Echoplex Restoration Story

[rgorke]

Great Thread, I will have to wait til tomorrow to really delve into this. Great to show all the progress.

[spaceace76]

the black box is a transformer of some type. i've never seen one in a case like that before. very cool

[Xplorer]

Thanks guys. well both my ep3 have this transformer into this black box, i never saw any others without it ( ? )
back to work a bit this afternoon, going to work on the parts i have and parts i should buy.

the toughest parts of this restoration, to me, will be to fully check ( it's not only about measuring the impedance , right ? ) he heads, select the right transistors ( this ep3 II came without tis58, but with a metal can transistor instead ) , see where s, d and g are on this fet .. find the right hfe for the other transistors, things like that ... and insure myself to make the effort to check every part

[vanhalen5150]

[rgorke]

Originaly, there was some kind of guide for the tape, ( picture 7 ) i removed it and replaced it with whatever i had, because it wasn't practical and it didn't help the tape really, quite the opposite.
you can see how different the mechanics are compared to my first ep3. picture 8 is my first ep3, ( ep3 I ) picture 9 with the black top is my second ep3 ( ep3 II ). Now, there's a bridge coming from ebay, someone who was ok to sell me one of the pieces he put in auction. i could then instal the heads on it, remove the extra boards, making it standard.
i don't know who tried to mod this ep3, i don't think it was original because it didn't work : the tape simply didn't have enough contact with the heads. but the extra boards were original so ... i just don't know, anyway it was unique, never seen any other like that. i still have the pieces anyway.

I have an EP3 just like this one (unmolested). It has the black chassis (serial number 14,000ish) and that odd guide thing. Every other EP3 I have seen that is not black does not have that guide. Seems like it may be part of an early design that Battle decided was unnecessary. That little piece sticking up should be bent so that is lines up with the top of the screw thing and leaves a small space to put the tape through. If that makes sense. I will take a couple pics tonight and post them.

[rgorke]

The Power board

I recently picked up 4 - GE 500uf, 50 volt caps in anticipation of changing out the power electrolytics. I am think I might need to reform them but wondering if it makes a big difference???

[Xplorer]

yes, i prefered to remove this guide, but anyway the later design is better, for the mechanic.
about the 500uf caps ... i'll simply take some great modern ones, the sprague atom are very nice. i don't think it would be better with these old yellow caps, reformed.

Here it is , a big start for the part list. i'd need to figure out more infos about the potentiometers, if they're log, lin, reverse, with a switch included ...
Feel free to comment these values. on my first ep3, two orange drops had a different value compared to the schematic, and i had some extra parts too ( still have ) .

a tough point for me will be to manage correctly the "half shielded" wires. i remember that for some mysterious reasons they weren't "easy", reacting wierd if a tiny change was made. i'll come back on it later.

Edit, i'd need to make my infos clear about the right pots, diodes, potential replacement parts ( variable caacitor .. ceramic discs .. )

The part list
(took me a while to make it and verify

[rgorke]

OK, Now, the electronic !!

Here it is, what i did for my ep3 I, to help me. ( when i'll work on it i'll make it closer to the stock values and parts of the original schematic, because there were some "improvments and differences" on mine )

I hope that this thread will help peoples. i think it'll do, because it'll be complete, with no much compromises ...
Clips in the end.
Some help is welcome off course

The preamp board :

What affect does CV4 have? I presume one adjusts this by turning the screw. What does it do? Is this board "on" all the time or only when Echo is engaged? I also presume that no signal is going through the Q1Q2 board unless the SOS is engaged.

Thanks

[Xplorer]

here it is, what i had in my archives. But it doesn't help me get clearer about it anyway.
i'm not sure if it's always on, but i'd say no : it affects only the echo, to adjust the circuit bias to the kind of tape.
Q1 and Q2, i don't remember.

[Xplorer]

i've found some interesting stuffs in the manual. i couldn't understand these stuffs back then, especialy about the heads alignement etc ... with an oscilloscope. i think i'll get into it later.

i have most parts but didn't order the rest yet.

i also need to find the exact pots values required, an diodes, and transistors hfe. any knowledge about it ?
i'll also look for a replacement of the variable capacitor. 90 - 400pf.
heads tests also, how to.

[Tazin]

Here's some info based on my EP-3 Echoplex.
Bias Trap stuff:
Both varnished RF Chokes: (mfg) J.W. Miller, PN# 70F182AI (PR1 and PR2 on "Xplorer's" layout)
Trimmer Capacitor: (mfg) Sprague, PN# GMC30900 (CV4 on "Xplorer's" layout)

Potentiometer stuff:
Echo Sustain: (mfg) CTS, 500k - Linear with switch
Record Level: (mfg) CTS, 500k - Aud
Echo Volume: (mfg) CTS, 500k - Aud

Bridge Rectifiers:
Both bridge rectifiers: (mfg) International Rectifier, Type: BS2 2B, PN# 11597E, Rating: 1A 200PIV (D2 and D3 on "Xplorer's" layout)

Hope this helps a little.

[Xplorer]

oh, many thanks i appreciate. sure it helps.
what is "mfg" please ?

[Tazin]

(mfg) is short for manufacturer. Also, when I build my EP-3 clone years ago I used Recticon, pn# RS102 bridge rectifiers which are rated at 1Amp 100PIV. The rectified voltages between my original EP-3 and the clone are pretty much the same.

[Xplorer]

oh, you really built an ep3 clone ? Fantastic ! did you show it on internet ? Really ? on a personal mechanic base ?
what did you use for "D1" ? and Q1-Q4 ( some tis98 , or maybe mps8098 ? wich hfe ? ) , and Q6 -Q7 ? ( i don't think i'll change Q6 and Q7 )

[Tazin]

Sorry, I never put any pictures of the clone EP-3 I built on the internet. I made the whole thing from scratch; fabricated/machined all the metal parts, made the solenoid from scratch, circuit boards, plastic parts, wooden case, etc,. As for the semiconductors I used the same manufacturer and part numbers that I have in my original EP-3. For "D1" I used a 1N4748A zener diode. I used RCA 2N3053 for "Q6 - Q7". All the other transitors I used were the Texas Instruments TIS58 and the TIS98.