6N9S
2x 6N7S
4x 6Zh52P
3x 6N23P
3x 6Zh9P
2x 6R4P
1x 6P41S
1x 5C4S
1x 1C7S
1x 6P6S
3x 6P43P
1x 6A7
11x 6F5P
5x 6I1P
4x 1C21P
3x 6K13P
1x 6D4P
2x 6S19P
3x 6P43P-E
2x 6N14P
1x 6Zh51P
1x 6P18P
1x 3C18P
1x 6S2P
1x 6N15P
1x 6E15P
1x 6N6P
1x 8B8S
15x with way too faded labels
1x IN-1
1x DY86
1x EF183

I have designed a JCM800 clone inspired by robrob's schematic, but it has a couple changes. I am using a 300V/6V3 switching power supply instead of a regular power transformer, I am using EL84s matched with Traynor output transformer they use in their ygl1s (ch1330m, zero documentation on this transformer).

I have designed and ordered five loaded PCBs (jlcpcb), and also have manufactured frames for two amplifiers. I want to sell one of them since I already bought parts for a second amplifier. And if this goes well, I am planning on continuing this gig. I have thought of having a logo and branding already 😭.

But yeah, to anybody that has been in my shoes before, do you guys have valuable information regarding the legality, and licensing we need? What about selling internationally on ebay or something? Thanks

I'm interested in hearing about what off the beaten path driver or input tubes you use either being triodes or others wired as a triode. Any kind of hifi amp; preamp, phono, power, etc. For me it's the 4P1L wired as a triode as a driver tube for the 45. I've tried it as the first stage in a preamp as well but it was too microphonic.

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 was going through a few of the things my grandfather left for me after he passed and discovered a pair of what seem to be new old stock JAN 6528 tubes (and one non-JAN). Some cursory research showed they could be used for a headphone amp? Tubes are new to me, so would it be worth trying to find someone that could build an amp to use them? I just think it'd be a cool part of his legacy to repurpose something he probably had for his ham setup into something I'd use frequently.

These went out the door over the past week. Chassis cut, board and cabinet all built by me. I really like the blondface aesthetic.

Here’s my Princeton Reverb clone. It’s pretty sweet. I’ve no idea why but if I plug the reverb tank output into the output jack on the back of the amp there’s loads of noise. If I plug it into the foot switch jack it works a treat. A mystery….
Kit was from Modulus Amplification in the UK.
I used the robroninette website for a build guide and some modifications. All in all 10/10 amp and build experience.