Gibson EH-185

[ratgon]

I've been following this thread with great interest for awhile now. I've been wanting to try and build a 185 since playing an original one a friend got lucky enough to buy pretty cheap on Craigslist. The thing is amazing.

Since then I've bought a couple old 16mm projector amps. They use very close to the same tube compliment so I'm hoping to be able to salvage a lot of what I need from these two including the transformer.
They both came with their field coil speakers. One's kinda shot but the other works fine and sounds pretty good when i play through it's amp.

i also picked up a reconed vintage Gibson 10 inch FC so hopefully with all that and the great info on this thread I might be able to make a go of it.

[pompeiisneaks]

Oh soooo cool!  Definitely keep me posted.  I found some interesting news.  There's a guy on facebook that told me he's got a '39 EH-185 and it uses the 6SQ7's like mine, instead of the 6J7 like you've got there, but it would definitely be cool to see that build too.  Keep me posted! I'll have some audio samples in the next video I think, I end up usually with an hour or more of footage on each build and try to break the videos down to 10 min segments so they don't get too boring :)

~Phil

[ratgon]

I'll def keep ya posted! And so you ARE the guy posting the 185 videos on YouTube??

I'm subscribed if so. Actually found those before even seeing this thread.

And I'm gonna open up my friends 185. I'll post some pics if it's interesting enough.

[pompeiisneaks]

Yup that's me, I've also done a video on my Vox AC100/2 build from scratch there as well.  The forum members have saved me time and again when I get stuck lol :)  I've finished it and have an audio demo coming soon.  I also am starting an 5F6A bassman  build I'm putting up there.  Let me know if you think I need to add/remove things etc.

~Phil

[pompeiisneaks]

Well one more thing I learned today.  The damn thing still had this odd squeal from time to time, and it seems variable.  At one point today I noted that if I touched the preamp tube with my finger the noise disappeared... I then remembered that pin 1 on the 6SQ7's is connected to the metal chassis of the tube.  I tried clipping an aligator clip on that and the chassis and boom, sound gone.  I've since soldered a grounding wire between all three pin 1's of the 6SQ7's and then to ground and its completely noiseless.  I thought I may have had one tube microphonic, but they somewhat ALL were until I did that ;)

~Phil

[Coastrider]

I've got a first draft at a schematic in easysch for the gibson eh-185.  I'm interested in the amp because one of my favorite guitarists, Joshua Homme used it when he played in Them Crooked Vultures. 

I noted the common pictures of this amp show it with a treble and bass control, and saw two versions on the schematics page here:

http://el34world.com/charts/Schematics/files/gibson/Gibson_EH-185_65Q7_PRE.pdf

which seems very much like a clone of the EH-150, but doesn't have a bass tone stack element.  Then there is:

http://el34world.com/charts/Schematics/files/gibson/Gibson_EH-185_6J7_PRE.pdf

which does have it, and seems a bit more complex all in all.  I was considering basing it off the second, but found that the tubes (6J7) require the anode connector, and don't know how feasible that is to build nowadays...  So I kept my schematic based on the earlier one.  (If I'm off base on that assumption, please do comment).

I also may end up building this amp as my next build (some day in the future), but am first just trying to sort it out logically.  I have a few questions in general about the schematic, as its a bit 'empty' of some data:

1. There is no listed output transformer.  Is there a pretty common output transformer for 2 6L6's?   Or do you need to fit an OT based upon the entire preamp and power amp stages impedance? 
2. There's a named PT, but it seems hard to find, the one I did was pretty pricy, 200$ or so here: http://www.mercurymagnetics.com/pages/catalog/manufacturers/MM_gibson.htm which specifies it is for a EH-150 and there's a separate one for the EH-185.  Could I just use a modern one that can push the right power to the 6L6's and the other tubes? 6SQ7/6N7?  I can look that up on the data sheet, and get the total amp required for hte tubes, and see the levels there, that's what you do right? Then I look at normal voltages for these tubes and can look at the expected voltages?  (since they're also not noted anywhere on the original schematic?)
3. Could I just add the same bass controls from the second one into the first and get the same effect?  Or is the latter schematic above just the more modern version and will likely have a massively different tone than the second type EH-185?

At any rate, here's the .sch as well.  Let me know what you see is off/wrong, etc.

Edit: With latest layout and schematic.

Edit: Adding the latest mods as well.

Hello,

I hope this helps with some of the confusion.

Gibson made the EH-185 from 1939-1942.

The first 60 built they actually still had the EH-150 stamped on the faceplate but they were 185's.

The early 185's had separate bass and treble controls and then shortly after they switched to the single tone control.

I have one of the early EH-185's and it is working great and sounds awesome. I also recently picked up a great playing condition Gibson ES-150 (1942)  guitar which was the first successfully produced electric guitar and is what would have been sold with the guitar.

I tried to post a few pics but said the file was too large sorry but hope this helps a little.

Cheers,

Mark

[Coastrider]

I've been following this thread with great interest for awhile now. I've been wanting to try and build a 185 since playing an original one a friend got lucky enough to buy pretty cheap on Craigslist. The thing is amazing.

Since then I've bought a couple old 16mm projector amps. They use very close to the same tube compliment so I'm hoping to be able to salvage a lot of what I need from these two including the transformer.
They both came with their field coil speakers. One's kinda shot but the other works fine and sounds pretty good when i play through it's amp.

i also picked up a reconed vintage Gibson 10 inch FC so hopefully with all that and the great info on this thread I might be able to make a go of it.

The EH-185 had a 12" field coil speaker made I believe by Jensen.

Cheers,

Mark

[pompeiisneaks]

Cool, I'd love to see them, you could upload them somewhere like imgur or google photos and link that page here?

~Phil

[Coastrider]

Cool, I'd love to see them, you could upload them somewhere like imgur or google photos and link that page here?

~Phil

I hope this works

Cheers,

Mark

[Coastrider]

Okay I uploaded the pics by texting them to myself and that downsized the files so a I could then upload them.

You can see where the faceplate still shows EH-150 because the first 60 they made they were just thinking it would be the new model 150 before they decided to call it the EH185.

Cheers,

Mark

[pompeiisneaks]

Outstanding, thanks!  I'll bet it sounds incredible. 

~Phil

[murrayatuptown]

I just started looking at EH-185 schematics.

The very high resistances between the 6L6 plates and ground are not typical in more modern amps...I know these are quite old (late 30's?).

Any idea what they are for...stability technique prior to, or in addition to grid stoppers?

Thanks

Murray

[sluckey]

The very high resistances between the 6L6 plates and ground are not typical in more modern amps...I know these are quite old (late 30's?).

Hmmm. I have very high resistance between plates and ground in all my amps. Can you be more specific?

[Tony Bones]

Do you mean the 20K bleed resistor in the power supply? That's probably there to guarantee at least a minimum current through the field coil under all conditions

[murrayatuptown]

Some schematics online show resistors from 6L6 plates to ground with very high values...like 500 M each, and a smaller value (250 M?) I'd have to download schematic again (will do) to clarify what/where & component designators. PS bleeder makes sense and would swamp the hundreds of megohms, but I'm looking at a schematic only - no measurements :0)

[sluckey]

I've never seen an EH185 schematic with any resistor connected from 6L6 plate to ground. I think you are mistaken about that. But if you have seen such a schematic please post it and we'll get in put into Hoffman's schematic library.

During the era when those schematics were drawn "M" was used to denote thousand, not million. Remember Roman numeral "M"? If something was supposed to be million, it would usually be denoted as MEG.

Around 1950 maybe a bit earlier, the symbol M was replaced with K (Kilo, 1000). There was an overlap time before K was adopted by everyone, so you would see both symbols, sometimes even on the same schematic. So, that 500M is really 500,000 or 500K.

[shooter]

EH185 schematic

 
It's a Gibson, they put all manner of things they didn't mean on schematics 

[murrayatuptown]

I was initially going to say someone handwrote the M's incorrectly and they have been written on every copy since (graffiti syndrome...too focused on the spray can nozzle or marker tip to notice one's errors).

I then interpreted the M to be a tolerance of +/- 20%, believable for that era. There might be annotation on the schematic clarifying all values are in k unless otherwise stated, but I'm on my phone & that's just a lousy way to check carefully.

I see M's all over the schematic so at least they were consistent. With all due respect, I don't like the M changing to k historical theory, unless that is just referring to Gibson when they replaced the woodworkers in the documentation dept. with draftsmen.

Changing ,000 to k I'd buy...

Sure, there were uuF's before pF, but Mm =k =1E6*1E-3=1k is as weird as writing in Roman numerals. Oh krap, M = 1000 in Roman numerals...I was joking, but this is turning into a joke that isn't funny (like at work).

I'll just call them k then, but that gives me little confidence in (scope TBD).

Thank you.

Today is Monday isn't it...

And I NOW see sluckey posted the Roman numerals explanation.

Browsing on a phone sux.

This must date back to burning poplar bark to make resistors.

[vampwizzard]

Uncle Doug went through a 1946 Gibson BR-1 with a similar power amp topology.. the high current/low voltage and it worked pretty well it appears. Also had the big ole resistor to chassis ground. schematic around the 19:50 mark.

https://www.youtube.com/watch?v=cPnPN8Z_BH8&list=UUuR4hQTXkG_KxozLxwPzEjQ&index=3&t=1462s

[bmccowan]

With all due respect, I don't like the M changing to k historical theory, unless that is just referring to Gibson when they replaced the woodworkers in the documentation dept. with draftsmen

M is still used in many engineering arenas. MBTU is thousand BTU not million.

The MM is used widely in the oil and gas business; it stands for "a thousand thousands". The original symbol for thousand was M, based on the Latin word "mille". Often the lower case is used. So, for example, a million Btu is mmBtu.

https://www.quora.com/What-should-be-the-abbreviation-for-million-M-or-MM

[sluckey]

Also had the big ole resistor to chassis ground. schematic around the 19:50 mark.

That's true. But the resistor is not connected from 6L6 plate to ground. BIG DIFFERENCE.

It was quite common back in the days of field coil speakers to see a big, high current bleeder resistor such as u. doug shows.

[sluckey]

You will find in the electronics world that M=1,000,000, m=.000001.

https://www.quora.com/What-should-be-the-abbreviation-for-million-M-or-MM

Whoever wrote that has never become familiar with electronics or computer jargon. G is a very common symbol for 1,000,000,000 (billion). It's used everyday by even non-tech people. Ie, my dad just bought me a 256Gbyte thumb drive. I'm stoked! Or my new Motorola cable modem, the MG7550 is a dual-band Wi-Fi router, and supports clients that operate on both the 2.4GHz and 5GHz bands.

So, Bill Gates may never use a "G" when he writes a check, but I bet he knows what "G" stands for. Most people have no clue and don't care. 

[shooter]

m=.000001.
I missed something, I use m for milli, .001  u for micro .000001
and I think we were both using GHZ before the cool kids 

[bmccowan]

And I have an MG. Its a 1960 MGA 1600. It even starts occasionally.

[sluckey]

m=.000001.
I missed something, I use m for milli, .001  u for micro .000001
and I think we were both using GHZ before the cool kids 

Oops! You got me! 

[DummyLoad]

I see M's all over the schematic so at least they were consistent. With all due respect, I don't like the M changing to k historical theory, unless that is just referring to Gibson when they replaced the woodworkers in the documentation dept. with draftsmen.

old US manufacturer generated schematic notations 30s-50s:
m = milli.
M = Mille (america shortened to Mill-Ohms).
mm = milli-milli Farad = micro Farad.
MM = Mille Mille = Meg Ohm.

fender used the same plate to plate NFB scheme in the AB165 that gibson used in the EH-185 ver.1

--pete

[PRR]

I'll attach the Gibby with power tube plate-grid NFB resistors.

Pre-WWII plans "often" used "M" for 1,000. Post-war, "K" became common. The change took a couple of decades.

I remember when there was no "pico", only "micro-micro", strangely spelled "MM".

The 6N7 cathode resistor surly must be "1 K". Small plate resistors are 100K just like so many other amplifiers. (Anyway a cheap composition "100Meg" would be real rare and real unreliable.) Pots are 500k. B+ drop resistors 10K.

The 750K 6L6 plate-driver resistors tend to give NFB on the OT primary, which is nearly as good as taking from OT secondary, and avoids bring signal back from the jack; also uncertainty about OT polarity). They actually give very little NFB at nominal load; this is to damp speaker bass resonance where load impedance (and gain) could be very high. You could play with none or with 330K to taste.

[DummyLoad]

I'll attach the Gibby with power tube plate-grid NFB resistors.

Pre-WWII plans "often" used "M" for 1,000. Post-war, "K" became common. The change took a couple of decades.

I remember when there was no "pico", only "micro-micro", strangely spelled "MM".

The 6N7 cathode resistor surly must be "1 K". Small plate resistors are 100K just like so many other amplifiers. (Anyway a cheap composition "100Meg" would be real rare and real unreliable.) Pots are 500k. B+ drop resistors 10K.

The 750K 6L6 plate-driver resistors

i believe that those plate to grid are 250K - not 750K 

--pete

[sluckey]

those plate to grid are 250K - not 750K 

That's what I see too. That schematic is in Doug's library. Still no resistors from plate to ground.

[bmccowan]

Is someone able to school me/us on that tone stack in the 6J7 version? I understand the treble pot, but the bass pot filters to ground through an unlabeled inductor? Was that somehow common back in the day?
Thanks

[PRR]

I like 250k better now.

If you understand how the treble pot cap shorts highs to ground, then it is clear how the bass pot choke (the opposite kind of reactance) shorts lows to ground. It is labeled GQ13, which is probably a factory code.

[bmccowan]

Thanks PRR. I had not noted the GQ13 as the label for the inductor. Did a search and it does seem to be a factory code. Later I may look for a spec, but most of what I see are folks calculating a likely value of 1.5 - 10 H.

[PRR]

For full deep bass working it wants to be 5H-10H.

Also try increasing the 10K in the cathode to 22k or 47k. You get less gain, but more symmetric curves.

Choke location may be critical because it is a potent hum pick-up. (A gyrator wouldn't pick-up hum but was much too costly for the time, and even now is awkward because of high signal voltage.)

I think we see why this type plan was not popular.

[bmccowan]

Yes - I read elsewhere that the choke could be a hummer - the wrong kind.
But it was more for my learnin' that I asked about the choke.
I do have sitting in my project pile a Stromberg Carlson Muzak amp. It is an all 6SJ7 preamp (5 of them - two are paired up for the PI) I have rebuilt several old Gibson, Valco, and Magna amps with one or two 6SJ7s in the preamp, but not 5! I was thinking of loosely following an old Dan Electro schematic, or an Electromuse, but this thread got me thinking. If I follow the Gibby route, I would use a more conventional tone circuit.

[brewdude]

I would like to see a schematic of that amp with 5 6SJ7's.
Do you know the model?

[bmccowan]

Hi Brewdude,
It's a Muzak 908B made by Stromberg Carlson.
I pulled it from the shelf to make sure of the model # and it has 4 rather than 5 6SJ7 tubes. (faulty memory)
The only schematic I have is very aged - brown - glued to the base cover. I will try to take a photo of it later.
I will likely redraw the schematic in order to track circuit changes, and will share when I do.
Tube lineup is 4 6SJ7 - 2 6V6 - 5Y3.
It looks like it had an easy life - probably elevator music in a Macy's, eh?
There are a couple of Youtube vids of this model, and an expired Reverb listing for a 908A that I have seen.

[brewdude]

Thanks. I’ll have to check into that amp.