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Author Topic: Honeytone Tube conversion using subminiature tubes  (Read 2103 times)

blackcorvo

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Honeytone Tube conversion using subminiature tubes
« on: February 22, 2018, 11:00:07 PM »

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:

https://www.youtube.com/watch?v=B79d7bydqr0

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

Or you can see those and more over here:

https://drive.google.com/open?id=1v7-ppCu_mGSNfZdqfjUrZtzhPhdUXQ48
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phatt

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Re: Honeytone Tube conversion using subminiature tubes
« Reply #1 on: February 23, 2018, 08:20:25 AM »

Great stuff, sounds good :dbtu:
A lot of work for such a small amp.
Can I ask what the heat sink is doing?
Phil.
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blackcorvo

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Re: Honeytone Tube conversion using subminiature tubes
« Reply #2 on: February 24, 2018, 02:33:35 AM »

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  ;)
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blackcorvo

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Re: Honeytone Tube conversion using subminiature tubes
« Reply #3 on: October 17, 2018, 02:49:35 PM »

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: https://www.ebay.com/itm/141728332617
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!
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