New Build: Early Ampeg Reverb Rocket...ish amp

Discussion in 'Amps and Cabs' started by Leonc, Apr 3, 2015.

  1. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    Inspiration
    I've been a long-time Ampeg fan; I've owned VT-40s, Reverb Rocket 2s, Geminis, GU12, Mercury, Reverb-o-Jet, etc, etc....but never an early, tube-rectified Reverb Rocket. I tried one a few months ago and really dug it. It had a very nice, musical voicing overall...not too dark, not to bright...really rich midrangey sound that octal preamp tube seems to produce. Notes stay nice and firm, no mush and very little ghosting (there's plenty of filtering in this circuit). The reverb was great as was the tremolo.

    After a couple months looking, I couldn't find one in decent shape at an acceptable price so I decided to just build one. I figured I've probably built 20 amps at this point, so it shouldn't be an issue.

    Getting Started
    So I set about collecting the parts and developing a layout. The challenge began when I got really got into the layout. I've grown to like the idea of keeping the filter caps grounded with the portions of the circuit that they supply...so that's been one of my design goals. This was a challenge as was the complexity of the circuit in general...the reverb circuit alone uses 3 triodes...then you have the tremolo and a somewhat "parts-rich" phase inverter and 6 filter sections. I did eventually come up with a layout that seemed to be a good compromise between my various goals. I'm not sure I couldn't do better if I worked at it a bit more...but this did work out really well overall in terms of the amp performing well and the amp having a low noise threshold.

    [​IMG]

    Parts
    I've been really happy with the transformers I've used from Magnetic Components so I decided to use them again. I found two that while not Ampeg replacements per se, seemed to be a pretty good match, though I eventually decided to use a Zener diode to lower the high voltage winding by about 15V. My OT is tapped at 8ohm and 4ohm which is nice because I do love playing through a 4 ohm cab I built with a couple of old Jensens in it as well as a lot of 1x12 or 1x15 cabs with 8 ohm speakers.

    I really like the sound of PS series Orange Drop caps, particularly in "American-voiced" amps so I decided to use them pretty much throughout. I may putz with these a bit more...but I'm really happy with the result...so, maybe I'll just leave well enough alone too. ;)

    Design Alterations
    I did decide to part ways with the original design in a few respects. First I opted to use 7591s rather than 6V6s. Why? Well...I like them :) and I have a decent number of some really nice old Sylvanias and others. Plus I already have gobs of 6v6 amps and only one other 7591 amp. Plus, I know my PT is putting out a bit more power than the original...and I know 7591s can handle more than 6V6s.

    Next, I figured...why do I need two open inputs? I'm not going to be plugging two guitars and a microphone :bong. So I went with one open (47k) input and the "mic" input (47k) with the 470k short to ground. That gives you high and low "input sensitivity" options.

    I also wanted my amp's reverb and tremolo to work without footswitches plugged in. Ampeg used to just hardwire the footswitch in place, but I opted to use 1/4" jacks instead...but you have to use a shorting jack for the tremolo and a non-shorting jack for the reverb if you want them to work w/o footswitches plugged in.

    [​IMG]

    Problems
    After initially finishing the chassis, I ran into a couple of problems. First, I couldn't get the heaters working on all the tubes. I thought something was wrong with my wiring...but it turned out to be the damned tube sockets! Damned modern, ceramic sockets--they all needed some serious re-tensioning to work with my old stock octal tubes. I couldn't get good connections on all of them and wound up just replacing one of them. Man...PITA!!! Lesson learned--try the sockets with your tubes first.
    :peenut

    Then...while everything was working, I was getting this bad oscillation if I cranked the amp...but only if the reverb was engaged. I tested, re-tested voltages, ground connections...got out the scope and tried to pin it down...it was clearly in the reverb circuit somewhere. I tried letting more signal bleed to ground before feeding signal to the PI.

    Then it dawned on me...didn't Ampeg typically use shielded cable to wire the reverb send and return? ...and a few other spots? I didn't have access to an original to verify this but I wrote Gear Pager Slider13 who I know is also an Ampeg enthusiast and very familiar with these amps. He was kind enough to check out one of his RR and sure enough, he confirmed that the r/s and r/r are done with shielded cable.

    I rewired the r/s and return, input to grid and one other long "grid run" with shielded cable. Boom...oscillation gone.

    [​IMG]

    Tweaks
    I've been testing / playing the amp through other cabs for a week now and I'm really digging it. I decided to switch the tremolo pots from log to linear and I like the "throw" on them better now. I've also putz with the caps in the oscillator...but decided the stock values are fine (and safe). I may try to slow the trem down a little though so there may be some more tweaking there.

    I also decided that I like having the option of goosing the very-high end a wee bit. So I added a bright switch so I can go stock or get just a scootch more brightness

    [​IMG]

    Finally, after a bit of experimenataion, I went with a slightly larger cap in the first filter section, 33uA, and a 150k NF resistor based on recommendations from Slider13.

    Tones and Performance
    Well, I've not settled on a particular cab/speaker combo yet...but the octal preamp tubes tend to be very microphonic so I may wind up going in the direction of head + cab. I really dig the sound of the amp through big old Jensens. The best sound I've heard was plugging it into the big 1x15 cab of my National Professional which features an old P15N. Man...killer sound. I've also really dug the sound through a reconned C15P and a Celestion G1265. I'm going to try a Greenback too.

    I'll get some vids up soon and will add more pics when I build the cab(s).

    But I've got to say, the amp really meets or exceeds my expectations based on the old RR I played a few months ago. It's got that same "soft-edged" firmness and bouncy response. The low-end remains clear and distinct...no tweedy mush here! The overdrive is just wicked...I'd say it's the most "valco-sounding" Ampeg type circuit I've ever played though there is a bigger low-end response here than on your typical Valco-made amp. I really like the interactivity of the Tone and Volume knobs. You really get more mid-range and overdrive as you crank the tone so you play with the tone and volume knobs together to get the right ratio of overdrive / brightness volume. Just use your ears (rather than eyes) and it's a pleasure to work with...not a bad tone in there.

    One note about the reverb...boy...I love this reverb circuit!! Ampeg sure knew how to make great sounding spring reverb, if you ask me. Capacitor driven. The sound is very subtle, almost echo-like. Not nearly as sproingy/boingy as your typical Fender. It's a matter of personal taste, but I find this style of reverb greatly preferable. It not only works well on clean sounds, but it works surprisingly well with the amp heavily overdriven as well. My hat's off to Jess Oliver or whoever designed that circuit!

    The amp just loves pedals too. I like it best with my Timmy, which I set for a transparent boost. With a little extra voltage and 7591s, the amp is plenty loud for any gig I'll be doing.

    Mike - thanks very much for your opinion and input!
     
  2. FFTT

    FFTT Member

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    Very exciting to read Leon!

    I love that you put in a top boost like the Gemini I's

    Kinda hard to get to spy surfer land without that top boost.

    As far as practical access to new speakers, I think the new Fane Ceramic 70
    watter may be just perfect.

    Head and cab or combo, tough call. These are such good grab a go's, but having alternate cab options would be great for recording too.

    Mine is the 7868 - 12AX7 version, so a bit more aggressive than the Octal versions. My tech tested mine at 21 watts RMS clean, about 28 peak.
    Where is your coming in?
     
  3. WahmBoomAh

    WahmBoomAh World Crass Guitarist Silver Supporting Member

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    Thrilled to see a potential future for the mighty Ampeg sound.
    I absolutly LOVE my `66 Gemini VI w the 7591`s (and an oddball pre tube too)
    2 Problems
    1. too damn big and heavy (can`t use it anymore)
    2. Would like more headroom (although the orig. 15 is inefficient)
    SO...
    Do you think a 4 x 7591 head could work ?

    thanks !!!!
     
  4. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    Thanks guys.

    Robb - I don't have all the stuff needed to measure/calculate output wattage accurately, but my gut is that it's close to Deluxe Reverb range in terms how how loud it is when is starts to break up. That's relatively loud in my book.

    Wham - Man, that seems like it would be plenty loud...not sure what PT would work though...may require something custom. But first, try your Gemini with an Emi Legend 1518. It's WAY more efficient than your tired old Jensen. I think you'll be pleasantly surprised how much louder it is.
     
  5. FFTT

    FFTT Member

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    Leon, even though it is not customary in the original Ampegs, my tech found a nifty 3 way Off/Standby/On switch that fits right into the original power switch location.

    The way power tubes are these days, might not be a bad idea, especially with
    NOS 7591's running $120.00 for a matched pair.

    Also are you set up fixed adjustable bias or cathode biased?
     
  6. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    I've got one of those switches in there now :) I'm using a Fender style standby circuit.

    This is cathode-biased, like the original design.
     
  7. FFTT

    FFTT Member

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    Good to know thanks!

    I know you know what you're doing. :aok
     
  8. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    I'm actually more of a monkey-see-monkey-do kinda guy, heheh, but thanks for your confidence. :beer
     
  9. FFTT

    FFTT Member

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    Oh you mean the ever popular " What Happens When I Do This?" method?
     
  10. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    Well, I figure it beats the "Hey y'all - watch this !" method,

    :bong
     
  11. WahmBoomAh

    WahmBoomAh World Crass Guitarist Silver Supporting Member

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    Unfortunately I`ve had to retire the Gemini because of the size ...I`m mostly on the road and it`s tucked away ..but yeah , I rember that Emi being recommended . I`ve not heard the circuit with a more efficient speaker yet ...thanks
    post clips !!!
     
  12. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    I hear that. The Supros with 15s were really so much smaller...but they don't develop the low-end that the big-ass Gemini 2 does. (But my National Professional...boy Valco got that cab right in the sweet spot.)

    Keep in mind, the Reverb Rocket circuit in this amp is notably different from your Gemini. Tube-rectified...cathode-biased...lower voltages...totally different tone circuit. Man..it's really a different amp. Two different flavors of Ampeg goodness.
     
  13. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    I've made a great deal of progress on the cab. I've got it completely roughed in. I've made two baffles so far -- a 2x10 and a 1x15. I've been most curious about the 2x10 configuration, which I love with so many other amps.

    Hooked it up just now with a pair of 8 ohm Celestion Golds...all I can say is wow!! Firm but rich cleans with plenty of sparkle yet far from fatiguing...solid and very present Ampeg low-end...seems damn near perfect. I'll finish of the 1x15 baffle so I can try it out with my Legend and a few old Jensens...but man, I'm really diggin the two Cele Golds!!

    [​IMG]

    [​IMG]
     
  14. FFTT

    FFTT Member

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    Schweet! What a cool configuration!

    It's gonna be more like a condensed Echo Twin, neato!
     
  15. MVrider

    MVrider Member

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    Clips!! Clips!! Clips!!! Are you considering making these part of your product line?
     
  16. slider313

    slider313 Silver Supporting Member

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    Looks good Leon and you're welcome. I like the idea of the 2x10's with the Reverberocket type circuit and can't wait for the clips.
     
  17. MVrider

    MVrider Member

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    here's one for you Peg-heads...

    A buddy called me one night and said. "Hey, I just came up with a really cool old amp. Let me play a bit (over the phone) and you see if you can guess what kind it is...."

    So he plays a bit and when he picks up the phone I say, "Ampeg ReverbeRocket." Dead silence.

    Oh, that classic Ampeg reverb. Nothing else like it.
     
  18. zenas

    zenas Member

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    I like your layout better than the original R12R. They work fine but dam are they cramped inside !

    Actually I've been thinking about doing an R12R clone myself I have two of the 5Y3. 6V6 ones but I told my brother he could have one. I'm thinking I'll just build him a clone with a few minor improvements like no cap can and jacks for the speaker and foot switches.
    Be nice of you could still get the blue check tolex.
     
  19. MVrider

    MVrider Member

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    No kidding.
     
  20. zenas

    zenas Member

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    MV these really help. [​IMG]
     

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