anyone have a schematic for BrownNote Foxy 18?

[rstoeck]

Hi all. I am trying an amp build using this wiring diagram: https://el34world.com/Forum/index.php?a ... 1032;image

I am wondering if anyone has come across a schematic for this amp. I can't find one (even using the Way Back Machine to look up the old Brown Note site).

The problem is there is no sound (no sound at all--not a hiss, hum, crackle--nothing) and I'm wondering if a schematic would help. I've tested everything I know how to test (power transformer voltages, output transformer resistance, tube connectivity). The tubes have that nice orange glow, with no evidence of red-plating, and the heater voltages are fine. I'm not sure I understand the math well enough to figure out the other voltages. There's no smell, smoke, or explosions. I tested with (and without) a light bulb limiter, and with a chopstick. I checked the speaker and cable on another amp, just to make sure. I've quadruple-checked my wiring and it all follows the wiring diagram. My solder joints seem to be OK, certainly better than on my previous build which is still working fine. So either a component is bad and I'm not smart enough to find it, or something is incomplete or grounding out. A schematic might at least help me confirm whether there is something off in the wiring diagram or it's just that I have more to learn. I'm also grateful for any further reading to help me learn how to troubleshoot.

Thanks in advance. This is such a helpful forum.

[Bieworm]

Maybe start with posting all voltages to see if there’s anything weird

[JMPGuitars]

As Bieworm suggested, post your voltages. I'd also post some high res photos of your build.

That layout doc looks like a modified EF86 Lite (original, not 2P) with a master volume added. Compare your build to that. You can try bypassing the rotary switch based on the EF86 Lite schematic to see if that helps.

[rstoeck]

Thanks all. Here is my first attempt to check voltages, after doing some reading. What I read said to test voltages with the power tubes out, so these readings are without the power tubes, which probably accounts for those zeros (except for the ground pins on the EF86 of course). Apologies in advance if I should have put the power tubes in--I'll redo. I took photos, but they're pretty big, so prepping them to post will take some work. If this doesn't show anything obvious I'll work on those next.

[JMPGuitars]

Put all the tubes in, and use this to record your voltages: files/JMPGuitars_18_Watt_EF86_Voltage_Test_Chart.pdf

[rstoeck]

Thanks, here they are.

[JMPGuitars]

Your voltages are still way too high. Did you put the power tubes back in?

[rstoeck]

yes, I noticed that. And that's with power tubes in. I saw your post on the voltage dropping zeners but this looks like more than that could fix. Could that account for no sound or would that cause bad sound, so I have more than one problem to solve?

[rstoeck]

Sorry, should have also mentioned that some of the cap and resistor values connecting to the power tubes are quite different between the Foxy 18 and the EF86 18 watt lite, but I don't know how to judge such differences in terms of voltage.

[JMPGuitars]

Sorry, should have also mentioned that some of the cap and resistor values connecting to the power tubes are quite different between the Foxy 18 and the EF86 18 watt lite, but I don't know how to judge such differences in terms of voltage.

Well, if the tubes are loaded, those voltages are too high for EL84 tubes. You can use the calculator here and see how bad: https://robrobinette.com/Tube_Bias_Calculator.htm

We generally target 85% dissipation.

Your B+ voltage is also way too high, it's possible your rectifier tube is bad. Either way, you want that voltage lower.

[rstoeck]

Thanks. It seems there are three options. Replace the tube, mod the power supply to the rectifier,

TMBEFceriatoneez81.png

, or use a solid state rectifier like from your 18 watt Superlite that built so easily for me. I think I'm leaning toward the solid state rectifier, since the tiny difference I can hear online comparing solid state to tube rectification I actually like the solid state better. I think I will also change the caps and resistors to match the EF86 Lite since I can double-check against the schematic. If you have any cautions I will appreciate hearing them, otherwise I will report back when I've hopefully got it working. Thanks a lot again.

[JMPGuitars]

Thanks. It seems there are three options. Replace the tube, mod the power supply to the rectifier, TMBEFceriatoneez81.png, or use a solid state rectifier like from your 18 watt Superlite that built so easily for me. I think I'm leaning toward the solid state rectifier, since the tiny difference I can hear online comparing solid state to tube rectification I actually like the solid state better. I think I will also change the caps and resistors to match the EF86 Lite since I can double-check against the schematic. If you have any cautions I will appreciate hearing them, otherwise I will report back when I've hopefully got it working. Thanks a lot again.

That sounds like a good plan. I would change to solid state, and make sure the power amp section matches the EF86 Lite. Then you can leave the preamp section to the brown note specs if you want. Then you'd have a fun little amp if the preamp setup works.

[rstoeck]

Hi all,

Just reporting back. After trying countless fixes and options I finally found that I in fact did miss a connection. Because of all the fixes I've ended up with an amp that's part Foxy 18 (I kept the PPIMV, rotary switch with a bit more breadth in the cap values, and high-cut with a mod I found from research), part JMP ef86 Lite, and part original ef86 (the latter two from designs on this site). I ended up putting the tube rectifier back in and the voltages are all what they should be. To my ears, the result has amazing chime and tube distortion through a 12" Warehouse Retro 30. And I met my main goal of learning a lot. I'm getting close to designing my own variation. Thanks!

[crgfrench]

If I get a chance, I'll draw up a schematic for the Foxy 18. It looks like it will be very similar to the Vox AC15 with channel 2 deleted. The schem for that is in the Vox AC15HTVH service manual from Vox R&D UK 5/2/07.