Gibson EH-185 clone build

[edsonmarquezani]

I recently built a successful Gibson EH-185 clone, and since information about this project and build experiences are quite scarce, I thought it would be nice to leave it documented for possible future builders.

My build was heavily based on Phil Davis's schematics (originally posted on el34world.com forum on this thread) but with a custom layout made by myself. They are below.

- Schematics

- Layout

* pay attention to the jumpers below the board, they're very important

Only things different from the original is the following:
- backup diodes added on rectifier as backups
- screen resistor on power tubes for reliability
- grid stoppers on power tubes also for reliability
- 750R resistor as replacements for the field-coil speaker (or a choke)

- Build

I used handmade custom transformers made specially for this project, following what is supposed to be the original specs, with secondary high voltage as a 405V-0-405V, 200ma (the current was estimated and may be in the edge of what this beast demands, so something a little bittler may be ideal). I used US-made NOS tubes for pre-amp (acquired from Tubedepot) and modern JJ Tesla 6L6GC and 5U4.

Chassis was designed by a friend according to the layout and worked very well.

* Small box on the right is a voltage auto-selector for main power because I forgot to make a hole in the chassis for a proper switch.

I also had built for me a cool cabinet trying to mimic the original (with tweed tolex).

Highlights/impressions:

- Instrument and mic channels are completely different things. The instrument is clean and very beautiful, it surprised me positively, but it doesn't get very loud, nothing near to the expected 20W. The mic channel, on the other hand, is nasty, gainy, loud as hell and breaks up very very early (on 1).
- The tone control works well for my taste, being quite versatile, more than one would expect for such a simple control.
- I didn't find it so noisy, considering how ancient this circuit is (of course the mic channel IS noisy, considering how gainy it is).
- It does get hot (resistors, transformers, tubes, everything), it's quite a heat generator, and after putting it on the cabinet, obviously, it got worse, so take that in consideration when building one.
- Overall, this turned out to be much more useful and interesting than I was expecting, but of course it's an old design, very inefficient in terms of resources (power, number of tubes, etc). But, for jazzists seeking for vintage sound, it's totally build-able.

- Sound demos:




- Measurements:

B+1 - 450V
B+2 - 330V
B+3 - 287V
B+4 - 164V
V1 plate - 125V
V2 plate - 86V
V3 plate - 86V
V4 (PI) plates - 142V
6L6 plates - 332V
6L6 screens - 340V
6L6 bias (200 ohm shared resistor) - 25V

I would like to thank everybody in the amp building community, including folks on this forum who helped me with a newbie issue. I hope this information here can be useful for other people in the future. Feel free to get in contact with me on edsonmarquezani at gmail dot com, it you fell like.



* References I used for this build:
- https://el34world.com/Forum/index.php?topic=20042
- https://el34world.com/Forum/index.php?topic=24429
- https://guitar.com/features/opinion-analysis/amp-faq-gibson-eh185-clone

 

[Jerry garrcia]

Beautiful!!!!

 

[NTC]

Interesting that it has individual 6SQ7's instead of a dual triode of some sort, but they were the only available triode with an amplification factor of 100 then. With a 450V B+, that thing should be able to put out 40 watts. Also, that would have been aquite high voltage for the 6L6'S of the 40's. What is the OT primary impedance?

 

[edsonmarquezani]

Interesting that it has individual 6SQ7's instead of a dual triode of some sort, but they were the only available triode with an amplification factor of 100 then. With a 450V B+, that thing should be able to put out 40 watts. Also, that would have been aquite high voltage for the 6L6'S of the 40's. What is the OT primary impedance?

I don't have the full specs of the OT, since it was made by request specially for this project. But I know it was designed with a target 20W output, which was the advertised power of the original one. Of course, with such a huge PT and two 6L6, we could get waaay more than only 20W, but the idea was to reproduce the thing as much as possible.