Epiphone Pacemaker EA-50T

[cmm71]

I picked up a mid to late 60s Epiphone Pacemaker recently and had a question for those who may be familiar with it. It has a very bright tone and I'm wondering if that's how they were voiced or if maybe I have a problem.

Mine has 2 6BQ5s (EL84s), 1 6EU7 and 1 6C4. It has a tremelo circuit. It has Bass and Treble controls and I find that I need to turn the Treble down to 3 and the Bass up nearly all the way just to get a usable tone...and it's still bright. I'm using a Les Paul with Burstbucker Pros. The previous owner had two large caps changed (they are huge...he left them with the amp) but I think they were power supply components. It looks like the rest of the amp has all original components. It also looks to have original tubes. The speaker looks original and it doesn't inspire much confidence as it's pretty ratty.

I ordered all new tubes just to eliminate the "maybe the tubes are shot" voices in my head. I also ordered a new Jensen speaker (I know Jensens aren't well spoken of on this forum but I've always liked them). I'm hoping that between the speaker and tube changes I'll notice some more low end/mid-range. If anyone else has this amp what are your experiences, is yours bright as well?

[Wally]

"I know Jensens aren't well spoken of on this forum but I've always liked them)."

Vintage JEnsens are the standard for many folks. Modern Jensens?....Jensens in name only, imho. IF one likes them, then they are a good speaker to use.
THe Epi Pacemaker....many Gibsons of this era can be very bright. ONE could probably find a capacitor ina spot or two that could affect the tone. I don't think the tubes and the speaker are oging to change the basic sonics of that amp. For that, it is tech time.

[TNO]

Your amp probably has .001 coupling caps (compared to .01 in a blackface fender and.1 in a tweed). Going to larger coupling caps will help. Some of those amps have a Sprague tone filter that can be bypassed. I love Jensens but I don't think it's the right speaker for this amp. An eminence c-rex or lil-buddy would add a lot of fullness and smooth out the highs.

[cmm71]

OK, good thoughts. I chose the Jensen because I do want to keep this relatively "vintage" and Jensen has that vintage look. It's also rated at 35 watts so I was hoping it might fill out the sound a little and bring in some low end. I'll look into the coupling caps but I fear I may be a little out of my depth. Thanks for the replies.

[mojo2001]

I have had bad experiences with mid 60s Gibsons, in the way you describe.

First, if it has the stock CTS speaker in it, these are some of the nastiest, most mechanical and thin sounding speakers you will ever find. Try a nice fat Eminence, as suggested above.

But that most likely will not be enough.

That amp is so simple there isn't much to blame. Usually the tonestacks are dubious in this era Gibbys, but you don't have one.

I's suggest swapping out the "250pf" cap between the 6EU7 and the 6C5 with a .01--or to make it easy, just wire a .01 in parallel.

Actually it can't be "250 pf" as indicated on the schematic because that would give you a corner frequency of 1100hz...must be 2500pf or .0025, which would be -3dB @ 111hz.

Still cutting it short. Put in a .01 If you need one, I'll send it to ya.

Furthermore, Gibson amps seldom match the published schematic, so who knows what you got.

I tried a few and now won't waste my time on any post 1962 Gibsons. The Kalamazoo Model 2 aka 1965 vintage GA-5 being the only exception.

[cmm71]

Wow, I'm losing heart. I was hoping this was a gem of a find. I have a little fetish for small, low wattage tube amps and this one was found tucked away at my local used guitar store. Physically it's in mint condition, the tolex is gorgeous. I was hoping with a re-tube (and I spent a fortune ordering NOS tubes) and a new speaker that I'd be blown away. Not feeling so good now. I'll post back when I get it all back together.

[mojo2001]

Hey don't mean to bum ya out! But you did ask...

The speaker is probably the main thing to change. If there is a 10" CTS in the amp, that is a highly suspect speaker in my experience.

I would expect that a new Jensen would help a lot, even if it isn't a one of the more dark and mellow speakers out there.

I just looked at my Gibson schematics and found three versions of the EA-50T. One version does list the infamous Sprague midrange notch filter (one inch square flat brown thing with three leads) and has smaller coupling caps than the others. If you want to get involved with minor electronic mods, email me close up pics of the circuit or post em here and I'll assist if I can.

My point is that some of the mid-60s Gibsons were voiced for wicked bright sound. Clean is one thing but they went too far around 1964-65, if you know what I'm sayin.

In any case, a new speaker is certainly a first step in the right direction.

[TNO]

Hang in there with it. Some of those amps compress in a very cool way when you crank them. Reverb and trem are very cool and unique. The '62 and earlier amps are the real jems though.

[cmm71]

I'll try to post some pics, I've taken quite a few of the circuit. I've got a little electronics experience and I think I could probably swap out some caps if necessary. The speaker and tubes are due in this week so once I get them in I'll decide if I want to go any further. I've already installed the 3 prong power cord and removed the "death cap", I may be up for some experimenting with the circuit if that's what it takes.

The speaker doesn't have any distinguishing marks except for some numbers in ink on the magnet. It's an AlNico speaker but it looks like someone messed with it...the lugs have massive amounts of solder built up.

[Wally]

cmm71, mojo2001 has good suggestions and observations there. I have had some good Crest era Gibsons from '63 and early '64. The double-angled cabs that came later are not as good....as mojo said....bright.
RE: JEnsens and 'vintage correct'. For Gibsons, JEnsens were usually silver in color and not blue as the Fender JEnsens were or as the modern JEnsen speakers are.
Good luck with it. IT is a hand-wired amp and can be modded. Take advantage of MOjo's offer. You can learn more from a challenging amp than you can from one that is 'good to go'.

[zook]

To the best of my knowledge the EA50 and EA50T had two 6AQ5's not 6BQ5s.

Also they only had a volume comtrol, no tone stack.

http://www.schematicheaven.com/gibso...maker-trem.pdf

Yours may be a later version, but I can't find a schematic that shows the tone controls or the 6BQ5s.

Winnie

[cmm71]

Yeah, I've encountered many, many schematics showing the earlier 6AQ5 versions. Mine has a schematic attached that is showing 6BQ5s. Mine is the double-angled cab that Wally refers to above. I'll try to some pics up tonight.

[cmm71]

Epiphone Pacemaker(web).jpg

See if this one works.

[telel6s]

I used to have a '65 EA-50t. Cool little amp. Sounded much better with a Weber Blue Pup alnico than the original speaker. I never did find the correct schematic for it (or it's Gibson cousin). From what I could find out, this cab style was first produced in '65 and that's when it switched to the 6BQ5 (el84) power tubes.

It was a good in-the-house amp (not enough power for gigs) and probably good for recording (although I never had that chance). One of the joys of a lower power amp like this is you just turn the volume to 10 and then play your guitar.

I ended up selling mine after I got a '71 Princeton NR. Same type of amp -- low power, trem, 10" speaker, no reverb -- but the Princeton has more punch, bite and depth plus more volume.

But have fun with your Epi. It is a nice amp and you don't see many of them around.

ea50t_front3.jpgea50t_back02.jpgea50t_inside02.jpgea50t_speaker_back.jpg

[Wally]

cmm71, that is a clean little amp. The circuit is very accessible for mods, isn't it?
You should be able to delve into tonal manipulations easily. That scematic would be a good submission to Schematic HEaven, if it isn't already there.

[zook]

Boy it sure is clean. The Orange caps are replacements, by the way.

Can you scan and post the schematic? I'd like to see it. There might be some change you can make to the circuit to improve the bass response.

Winnie

[cmm71]

I'll give the schematic a try, it's stapled and glued to the inside of the cab so I don't want to destroy it. The glue is failing so I may be able to pull it off.

[cmm71]

Now that you mention it it does definitely look like those orange caps are not original. That doesn't bother me at all.

[zook]

You could try photographing it in large format, That might do it. It will be important to see the values of the components though.

Winnie

[Wally]

I would suggest trying everything before removing that schematic. You can get a good picture with the paper in the cab if you have a good camera. Even if I had to remove the speaker to get a good shot, I would try that first. IF you can't get a pic with the schematic still in the cab, you might consider making a hand-drawn copy of it before trying to remove the paper. This would serve a second purpose....it would familiarize yo with the schematic and make it easier for you to take note of what values should be there, what values are in the circuit now, and what values might need to be changed to enhance bass response.

[Wally]

IF you have to pull the paper, some steam might make things come off more easily.

[cmm71]

Epiphone Pacemaker9(web).jpg

Pic of schematic...I have a bigger version but I had to shrink it to fit the requirements.

[Wally]

I saved it to 'My Pics' so I could enlarge it, and it needs a bit better focus. Any chance of trying some more? Try enlarging it to see if it is readable after one makes it big enough to see. When you get a better one, send it on to us.
OR...could it be my eyesight?

[mojo2001]

You can download the "complete" Gibson Service Manual here:

http://www.schematicheaven.com/manuals.htm

In fact there is no complete manual. There are 5000 variations it seems!

That amp does not match any of the printed schematics for EA50T. It has an interstage phase splitter/driver transformer like the GA15RVT (the brightest amp I ever heard).


Interestingly the power tubes are cathode bias, whereas most amps using an interstage trans like that feed a fixed bias through the secondary of the interstage trans to the grids of the power tubes. This one feeds the bias-vary trem signal through the secondary. That much is cool design.

Two things leap out at me

1) The interstage trans has DC flowing through the primary. I assume it is a 6C4 driver. To get good LF response in this arrangement, the transformer must be air gapped. I'm guessing that the transformer could be getting saturated with the 8-12 mils of DC and thus is light on the lows.


2) The tone circuit looks funky (can't read the values) but it looks like a variable midrange suck out design (i.e. a "Bridged T filter") with provisions for rolling off highs in a more traditional filter coming off of the top of the volume control.

This first tone circuit is basically the circuit that was in the Sprague couplates mentioned above, designed to put a big midrange scoop in the response.

For an interesting experiment, try jumpering this crazy thing out with a clip lead, going from the output of the coupling cap before the tone control into the resistor after the tone control. Or lift the ground of the cap in the tone circuit...that will also disable it.


There might still be room for some easy mods, but the fixes for the interstage trans circuit are relatively involved, aside from getting a beefier interstage trans designed for unbalanced DC in the primary.

It would help a little bit to replace all the old black cathode bypass electrolytics. I can provide a few for the experiment.

Hopefully, the new speaker will be good enough to make it enjoyable to play but there are a few other easy things to try. Send me the photo direct from the camera and I'll try to get the values off it --jroberts--at--io.com

[mojo2001]

Link to a bigger image of the schematic:

http://silbatoneacoustics.com/images...makerTDPRI.jpg

Download that and blow it up with your viewer.

[zook]

The amp is fascinating. Interstage transformer like a Musicmaster Bass amp (which is cathode biased, by-the-way).

I think the 6C4 is the recovery stage for the preamp (for want of a better expression) That tube has only a gain factor of 16.94 You could put in a single triode with higher gain just for fun too.

Winnie

[mojo2001]

Here is a copy of the EA50T schematic with the freequency shaping elements notated.

http://silbatoneacoustics.com/images...erTDPRImod.pdf

1) C1 and R3 at the input roll off bass (-3dB@72hz) and limit the range the amp is working with to guitar frequencies.

Reactance calculator is here: http://ourworld.compuserve.com/homep...Bowden/XLC.htm

At the frequency where the reactance of the cap equals the resistance, this is like a volume control turned halfway down at that AC frequency--> 72hz. Below that it is rolled off more.


2) The amp uses small (2uF and 5uF) cathode bypass capacitors. This will roll off bass...which can be good to liven up an amp, but not what we need here.

This is more complicated to calculate than it looks, but basically the cap shorts out the resistor for AC signals above a certain frequency so that the resistor cant burn off any signal. Below the bass cutoff frequency of the cap, the cathode resistor "turns down" the signal.

The cap values that are in there will have a rolloff effect below open D (~150hz) and maybe open G string (~200hz) frequencies.

Switching to Fenderish values of 20-25uF, will let all guitar frequencies through with bandwidth to spare.

Fresh caps will also help restore character.


3) The tone circuit is a midrange notch. Did not calculate the center frequency. I cant tell how the pot is wired but this might want to sit at "0" for the flattest response, with 10 as the most radical midrange suck-out.
Putting it at "5" is probably a lot of scoop, not the OFF position.

The resistor after the tone control, R8, is a voltage divider throwing away a lot of available signal voltage. If you bypass around it, as notated, it will help to drive the snot out of the output stage. If you leave it in, the amp will be much more clean at high rotations of the volume control.

If you replace the bypass caps and take out the notch circuit, you can hear what the tubes and iron are doing independent of the tone shaping.

Maybe the amp will be great without the engineered tone shaping or maybe that interstage trans phase splitter implementation totally sucks at a deep fundamental level...but this is how you can find out.

I suspect that whoever designed this amp had some crazy vision of mid-sucked, bass rolled, stupid bright sound as the ultimate flavor for electric guitar. Nobody else thinks so, so try backing out some of these "improvements" as described above!!

You could have a switch that bypasses the tone circuit and/or 470k if experiments suggest that these settings are useful.

[cmm71]

Thanks Mojo2001 for all your work on this, and thanks to all who have helped. I put it back together with the old speaker (the new one should arrive soon) and it is usable with the Bass at 7 and the Treble at 3...still bright, but usuable. I plugged in a DS-1 distortion pedal and dialed the tone back and it sounds great; ofcourse I don't want to leave the distortion pedal ON all the time so I may have to eventually address the changes you suggest. I've worked a lot with guitar mods and feel comfortable tearing down and rebuilding $2,000 Les Pauls but for some reason modding and messing with an old amp seems pretty overwhelming to me. I'll throw this new speaker in when I get it and see where I'm at, I may juts live with it the way it is until I feel up to the task of experimenting.

Thanks again everybody.