Rebel 20 Chronicles

[hotrodder]

The Rebel 20 Chronicles

Hi everyone,

I've posted before concerning the Egnater Rebel 20, and lamented the lack of schematics on this model. Some of you fellow TDPRI's have told your stories of poor service, funky problems, and general lack of support if real problems rear their ugly heads. It seems that the only people who can reliably fix these amps are the manufacturer. In my area, I have looked around and so far, have found no service tech who is knowledgeable in regards to Egnater in general. (OK, I haven't looked Really hard.)

In looking for schematics on the Internet, I found that Ben Fargen is modding these, and had posted a Mercury Transformer set on ebay. I have been unhappy with the performance of my Rebel 20, (I've replaced preamp tubes and improved it a little) and decided to take the leap.

I cataloged, and then ordered Mallory, Jupiter, F&T, and Silver Mica caps, the Mercury kit, and decided to sit down and make my own schematic of the Rebel 20. So, I documented every connection and wire location on the three pcb's, switches, transformers, and sockets. I then dis-assembled the amp, and traced all the pcb's in order to map out a schematic.

When the parts came, I replaced the caps, and modified the power supply. The Mercury OT and choke required new mounting holes to be drilled, modification of the preamp pcb to install the choke, and connectors installed on the wires.

I had read one of Gerald Weber's fine books, and in order to change the amps voicing, I performed several of his mods. If you have any desire to mod or repair a guitar amp, his books are worth their weight in gold.

POWER SUPPLY:

I installed a larger capacitor for the main filter section, and doubled the capacitor on the screens supply. This gave more punch, and a more solid "low-E". The amp doesn't seem to run out of gas on the chunky bottom end as quickly.

BIAS:

I have changed the EL 84 tubes to a switchable bias; that is, the ability to have cathode bias. This gave the amp a more "singing" quality, and there is a bloom to the note decay that is very nice. It takes a little punch out of EL 84 side of the power tubes, but you can dial in punch with the 6V6's now, and there is a real difference in the way the amp reacts when you use the tube mix control. As an added benifit, the watts control really does dial down the output now - when I first got this amp, the watts control didn't do a whole lot.

CUT:

I don't know about other Rebel 20's, but my unit had WAY TOO Much top end! When cranked, it had a definite "icepick" quality, that after a short while, got on my nerves! (Part of the reason I decided to either sell it or modify it.) So I added a switch that engages one or two .01uf capacitors to the number one pin of V2 (this is the first preamp stage). Now I can use single coil guitars (Teles and Strats of course!) and control the amount of top end the amp has. Added bonus: Now I can use the bright switch without the risk of breaking glass!

VINTAGE:

When you listen to old amps, they generally have a nice, round tone quality. There can be a lack of harshness in the sound. My Rebel 20 lacked this facet of character. Gerald Weber, in his books, writes about adding a "browner" quality to the sound of an amp by reducing the voltage to the first preamp tube. I added a switch that allows this reduction in first stage preamp voltage. When engaged, the amp looses a little punch, but the harsh edges are rounded off.

Mercury Transformers:

Changing out the OT and adding a choke requires the complete dis-assembly of the amp. This is not for the faint of heart, or someone who does not document the procedure. However, the results are worth the price of admission. The amp has much more "meat" overall, more definition in the individual notes, the bottom end holds together much better, and a lot more punch than before. It's a pleasure to hit a nice G chord and hear all the strings chime. When you push the amp now - dime it - it's got a lot more crunch. It doesn't squeal nearly as much as it used to, and it can produce those "woman tones" we hear so much about in the reviews.

Conclusion:

This was worth doing, but it did take some late night sessions, concentration, a bit of research, and it required commitment. Electronics are both a job and hobby for me, but I'm not an amp tech - I'm a guitar player who can't leave anything alone. If there is enough response, and people are interested, I would be willing to share my notes and pictures of this project. This is not a beginner project, more like advanced intermediate. But the individual sections could be completed in an evening, giving the ability to do thie job in increments. So - is anyone interested in more?

Thanks for viewing -

NOTE: Amplifiers can and do contain LETHAL voltages, even when unplugged! Don't try to work on one unless you have paid up your life insurance, know what you're doing, and follow all safety precautions.
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Ask Me What Time It Is, And I'll Tell You How To Buld A Watch

[printer2]

More than a little interested. Always like to see how to improve things.

[samato]

This is very cool. Looks like you are now one of the foremost authorities on this amp.

Can you elaborate on your "Vintage" switch? I'd like to see if it might be some worth trying on my amp (not an Egnater).

[hotrodder]

Can you elaborate on your "Vintage" switch? I'd like to see if it might be some worth trying on my amp (not an Egnater).

Thanks for the interest. By reducing the voltage to the plate of the first preamp tube, as per Gerald Weber, you can give the amp a "browner" sound, sort of like a Tweed amp. you have to find the resistor that feeds the power supply voltage to the plate of the first stage of the preamp. The plate is usually pin 1 of the tube. (I am speaking of a 12AX7 or similar). This resistor will probably be a 1 watt or higher rated resistor. You will need to check the DC voltage on that resistor. The Egnator had a voltage of 260. By inserting a 120k 1 watt resistor via a switch between that resistor and the 100k plate resistor and cap, I reduced the plate voltage from 260v to 200v. You can go further, but you will hear a degradation as you reduce the voltage. Amps set up for use with harmonicas can have as low as 80v going to the plate, but I understand that that sounds terrible for guitar. Gerald Weber has explained this mod in his books. If you look at schematics of older tube amps that have voltage notations, you will find anywhere from 100v (AC30 top boost channel) to 180v (Fender Tweeds), to 200v (BF's). To do this mod on an Egnater, you will have to cut a trace that goes between the 100k resistor/cap plate inputs in order to isolate the first stage (V2-pin1) from the gain stage. This mod will allow the first stage to break up sooner (less headroom), and so if you are using overdrive pedals, their effects will kick in more quickly. You'll also see less overall gain in the amp because of this mod. In the Rebel 20's case, it's not a problem, as there is plenty of gain available, so a little loss is OK.

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Ask Me What TIme It Is, And I'll Tell You How To Build A Watch

[kyussmyson]

I have a rebel 20 and I've had no problems with it!!! Very pleased with it! Mines a lil ice picky when I turn it up and have the highs above like a 2 or 3!! I also can't hear a difference in the tube mix section at all!!! I just keep it straight up! I was wanting to mod it so there would be a difference, change the EL84s to a different type, KT88s or something outta military airplanes cuz those are phenomenally built and good sounding tubes, just something to get a difference between them!! How much did it cost you to do everything you mentioned above??? I was gonna send it away to fargen amps but I want to get the "browner" sound as well as have loads of gain and distortion! would that mod work after I get the fargen mod on a switch so I can get brown when I need it, a setting close to the stock sound and have the fargen hot mod sound too?? I want to get very heavy articulate metal sounds from it but also want the cleanest, prettiest clean sound too? Any suggestions??? I was also gonna re tube it with cryo set tubes! have you heard anything about cryoset tubes?? Good, bad, worth every penny?? The logic behind them makes sense? They should be better structurally and musically!! You can email me if you want!!

[thickwood]

My rebel 20 lows got too huge when loud and gained up enough too sustain well,thanks for the tight switch.
I retubed the power tubes with tungsol 6v6 and mullard el84 and 12ax7 are mostly tungsol gold pin a bit pricy for sure.
The is a ruby 12ax7 ac7 hg in there as well.
Im going too try those power tubes in the rebel 30 i just bought.
That amp is has a sweeter disposition for sure.
The recording playback playing slide floored me using the R20 the growling sustain was incredible. That aggessive sound made the attitude of the vibe i was doing take it too the next level.
Some folks cant deal with the attitude this amp has,the character is why i luv it so,and the power tubes overdriven abit smooths any harshness out.
Im going to buy a webermass attenuator 50watt i think.
I built the bitmo 23 watt attenuator but it barely can do the job.

[hotrodder]

I put Russian 7189's in the EL84 spots, and it improved the chime. The 7189's are also a bit more robust (the amp burned the screens on the original tubes.) After about 100 hours of playing, the mullard caps are finally broken in, and it really is a nice little amp. Not up to my JTM 45, but I can get it to sound very close to my AC 50 with the tone settings.

[dorrisant]

I have a friend who is a Nashville session player and gigs with David Ball. He has a Rebel 20 and has asked me about mods. I was curious if you would be willing to pm me a copy of the schematic. I would love to see what makes it tick. Thanks in advance for any help.

Tony

[gitold]

I had my Rebel for a year and sold it. Wanted to love it but the two sets of power tubes didn't make much difference and the icepick highs turned me off. Sounds great in the music store. I know the fellow who bought it and he loves it. Glad you were able to make yours work for you but I just bought a different amp.I'm all thumbs when it comes to working on electronics.

[hotrodder]

It's a real shame that Egnater won't release their schematics to anyone, even repair shops! I believe that they are doing a dis-service to both their customers and themselves by not releasing the info needed to keep the gear running. Mt schematics aren't what you'd call pretty, and there may be a mistake or two in them. I made them for my own knowledge, and to change the areas I thought could benefit from modification (almost all the caps, for instance.) I'll try to clean up the schematics a bit, sometime in the future. If you can find a competant tube amp tech, he can look at most of it and figure out what to do for you. The power supply mods, and the top end bleed caps on V2 made a big change, and those can be done without a detailed schematic, along with the OT change. Russian output tubes (Tungsols 6V6's and 7189's) made it very useable. A decent tech can do these, although the OT requires a tear down.

[dorrisant]

What you have for notes may be exactly what I'm looking for. I'm sure I will be able to get one in front of me on the bench... I was just looking for even a glimpse into the topology. Get a head start, so to speak. If you can... send them to me, please. If you don't want to, it's quite alright ... I have several ideas that work but would not really feel comfortable showing my notes just yet.
If it is any consolation, I have helped several of my forum friends refine schematics. As I said, I will have full access to one in the very near future. I would also be willing to refine what you have, or at the least verify what you have.
No one has this schem posted... isn't it about time?...

I am already using the "watts" control in one of my amps... I just want to see what tweaks I can do. I really appreciate what you have posted in that effort.

By all means pm me if needed!

Let me know.
Tony
tony@volitionamps

[Jimmy D]

Bumping this back up to see if there is a schematic available yet. Thanks!

[hotrodder]

Not yet - I PM'd Dorrisant but he never got back to me - I might finish it up for viewing by myself... my notes are a bit crude, but the dis-assembly notes will work well if you're gonna take the puppy apart completely, as required if you change the OT. Anyone interested in that? If so, I'll post 'em...

[jrd6867]

Hey yeah I just bought a used rebel 20 off ebay I would be interrested in seeing your notes. would be kool to find a schematic that would save alot of circuit tracing!

The egnater boys can't keep it a secret even without releasing it. To me it's bad customer service to not release the schematic.

[jrd6867]

ok Recieved mine yesterday way less than impressed! So tnight I took it out of the cab and started tracing the circuit. Ok starting with pin 1 on valve 2 the first input tube thats hooked to the input jack.


Pin 1 has a 100 k resistor that is bypassed by a pf cap. I never liked that system it seems to add harsh cutting fizz.


Pin 3 is hooked to a 2.7k resistor and is bypassed by a 1uf cap. its already not letting a full guitar sound in


pin 8 is run into a 2.7k resistor that goes to ground and is bypassed by a .68 resistor. even moore high boost.

Pin 7 is hooked to a 10 k resistor that runs in series to a c108 to the bright switch.

pin 6 is alsohooked to a cap that runs to the gain control.

This first stage while very similar to the old jmp mk11 master models also has alot of high boost and low cut that the jmp mk11 master models don't alot of highend boost! and low cut. These rebel 20 amps are made to hold together under high gain and hot humbuckers. Not a old school hard rock or blues sound

[jrd6867]

Still havn't decided to keep and mod it for a more touch sensitive and singing amp with some punch or just get rid of it.

[robt57]

2 cents:

I just went on a tube fest, in the end 1970 RCA 6V6, 1968 Mullard 6BQ5s, TunSol RI 12AX7 PI and a JJ 12DW7 v2 & TungSol RI 12AX7 V1.

Just reversing the V1/2 surprised me, I usually will do the DW7 in V1.

Speaker Cab is a 5E3 clean pine with a Red Fang, and I don't know if I just got lucky, but it is stellar. I always read the tube pot does little, well it does a lot after the tubes choice I made I can say.

I run it usually leaning 6v6, gain about 6 and full power and volume and dial back with the Tele Vol pot. Bright on is out of the question unless HB guitar is used...

I love this thing, If I had to sell this or my SFDR I just got, probably sell the DR.

YMMV

[jrd6867]

Yeah I tried numerous nos 6v6's like the rca's the jan phillps, and marconi's, along with rca blackplate square getter 12ax7's and they grey plate rca 12ax7's also jan sylvania, some old ge's and such. The nos tubes did help alot but its still way ice picky with no punch or midrange and tinny sounding make no mistake it will sustain for days just not in a way my ears like always has ice picks and fuzzy buzzy thing goin on. I built several amps probably 20 or so anyway! also had several new amps includind Dsl 50, 2 blues juniors, 3 projuniors, a hot rod deville, hot rod deluxe, 2 laney cub 10's, and 1 fender prosonic. None of them were this harsh and thin and ice picky and all of them had punch and clarity when driven hard.

My favourite new small amp is still the laney cub 10 my fav but they have quality issues. Other than that my buddy has a jmp mk11 master model sounds great! The ones I build sound great! My rebel 20 must be a dud it doesn't sound like any of the youtube vids it is just flat and harsh sounding

[robt57]

I should say in the context of ice-picky, my main Tele had 6k pickups and no tone control. And stainless frets. It only gets a touch brash with the Vol Pot wide open.

Tone setting [FWIW] 10/2/8 o'clock on Treb/Mid/Bass and I do not remember that last time I touched the EQ settings, except the bright switch 'on' with a HB guitar....

[robt57]

Originally Posted by jrd6867

My rebel 20 must be a dud it doesn't sound like any of the youtube vids it is just flat and harsh sounding

Try an open back 112 with a G12H-30 or A greenback with the bright switch on.. I know g12M are really more popular with closed back cabs. Or a Red Fang, my favorite speaker...

I had taken the Rebel on trade and though it would just be a little gain head, but I find anything but this to be true with the tubes and the Red Fang. I am sure the voice the RF gets with the pine cab resonance is something it add I like.