Reverberocket tank?

Discussion in 'Amp Tech Center' started by radiocaster, Dec 14, 2019.

  1. radiocaster

    radiocaster Poster Extraordinaire

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    I don't have this amp or planning to build one soon (eventually I may make something), but I'm really curious because on the schematic there is no indication of a transformer for the reverb.

    Does it use some kind of tank with a 20 something K ohm input impedance?


    Also, somewhat related, does the Fender stand-alone Reverb with a 6V6 use a Champ output transformer?
     
  2. Wally

    Wally Telefied Ad Free Member

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    The tank for that amp is the 4FB2A1C with an input impedance of 1475ohms and output of 2250ohms. It is a vertical mount tank.
    https://amprepairparts.com/reverb.htm

    Odd coincidence, I pulled an add-on Reverb unit from a tweed amp many years ago because it caused a large hum problem...and the owner of the amp did not want the reverb anyway. I boxed it up and forgot about it. I ran across it the other day, and the number on the tank was not familiar to me....I do believe it is that tank number. There is a small transformer used in the unit...perhaps the tank is what caused the hum....because someone used a tank that was not compatible with the circuit they built???

    as I understand it, the 6G15 does use that transformer.
     
    Last edited: Dec 14, 2019
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  3. radiocaster

    radiocaster Poster Extraordinaire

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    That is a pretty standard impedance. So the Reverberocket has a transformer or not?
     
  4. radiocaster

    radiocaster Poster Extraordinaire

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    by "that" you mean the kind for a Champ or Vibro Champ?
     
  5. Wally

    Wally Telefied Ad Free Member

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    That is not a ‘standard’ impedance if you count the number of Fender tube Reverb tanks that were produced, imho. check that link I gave for the comparison. The tank for a Fender has a much lower impedance on the input. And no....the Ampeg does not use a driver transformer.
     
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  6. Wally

    Wally Telefied Ad Free Member

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    Those two amps use the same OT. And...I will stand corrected. I was repeating what I have read. However, the schematics for the Champ show the OT to be a 125A35A while the 6G15 uses a 125A12A.
    Hmm...I have read that erroneous ‘fact’ many times over the years????.
     
  7. radiocaster

    radiocaster Poster Extraordinaire

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    I meant it is not way weird that it's not manufactured anymore or the value is extremely off. Anyway, you missed a number, output imp. is 2250 ohms. No big deal, everyone makes mistakes. Thanks for the answer.
     
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  8. radiocaster

    radiocaster Poster Extraordinaire

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    Well, the 6G15 uses a 6K6, not a 6V6...
     
  9. Wally

    Wally Telefied Ad Free Member

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    Thanks for the correction, radio. I corrected it. The fingers must have missed the keyboard. Waking up is.
    standard to me implies that it is well...standard....as in seen often. When I pulled that tank out of the box Wednesday and saw that 4Fxxxxx number, I wondered what in the world is that tank??? It is standard for Ampeg tube amps, I suppose, right?!? Lol....
    There just aren’t enough Ampeg Reverb amps in the world to outnumber of Fender type Reverb tanks. And....I would not call 4AB3C1B tanks standard either...except for Fender tube Reverb amps that use a long, 2 spring, long decay, horizontal, open side down tanks.
     
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  10. Wally

    Wally Telefied Ad Free Member

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    very similar tubes, but they do have a difference in plate resistance. You can run either tube in sub for the other, but I am sure that Leo paid attention to the spec sheet for some reason. The 6V6 has more output.
     
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  11. zook

    zook Friend of Leo's

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    If you read the resistance of the transformers they will indicate what the impedance of the tank it. Use this chart:

    https://amprepairparts.com/reverb_numbering.htm

    The first number is the impedance, the second is the resistance. An Ampeg tank will show 26 ohms input indicating a 150 ohm impedance.
     
  12. slider313

    slider313 Tele-Afflicted

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    Ampeg reverb is tube/capacitor driven and does not use a transformer.
     
  13. BobbyZ

    BobbyZ Doctor of Teleocity

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    Fliptops has Ampeg tanks.

    Which Reverberocket you wanting to build?
     
  14. zook

    zook Friend of Leo's

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    if you were commenting on my post, I was referring to the transformers in the tank. I am aware that Ampeg drives the reverb with a capacitor.
     
  15. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    My impression is that the Ampeg reverb circuit was used for lower price?
    The Reverberockets with a big cap I've had were OK sounding in terms of the reverb, but I always felt they were sub par compared to Fender reverb.
    Is there any reason other than lower cost to use that reverb drive/ coupling?
    I'm also not sure if the old Ampeg reverb was less washy/ surfy because of that electronic difference, or primarily for other reasons while the lack of a transformer maybe has little effect on the sound.
    Then the two I had were running original tanks which may have hurt the reverb sound, as it did on some old Fender reverb.
    The Fender reissue reverb also used a 6v6 instead of the original 6k6 because there were no 6k6 tubes in production when Fender reissued the 6g15.
    I bought that reissue when it first came out and subbed in a 6k6 but IIRC it didn't change the sound much if at all.
    Maybe the RI had a different tank impedance to better suit the higher output driving it?

    Given the low price of vintage Reverberockets I'd really consider what parts of the design are maybe better off skipped over in favor of better sounding circuitry, before building a new one.
    The octal pre Jets and RRockets are the best of those Ampegs IMO in terms of building a new repro amp, and the reverb was the least cool part of what made them cool and desirable. Then again maybe the later RRockets had better reverb, I just never liked them for the overall sound compared to what else was on the used amp showroom floor.

    Taste and opinion of course, but might be worth considering?
     
  16. radiocaster

    radiocaster Poster Extraordinaire

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    I just needed the specs, I may use a smaller tank.

    It's not something I'll build next year or anytime soon, but a heavily modified version of the 6V6 version, maybe sharing as much as 30-40% of the same circuit.
     
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  17. Wally

    Wally Telefied Ad Free Member

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    Radiocaster, I finally ran across that add-on reverb circuit and tank that I removed from some old tweed Fender. The tank is a 4FB2A1D....same specs as the 4FB2A1C that the Ampeg used except the last letter in those specs differentiate between connectors ‘up’ for the C and connectors ‘down’ for the D. I need to draw out this scheme for this mod unit to see what they were thinking. There is a driver transformer there, though....and there was a huge hum that came from the unit. Perhaps this tank and the circuit used are incompatible.
    Thanks for the thread....it made me learn more about this thing I pulled out of that tweed Pro over two decades ago.
     
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  18. BobbyZ

    BobbyZ Doctor of Teleocity

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    Just a heads up on the 6v6 RRs. I've got two of those, each is different in a few ways from the other, circuit changes. Ok they each have a schmatic inside, those don't exactly match either amp, and they're both different. The RR schmatic you'll find in the tube amp books and online, as well as the one drawn up by Joe (forget his last name) are also different.
    As the story goes Hull hated those amps because they distorted. Apparently they kept changing them to clean them up. One change they made before dropping the 6v6s and going to 7591s was more filtering. Too much for a 5y3.
    Just stick with the 20uf filter caps like the early ones and the 5y3 will last. If you're ever servicing one with bigger caps put 20uf caps in it.
    That said they are fantastic amps! At some point I want to build a copy of my earlier one. It's just a wee bit sweeter than the later one.

    It's also amazing how they packed in reverb and trem into that small of space and got them working so well. They used the empty terminals on the rectifier socket for tie points for the AC wires. You'd seriously have a hard time finding room anywhere else.
     
  19. Wally

    Wally Telefied Ad Free Member

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    BobbyZ, regarding the filtering with a 5E3. Ampeg was not the only one to push beyond the specs. Fender used a 40mfd cap in the first stage of the ‘64 VibroChamp circuit. I don’t understand all of the aspects of this capacity rating of a rectifier tube. I came across some of the big military 5R4 tubes and learned that some use them to lower voltage. I did some research and found that they have a limit of 4mfds...yes FOUR...microfarads. When I questioned the use of these in an old tweed in which I wanted to lower the voltage from the level that the stock 5U4 yielded, I found that indeed this spec was of little concern in that circuit. ????. Obviously, Leo and Co. were not concerned about going above the 5Y3’s started limit there...for some reason.

    Joe Piazza is the fellow wo has drawn many Ampeg schematics. Just an observation, but when the original circuits can be so different from schematics and from amp to amp, then it is hard to label someone’s schematic drawing as incorrect, it seems??? I once owned three Gibson amps...2 x RVT’s and one Epi EA-16RVT...iirc...all the same amp. They were all original and built within weeks of each other. Each of them differed from the schematic in some way...and all were different from each other. Lol.....I could have drawn three ‘correct’ schematics and none of them would have been exactly like the other or the factory schematic!!!! eeeehaw...
     
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  20. BobbyZ

    BobbyZ Doctor of Teleocity

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    Wally I certainly didn't mean Joe Piazza's schmatics were inaccurate. I meant he obviously had a different example in front of him when he drew them.

    As I recall the RRs went to 60uf. I've probably still got the old cap can out of my somewhat later RR, in a box somewhere. But I think it was 60uf. Apparently a 5y3 will last at 40uf because Fender did it and they held. I really don't recall how the caps are wired in the RRs could be they're wired at 40uf with two 20uf caps. I'd have to pull one apart to look.
    People use 5R4s so it seems the original spec is pretty conservative. I haven't tried one yet because I'd get the one built right to spec and blow something up. I'm not very lucky. :)
     
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