Hagerman - Boost - EF86 Tube Pedal [traced]

[modman]

I was looking for EF86 information and came across this thing:the schematic is freely available from the website, albeit inside the user's manual, the schematic links are dead
https://www.hagamps.com/products/boost

hagman boost-bottom_1024x1024.jpeg (35.39 KiB) Viewed 4100 times

boost-top_1024x1024@2x.jpeg (19.06 KiB) Viewed 4100 times

EDIT: only now did I see this earlier thread: viewtopic.php?f=7&t=31471

[Dr Tony Balls]

Interesting, but they dont show the power supply for B+ or the filament voltages, which i'd think the most interesting part.

[modman]

Interesting, but they dont show the power supply for B+ or the filament voltages, which i'd think the most interesting part.

Couldn't you calculate your way back from the 115V plate voltage? Top right is the filament wiring, I think, running off DC (why not?)
Isn't the distortion coming from the tube overdriving the transistor? If so, isn't that a missed chance, and wouldn't the inverse better show the overdrive characteristics of the EF86?

Inspiration may be found here: viewtopic.php?p=180066#p180066

[Dr Tony Balls]

Interesting, but they dont show the power supply for B+ or the filament voltages, which i'd think the most interesting part.

Couldn't you calculate your way back from the 115V plate voltage? Top right is the filament wiring, I think, running off DC (why not?)
Isn't the distortion coming from the tube overdriving the transistor? If so, isn't that a missed chance, and wouldn't the inverse better show the overdrive characteristics of the EF86?

Inspiration may be found here: viewtopic.php?p=180066#p180066

I dont think it's very easy to calculate back from the B+ to figure out the power supply, though I could be wrong. The manual says to use their included "high-current +9V wall wart" power supply, and that says 9VDC is powering the thing. The disconnect is how to get ~240VDC B+ from a 9VDC supply. There's a historic example from I think a Geofex article about getting 33VDC from a 9VDC supply using a charge pump (http://www.generalguitargadgets.com/pdf ... p17_sc.pdf) but that's nowhere near ~240VDC.

The top right bit could be the filament power, maybe. That H1 symbol looks like a fuse to me, but who knows. I'm guessing that R8 is used to drop the voltage to ~6V for filaments but why not just use a linear voltage regulator?

And YES you're very correct about the placement of the transistor and tube stages. I've built the inverse before with a Rangemaster type circuit pushing a pentode.

Also the thread you linked (Fryette EF86 Overdrive) is fully different. That uses a 12VAC power supply to feed a transformer for the ~300VDC B+ voltage. The filament voltage is rectified direct from the 12VAC supply and regulated down with a LM317 to 6.3VDC.

So yeah....the curious point still remains to me. How are they getting 240VDC from a 9VDC supply?

[ppluis0]

So yeah....the curious point still remains to me. How are they getting 240VDC from a 9VDC supply?

Hi Tony,

The usual way to obtain relatively high voltage at low current is by means a step up converter.

Several tube implementations employs a gadget named "nixie power supply" as per the following schematic:



Take a look at the gutshot posted by Modman that has an inductor, transistor (perhaps fet?) and 8 pin ic placed near the footswitch area.

Cheers,
Jose

[ppluis0]

Isn't the distortion coming from the tube overdriving the transistor?

Hi Modman,

The distortion is produced by the tube itself as the transistor is used as emitter follower having gain close to unity, but enough drive capability to be loaded by the volume potentiometer.

Personally I think that any low power TV pentode can be employed to build our own distortion box. There are several thousands of TV tubes manufactured years ago waiting the opportunity to bring us lots of distorted sounds...

Cheers,
Jose

[Dr Tony Balls]

So yeah....the curious point still remains to me. How are they getting 240VDC from a 9VDC supply?

Hi Tony,

The usual way to obtain relatively high voltage at low current is by means a step up converter.

Several tube implementations employs a gadget named "nixie power supply" as per the following schematic:



Take a look at the gutshot posted by Modman that has an inductor, transistor (perhaps fet?) and 8 pin ic placed near the footswitch area.

Cheers,
Jose

Good to know, thanks!!

[Manfred]

There is a PSU-kit available:
https://www.tube-town.net/ttstore/tt-vp ... erter.html