Echoplex Build Thread

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Reo

Reo

Member
Joined
May 2, 2013
Messages
19
Location
Dallas
Hey - I'm actually almost done with this project.  :D I'm gutting an old Tube R2R I picked up for $20 on Craigslist and building the EP-2 Echoplex circuit inside the chassis. I just have a couple of points I'm still unclear about...

Can anybody explain please what's going on in the circled areas of the schematic?

It appears that, when engaged, the "Playback Footswitch jack" grounds the cathodes of V2b and the Bias Oscillator triode, which allows those tubes to function (correct me if I'm wrong).

What I'm confused about is the are surrounded by the blue line - the two 100k resistors and the lamp.

So my questions are:

Why are those resistors there?

EP-2+schematic+Annotated.jpg


This may be irrelevant since I'm using a different bias oscillator circuit, but I'm trying to understand what's going on in the original schematic before I modify it.

Also, what kind of quiescent current draw can I expect from a bias oscillator triode? 5ma or so?

Thanks!

Reo

 
Lamp is the REC light.

Lamp is a Neon. Needs a series resistor, R35.

R36 has nothing to do with the lamp. It pulls-up the common return for rec amp and bias osc so that they feel "no!" power when not in REC.

> what kind of quiescent current draw can I expect from a bias oscillator triode?

It's on the plan (sneaky basterds). There's 200V(?) one place, 170V another place, and 3.9K between. This path also feeds V2B, but the large plate resistor means low current, and again there's numbers so you can figure V2B, estimate NE1 (assume 90V, the rest in R35), and the difference is V3.
 
Thanks, PRR

I  changed the title of the thread to "Echoplex Build Thread," and I thought I'd post some updates from the build, just for posterity or incase anyone gets interested in doing a similar project....

Here's a video of us turning on the transport for the first time. It still needs a lot of adjustment but, since taking the video, I've got it mostly leveled out and running more smoothly. I opted for a free-ranging type loop like on the Roland Space Echo.

http://youtu.be/7eu6Uw2V1WE
 

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