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Messages - blackcorvo

Quote from: joecool85 on January 11, 2020, 04:51:08 PM
Quote from: tonyharker on January 11, 2020, 03:25:58 PM
As far as I can see these Nu-tubes are just a gimmick. You dont get a lot of gain from them so they are not going to have much effect to the signal.  Snake oil :)

I disagree. While I haven't played with one myself, I've listened to a bunch of clips of the Vox MV50 series, the AC in particular. It sounds fantastic! How much is the nutube and how much is the rest of the circuit if anyone's guess right now though.

This demo from 2017 shows the sound of the NuTube itself. It's indeed very tube-y:
Amplifier Discussion / Re: Vox Pathfinder 10 mods
April 22, 2019, 02:20:12 AM
j_flanders, thanks again for the photo of the board. I decided to do a simple diagram on it of how to do the mod. I'll leave the coupling cap and bass pot I changed out of it, as I don't think it changes much in regards to the overall response of the amp.
I decided to recommend removing R8 along with the Red LEDs, as I think it muffles the amp too much.
The speaker I used is 8 Ohms, rated at 2.5 Watts. The output transformer was made to order from a brazillian transformer manufacturer (, 3k:8R/4R, with bass response starting at 120Hz (due to the space I had available).
I have a switch on the speaker output to change from the 4R to the 8R tap, but looking back at it, I could probably fit 2x switching jacks in there and a larger O.T., no problem. Specially now that I got some 3" alnico speakers off eBay, with much smaller magnets.

I just need to find another fried Honeytone! :P
Software / Re: Simple budget oscilloscope for Android
January 22, 2019, 07:40:23 PM
Buy one of these little digital Oscilloscope kits:

DSO138 -
DSO150 -

They're plenty good for most applications, and cheap to replace if you ever fry them.
And while at it, get some "proper" probes as well:
Amplifier Discussion / Re: DanElectro Nifty Fifty pots
October 30, 2018, 03:49:39 PM
That looks like a 9mm potentiometer to me. Check the measurements in milimeters and see if they match.
Fun fact, if you ever need to use those in a perfboard or protoboard, you can mount them diagonally. The clearance for the holes in that orientation is perfect for them.
Just a small update to this project.

To deal with the noise issue I mentioned on my last post, I tried many things but none of them worked. I ended up using a different DC-DC converter board, which is smaller, and that allowed me to place it further from the preamp tube and, thus, avoid inducing noise onto it.

The board in question is this, from eBay seller VFDClock:
Still has plenty of power to feed this amp, no problems. I just needed to adjust the bias on the 5902, by increasing the cathode resistor from 330R to 1k. Works great!
Schematics and Layouts / Re: Adding Bluetooth to lm386amp
September 16, 2018, 12:17:27 AM
Here's an easy way to do it. Get one of these:

And just connect the headphone output from it into your LM386 amp. You can find them by looking up "bluetooth headphone adapter", and there's many different prices, sizes and shapes.

I've used one just like the one on the link, to have my Talk-A-Phone (tube-intercom-turned-guitar-amplifier) as a little "vintage boombox" to play some tunes when I'm relaxing at home, but I currently use it with a pair of Sony Ericsson Bass Reflex earbuds as my daily-driver bluetooth headset.
Amplifier Discussion / Re: Vox Pathfinder 10 mods
April 11, 2018, 08:16:09 AM
Quote from: ehsan_zt on March 05, 2018, 02:39:23 PM
2- Another interesting thing I found out was this video:
what this guy did is he simply removed C12 2A274K!
I tried this,and it's AMAZING ! when you remove C12, amp will sound clearer and there is an increase in volume. I really suggest trying this and removing it or replacing it with something lower (like 2A272K).
I'd love to know the science behind it,if some one can explain?!

C12 is part of a filter on the second op-amp. It goes in parallel with the feedback resistor R15, but isn't completely across the feedback loop because of R17.
I believe it's a low-pass filter (again, I'm not super well versed in filters), which would explain the change in volume. I'd guess it's there to remove some of the harshness coming from the preamp, and possibly to limit the volume some before it hits the power amp.

Personally, I'd rather play around with the filter instead of just removing that capacitor. You might be able to emulate a cab if you do some clever use of that op-amp. Perhaps copy the values from something like RunOffGroove's Thor output circuit? Or more appropriately, their Britannia circuit? Food for thought.
Get in contact with Retro Radio Farm at
They have a lot of interesting radios, and maybe they might either buy yours or exchange it for a more interesting one off their catalog (pretty sure they could easily add a guitar input if you talked to them about it).

I wouldn't gut this particular radio, because it's in very good shape, and it probably just needs a little cap job or something simple like that.

If you really want to build something yourself, I'd advise you look for radio shells/cabinets to turn into a guitar amp, or even buy a cheap "retro bluetooth speaker" that looks the part and gut it (which I'm actually in the process of doing).

But, at the end of the day, the radio is yours and yours is the choice of what it's destiny is. Good luck with it either way!
The heat sink was originally on the switching transistor for the High-Voltage board, but since the circuit pulls only about 5 watts for the B+ rail, the thing doesn't even get warm enough to the touch (the board can handle loads up to 45 watts, so 5 is almost a joke for it). I removed it from the transistor because the board fit in the enclosure better that way.

I had to put it back in the new position to work as a shield for the 6N21B tube, because the switching noise from the transformer was being induced onto that tube. The shielding worked perfectly well, being grounded to the common of the circuit.

A better solution would be adding a piece of metal attached to the chassis, sitting between the tube and the High-Voltage board's transformer, that wrapped around the tube a bit, for proper isolation.
It works as a proof of concept, at the very least. But now that I know, I can avoid this issue on future versions of the project, should those come to be. Wink wink  ;)
Recently, I finished a project I've been work on and off over the last year. It's a subminiature tube amp fitted inside of a Honeytone mini amp enclosure. The original circuit board was busted beyond repair, and I had gotten some subminiature tubes to play with, so I decided to put them to good use.

Here's the final result:

Check the video's description for the schematic, layout, pics, etc.

Or you can see those and more over here:
Have you checked that it is in fact the BC transistors? What are the voltages on them? Do that first if you haven't checked.
If you HAVE checked and you think they do need replacing, any General Purpose NPN with similar specs will probably work fine.
Amplifier Discussion / Re: Vox Pathfinder 10 mods
January 30, 2018, 07:32:05 AM
j_flanders, I have only a crude understanding on filters, but in my simple terms, what I see with C5 is a high-pass filter, not a coupling capacitor.
The difference lies in the resistor (potentiometer in this case) in parallel with the capacitor, as it "leaks" the frequencies that can't get throught C5. What I did by changing C6 was allow more of these lower frequencies throught to the next stage.

About the clipping, the amp came modded with a Si+Ge clipper, so poorly added in there that the copper foil was coming off the board. I originally put it back to the stock red LEDs, but after having connection issues, I added screw-in terminals to that point of the board for testing. They're still there, in case I wanna mess with that in the future.
I decided for the soft clipper because I don't like how the op-amps sound overdriven. There's a harsh change between clean and driven tone I don't like, and using white LEDs (which take like 3v to conduct) that harshness is reduced a lot. I haven't tried mixing a hard clipper in there yet, but I don't feel it's necessary at this moment.
Amplifier Discussion / Re: Vox Pathfinder 10 mods
January 30, 2018, 05:57:27 AM
Quote from: j_flanders on January 30, 2018, 05:41:43 AM
Here's the correct schematic by the way.

Thank you for the revised schematic! I didn't even notice the drive switch position thing until you pointed out. It's also wrong in my modified schematic... whoops!

I'm now thinking about possibly adding an FX loop to this amp, but I'm still debating how I should approach it.
Quote from: dazz on January 29, 2018, 09:43:13 AM
I have loads of hum and noise from the power supply though, a 12V 1.5A unit that came with an external hard drive

Time to check this out I guess: Topic: Grounding techniques

Perhaps if we see some pics of your build so far, we might see what's wrong. Also, measure the voltage of the power supply when you have the amp running, maybe the amp is loading the supply down.